HK1148610B

HK1148610B - Spatial information detecting device

Info

Publication number: HK1148610B
Application number: HK11102624.7A
Authority: HK
Inventors: 桥本裕介; 高田裕司; 今井宪次; 常定扶美
Original assignee: 松下电器产业株式会社
Priority date: 2005-11-14
Filing date: 2011-03-15
Publication date: 2013-11-01

Description

Spatial information detection device

This patent application is a divisional application of a patent application entitled "spatial information detection device and photodetector suitable for the same" having an international application date of 14/11/2006 and a national application number of 200680042102.3 (international application number of PCT/JP 2006/322652).

Technical Field

The present invention relates to a spatial information detecting device and a photodetector suitable for the device.

Background

In a conventional photodetector for generating electric charges corresponding to the amount of light received from a target space and taking out information of the target space as a received-light output, the maximum value of the received-light output is generally limited by the size of a portion for taking out the generated electric charges.

In order to expand the dynamic range of the channel for taking out the generated electric charges, it is proposed, for example, in japanese patent laid-open nos. 7-22436 and 7-22437 to remove unnecessary electric charges other than the information signal in the charge transfer channel by using a CCD and use the remaining electric charges as effective electric charges. According to this configuration, since unnecessary electric charges are not transferred, the size of the charge transfer channel can be reduced by reducing the amount of electric charge transfer.

However, in this configuration, since the removal of the undesired electric charges is performed in the electric charge transfer channel, a so-called saturation phenomenon occurs when the undesired electric charges generated by receiving light from the object space exceed the photoelectric conversion capability. In this case, there is a possibility that information to be detected before the charge transfer channel is lost.

Therefore, according to the above-described prior art configuration, the size of the charge transfer channel can be reduced. However, there is a problem that a photoelectric conversion portion for receiving light from a subject space to generate electric charges cannot be reduced.

Disclosure of Invention

In view of the above-described problems, a primary aspect of the present invention is to provide a spatial information detecting device with high operational reliability, which is capable of reducing the size of a photoelectric conversion portion and preventing a saturation phenomenon even when a large amount of unnecessary electric charges are generated by receiving light from a subject space.

That is, the spatial information detecting apparatus of the present invention includes: a light emission source configured to project signal light intensity-modulated by a modulation signal to a target space; a photodetection section configured to separate a constant amount of offset component from the electric charge corresponding to the received-light amount detected from the object space at a timing synchronized with the modulation signal, thereby providing a received-light output reflecting a fluctuation component of the signal light; and a signal processing section configured to detect spatial information of the object space by using the received light output. The photodetecting section includes: a photoelectric conversion portion configured to receive light from a subject space to generate electric charges; a charge separating section configured to separate a prescribed constant amount of undesired electric charges corresponding to the bias component from the electric charges generated by the photoelectric converting section, wherein the electric charges generated by the photoelectric converting section correspond to a sum of the constant amount of the bias component independent of the fluctuation of the signal light and a fluctuation component varying in accordance with the fluctuation of the signal light; a charge accumulating portion configured to accumulate, as effective charges, residual charges obtained by separating unnecessary charges from the charges generated by the photoelectric converting portion; and a charge extracting section configured to extract the effective charges accumulated in the charge accumulating section as the received-light output.

According to the present invention, since a constant amount of electric charges corresponding to the bias component is separated as the unnecessary electric charges and the residual electric charges corresponding to the fluctuation component are output as the effective electric charges, the occurrence of saturation can be reduced by reducing the total amount of electric charges while reflecting the increase or decrease of the electric charges generated by the photoelectric conversion portion. In other words, even when the electric charges generated by receiving light from the subject space contain a large amount of bias components, it is possible to efficiently take out the effective electric charges while preventing the occurrence of the saturation phenomenon by removing only the bias components. As a result, a compact photoelectric conversion portion can be obtained.

In the conventional configuration, the amount of electric charges separated as the undesired electric charges is determined with respect to the electric charges taken out as the received-light output. On the other hand, in the present invention, the amount of the undesired electric charges is determined with respect to the electric charges supplied from the photoelectric converting portion to the electric charge taking-out portion. Therefore, it is possible to significantly reduce the possibility of saturation by separating out undesired electric charges. In this regard, when saturation is prevented by using overflow drain (overflow drain) of the electronic shutter, the electric charge corresponding to the received-light amount is reduced at a constant rate. This means that the ripple component is fully compressed and results in a reduction of the charge corresponding to the ripple component. In contrast, in the present invention, since the bias component is separated as the unnecessary electric charges, the electric charges corresponding to the ripple component can be kept unchanged.

In addition, by removing the electric charges generated at the photoelectric conversion portion by receiving the environmental light from the target space as the unnecessary electric charges, it is possible to increase the contribution ratio of the light projected from the light emission source and the received light output. Therefore, when the spatial information is detected based on the relationship between the light projected from the light emission source and the light received at the photodetecting portion, it is possible to sensitively detect the change of the light projected from the light emission source and to improve the detection accuracy of the spatial information.

In the present invention, the constant amount of charge corresponding to the bias component refers to the charge in the following case. First, regarding the electric charges generated by the photoelectric conversion portion in a desired period, the bias component refers to a component that does not substantially change with time in the desired period or a component that does not substantially change with position in the desired period. That is, the bias component refers to a stable component that is not time or space dependent. For example, when the active type sensor is formed in combination with a light emission source for projecting signal light, the bias component is contained in the electric charge corresponding to the received-light amount of the environmental light other than the signal light. Second, the bias component is a component that matches the amount of charge corresponding to the amount of received light of the ambient light. Third, the bias component refers to a component smaller than the amount of charge corresponding to the received light amount of the ambient light. Fourth, when the intensity of the signal light is modulated and the minimum received-light amount of the signal light is not zero, the bias component refers to a component equal to or less than the amount of charge corresponding to the sum of the received-light amount of the ambient light and the minimum received-light amount of the signal light. That is, the bias component is provided in most cases by light other than the signal light like the ambient light existing in the object space. On the other hand, as in the case of using the intensity-modulated signal light, there is a case where a component that fluctuates with the signal light is contained in the bias component. In addition, an offset current (offset current) or a dark current (dark current) may be included in the offset component. It is assumed that the fluctuation component mainly changes with time. However, when a plurality of photoelectric conversion portions operate, there is a case where the fluctuation component refers to a difference in the received light amount between adjacent photoelectric conversion portions.

In the above invention, it is advantageous that the charge separating portion and the charge accumulating portion are potential wells formed in the semiconductor substrate, and the photodetecting portion further includes a charge amount adjusting means configured to form a potential barrier between the charge separating portion and the charge accumulating portion and to adjust an amount of charges flowing from the charge separating portion into the charge accumulating portion through the potential barrier. The charge amount adjusting device advantageously includes: a barrier control electrode arranged on the semiconductor substrate to form a potential barrier between the charge separating portion and the charge accumulating portion; and a control section configured to control a voltage applied to the barrier control electrode to change a height of the potential barrier. Alternatively, the charge amount adjusting means may include: a separation electrode arranged at a position corresponding to the charge separation portion on the semiconductor substrate; and a control section configured to control a voltage applied to the separation electrode to change a depth of the potential well of the charge separation section.

In this configuration, the charge amount adjusting means can be easily realized by forming the electrode on the main surface of the semiconductor substrate using a conventional semiconductor processing technique. In addition, the amount of the undesired electric charges can be easily adjusted by controlling the voltage applied to the barrier control electrode or the separation electrode to change the height of the potential barrier or the depth of the potential well serving as the electric charge separating portion. As a result, the electric charges flowing into the charge accumulating portion through the potential barrier formed between the charge separating portion and the charge accumulating portion can be accumulated as effective electric charges.

In addition, it is advantageous that the spatial information detecting apparatus further includes a timing control section configured to determine operation timings of the photoelectric converting section, the charge separating section, and the charge accumulating section in association with a light receiving period in which the photoelectric converting section generates electric charges by receiving light from the subject space to which the intensity-modulated light is irradiated and a weighing period in which unnecessary electric charges are separated from the electric charges generated by the photoelectric converting section by using the charge separating section and the charge accumulating section. According to this configuration, there is an effect that the undesired electric charges can be separated from the electric charges generated in the light receiving period in the weighing period.

The spatial information detecting device according to the preferred embodiment of the present invention further includes a semiconductor layer of the first conductivity type; a well of the second conductivity type formed at a main surface of the semiconductor layer; a discharging portion to which the unnecessary electric charges are discharged from the charge separating portion; a plurality of electrodes arranged on a major surface of the well; and a control section configured to control the voltage applied to the electrodes in association with a light receiving period in which the photoelectric conversion section generates electric charges by receiving light from the object space to which the intensity-modulated light is irradiated and a weighing period in which unnecessary electric charges are separated from the electric charges generated by the photoelectric conversion section. The electrode includes: a separation electrode for forming a potential well as a charge separating portion in the well; an accumulation electrode for forming a potential well as a charge accumulation portion in the well; and a barrier control electrode for forming a potential barrier between the charge separating portion and the charge accumulating portion. According to this configuration, the operation of separating the undesired electric charges from the electric charges generated in the light receiving period in the weighing period can be easily realized by using the semiconductor substrate. The undesired electric charges removed from the electric charges generated in the light receiving period are discharged from the charge separating portion through the discharging portion. In addition, the light receiving period and the weighing period can be easily realized by controlling the voltage application timing. In addition, since potential wells as the charge separating portion and the charge accumulating portion are formed by using the separating electrode and the accumulating electrode, and potential barriers are formed by using the barrier control electrodes, a refined structure having the arrangement of these control electrodes is obtained.

Particularly advantageously, the control section controls the voltage applied to at least one of the separation electrode and the barrier control electrode to change at least one of the height of the potential barrier and the depth of the potential well formed as the charge separating section, thereby adjusting the amount of the electric charges flowing from the charge separating section to the charge accumulating section across the potential barrier.

In the spatial information detecting device described above, it is preferable that the light emission source irradiates the target space with light intensity-modulated by the modulation signal to have a light emission period during which the intensity-modulated light is projected from the light emission source to the target space and a rest period during which the intensity-modulated light is not projected to the target space, and the photodetecting section includes charge amount adjusting means configured to adjust an amount of electric charges separated as the unnecessary electric charges from the electric charges corresponding to the received-light amount obtained in the light emission period, in accordance with an amount of electric charges generated by the photoelectric converting section in the rest period. In this case, it is particularly advantageous that the charge amount adjusting means increases the amount of the undesired electric charges separated from the electric charges corresponding to the received-light amount obtained in the light emission period when the amount of the electric charges generated by the photoelectric converting portion increases in the rest period.

According to this configuration, since the amount of the undesired electric charges to be separated is automatically determined according to the amount of the electric charges generated by receiving the ambient light in the rest period, it is possible to reduce the influence of the ambient light and to easily detect the information of the target space by the light projected from the light emission source.

In addition, as a preferred embodiment of the present invention, the charge separating portion and the charge accumulating portion are potential wells formed in the semiconductor substrate, and a barrier control electrode is disposed between the charge separating portion and the charge accumulating portion to form a potential barrier. The charge amount adjusting means controls the voltage applied to the barrier control electrode to change the height of the potential barrier in accordance with the amount of charge generated by the photoelectric conversion portion in the rest period, thereby adjusting the amount of charge flowing from the charge separating portion into the charge accumulating portion through the potential barrier. Alternatively, it is advantageous that separation electrodes are further arranged on the semiconductor substrate at positions corresponding to the charge separating portions, and the electric-charge amount adjusting means controls the voltage applied to the separation electrodes in accordance with the amount of electric charge generated by the photoelectric converting portion in the rest period to change the depth of the potential well formed as the charge separating portions, thereby adjusting the amount of electric charge flowing from the charge separating portions into the charge accumulating portions through the potential barriers.

According to this configuration, since the height of the potential barrier is automatically adjusted in accordance with the received-light amount of the environmental light received in the rest period and unnecessary electric charges are removed from the electric charges generated in the light-emitting period by using the potential barrier, it is possible to reduce the influence of the environmental light, and thus it is easy to detect the spatial information of the target space by the light projected from the light-emitting source. Further, since the photodetecting portion automatically determines an appropriate height of the potential barrier, the external circuit used in conjunction with the photodetecting portion can be formed by a relatively simple circuit configuration.

In the case of changing the height of the potential barrier, it is advantageous that the electric-charge amount adjusting means has a charge holding portion which is a potential well formed in the semiconductor substrate to hold the electric charges generated by the photoelectric converting portion in the rest period, and the electric-charge amount adjusting means applies a voltage determined according to the amount of electric charges held by the charge holding portion to the barrier control electrode. In this case, it is further advantageous that the charge amount adjusting means includes a holding electrode formed on the semiconductor substrate at a position corresponding to the charge holding portion through the insulating layer and electrically connected to the barrier control electrode. Alternatively, it is also advantageous that the barrier control electrode is electrically connected to a portion of the semiconductor substrate corresponding to the charge holding well formed as the charge holding portion.

On the other hand, in the case of changing the depth of the potential well formed as the charge separating portion, it is advantageous that the electric-charge amount adjusting means has a charge holding portion which is a potential well formed in the semiconductor substrate to hold the electric charges generated by the photoelectric converting portion in the rest period, and applies a voltage determined according to the amount of electric charges held by the charge holding portion to the separating electrode.

In either case of changing the barrier height or the potential well depth, it is advantageous that a gate electrode is formed on the main surface of the semiconductor substrate between the photoelectric converting portion and the charge holding portion, and the gate electrode is configured to control the timing of transferring the electric charges generated by the photoelectric converting portion to the charge holding portion. According to this configuration, since the timing of transferring electric charges from the photoelectric conversion portion to the electric charge holding portion is controlled by the gate electrode, it is possible to transfer the electric charges to the electric charge holding portion at a desired timing.

In the spatial information detecting device described above, it is also advantageous that the signal processing section increases the amount of the undesired electric charges separated in the next light emission period when the amount of electric charges generated in the light emission period reaches a predetermined saturation level. According to this configuration, even when the received-light output reaches the saturation level, saturation is hardly caused in the next light-emitting period. Therefore, it is possible to improve the detection possibility of spatial information.

In the spatial information detecting device according to a further preferred embodiment of the present invention, the photodetecting section has a plurality of photodetecting units, each photodetecting unit corresponding to one pixel. Each of the photodetecting units includes: a semiconductor layer of a first conductivity type; a well of the second conductivity type formed in a main surface of the semiconductor layer; a photoelectric conversion section including an array of a plurality of sensitivity control electrodes formed on a prescribed region of the well through an insulating layer; a separation electrode for forming a potential well as a charge separating portion in the well; a barrier control electrode for forming a potential barrier in the well; an accumulation electrode for forming a potential well as a charge accumulation portion in the well; and a discharging portion to which the unnecessary electric charges are discharged from the charge separating portion. Wherein the electric-charge amount adjusting means has a charge holding portion which is a potential well for holding electric charges generated by the photoelectric converting portion in the rest period. The charge amount adjusting means applies a voltage to at least one of the barrier control electrode and the separation electrode in accordance with the amount of charge held by the charge holding portion.

In this case, it is further advantageous that the separation electrode, the barrier control electrode, and the accumulation electrode are formed in an array of the sensitivity control electrodes, and the charge holding portion is formed adjacently in a direction perpendicular to the array of the sensitivity control electrodes. By providing the sensitivity control electrodes at equal intervals, there is an effect that the operation of transferring electric charges along the sensitivity control electrodes can be easily controlled. Alternatively, it is advantageous to arrange the separation electrode, the barrier control electrode, the accumulation electrode, and the charge holding portion in an array direction of the sensitivity control electrodes in a column adjacent to the array of the sensitivity control electrodes. Since the undesired electric charges can be separated in the same direction as the direction in which the electric charges are transferred along the sensitivity control electrode, the separation efficiency of the undesired electric charges becomes higher. In addition, there are also other effects of reducing the operation of transferring electric charges in a direction different from the array direction of the sensitivity control electrodes and achieving simplification of the control wiring and the control operation.

Another aspect of the present invention is to provide a spatial information detecting apparatus characterized by including the following configuration. That is, the spatial information detecting apparatus includes: a light emission source configured to irradiate light intensity-modulated by the modulation signal to the target space; a photodetection portion configured to provide an electrical output in accordance with light received from the object space; and a signal processing section configured to detect spatial information of the object space by using the electrical output. The photodetecting section includes: a photoelectric conversion portion configured to receive light from a subject space to generate electric charges; a charge separating section configured to separate an amount of unnecessary electric charges determined according to an amount of electric charges generated by the photoelectric converting section in one of two sections having different phase ranges of the modulation signal from the electric charges generated by the photoelectric converting section in the other section; an electric charge accumulating section configured to accumulate, as effective electric charges, residual electric charges obtained by separating unnecessary electric charges from electric charges generated by the photoelectric converting section in one of two sections having different phases of the modulation signal; and a charge extracting section configured to output the effective charge accumulated in the charge accumulating section as an electrical output.

According to this configuration, since the difference between the received-light amounts obtained in synchronization with the two sections having different phase ranges of the modulation signal is determined, it is possible to effectively reduce the influence of the ambient light by using the difference, and therefore the spatial information of the target space can be easily detected by the light projected from the light emission source. Further, the amount of the undesired electric charges is determined by the received-light amount obtained in one of two sections of the modulation signal having different phase ranges, and the amount of the effective electric charges corresponds to the difference in the amount of electric charges between the two sections. That is, it is possible to obtain a received-light output corresponding to the difference in the received-light amount between the two sections.

As a preferred embodiment of the above-described spatial information detecting device, the charge separating portion and the charge accumulating portion are potential wells formed in the semiconductor substrate, the spatial information detecting device having: a barrier control electrode arranged on the semiconductor substrate to form a potential barrier between the charge separating portion and the charge accumulating portion; and a charge holding portion configured to hold the electric charge generated by the photoelectric conversion portion in the other of the two sections of the modulation signal having different phase ranges, apply a voltage to the barrier control electrode in accordance with the amount of electric charge held by the charge holding portion to determine an amount of the undesired electric charge, and separate the amount of the undesired electric charge from the electric charge generated by the photoelectric conversion portion in one of the two sections of the modulation signal having different phase ranges by the charge separating portion. According to this configuration, the amount of undesired electric charges is automatically determined by the received-light amount obtained in one of two sections of the modulation signal having different phase ranges, and the amount of effective electric charges corresponds to the difference in the amount of electric charges between the two sections. That is, it is possible to obtain a received-light output corresponding to the difference in the received-light amount between the two sections.

Another aspect of the present invention is to provide a photodetector suitable for use as the photodetecting portion of the spatial information detecting device described above. That is, the photodetector is characterized by comprising: a photoelectric conversion portion configured to receive light from a subject space to generate electric charges; a charge separating section configured to separate a prescribed constant amount of undesired electric charges corresponding to the bias component from the electric charges generated by the photoelectric converting section, the electric charges generated by the photoelectric converting section corresponding to a sum of the constant amount of the bias component and a fluctuation component that varies with an increase or decrease in the received-light amount; a charge accumulating portion configured to accumulate, as effective charges, residual charges obtained by separating unnecessary charges from the charges generated by the photoelectric converting portion; and a charge extracting section configured to extract the effective charges accumulated in the charge accumulating section as the received-light output. The photodetector advantageously comprises a device formation layer made of a semiconductor of the first conductivity type; a well of a second conductivity type formed on a main surface of the device formation layer; a discharging portion to which the undesired electric charges are discharged from the charge separating portion; and a plurality of electrodes disposed on the major surface of the well. The electrode includes: a separation electrode for forming a potential well as the charge separating portion in the well; an accumulation electrode for forming a potential well as the charge accumulation portion in the well; and a barrier control electrode for forming a potential barrier between the charge separating portion and the charge accumulating portion.

Drawings

FIG. 1 is a sectional view showing a first embodiment of the present invention;

FIGS. 2A to 2E are operation explanatory diagrams showing potential energy relationships in the present embodiment;

3A-3C are operation explanatory diagrams showing voltage relationships in the present embodiment;

fig. 4 is a block diagram showing a schematic configuration of a spatial information detecting apparatus according to the present embodiment;

fig. 5A and 5B are explanatory diagrams of an operation example in the present embodiment;

fig. 6A and 6B are explanatory diagrams of another operation example in the present embodiment;

fig. 7A and 7B are explanatory diagrams of a further operation example in the present embodiment;

FIG. 8 is an explanatory view of another operation example in the present embodiment;

fig. 9A is a sectional view showing a second embodiment, and fig. 9B is a sectional view showing a modification of the second embodiment;

10A-10D are operation explanatory diagrams showing potential energy relationships in the present embodiment;

11A-11C are operation explanatory diagrams showing voltage relationships in the present embodiment;

fig. 12A is a plan view showing the third embodiment, fig. 12B is a sectional view taken along line X-X in fig. 12A, and fig. 12C is a sectional view taken along line Y-Y in fig. 12A;

fig. 13 is a plan view showing a fourth embodiment;

fig. 14 is a flowchart for explaining the operation in the present embodiment;

fig. 15 is a plan view showing the fifth embodiment;

fig. 16 is a sectional view showing the sixth embodiment;

17A-17H are operation explanatory diagrams showing potential energy relationships in the present embodiment;

fig. 18 is a sectional view showing a seventh embodiment;

FIGS. 19A to 19O are operation explanatory diagrams showing potential energy relationships in the present embodiment;

fig. 20 is a sectional view showing an eighth embodiment;

fig. 21 is a sectional view showing a ninth embodiment;

FIGS. 22A to 22E are operation explanatory diagrams showing potential energy relationships in the present embodiment; and

fig. 23A and 23B are operation explanatory diagrams showing the voltage relationship in the present embodiment.

Detailed Description

The present invention will be described in detail below based on preferred embodiments.

(first embodiment)

The spatial information detection apparatus of the present embodiment includes: a light emission source for projecting light intensity-modulated by the modulation signal to the target space as signal light; a photodetection section configured to provide a received-light output reflecting a fluctuation component of the signal light by separating a constant amount of bias component from electric charges corresponding to a received-light amount detected from the object space at a timing synchronized with the modulation signal; and a signal processing section configured to detect spatial information of the object space (for example, a distance to an object in the object space) by using the received light output. In the following embodiments, the photodetection portion is provided by a photodetector. In addition, in order to avoid the complication of the description of the present invention, only the minimum unit cell of the photodetector and the operation thereof are described in some cases. By arranging a plurality of unit cells, it is possible to obtain an image sensor as the photodetector.

As shown in fig. 1, in each cell 1, a device formation layer 11 formed on a substrate 10 is a semiconductor (e.g., silicon) of a first conductivity type (e.g., p-type), and a well 12 formed at a main surface of the device formation layer 11 is a semiconductor of a second conductivity type (e.g., n-type). On the main surface of the well 12, a separation electrode 14a, an accumulation electrode 14b, and a barrier control electrode 14c are arranged through an insulating layer 13 (e.g., silicon oxide or silicon nitride). The barrier control electrode 14c and the separation electrode 14a function as means for adjusting the amount of unnecessary electric charges. The voltages applied to the barrier control electrode 14c and the separation electrode 14a are determined by a control section (not shown). The substrate 10 has a second conductivity type. The separation electrode 14a, the accumulation electrode 14b, and the barrier control electrode 14c have translucency. In the present embodiment, a description is given of a case where the electric charges generated by receiving light from the target space are electrons. Alternatively, holes can be used as electric charges by reversing the conductivity type of the semiconductor and the polarity of a voltage described later.

In fig. 1, the separation electrode 14a, the accumulation electrode 14b, and the barrier control electrode 14c are designed to have different widths from each other, so that the accumulation electrode 14b has a larger width than the separation electrode 14a and the barrier control electrode 14 c. Alternatively, a plurality of electrodes having the same width may be arranged. In this case, by applying the same voltage to a plurality of electrodes arranged consecutively adjacent to each other, the plurality of electrodes can be equivalently used as a single electrode having a large width. For example, when the separation electrode 14a is provided by two electrodes arranged adjacent to each other, the accumulation electrode 14b is provided by three electrodes arranged successively adjacent to each other, and the barrier control electrode 14c is provided by a single electrode, the functions of the separation electrode 14a, the accumulation electrode 14b, and the barrier control electrode 14c can be realized by using these six electrodes having the same width.

The n-type well 12 is surrounded by the p-type device formation layer 11. Therefore, when no voltage is applied to the separation electrode 14a, the accumulation electrode 14b, and the barrier control electrode 14c, the potential of the well 12 is lower than that of the device formation layer 11 with respect to electrons. That is, the region corresponding to the well 12 forms a potential well for electrons. In fig. 1, the shaded area represents electrons. The potential of the well 12 can be controlled by applying voltages to the separation electrode 14a, the accumulation electrode 14b, and the barrier control electrode 14 c.

Here, a case where light is irradiated when the well 12 is in an empty charge state will be described. In order to obtain an empty state of the well 12, electrons are discharged through a drain (not shown) formed adjacent to the well 12. Alternatively, the electrons in the well 12 may be taken out to the outside as the received-light output by a charge take-out portion (not shown). The charge extracting portion may have the same configuration as a vertical transfer portion or a horizontal transfer portion of a conventional CCD image sensor.

As illustrated in a period Ta in fig. 3A to 3C, when light is received from the target space without applying voltages to the separation electrode 14a, the accumulation electrode 14b, and the barrier control electrode 14C, electrons and holes are generated in the device formation layer 11 including the well 12. As shown in fig. 2A, the generated electrons are collected in the well 12. That is, the well 12 functions as the photoelectric converting portion D1. When a voltage having a higher potential than the reference potential of the device formation layer 11 (i.e., a positive voltage) is applied to any one of the separation electrode 14a, the accumulation electrode 14b, and the barrier control electrode 14c, it is possible to obtain a potential well having a larger depth and improve the collection efficiency of electrons.

After the electrons are collected into the photoelectric converting portion D1, a potential barrier B1 is formed in the well 12 as shown in fig. 2B by applying a negative voltage to the barrier control electrode 14C as shown by a period Tb in fig. 3A to 3C. The potential barrier B1 divides the potential well of the well 12 into two potential wells: a charge separating portion D2 and a charge accumulating portion D3, in which the charge separating portion D2 is a region corresponding to the separating electrode 14a and the charge accumulating portion D3 is a region corresponding to the accumulating electrode 14 b.

In the case where the potential barrier B1 is formed to separate the charge separating portion D2 and the charge accumulating portion D3, when electrons in the charge separating portion D2 are discharged through a drain (not shown) formed near the well 12, the electrons remain only in the charge accumulating portion D3 as shown in fig. 2C. The amount of residual electrons in the charge accumulating portion D3 corresponds to the amount of received light obtained in the period Ta shown in fig. 3A to 3C. In order to discharge electric charges, it is advantageous to form a gate between the drain and the charge separating portion D2, and to open the gate to discharge electric charges from the charge separating portion D2 to the drain. The gate and drain structures may have the same configuration as conventional MOSFET or CCD structures.

Next, as shown by a time period Td in fig. 3A to 3C, a positive voltage is applied to the separation electrode 14a, and the voltage applied to the barrier control electrode is removed. At this time, as shown in fig. 2D, the charge separating portion D2 becomes a potential well having a larger depth than the charge accumulating portion D3. Further, since the potential barrier B1 between the charge separating portion D2 and the charge accumulating portion D3 is eliminated, all the electrons accumulated in the charge accumulating portion D3 flow into the charge separating portion D2. That is, all the electrons accumulated in the charge accumulating portion D3 are transferred to the charge separating portion D2.

After all the electrons in the well 12 are moved into the charge separating portion D2, a predetermined negative constant voltage is applied to the barrier control electrode 14C as shown by a period Te in fig. 3A to 3C, and the voltage applied to the separation electrode 14a is removed. That is, as shown in fig. 2E, the potential barrier B1 is formed again to divide the potential well 12 into the charge separating portion D2 and the charge accumulating portion D3. At this time, the potential well of the charge separating portion D2 was formed to have a shallow depth. Further, the capacity (volume) of the charge separating portion D2 is determined by the height of the potential barrier B1. That is, the capacity of the charge separating portion D2 is determined according to the voltage applied to the barrier control electrode 14 c. The voltage applied to the barrier control electrode 14c is set so that the potential of the potential barrier B1 does not exceed the potential of the device formation layer 11.

When the amount of electrons flowing into the charge separating portion D2 in the state of fig. 2D exceeds the capacity of the charge separating portion D2 in the state of fig. 2E, a part of the electrons flows from the charge separating portion D2 into the charge accumulating portion D3 through (over) the potential barrier B1. Since the amount of electrons flowing into the charge separating portion D2 in the state of fig. 2D corresponds to the amount of electrons generated by light irradiation (actually, the amount of electrons in fig. 2C), the amount of electrons flowing into the charge accumulating portion D3 in the state of fig. 2E is equal to an amount determined by subtracting electrons corresponding to the capacity of the charge separating portion D2 set in the state of fig. 2E from the electrons generated by light irradiation.

In the following description, the electrons separated by the charge separating portion D2 are referred to as unnecessary charges, and the electrons flowing into the charge accumulating portion D3 are referred to as effective charges. In general, unwanted charges are discharged, and effective charges are taken out as a received-light output. That is, the electrons generated by the photoelectric converting portion D1 can be regarded as the sum of a constant amount of bias component such as ambient light and a fluctuation component including information to be detected that fluctuates based on an increase or decrease in the received-light amount. Since the bias component does not contain information to be detected, it is discharged as an unnecessary electric charge. On the other hand, the obtained effective electric charges correspond to electric charges obtained by simply removing a constant amount of electrons from the amount of electrons corresponding to the received-light amount. Therefore, the fluctuation component of the received-light amount remains in the effective electric charge, and there is no change in the amount of information contained in the received-light amount.

In addition, during the time period shown in fig. 2A to 2E, light is received during the movement of electrons in the well 12, and the generated electrons are continuously collected in the well 12. Therefore, the amount of electrons generated in the period shown in fig. 2B to 2E needs to be reduced to tend to zero as compared with the amount of electrons generated by the photoelectric converting portion D1 in the period shown in fig. 2A. To minimize the error that occurs, it is advantageous to set the time periods of fig. 2A on the order of milliseconds (ms) and the time periods of fig. 2B-2E on the order of microseconds (μ s), for example.

In the present embodiment, as described above, a prescribed constant amount of electrons are separated from the electrons generated at the photoelectric converting portion D1 by receiving light from the object space by the charge separating portion D2, and then the remaining electrons are transferred as effective charges to the charge accumulating portion D3. In this case, the amount of the effective charges accumulated in the charge accumulating portion D3 becomes smaller than the amount of electrons corresponding to the received-light amount (time integral of the received light flux). However, the amount of information contained in the received-light amount is reflected on the effective electric charges. Therefore, even when the received-light amount increases, saturation hardly occurs because a constant amount of generated electric charges are removed as unnecessary electric charges by the electric-charge separating portion D2.

In the present embodiment, the photoelectric converting portion D1 is formed in the well 12. Alternatively, the photoelectric conversion portion may be formed at a different position from the well 12. The electrons generated by the photoelectric conversion portion are transferred to the well 12, and then a part of the electrons are separated according to the above-described procedure. In this case, since the well 12 can be light-shielded, it is possible to reduce errors caused by the charges generated in the periods shown in fig. 2A to 2E.

Further, in the above explanation, in the period of fig. 2D, the potential energies of the charge separating portion D2 and the potential barrier B1 are reduced without changing the potential energy of the charge accumulating portion D3. Alternatively, electrons can be moved from the charge accumulating portion D3 to the charge separating portion D2 by lowering the potential energy of the potential barrier B1 so as to be higher than the potential barrier B1 of fig. 2E and increasing the potential energy of the charge accumulating portion D3 so as not to be smaller than the potential barrier B1 without changing the potential energy of the charge accumulating portion D2.

In addition, in order to separate a constant amount of electrons as undesired electric charges by the charge separating portion D2 in the state of fig. 2E, all the electrons that need to move across the potential barrier B1 flow into the charge accumulating portion D3. When the amount of electrons moved into the charge accumulating portion D3 exceeds the capacity of the charge accumulating portion D3, a constant amount of undesired electric charges cannot be separated by the charge separating portion D2. To solve this problem, while increasing the capacity of the charge accumulating portion D3 without changing the depth of the charge accumulating portion D3, the occupied area of the well 12 with respect to the device forming layer 11 is increased. As a result, this leads to an increase in the size of the photodetector. Therefore, in order to solve the above-described problem, it is advantageous to use a technique of adjusting the depth of the charge accumulating portion D3.

The depth of the charge accumulating portion D3 depends on the height of the potential barrier B1. The amount of undesired charge is determined by the relative height of potential energy of the potential barrier B1 from the bottom of the charge separating portion D2. Therefore, by adjusting the potential energy of the bottom of the charge separating portion D2 without changing the height of the potential barrier B1, it is possible to measure and separate a constant amount of undesired electric charges by the charge separating portion D2 even if the received-light amount increases or decreases.

In order to appropriately set the enable of the bottom of the charge separating portion D2, it is necessary to estimate the received-light amount. In the estimation of the received-light amount, it is advantageous that the electrons collected in the photoelectric converting portion D1 are moved to the outside of the photodetector and then estimated by the external circuit of the photodetector. In this case, the estimation result supplied from the external circuit is reflected on the voltage applied to the separation electrode 14 a. In response to the estimation result of the received-light amount, there is a case where it is not necessary to separate the undesired electric charges by the electric-charge separating portion D2. In this case, electrons remaining in the charge accumulating portion D3 in the state of fig. 2C are taken out as the received-light output.

Specifically, the voltages applied to the separation electrode 14a, the accumulation electrode 14b, and the barrier control electrode 14c are controlled by an external circuit (not shown) as a control section, so that the photodetector performs two operations: a received-light output for estimating the amount of received light is taken out and the received-light output is taken out after the unnecessary electric charges are separated out. In the period of time for which the received-light output for estimating the received-light amount is obtained, the electric charges accumulated in the photoelectric converting portion D1 are directly taken out. By using this received-light output, voltages applied to the separation electrode 14a, the accumulation electrode 14B, and the barrier control electrode 14c are determined to adjust one of the height of the potential barrier B1 and the depth of the charge accumulating portion D3. Next, with respect to the electric charges corresponding to the received-light amount, unnecessary electric charges are separated according to the above-described procedure, so that residual electrons are taken out as a received-light output.

In addition, the received-light output obtained by separating out the unnecessary electric charges must retain information contained in the received-light amount. Therefore, in the case of a passive sensor without a light emitting source, by keeping the amount of the undesired electric charges to be separated constant, the fluctuation component of the received-light amount can be reflected on the received-light output. On the other hand, in the case of an active type sensor using a light emitting source, a period during which the light emitting source emits light (hereinafter referred to as "light emitting period") and a period during which the light emitting source is off (hereinafter referred to as "pause period") are set. After the received-light amount obtained in the rest period is estimated, unnecessary electric charges are removed from the electric charges obtained in the light-emitting period. According to this operation, it is possible to remove the amount of the undesired electric charges determined according to the environmental light such as the natural light and the illumination light from the electric charges obtained in the lighting period and to substantially improve the dynamic range with respect to the light projected from the light emission source.

In the above operation, it is assumed that an operation of separating the undesired electric charges is performed once, and the amount of the undesired electric charges is determined by adjusting only the height of the potential barrier B1. Alternatively, the amount of the undesired electric charges may be adjusted by changing the number of operations of separating the undesired electric charges. In this case, the capacity of the charge separating portion D2 is kept constant. After the undesired electric charges are separated by the charge separating portion D2 in the state of fig. 2E, the undesired electric charges are discharged from the charge separating portion D2. Then, the state of fig. 2D is reproduced, the electric charges are returned from the charge accumulating portion D3 to the charge separating portion D2, and the undesired electric charges are separated again by the charge separating portion D2 in the state of fig. 2E. By repeating the above process as many times as necessary, the amount of the undesired electric charges can be adjusted.

In the operation shown in the figure, after the electric charges are moved to the charge separating portion D2 to separate out the unnecessary electric charges, the voltage applied to the barrier control electrode 14c or the voltage applied to the separation electrode 14a is adjusted. Alternatively, after the capacity of the charge separating portion D2 is determined by adjusting the voltage applied to the barrier control electrode 14c or the voltage applied to the separating electrode 14a, the electric charge may be moved into the charge separating portion D2.

In the following description, as shown in fig. 4, light is projected from the light emission source 2 to the object space so that the resultant light from the object space is received by the photodetector (i.e., photodetection portion) 1 as signal light. In this configuration, it is assumed that the light received by the photodetector 1 contains ambient light, such as natural light and illumination light, and the received-light output is obtained by reducing the ambient-light component. Therefore, the amount of electrons separated as the undesired electric charges is determined to reflect the received-light amount of the ambient light. The received light output of the photodetector 1 is sent to the received light processing circuit 3 to extract desired information from the received light output. The operations of the photodetector 1, the light emission source 2, and the received light processing circuit 3 are controlled in accordance with a timing signal output from the timing control circuit 4.

That is, the voltages applied to the barrier control electrode 14c and the separation electrode 14a serving as means for adjusting the amount of charge separated as the unnecessary electric charges are controlled by the timing control circuit 4. In addition, the timing control circuit 4 outputs a timing signal to the light emission source 2 so that the light emission period and the rest period are alternately repeated. The timing control circuit 4 also supplies timing signals to the photodetector 1 and the received light processing circuit 3 so that operations described later are performed in the light emission period and the pause period. That is, in the configuration shown in the figure, the signal processing section includes the received light processing circuit 3 and the timing control circuit 4. The signal processing section may be configured by a microprocessor for executing an appropriate program.

In the following description, a desired amount of undesired electric charges are separated by performing a charge weighing operation (charge weighing operation) a plurality of times. That is, when the amount of the undesired electric charges to be discharged is Qg, it can be discharged by repeating the charge weighing operation "k" times (k is a positive integer). Therefore, the amount of the undesired electric charges discharged per charge weighing operation is represented as Qg/k. In order to discharge the undesired electric charges, there are a method of repeating the charge weighing operation a plurality of times at predetermined time intervals, and a method of continuously repeating the charge weighing operation a plurality of times. In the following description, the two methods are performed in a mixed manner.

That is, a weighing period in which an operation of separating and discharging the undesired electric charges is continuously repeated "m" times (m is a positive integer of 2 or more) is defined, and the weighing period is repeated "n" times (n is a positive integer of 1 or more) in the light emitting period. This relationship is shown in fig. 5A and 5B. In each of fig. 5A and 5B, one rest period "Pd" and one emission period "Pb" are shown. Actually, the rest period "Pd" and the lighting period "Pb" are alternately repeated a plurality of times. In the operation shown in fig. 5A, the weighing period "Pt" is performed "n" times (2 times in the figure) in the lighting period "Pb", and the operation of separating and discharging the undesired electric charges (hereinafter referred to as the weighing operation "W") is repeated "m" times (5 times in the figure) in each weighing period. That is, the number of times of the weighing operation "W" performed in the lighting period "Pb" is represented as "n" x "m". In each weighing period "Pt", unnecessary electric charges are discharged so that only an amount of electrons corresponding to the received-light amount of the signal light is left. Therefore, the amount of the undesired electric charges discharged per one weighing operation "W" is determined by dividing the amount of the undesired electric charges discharged in the weighing period "Pt" by the positive integer "m". In addition, the amount of the undesired electric charges discharged per one weighing operation "W" is set according to the received-light amount obtained in the rest period "Pd". That is, in the operation explained below, "k" is "m".

First, an advantage of the case where the unnecessary electric charges are separated step by a plurality of weighing operations, as compared with the case where the unnecessary electric charges are separated at one time by a single weighing operation, will be described. In general, the charge amount "Q" (the amount of electrons) accumulated in response to the received-light amount of the photodetector is proportional to the area "S" of the photoelectric converting portion D1 (the charge accumulating portion D3) and the light receiving time "t". When the amount of accumulated charge per unit time and unit area is "Q", Q "is" Q "x" S "x" t ". In the present description, since the height of the potential barrier B1 is determined according to the amount of charge accumulated in the rest period "Pd", the height Δ V of the potential barrier B1 can be expressed as a function of the amount of charge "Q" accumulated in the rest period "Pd". For example, it can be calculated from the relation Δ v (Q) ═ α "x" Q "x" S "x" t ", where" α "is a coefficient for converting the charge amount" Q "to the height Δ v (Q) of the potential barrier B1. The amount of undesired electric charge discharged per weighing operation can be adjusted by changing the height Δ v (q) of the potential barrier B1.

The height Δ v (q) of the potential barrier B1 can be adjusted by varying any of the four variables described above. As described above, the time "t" is set on the millisecond (ms) level, and the time required for the weighing operation is set on the microsecond (μm) level. Therefore, by reducing the time "t" for determining the amount of the undesired electric charges, it is possible to shorten the rest period "Pd" and relatively increase the time taken to collect the spatial information. However, as the time "t" shortens, the amount of charge Q discharged per weighing operation decreases. Therefore, the number of weighing operations is increased to discharge a desired amount of undesired electric charges.

In order to shorten the time "t" without reducing the charge amount Q discharged per weighing operation, it is considered to increase at least one of the coefficient "α", the charge amount "Q", and the area "S". However, as the coefficient "α" becomes larger, a noise component such as shot noise (shot noise) increases. As a result, measurement errors increase. In addition, since the charge amount "q" depends on the specification of the photodetector and the received light intensity, it is difficult to adjust the charge amount "q". On the other hand, as the area "S" becomes larger, the increase in the size of the device becomes a problem. Therefore, the coefficient "α", the charge amount "q", and the area "S" are not changed.

As described above, the amount of the undesired electric charges discharged per weighing operation "W" is determined by the amount of the electric charges accumulated in the rest period "Pd". The amount of charge is expressed as a function of the received light intensity of the ambient light and the length (time "t") of the rest period "Pd". That is, the amount of the undesired electric charges discharged per one weighing operation "W" is defined to become larger as the rest period "Pd" becomes longer. In practice, it is defined by a first order function or a third order function. Therefore, as described above, when the amount of the undesired electric charges discharged in the weighing period "Pt" is "Qg" and the amount of the undesired electric charges discharged per weighing operation "W" is represented as "Qg/m", the length of the rest period "Pd" required for one weighing operation is 1/m of the length of the rest period required for one discharging of the charge amount "Qg". In short, since "m" times of the weighing operation "W" are repeated, the length of the rest period "Pd" required for one weighing operation for discharging unnecessary electric charges can be reduced to 1/m.

In the above operation, the rest period "Pd" is shortened, and on the other hand, a time corresponding to the number of repetitions of the weighing operation "W" is required to complete the discharge of the undesired electric charges. Since the time level of the rest period is in the order of milliseconds (ms) and the time level of the weighing operation "W" is in the order of microseconds (μm), the total time required for the rest period "Pd" and the light emitting period "Pb" can be shortened as compared with the case where the unnecessary electric charges are discharged at once. For example, when the rest period requires 7 milliseconds (ms) in the case where the undesired electric charges are discharged once, the time required for the rest period in the case where the undesired electric charges are discharged by repeating the weighing operation "W" 7 times can be shortened to 1 ms. That is, even when 100 microseconds (μm) are required to perform each weighing operation "W", the total time of the rest period "Pd" and the lighting period "Pb" is less than 2 milliseconds. Thus, a significant time reduction can be achieved.

Therefore, the signal processing section determines the amount of the undesired electric charges separated from the electric charges corresponding to the received-light amount obtained in the prescribed constant light-emission period, based on the received-light amount obtained in the rest period. In addition, the signal processing section controls the photodetector such that the unnecessary electric charges are discharged by repeating the weighing operation a plurality of times. The larger the amount of the undesired electric charges discharged per weighing operation, the longer the duration of the rest period becomes. Therefore, it is possible to shorten the duration of the rest period compared to discharging unnecessary electric charges at once. That is, since the time required for the weighing operation is two or three orders of magnitude shorter than the rest period, the processing time corresponding to the total time of the rest period and the light emitting period can be effectively shortened by shortening the rest period. As a result, it is possible to efficiently collect information of the signal light in the light emission period and increase the amount of spatial information collected per unit time.

As described above, the time required to take out the received-light output can be shortened by shortening the rest period "Pd" and removing the undesired electric charges by repeating the weighing operation "W" a plurality of times, as compared with the case where the undesired electric charges are removed at a time. In addition, even when the intensity of the ambient light received in the rest period "Pd" is relatively increased, it is possible to reduce the amount of electrons generated at the photoelectric converting portion D1 by shortening the rest period "Pd" and thereby prevent the photodetector 1 from being saturated.

In the above-described operation, "m" times of the weighing operation "W" are performed in the weighing period "Pt", and "n" times of the weighing period "Pt" are performed in the lighting period "Pb". In this case, each lighting period "Pb" is constant. By performing the weighing operation "W" a plurality of times per one weighing period "Pt", the effect of shortening the rest period "Pd" becomes higher. The number of times of the weighing operation "W" performed in the lighting period "Pb" can be appropriately determined. For example, a single weighing period "Pt" in which a desired number of times of weighing operations "W" are performed may be set in the lighting period "Pb". Alternatively, a single weighing operation "W" may be performed in each weighing period "Pt".

It is advantageous to set a plurality of weighing periods "Pt" in the lighting period "Pb" from the viewpoint of the received light intensity of the ambient light. In particular, when a large received-light amount is obtained in the rest period "Pd", in other words, when the received-light intensity of the ambient light increases, the number of times of the weighing periods "Pt" in the lighting period "Pb" needs to be increased. The reason for this is explained with reference to fig. 6A and 6B.

For example, when the number of times of the weighing periods "Pt" is set to 4 times in the lighting period "Pb", as shown in fig. 6A, in the lighting period "Pb" between the time "t 0" and the time "t 2", a constant amount of the undesired electric charges are discharged through the four weighing periods "Pt". In this case, although the undesired electric charges are removed every weighing period "Pt", the electrons accumulated in the charge accumulating portion D3 gradually increase as a whole.

In the above operation, when the amount of the undesired electric charges discharged through one weighing period "Pt" and the number of times of the weighing periods "Pt" are appropriately set, the amount of electrons accumulated in the charge accumulating portion D3 does not exceed the saturation level L1 of the photodetector 1. However, when the ambient light is larger than the initial assumption, before the end, that is, before the time "t 2" of the light emission period "Pb", a phenomenon may occur in which the amount of electrons accumulated in the charge accumulating portion D3 exceeds the saturation level L1. In fig. 6A, the charge amount exceeds the saturation level L1 at time "t 3". In this case, information of a part of the signal light is lost from the received-light output taken out from the photodetector 1.

For this reason, it is necessary to detect whether the charge amount has reached the saturation level L1 in the light emission period "Pb". In order to detect that the charge amount has reached the saturation level L1, it is advantageous to set the weighing period "Pt" such that the lighting period "Pb" ends after a constant period of time from the last weighing period "Pt" in the lighting period "Pb", for example. The period between the last weighing period "Pt" and the end of the lighting period "Pb" is set to be equal to the time interval between the adjacent weighing periods "Pt".

It is assumed here that four weighing periods "Pt" are set in one light emission period "Pb", and that saturation occurs between the third weighing period "Pt" and the fourth weighing period "Pt". In this case, since the unnecessary electric charges are discharged through the fourth weighing period "Pt" so that the amount of electric charges is lower than the saturation level L1, saturation cannot be detected when the received-light output is taken out at the end of the last (fourth) weighing period "Pt". On the other hand, as described above, when the lighting period "Pb" ends after a lapse of the constant period from the end of the last weighing period "Pt", and then the received-light output is taken out, it is possible to detect saturation in the lighting period "Pb", because the received-light output reaches the saturation level L1 again.

In addition, even when the amount of electrons accumulated in the charge accumulating portion D3 exceeds the saturation level L1 before the time "t 2", there is a case where the amount of charge is controlled so as not to exceed the saturation level L1 by increasing the number of times of the weighing period "Pt" without changing the light emission period "Pb". For example, as shown in fig. 6A, assuming that four weighing periods "Pt" are set in the light emission period "Pb" between the time "t 1" and the time "t 2" and that the amount of electrons accumulated in the charge accumulating portion D3 immediately before the fourth weighing period "Pt" exceeds the saturation level L1, it is possible to prevent the amount of electrons accumulated in the charge accumulating portion D3 from exceeding the saturation level L1 before the time "t 2" by increasing the number of times of the weighing periods "Pt" in the light emission period "Pb" from 4 times to 5 times, as shown in fig. 6B. In other words, when each weighing period "Pt" is set relatively short, unnecessary electric charges can be discharged before the photodetector 1 is saturated. As a result, it is possible to increase the ratio of electrons corresponding to the signal light in the received light output even under a larger amount of ambient light. That is, even when the received-light intensity of the ambient light increases, the received-light output having the information of the signal light can be obtained.

The number of times of the weighing periods "Pt" in the lighting period "Pb" is determined by using the received-light output obtained from the photodetector 1 at least in the rest period "Pd". The received-light amount obtained in the rest period "Pd" may also be used if necessary. The procedure for determining the number of times of the weighing period "Pt" is explained below. Since the weighing operation is performed a plurality of times in the weighing period "Pt", each weighing period "Pt" can be regarded as an operation for discharging unnecessary electric charges. In addition, when the weighing period "Pt" is performed a plurality of times in the lighting period "Pb" such that a time interval is set between adjacent weighing periods "Pt", it means that the weighing operation for discharging the undesired electric charges is performed a plurality of times at the time interval.

Since the received-light intensity of the ambient light is reflected on the received-light amount obtained in the rest period "Pd", the amount of the undesired electric charges accumulated in the lighting period "Pb" can be estimated from the received-light amount obtained in the rest period "Pd". In addition, the amount of charge discharged per weighing period "Pt" is determined by the amount of received light obtained in the rest period "Pd". Therefore, by determining the received-light amount of the rest period "Pd", it is possible to recognize the tendency of the amount of electrons accumulated in the light emission period "Pb" to change with time. At this time, the amount of electrons corresponding to the signal light is unclear. However, it can be considered that the amount of electrons corresponding to the signal light is almost uniformly increased in the light emission period "Pb". Therefore, it is possible to estimate the amount of the undesired electric charges to be discharged in consideration of the saturation level L1, and to determine a candidate value of the number of weighing periods "Pt".

After the candidate value is determined, whether the number of times of the weighing periods "Pt" is appropriate is estimated by the received-light processing circuit 3 monitoring the magnitude of the received-light output obtained in the case of using the candidate value. To make this estimation, upper and lower limit values are set, and the number of times of the weighing periods "Pt" is adjusted by comparing the received-light output with the upper and lower limit values.

For example, when the received-light amount exceeds the upper limit value, a new candidate value is prepared by adding "1" to the candidate value of the number of times of the weighing period "Pt". On the other hand, when the received-light amount is smaller than the lower limit value, another new candidate value is prepared by subtracting "1" from the candidate value of the number of times of the weighing period "Pt". By repeating this process, the received-light amount can be maintained at an appropriate value between the upper limit value and the lower limit value. When the received light output is not between the upper limit value and the lower limit value, it is not employed. That is, the received light output for another time period is interpolated or replaced.

Instead of determining a candidate value for the number of times of the weighing periods "Pt" from the received-light amount obtained in the rest period "Pd", a predetermined default value may be used as the candidate value. In this case, only the received-light amount of the rest period "Pd" is used to determine the amount of the undesired electric charges discharged in one weighing operation "W". The number of times of the weighing operation "W" in one weighing period "Pt" is not changed.

In order to determine the number of times of the weighing periods "Pt" in the lighting period "Pb", the received-light processing circuit 3 performs the above-described processing in accordance with the received-light amount and the received-light output obtained in the pause period "Pd", and the timing control circuit 4 controls the operation of the photodetector 1 in response to the number of times of the weighing periods "Pt" determined by the received-light processing circuit 3. Processing for adjusting the number of times of the weighing periods "Pt" so that the received-light output is between the upper limit value and the lower limit value is not required for each lighting period "Pb". Depending on the usage environment, it is sufficient to perform the process every appropriate number of lighting periods "Pb". For example, a standard frequency may be set as a default value. When the ambient light changes greatly, the frequency is increased above the standard frequency. Conversely, when the ambient light changes less, the frequency is reduced below the standard frequency.

When the received-light output has reached the saturation level in the lighting period "Pb", the received-light output obtained in the lighting period "Pb" cannot be used to detect the spatial information. Therefore, this received-light output is discharged, and the amount of the undesired electric charges separated in the next lighting period "Pb" is changed to obtain an appropriate received-light output in the next or subsequent lighting period "Pb". As described above, as a technique for changing the amount of the undesired electric charges, it is preferable to change the number of times of the weighing period "Pt". Alternatively, as the rest period "Pd" expands, the amount of electric charge discharged in the weighing period "Pt" increases. In addition, as described later, when a plurality of sensitivity control electrodes 17a to 17h (fig. 12) are formed, the light receiving area can be substantially controlled by changing the number of sensitivity control electrodes to which a voltage is applied to form a potential well for collecting electric charges as the photoelectric converting portion D1 in the rest period "Pd". Therefore, by increasing the light receiving area in the rest period "Pd", it is possible to increase the amount of electric charge discharged in one weighing period "Pt".

As can be understood from the above-described principle, from the viewpoint of performing the weighing operation "W" so that the received-light output does not exceed the saturation level L1, it is advantageous to uniformly distribute the weighing operation "W" in the lighting period "Pb" as compared with the case where the weighing operation "W" is performed in total in the weighing period "Pt". That is, as shown in fig. 5B, it is advantageous to set a time interval between adjacent weighing operations "W" in the lighting period "Pb". In addition, as the received-light output obtained in the rest period "Pd" becomes larger, it is advantageous to set the time interval shorter. According to this technique, since the amount of accumulated charge hardly reaches the saturation level L1, it is possible to reduce the rate of increase in the amount of charge accumulated in the charge accumulating portion D3 and improve the effect of preventing the charge accumulating portion D3 from being saturated.

In addition, the amount of the undesired electric charges discharged in one weighing period "Pt" is calculated to hold all the electrons generated by the signal light. However, since the weighing operation "W" is performed a plurality of times in one weighing period "Pt" and the amount of the undesired electric charges discharged in one weighing operation "W" is determined by the received-light amount of the rest period "Pd", it may be difficult to hold only all the electrons corresponding to the signal light. Therefore, in actuality, the amount of electrons slightly larger than all the electrons corresponding to the signal light is maintained. In this case, in order to expand the dynamic range with respect to the signal light, it is desirable to minimize the excess amount of electrons.

The amount of the undesired electric charges discharged in one weighing operation "W" is determined by the received-light amount of the rest period "Pd", and the received-light amount is expressed as a function of the length (duration) of the rest period "Pd". Therefore, when the total amount of the undesired electric charges discharged in one weighing period "Pt" is calculated, it is possible to determine the amount of the undesired electric charges discharged in one weighing operation "W" so that the excess amount of electrons becomes minimum by changing the length of the rest period "Pd".

In addition, since the amount of the undesired electric charges discharged in one weighing operation "W" decreases as the rest period "Pd" becomes shorter, the excess amount of electrons can be reduced. Alternatively, it is also possible to reduce the excess amount of electrons by enlarging the rest period "Pd" so that one weighing operation "W" is performed in one weighing period "Pt". However, in the former case, the processing ratio of the weighing operation "W" in the lighting period "Pb" becomes large due to the increase in the number of times of the weighing operation "W". In the latter case, the pause period "Pd" is extended. Therefore, in these cases, the amount of information obtained from the signal light per unit time decreases.

In addition, it is preferable to set an upper limit and a lower limit with respect to the number of times of the weighing operation "W" in one weighing period "Pt", and to set an upper limit and a lower limit with respect to the length of the rest period "Pd". In this case, each of the amount of the undesired electric charges discharged in one weighing operation "W" and the number of times of the weighing operation "W" in one weighing period "Pt" is determined so that the excess amount of electrons in the range between the upper and lower limits becomes minimum. As a result, it is possible to set the condition for the weighing period "Pt" to prevent the number of times of the weighing operation "W" from being excessively increased while relatively shortening the rest period "Pd".

In addition, the amount of the undesired electric charges discharged in the weighing period "Pt" is calculated as a product of the number of times of the weighing operation "W" in the weighing period "Pt" and the amount of the undesired electric charges discharged in one weighing operation "W". The amount of the undesired electric charges discharged in one weighing operation "W" is determined by the received-light amount of the rest period "Pt". Further, the received-light amount of the rest period "Pt" is determined by the length (duration) of the rest period "Pt" and the received-light intensity of the ambient light.

In order to set the condition for the weighing period "Pt", a default value is set with respect to the length of the pause period "Pd". The received-light intensity of the ambient light is estimated by using the received-light amount obtained in the rest period "Pd" having a time length of a default value, and then the total amount of the undesired electric charges discharged per weighing period "Pt" is determined. In addition, the amount of the undesired electric charges discharged in one weighing operation "W" is determined by using the received-light amount of the rest period "Pd" having a time length of a default value.

Next, the total amount of the undesired electric charges discharged per one weighing period "Pt" is divided by the amount of the undesired electric charges discharged in one weighing operation "W" to obtain a quotient and a remainder. When the quotient is between the upper limit and the lower limit of the number of times of the weighing operation "W" of the weighing period "Pt", the amount of the undesired electric charges discharged in one weighing operation "W" is determined to reduce the remainder. Based on this amount, the length of the rest period "Pd" is back-calculated. When the length of the pause period "Pd" obtained from this back calculation is between the upper limit and the lower limit, the pause period "Pd" is set to the length determined by this back calculation.

When the length of the rest period "Pd" or the number of times of the weighing operation "W" deviates from the range between the upper limit and the lower limit, the number or length is adjusted within the range therebetween.

In the image sensor having the plurality of photoelectric converting portions D1, when the above-described processing is performed in each photoelectric converting portion D1, the processing load increases. Therefore, it is advantageous to set the rest period "Pd" short while setting the number of times of the weighing operation "W" large so that the amount of the undesired electric charges separated by one weighing operation "W" is smaller than a predetermined value with respect to all the photoelectric converting portions D1. As the amount of the undesired electric charges discharged by one weighing operation "W" becomes smaller, the number of times of the weighing operation "W" increases. However, the time required for one weighing operation "W" is very short. Therefore, the increase in the total time required for the photoelectric converting portion D1 to receive light, discharge unnecessary electric charges, and then take out the received-light output is small. On the other hand, since the rest period "Pd" is shortened, it is possible to relatively increase the time for detecting spatial information in the lighting period "Pb".

In the image sensor having the plurality of photoelectric converting portions D1, in order to simply control the operation timing in accordance with the output of the timing control circuit 4, it is advantageous to set the same number of times of the weighing operation "W" with respect to all the photoelectric converting portions D1. Therefore, as described above, in order to reduce the amount of the undesired electric charges separated by one weighing operation "W", it is desirable to set the number of times of the weighing operation "W" in the weighing period "Pt" as large as possible.

Therefore, the signal processing section reduces the amount of the undesired electric charges separated by one weighing operation "W" with respect to all the pixels, and also increases the number of times of the weighing operation "W" by shortening the rest period so that a remainder obtained by dividing by the amount of the undesired electric charges separated by one weighing operation "W" is smaller than a prescribed value. According to this configuration, when the undesired electric charges are separated by performing the weighing operation a plurality of times, the rest period is shortened, and the number of times of the weighing operation is increased. As a result, although the weighing operation is repeated the same number of times with respect to each photoelectric conversion portion of the photodetector, the amount of the remaining undesired electric charges that are not separated from the electric charges generated by each photoelectric conversion portion becomes small. Therefore, it is possible to reduce the amount of unnecessary components other than the signal light component mixed in the electric charges extracted as the received-light output.

In addition, as described above, when the undesired electric charges are separated and discharged, most of the received-light output corresponds to the signal light component. However, when the received-light intensity of the signal light increases, the photodetector 1 may be saturated. On the other hand, when the received light intensity of the signal light is lowered, the S/N ratio may be deteriorated due to the influence of internal noise such as shot noise. In the above operation example, the amount of the undesired electric charges is adjusted under the light emission period "Pb" of a constant length. In the case where the light receiving side adjusts the received-light amount of the signal light, it is also necessary to adjust the length of the light emission period "Pb".

For example, as shown in fig. 7A, it is advantageous that the length of the light emission period may be selected from a plurality of lengths (Pb1, Pb2, Pb 3). By selecting one of the lighting periods (Pb1, Pb2, Pb3) to obtain an appropriate received-light output, the dynamic range with respect to the signal light can be improved. That is, the length of the light emission period (Pb1, Pb2, Pb3) is determined so that the received-light output as large as possible is obtained under the condition that the photodetector 1 is not saturated. In the case of using this technique, the amount of the undesired electric charges changes due to the change in the length of the light emission period (Pb1, Pb2, Pb 3).

Description is made regarding a case where the length of the light emission period (Pb1, Pb2, Pb3) is changed in an environment with signal light and ambient light. When the unnecessary electric charges are not discharged, both the amount of electric charges corresponding to the ambient light and the amount of electric charges corresponding to the signal light increase as the light emission period becomes longer. Therefore, as described above, it is necessary to discharge the unnecessary electric charges so that saturation does not occur.

The amount of the undesired electric charges discharged per weighing operation "W" is increased or decreased in response to the received-light amount of the ambient light obtained in the rest period (Pd1, Pd2, Pd 3). Therefore, by changing the length of the rest period (Pd1, Pd2, Pd3) in response to the length of the light emission period (Pb1, Pb2, Pb3), the amount of the undesired electric charges separated by one weighing operation can be adjusted.

That is, the amount of the undesired electric charges collected in the light emitting periods (Pb1, Pb2, Pb3) is proportional to the length of the light emitting periods (Pb1, Pb2, Pb 3). In addition, the amount of the undesired electric charges discharged by one weighing operation "W" is proportional to the received-light amount obtained in the rest period (Pd1, Pd2, Pd 3). Therefore, when the weighing periods "Pt" are set the same number of times in each of the lighting periods (Pb1, Pb2, Pb3) regardless of the lengths of the lighting periods (Pb1, Pb2, Pb3), the amount of the undesired electric charges to be discharged can be appropriately adjusted by setting the proportional relationship between the lengths of the lighting periods (Pb1, Pb2, Pb3) and the lengths of the rest periods (Pd1, Pd2, Pd 3). In this case, since the weighing periods "Pt" need to be set the same number of times in the lighting periods (Pb1, Pb2, Pb3) having different lengths, the time intervals between the weighing periods "Pt" are adjusted according to the lengths of the lighting periods (Pb1, Pb2, Pb 3).

In the above operation, the length of the rest period (Pd1, Pd2, Pd3) is changed according to the length of the lighting period (Pb1, Pb2, Pb 3). Alternatively, as shown in fig. 7B, it is also advantageous that the length of the pause period "Pd" is kept constant regardless of the length of the lighting period (Pb1, Pb2, Pb3), and the number of times of the weighing operation "W" in one weighing period "Pt" is changed according to the length of the lighting period (Pb1, Pb2, Pb 3). Since the amount of the undesired electric charges discharged in the weighing operation "W" is determined by the received-light amount obtained in the rest period "Pd", it does not depend on the length of the light emission period (Pb1, Pb2, Pb 3). Therefore, the number of times of the weighing operations "W" in the weighing period "Pt" can be changed with respect to each of the light emitting periods (Pb1, Pb2, Pb 3).

In this operation, the amount of the undesired electric charges discharged in one weighing operation "Pt" is adjusted according to the length of the lighting period (Pb1, Pb2, Pb 3). Therefore, this is substantially equivalent to the operation of adjusting the length of the rest period (Pd1, Pd2, Pd 3). In this regard, since the amount of the undesired electric charges discharged in the weighing period "Pt" is an integral multiple of the amount of the undesired electric charges discharged by one weighing operation "W", there is a possibility that the amount of the undesired components other than the signal light component in the received-light output slightly increases as compared with the operation of adjusting the length of the rest period (Pd1, Pd2, Pd3) in accordance with the length of the light emitting period (Pb1, Pb2, Pb 3).

In the case where the weighing operation "W" is repeated a plurality of times in the lighting period "Pb", the amount of the undesired electric charges discharged by the one weighing operation "W" can be reduced, as compared with the case where the weighing operation "W" is performed only once in the lighting period "Pb". As a result, since the rest period "Pd" becomes short, it is possible to reduce the total time of the light emission period "Pb" and the rest period "Pd". In addition, by providing a plurality of weighing periods "Pt" in the lighting period "Pb", it is possible to accumulate electrons corresponding to the signal light while maintaining a state in which the saturation level L1 is not exceeded even if the ambient light increases.

On the other hand, in the case where a plurality of weighing periods "Pt" are set in the lighting period "Pb", since the amount of the undesired electric charges discharged in one weighing period "Pt" is set so that the component corresponding to the signal light is not discharged as the undesired electric charges, there is a possibility that the remaining undesired electric charges are accumulated during the operation of repeating the weighing periods "Pt" a plurality of times. That is, the amount of the undesired electric charges discharged in one weighing period "Pt" is ideally adjusted so that only the amount of electrons corresponding to the signal light is left. However, in practice, since residual electrons other than the electrons corresponding to the signal light are generated and accumulated every weighing period "Pt", a component corresponding to the residual electrons and a component corresponding to the signal light are contained in the received-light output.

That is, as shown in fig. 8, the amount V1 of electrons accumulated before the weighing period "Pt" in the lighting period "Pb" is larger than the sum of the amount V2 of the undesired electric charges to be discharged and the amount V3 of electrons corresponding to the signal light. After the unnecessary electric charges are discharged, there are residual electrons such as noise (electric charge amount V4) in addition to the electrons corresponding to the signal light. Since most of the residual electrons are generated by internal noise such as shot noise, the amount of residual electrons cannot be estimated from the received-light amount obtained in the rest period "Pd". In this regard, although the amount of residual electrons per weighing period "Pt" and the like caused by shot noise vary with the passage of time, it is almost constant on average.

The above-described residual electrons occur at each weighing period "Pt" and are accumulated during the light emission period "Pb". Therefore, when the weighing period "Pt" is repeated in the lighting period "Pb", there is a case where the amount of residual electrons reaches the amount of the undesired electric charges discharged by one weighing operation "W". As described above, since the average value of the amounts of the residual electrons can be estimated, it is possible to determine the number of times of the weighing period "Pt" required to accumulate the residual electrons corresponding to the amount of the undesired electric charges discharged by one weighing operation.

From this viewpoint, it is advantageous that the number of times of the weighing operation "W" is increased only "once" each time the number of times of the weighing period "Pt" reaches the estimated number of times. Thereby making it possible to significantly reduce the residual electrons. In addition, according to this operation, it is possible to prevent the dynamic range of the signal light from being deteriorated by the influence of the residual electrons.

In the case where the weighing operation "W" is repeated a plurality of times in the lighting period "Pb", since the amount of the undesired electric charges to be discharged can be estimated by using the received-light amount of the rest period "Pd", it is necessary to take out electrons corresponding to the received-light amount of the rest period "Pd" to the outside of the photodetector 1. This configuration is advantageously used in the present embodiment. In addition, in the following embodiment, electrons of the received-light amount corresponding to the rest period "Pd" may be taken out to the outside of the photodetector 1.

In addition, it is not necessary to alternately perform the rest period "Pd" and the light emission period "Pb" for estimating the amount of the undesired electric charges. The amount of the undesired electric charges estimated in one rest period "Pd" can be used in a plurality of lighting periods "Pb". In addition, since the time interval between the adjacent lighting periods "Pb" can be set shorter than the rest period "Pd", it is possible to increase the ratio of the period in which the signal light is received per unit time, and thus to increase the period for detecting the spatial information of the object space. The relationship between the rest period "Pd" and the lighting period "Pb" can be used in a similar manner in the following embodiments.

As described above, in the present embodiment, the signal processing section controls the photodetector such that a plurality of weighing periods in each of which the undesired electric charges are separated by an amount determined in accordance with the received-light amount obtained in the rest period are set in the light emission period. In addition, the weighing operation is repeated a plurality of times in each weighing period. The number of times of the weighing operation is increased at each timing of the weighing period corresponding to the prescribed number of times. The prescribed number of times can be determined by using the amount of electric charge derived from the noise component in one lighting period and the amount of unnecessary electric charge discharged by one weighing operation. Therefore, it is possible to reduce the ratio of undesired electric charges derived from a noise component in the received-light output and increase the dynamic range with respect to the signal light component.

Further, when the signal processing section increases the number of times of the operation of discharging the undesired electric charges in the light emission period to increase the amount of the undesired electric charges separated in the light emission period, the amount of the undesired electric charges to be discharged can be easily controlled by managing only the number of times of the operation of discharging the undesired electric charges.

In addition, in the case where the signal processing section controls the photodetector such that the operation of discharging the undesired electric charges is performed a plurality of times in the lighting period, a time interval is set between adjacent operations, and the time interval is decreased as the received-light output obtained in the rest period increases, when the electric charges collected by the photoelectric converting section in the lighting period increase, the undesired electric charges are discharged. Therefore, it is possible to reduce the rate of increase of the electric charges collected in the photoelectric conversion portion, and even when the received-light intensity of the ambient light increases, saturation of the received-light output can be prevented. That is, since the unnecessary electric charges are discharged gradually during the light emission period, the amount of electric charges collected in the photoelectric conversion portion hardly reaches the saturation level, as compared with the case where the unnecessary electric charges are discharged collectively at the end of the light emission period. Further, since the time interval between weighing operations is shortened when the ambient light increases, it is possible to reduce the rate of increase of the electric charges collected in the photoelectric conversion portion and prevent saturation caused by the ambient light.

In the above description, unnecessary electric charges may be discharged using one weighing operation or a plurality of weighing operations performed continuously. The time period during which the weighing operation is continuously performed a plurality of times corresponds to the above-described weighing time period.

In addition, when the signal processing section selects one of a plurality of lighting periods having different durations in accordance with the received-light intensity of the signal light, and increases or decreases the number of weighing operations in accordance with the duration of the lighting period, it is possible to expand the dynamic range with respect to the signal light. In addition, since the amount of the undesired electric charges to be discharged is controlled by increasing or decreasing the number of times of the weighing operation according to the variation in the duration of the light emission period, the duration of the rest period can be kept constant regardless of the duration of the light emission period. As a result, it is possible to relatively reduce the increase or decrease in the total time of the rest period and the light emission period. In other words, by setting the duration of the rest period to be relatively short, the increase or decrease in the total time of the light emission period and the rest period depends only on the increase or decrease in the duration of the light emission period. Therefore, the maximum value of the total time of the pause period and the light emitting period is smaller than the case of changing the duration of the pause period.

(second embodiment)

The present embodiment is characterized by using a photodetector capable of automatically changing the amount of electrons separated as unnecessary electric charges according to the received-light amount, without using an external circuit for controlling the potential barrier B1.

That is, as shown in fig. 9A, as a configuration for automatically adjusting the amount of the undesired electric charges, the photodetector 1 of the present embodiment has a holding well (holding well)15 formed at a position different from the well 12 on the main surface of the device formation layer 11. The holding well 15 has the same conductivity type as the well 12 and has a lower impurity concentration than the well 12. That is, the conductivity type of the holding well 15 is n +. In addition, the holding electrode 14d is arranged at a position corresponding to the holding well 15 through the insulating layer 13, and the gate electrode 14e is arranged at a position corresponding to a region between the well 12 and the holding well 15 on the device formation layer 11 through the insulating layer 13. The holding electrode 14d is electrically connected to the barrier control electrode 14 c. In addition, the region of the device formation layer 11 corresponding to the holding electrode 14d and the gate electrode 14e is light-shielded by the light-shielding film 16.

In addition, since the n + -type holding well 15 is surrounded by the p-type device formation layer 11, a potential well of electrons is formed in the holding well 15 as in the well 12. In this regard, since the holding well 15 has a lower impurity concentration than the well 12, a potential well having a larger depth than the well 12 is formed in the holding well 15 without applying voltages to the separation electrode 14a, the accumulation electrode 14b, the barrier control electrode 14c, and the holding electrode 14 d. The potential well formed in the holding well 15 functions as a charge holding portion D4 that holds electrons.

As the amount of electrons held in the holding well 15 increases, the potential of the holding electrode 14d decreases, and the potential of the barrier control electrode 14c connected to the holding electrode 14d also decreases. When the potential of the barrier control electrode 14c is lowered, the potential barrier B1 becomes high, so that the capacity of the charge separating portion D2 increases. That is, when the amount of electrons held in the holding well 15 increases as the ambient light becomes larger, it is possible to increase the amount of electrons separated as the undesired electric charges in response to the ambient light. Therefore, it is possible to keep the dynamic range almost constant with respect to the signal light regardless of the increase or decrease of the ambient light.

In order to increase or decrease the amount of electrons held in the holding well 15 in accordance with an increase or decrease in ambient light, it is necessary to transfer the electrons generated at the photoelectric converting portion D1 by receiving the ambient light to the holding well 15 and hold them there. That is, a period of time for transferring the electric charges generated by the photoelectric conversion portion to the holding well 15 is set. Since the holding well 15 is light-shielded by the light shielding film 16, the amount of electrons held in the holding well 15 does not change even when light is irradiated to the device formation layer 11 and the well 12.

In addition, in the present embodiment, since the barrier control electrode 14c is connected to the holding electrode 14d, the height of the potential barrier B1 formed at the region corresponding to the barrier control electrode 14c cannot be arbitrarily controlled. The height of the potential barrier B1 is determined by the amount of electrons held in the holding well 15. For this reason, the height of the potential barrier B1 cannot be controlled as in the first embodiment described with reference to fig. 2A to 2D. Therefore, the present embodiment uses a technique of adjusting the potentials of the charge separating portion D2 and the charge accumulating portion D3. So that electrons can be moved in the same process as the first embodiment.

This embodiment will be described in more detail. As in the first embodiment, it is assumed that a potential well formed in the well 12 with no voltage applied to the separation electrode 14a and the accumulation electrode 14b is used as the photoelectric converting portion D1. In addition, a drain (not shown) is formed adjacent to the holding well 15 to discharge the electrons collected in the holding well 15. First, electrons remaining in the well 12 and the holding well 15 are discharged. In this state, no voltage is applied to the separation electrode 14a, the accumulation electrode 14b, the barrier control electrode 14c, the holding electrode 14d, and the gate electrode 14 e. As in the case of fig. 2A, a potential well is formed in the well 12. This potential well serves as the photoelectric converting portion D1. At this time, the light emission source is not turned on, and only ambient light is incident on the photoelectric converting portion D1. Therefore, the electrons generated by the photoelectric converting portion D1 in this period correspond to the received-light amount of the ambient light.

After the electrons in the well 12 and the holding well 15 are discharged, the electrons in an amount corresponding to the received-light amount of the ambient light are collected in the photoelectric converting portion D1 during a predetermined period of time and then transferred to the holding well 15. That is, the amount of electrons corresponding to the ambient light obtained in the pause period in which the light emission source does not project light is held in the holding well 15. After the electrons are transferred from the photoelectric converting portion D1 to the holding well 15, a positive voltage is applied to the gate electrode 14e to lower the potential barrier B2 formed between the photoelectric converting portion D1 and the holding well 15. In addition, a negative voltage is applied to the separation electrode 14a and the accumulation electrode 14b, so that the potential of the photoelectric converting portion D1 is raised so as to be higher than the potential of the holding well 15. According to this operation, electrons can be moved from the well 12 into the holding well 15.

In this way, the amount of electrons transferred to the holding well 15 corresponds to the received-light amount in the pause period of the light emission source. Therefore, it is not necessary that all the electrons generated by the photoelectric converting portion D1 flow into the holding well 15. That is, it is important that the amount of electrons transferred from the well 12 to the holding well 15 is correlated with the received-light amount of the photoelectric converting portion D1 obtained during the rest period of the light emission source.

As shown in fig. 10A, when electric charges corresponding to the rest period of the light emission source are held in the holding well 15, the height of the potential barrier B1 formed at the region corresponding to the barrier control electrode 14c is determined. That is, the capacity of the charge separating portion D2 is determined. As the amount of electrons flowing into the holding well 15 increases, the surface potential of the holding well 15 decreases. In response to the decrease in the surface potential, the potential of the holding electrode 14d decreases. As a result, the voltage applied to the barrier control electrode 14c is reduced, so that the potential barrier B1 becomes high. In the period "Ta" shown in fig. 11A to 11C, since no voltage is applied to the separation electrode 14a, the accumulation electrode 14b, and the gate electrode 14e, the potentials of the barrier control electrode 14C and the holding electrode 14D are determined by the amount of electrons held in the charge holding portion D4.

After electrons are transferred from the photoelectric converting portion D1 to the charge holding portion D4, electrons remaining in the photoelectric converting portion D1 are not needed. Therefore, the remaining electrons are discharged by using the drain formed adjacent to the well 12.

Next, when the light emission source is turned on, both the signal light and the ambient light are incident on the photoelectric converting portion D1. At this time, since the potential barrier B1 is formed in the photoelectric converting portion D1 in accordance with the amount of electrons held in the charge holding portion D4, electrons are collected in an amount not exceeding the height of the potential barrier B1. That is, in the well 12, the region corresponding to the separation electrode 14a and the region corresponding to the accumulation electrode 14b function as the photoelectric converting portion D1. As in the operation shown in fig. 2B of the first embodiment, the well 12 is divided into two regions by forming the potential barrier B1.

Electrons collected in one of the two regions, i.e., the charge separating portion D2 corresponding to the separating electrode 14a are discharged without being used, and electrons collected in the charge accumulating portion D3 corresponding to the accumulating electrode 14b are used. Therefore, in the present embodiment, in the light emission period in which light is projected from the light emission source, the region corresponding to the accumulation electrode 14b in the well 12 substantially functions as the photoelectric converting portion D1. Therefore, the charge accumulating portion D3 also functions as the photoelectric converting portion D1.

As shown by the period "Tb" of fig. 11A to 11C, no voltage is applied to the separation electrode 14 a. As shown in fig. 10B, electrons in the charge separating portion D2 are discharged by using the drain. Subsequently, as shown by a period "Tc" in fig. 11A and 11B, a positive voltage is applied to the separation electrode 14a, and a negative voltage is applied to the accumulation electrode 14B. Thus, as shown in fig. 10C, the potential of the charge separating portion D2 is lowered. Further, when the potential energy of the charge separating portion D2 is considerably reduced, the potential barrier B1 is also reduced. As a result, electrons in the charge accumulating portion D3 (photoelectric converting portion D1) can flow into the charge separating portion D2.

Instead of lowering the potential of the charge separating portion D2, the potential of the charge accumulating portion D3 may be raised. In this case, in order to move all the electrons in the charge accumulating portion D3 into the charge separating portion D2, it is necessary to set the potential energy of the charge accumulating portion D3 to be equal to or larger than the potential energy of the potential barrier B1. In addition, the operation of lowering the potential energy of the charge separating portion D2 and the operation of raising the potential energy of the charge accumulating portion D3 may be performed simultaneously.

As shown by a period "Td" in fig. 11A and 11B, after all the electrons in the charge accumulating portion D3 flow into the charge separating portion D2, the voltages applied to the separating electrode 14a and the accumulating electrode 14B are removed. At this time, the capacity of the charge separating portion D2 was determined. As shown in fig. 10D, when the electrons collected in the charge separating portion D2 exceed the capacity of the charge separating portion D2, the electrons exceeding the capacity flow into the charge accumulating portion D3 through the potential barrier B1. That is, a constant amount of electrons corresponding to the capacity of the charge separating portion D2 and determined in accordance with the amount of electrons held in the charge holding portion D4 (i.e., the amount of electrons corresponding to the rest period of the light emitting source) is separated from the electrons generated by the photoelectric converting portion D1 as the undesired electric charges. On the other hand, the electrons returned to the charge accumulating portion D3 serve as effective charges.

In the above-described embodiment, the height of the potential barrier B1 is automatically adjusted inside the photodetector without using an external circuit. Further, since the amount of the undesired electric charges is determined in accordance with the received-light amount of the ambient light, the dynamic range of the signal light in the received-light output can be kept almost constant regardless of the received-light amount of the ambient light.

In the case where the image pickup device is formed by arranging the plurality of photoelectric converting portions D1, when the potential for determining the amount of the unnecessary electric charges is controlled for each pixel by using the external circuit, the configuration of the external circuit becomes very complicated. On the other hand, as described in the present embodiment, when the technique of automatically adjusting the amount of the undesired electric charges in accordance with the received-light amount of the environmental light is used, the external circuit for determining the amount of the undesired electric charges is substantially unnecessary. In addition, when the image pickup device and the external device are integrated in the semiconductor substrate, the S/N ratio may be deteriorated due to a reduction in the area ratio of the photoelectric conversion portion D1 with respect to the semiconductor substrate. However, in the present embodiment, since an external circuit is not substantially required, an improved S/N ratio can be obtained. The other configuration and operation are the same as those of the first embodiment.

Therefore, after the photoelectric conversion portion generates the electric charges, the electric charges corresponding to the received-light amount in a desired period of time can be transferred from the photoelectric conversion portion to the electric-charge holding portion by controlling the voltage applied to the gate electrode. After the transfer of the electric charges, an amount of undesired electric charges determined according to the potential of the holding electrode is separated from the electric charges corresponding to the received-light amount in a period of time. The timing of transferring the electric charges generated by the photoelectric conversion portion to the electric charge holding portion is controlled by the voltage applied to the gate electrode. As a result, effective electric charges reflecting the difference between the received-light amount in the period for generating electric charges transferred to the charge holding portion and the received-light amount in the subsequent appropriate period can be taken out as the received-light amount.

In the present embodiment, the gate electrode 14e is used to control the timing of transferring electrons from the potential well formed as the photoelectric converting portion D1 in the well 12 to the potential well formed as the charge holding portion D4 in the holding well 15. Alternatively, the gate electrode 14e may be omitted. In this case, electrons can be transferred from the photoelectric converting portion D1 to the charge holding portion D4 by controlling the voltages applied to the separation electrode 14a and the accumulation electrode 14 b.

For example, a positive voltage is applied to the separation electrode 14a and the accumulation electrode 14b to form a potential well. After collecting the electrons in the photoelectric converting portion D1, a negative voltage is applied to the separation electrode 14a and the accumulation electrode 14b, so that the electrons collected in the well 12 move to the holding well 15. By applying a negative voltage to the accumulation electrode 14b, the potential barrier between the well 12 and the holding well 15 is broken, so that electrons are easily moved from the well 12 to the holding well 15. In addition, since a negative voltage is applied to the separation electrode 14a, it is possible to prevent electrons collected in the well 12 from moving in the left direction of fig. 9.

After the electrons move from the well 12 into the holding well 15, a positive voltage is applied to the separation electrode 14a and the accumulation electrode 14b to form a potential well in the well 12. By these operations, it is possible to move electrons from the photoelectric converting portion D1 to the charge holding portion D4 without using the gate electrode 14 e.

Instead of fig. 9A, it is also advantageous that the barrier control electrode 14c is directly electrically connected to the holding well 15 formed as a charge holding portion in the semiconductor substrate. That is, as shown in fig. 9A, when the holding electrode 14d is formed on the insulating layer 13, the holding electrode 14d becomes a floating electrode (floating electrode). In this case, noise charges are easily accumulated in the wiring between the holding electrode 14d and the barrier control electrode 14c with the passage of time. Therefore, it is desirable to form a switch for removing (resetting) noise charges from the wiring between the holding electrode 14d and the barrier control electrode 14 c. On the other hand, when the switch is formed for each pixel, an increase in the device size and the production cost may result.

Therefore, the holding electrode 14d is not formed on the region of the semiconductor substrate corresponding to the holding well 15 through the insulating layer. Alternatively, direct electrical connection is made between the barrier control electrode 14c and the region of the semiconductor substrate corresponding to the holding well 15. In these cases, when the holding well 15 is reset, noise charges in the wiring can be reliably removed by using the adjacently formed reset means. The reset device shown in fig. 9B is formed by the reset drain 100, the reset electrode 14r formed at a position corresponding to the region between the holding well 15 and the reset drain 100, and the circuit 110 for discharging the charge from the reset drain 100. By applying a predetermined voltage Vr to the reset electrode 14r, it is possible to remove the electric charges from the holding well 15 through the reset drain 100.

(third embodiment)

In the present embodiment, as in the second embodiment, the charge holding portion D4 is formed, and the capacity of the charge separating portion D2 is automatically determined in accordance with the received-light amount of the ambient light. The present embodiment is characterized in that the intensity of light projected from a light emission source in a light emission period is modulated by a modulation signal having a constant frequency, and a received light output corresponding to the amount of received light obtained at timings synchronized with two different phase zones (phase zones) of the modulation signal is taken out. In addition, a sine wave is used as a waveform of the modulation signal to take out received light outputs corresponding to the received light amounts obtained in the phase zone of 0 to 180 degrees (hereinafter referred to as phase zone "P0") and the received light amounts obtained in the phase zone of 180 and 360 degrees (hereinafter referred to as phase zone "P2"), respectively. A rectangular wave, a triangular wave, or a sawtooth wave may be used as the waveform of the modulation signal. In addition, the phase zone for obtaining the received-light amount is not limited to the above-described phase zone.

In the present embodiment, the image sensor is configured by arranging a plurality of cells 1. The received-light outputs of the above two phase zones may be taken out simultaneously every operation of taking out the received-light output of 1 frame from the image sensor. In the case of taking out the received-light outputs of two phase zones by 1 frame, a configuration of detecting the received-light amount with respect to each phase zone and a configuration of accumulating the received-light outputs with respect to each phase zone are necessary for each cell 1. Therefore, the photoelectric converting portion D1 is formed separately from the charge separating portion D2 and the charge accumulating portion D3.

This embodiment is described in more detail with reference to fig. 12A-12C. The photoelectric converting portion D1 is provided with a well (not shown) formed on the main surface of the device formation layer 11 and a plurality of sensitivity control electrodes (for example, eight sensitivity control electrodes 17a to 17h) arranged on the well through the insulating layer 13. The well has a different conductivity type from the device formation layer 11. It is desirable that the well 12 serving as the charge separating portion D2 and the charge accumulating portion D3 be formed separately from the well and that charges be transferred to the well 12 via the gate. Alternatively, the wells may be formed continuously. In this case, charge can be transferred by potential control. Four sensitivity control electrodes (17a-17d) of the eight sensitivity control electrodes (17a-17h) are used as a group for one phase zone, and the remaining four sensitivity control electrodes (17e-17h) are used as groups for the other phase zones. The control line 21a is connected to each of the sensitivity control electrodes (17a to 17 h). Therefore, the voltage applied to each of the sensitivity control electrodes (17a to 17h) can be independently controlled. In the drawing, the symbol "X" denotes a connection point between the control line 21a and each of the sensitivity control electrodes (17a to 17 h).

The longitudinal direction of fig. 12A corresponds to the vertical direction of the image sensor. In the figure, only one unit 1 is shown in the vertical direction. That is, the one cell 1 has eight sensitivity control electrodes (17a to 17h) arranged in the vertical direction. In the figure, a part of another cell 1 adjacent to the cell 1 in the horizontal direction is shown. Each sensitivity control electrode (17a to 17h) extends in the horizontal direction over the range of two adjacent cells 1. Reference numeral 20 denotes a cell separation portion formed between adjacent cells 1 in the horizontal direction to prevent crosstalk between the cells 1 in the horizontal direction. The cell separation portion 20 is formed on the main surface side of the device formation layer 11 by using a semiconductor having a different conductivity type from that of the device formation layer 11. In the figure, four control lines 21a are provided on each of both sides of the unit separating portion 20. Therefore, the area of the control line 21a in the photoelectric converting portion D1 can be equally determined with respect to each of two cells adjacently formed in the horizontal direction. Therefore, the photoelectric conversion portions D1 of the adjacent two cells 1 can have the same sensitivity. In addition, the sensitivity control electrodes at the same positions in the plurality of cells 1 arranged in the vertical direction are connected to the same control line 21 a.

In the present embodiment, as described above, the photoelectric converting portion D1 having the sensitivity control electrodes (17a to 17h) is formed separately from the charge separating portion D2 and the charge accumulating portion D3. In addition, the charge separating portion D2, the charge accumulating portion D3, and the charge holding portion D4 are arranged adjacent to the sensitivity control electrodes (17a to 17h) in the horizontal direction. Although not shown in the drawing, the charge separating portion D2, the charge accumulating portion D3, and the charge holding portion D4 of the right one of the two cells 1 adjacently formed in the horizontal direction are disposed on the right side of the photoelectric converting portion D1. On the other hand, these portions of the left one of the two cells 1 adjacently formed in the horizontal direction are arranged on the left side of the photoelectric converting portion D1. In addition, each set of sensitivity control electrodes (17a to 17h) forms the charge separating portion D2 and the charge accumulating portion D3. The charge holding portion D4 is shared by two groups constituting one cell 1 because the charge holding portion D4 serves to hold electrons corresponding to ambient light, and it can be said that there is no change in ambient light between the two groups. Due to this configuration, when the same voltage is applied to the barrier control electrodes 14c of the two groups, the potential barrier B1 having the same height can be obtained in the two groups. Therefore, when a plurality of sets of the charge separating portion and the charge accumulating portion are formed and the charge holding portion is shared by two barrier control electrodes 14c formed adjacently, there is an advantage that the size of the device forming region is reduced as compared with the case where the charge holding portion is formed independently.

In each group, the accumulation electrode 14b is formed adjacent to the sensitivity control electrodes (17c, 17 f). Electrons generated by the photoelectric converting portion D1 may be transferred from a region corresponding to the sensitivity control electrode (17c, 17f) to the charge accumulating portion D3. At this point, by adjusting the potential energy relationship between the photoelectric converting portion D1 and the charge accumulating portion D3, it is also possible to move electrons from the charge accumulating portion D3 to the photoelectric converting portion D1. Alternatively, the flow of electric charges therebetween may be controlled by disposing a gate electrode (not shown) between the photoelectric converting portion D1 and the charge accumulating portion D3.

In addition, in each group, the separation electrode 14a is arranged adjacent to the sensitivity control electrodes (17a, 17 h). On the other hand, the holding electrode 14d shared by the two groups is arranged adjacent to the region straddling between the sensitivity control electrodes (17d, 17 e). The separation electrode 14a, the accumulation electrode 14b, and the gate electrode 14e are connected to the control line 21b, respectively. The barrier control electrode 14c is connected to the holding electrode 14d through a connection line 22. That is, the control lines 21b are used to make connections between the separation electrodes 14a of the group, between the accumulation electrodes 14b of the group, and between the gate electrodes 14e of the group, respectively. Therefore, the movement of electrons in the charge separating portion D2, the charge accumulating portion D3, and the charge holding portion D4 can be controlled by using these three control lines 21 b. In the figure, symbol "X" denotes a connection point between the control line 21b or the connection line 22 and the separation electrode 14a, the accumulation electrode 14b, the barrier control electrode 14c, the holding electrode 14d, or the gate electrode 14 e.

The voltage applied to the sensitivity control electrodes (17a-17h) is controlled so as to be synchronized with a modulation signal for modulating the intensity of light projected from the light emission source. For example, in the phase zone P0, a positive voltage is applied to each of the sensitivity control electrodes (17a to 17d) and the sensitivity control electrode 17 f. On the other hand, in the phase zone P2, a positive voltage is applied to each of the sensitivity control electrode 17c and the sensitivity control electrodes (17e to 17 h). When a positive voltage is applied to each of the sensitivity control electrodes (17a-17h), a potential well for collecting electrons is formed in a region corresponding to each sensitivity control electrode in the cell.

As described above, when the voltages applied to the sensitivity control electrodes (17a to 17h) are controlled, electrons generated in the phase zone P0 by the illumination are collected in the region of the sensitivity control electrodes (17a to 17d) corresponding to the wells, on the other hand, electrons generated in the phase zone P2 by the illumination are collected in the region of the sensitivity control electrodes (17e to 17h) corresponding to the wells. That is, the area where electrons are generated by light irradiation can be changed by controlling the voltage application pattern to the sensitivity control electrodes (17a to 17 h). This is substantially equivalent to controlling the sensitivity of the photodetector.

In the phase zone P0, since a potential well is also formed in the region corresponding to the sensitivity control electrode 17f, the electrons collected in the phase zone P2 can be held in the potential well. On the other hand, in the phase zone P2, the electrons collected in the phase zone P0 can be held in the potential well formed at the region corresponding to the sensitivity control electrode 17 c.

Thus, electrons generated by illumination with respect to each phase interval may be collected by a plurality of cycles of the modulation signal. For example, when the modulation signal is 10MHz and the time period for generating electrons at the photoelectric converting portion D1 is 15ms, the plurality of cycles corresponds to 150000 cycles. Electrons are generated in the region corresponding to the sensitivity control electrode (17c, 17f) even during a period for holding the electrons in the region corresponding to the sensitivity control electrode (17c, 17 f). However, since the electron collecting area in the period for collecting electrons is 4 times the electron collecting area in the period for holding electrons (i.e., the area ratio is 4: 1), it can be considered that the amount of held electrons reflects the received-light amount in each phase zone of the modulation signal. In short, the amount of electrons corresponding to each of the phase zones (P0, P2) can be held in the region corresponding to the sensitivity control electrode (17c, 17 f).

The electrons held in the region corresponding to the sensitivity control electrodes (17c, 17f) are transferred into the charge accumulating portion D3. In this transfer step, a positive voltage is applied to the accumulation electrode 14b, and a negative voltage is applied to the sensitivity control electrodes (17a to 17 h). In the case where electrons are moved in the charge separating portion D2, the charge accumulating portion D3, and the charge holding portion D4, a negative voltage is applied to the sensitivity control electrodes (17a to 17h) to prevent the electrons from moving to the photoelectric converting portion D1. In this regard, since the electrons collected in the phase zone P2 are held in the region corresponding to the sensitivity control electrode 17c and the electrons collected in the phase zone P0 are held in the region corresponding to the sensitivity control electrode 17f, the timing at which the charge accumulating portion D3 of one group receives the electrons from the photoelectric converting portion D1 is different from the timing at which the charge accumulating portion D3 of the other group receives the electrons from the photoelectric converting portion D1.

The electrons generated at the photoelectric converting portion D1 in the rest period of the light emitting source are transferred from the charge accumulating portion D3 to the charge holding portion D4 through the region corresponding to the gate electrode 14 e. In this regard, although the modulation signal is not required for the rest period of the light emission source, the voltage applied to the sensitivity control electrodes (17a to 17h) is controlled at the same timing as the light emission period of the light emission source to generate electrons in an amount corresponding to the received-light amount of the ambient light at the photoelectric converting portion D1. Therefore, in the two sets of one cell 1, electrons corresponding to the ambient light are transferred to the charge accumulating portion D3. It is sufficient that electrons are transferred from one charge accumulating portion D3 of the group to the charge holding portion D4. Alternatively, electrons may be transferred from both charge accumulating portions D3 of the group. After the electrons of an amount corresponding to the received-light amount of the ambient light are transferred, a voltage is applied to the barrier control electrode 14c connected to the holding electrode 14d through the connection line 22, so that a potential barrier B1 is formed in each well 12 in accordance with the received-light amount of the ambient light.

Next, in the lighting period of the light emission source, electrons are collected by each group by the photoelectric converting portion D1. As a result, the electrons collected in the phase zones (P0, P2) are held in the regions corresponding to the sensitivity control electrodes (17c, 17f), respectively. Then, the electrons move from the photoelectric converting portion D1 to the charge accumulating portion D3. The operation performed thereafter is the same as that in the second embodiment. That is, electrons move from the charge accumulating portion D3 to the charge separating portion D2, so that an unnecessary amount of electric charge determined according to the capacity of the charge separating portion D2 is discharged, and effective electric charge is returned to the charge accumulating portion D3. By this operation, it is possible to obtain effective electric charges in the charge accumulating portion D3. The amount of the effective electric charges corresponds to the amount of electric charges obtained by separating the undesired amount of electric charges determined by the received-light amount in the rest period of the light emission source from the electrons collected by the photoelectric converting portion D1 in the light emission period of the light emission source.

The present embodiment uses a configuration of returning the effective charges in the charge accumulating portion D3 to the photoelectric converting portion D1. That is, by applying a negative voltage to the accumulation electrode 14b and a positive voltage to the photoreception control electrodes (17c, 17f), electrons of effective charges are transferred from the charge accumulating portion D3 to the photoelectric converting portion D1. The electrons transferred to the photoelectric converting portion D1 are further transferred in the vertical direction by using the photosensitive control electrodes (17a to 17h) as vertical transfer electrodes, and then taken out as a received-light output to the outside of the photodetector as in a conventional CCD image sensor.

In the configuration of the present embodiment, portions other than the photoelectric converting portion D1 are preferably light-shielded. That is, by the light-shielding charge separating portion D2, the charge accumulating portion D3, and the charge holding portion D4, it is possible to prevent electrons generated by light irradiation during the operation of separating undesired electric charges from being mixed into effective electric charges as an error component. On the other hand, as in the above-described embodiment, since the weighing period for separating the undesired electric charges and taking out the effective electric charges is considerably shorter than the light receiving period for collecting the electrons generated at the photoelectric converting portion D1 by the light irradiation, the charge separating portion D2 and the charge accumulating portion D3 may not be light-shielded. Even in this case, the charge holding portion D4 should be light-shielded.

In the present embodiment, since the photoelectric converting portion D1 does not collect electrons generated by light irradiation during the operation of separating undesired electric charges, it is possible to achieve a reduction in error as compared with the case where the photoelectric converting portion D1 is also used as the charge accumulating portion D3. The other configuration and operation are the same as those of the second embodiment.

In addition, in the second and third embodiments, the explanation is made with respect to the following case: the spatial information detecting device is characterized by a combination of the photodetector having the charge holding portion D4 and the light emission source, and electrons of an amount corresponding to the received light amount in the pause period of the light emission source (i.e., the received light amount of the ambient light) are held in the charge holding portion D4. In this apparatus, by using the relationship between the received-light output of the photodetector and the light projected from the light emission source, it is possible to obtain information about the target space to which the light projected from the light emission source is projected. As the information on the object space, there are, for example, the presence or absence of an object in the object space, the reflection coefficient of the object, and the distance to the object. A circuit (not shown) for processing the received-light output can be appropriately designed according to information required about the object space.

For example, in the case of determining the distance to an object in the target space, the intensity of light projected from the light emission source is modulated by a modulation signal having a predetermined frequency. The photodetector detects the received-light amount at a plurality of timings synchronized with the modulation signal. This is a technique of detecting a flight time taken for light projected from the light emission source to be incident on the photodetector as a phase difference of the modulated light. To calculate the phase difference, the difference between the received-light amounts in two different phase sections of the modulation signal is used.

In the third embodiment, since the effective charge is obtained in each of the phase zones (P0, P2), the distance can be calculated using the difference between the effective charges of the phase zones. On the other hand, in the second embodiment, when electrons obtained in one of the phase zones (P0, P2) are held in the charge holding portion D4, an amount of electrons corresponding to the received-light amount of the phase zone is determined as an unnecessary charge, and the unnecessary amount of charge is subtracted from electrons obtained in the other phase zone. That is, the amount of the obtained effective electric charges corresponds to the difference between the received-light amounts of the two phase zones (P0, P2). Therefore, when the distance is calculated by an external circuit, it is possible to reduce the calculation amount for the received-light output of the photodetector.

In a configuration in which the amount of effective electric charges is equal to the difference between the received-light amounts of the two phase zones (P0, P2), when electrons collected in the two phase zones (P0, P2) are alternately held in the charge holding portion D4, an error occurs in a different direction depending on which of the received-light outputs of the two phase zones is held. . In this case, by determining the average value of the two received-light outputs, it is possible to eliminate an error caused by separating undesired electric charges. As a result, information on the object space can be accurately detected from the received light output.

As in the present embodiment, when a plurality of photoelectric conversion portions are arranged, the amount of the undesired electric charges separated in the weighing period may be set to be the same with respect to each photoelectric conversion portion. In this case, as compared with the case where the amount of the undesired electric charges is determined separately by each photoelectric converting portion D1, the control becomes easy by forming the common electric channel for controlling the amount of the undesired electric charges.

In addition, when the charge separating section is formed for each photoelectric converting section, and the signal processing section sets the amount of the undesired electric charges separated by one charge weighing operation for each charge separating section, it is preferable that the number of times of the charge weighing operations be set to be the same for all the charge separating sections. According to this photodetector, there is an advantage that the timing of the charge weighing operation can be controlled in total.

(fourth embodiment)

In the third embodiment, the charge separating portion D2 and the charge accumulating portion D3 are formed with respect to each of the received-light amount in the phase zone P0 synchronized with the phase range of 0-180 degrees of the modulation signal and the received-light amount in the phase zone P2 synchronized with the phase range of 180-360 degrees of the modulation signal. The present embodiment is characterized in that the charge separating portion D2 and the charge accumulating portion D3 are shared with respect to the received-light amounts in these phase zones (P0, P2).

That is, as shown in fig. 13, the present embodiment is the same as the third embodiment in the following respects: eight sensitivity control electrodes (17a to 17h) are formed with respect to each cell 1 of the photoelectric converting portion D1. In the third embodiment, the charge separating portion D2, the charge accumulating portion D3, and the charge holding portion D4 are arranged in a symmetrical manner in the vertical direction. On the other hand, these portions of the present embodiment are arranged in an asymmetrical manner in the vertical direction. In the photoelectric converting portion D1, a region E3 where the charge separating portion D2 and the charge accumulating portion D3 are formed is arranged on the side of the region E1 where the sensitivity control electrodes (17a to 17D) are provided. As described later, the photoelectric converting portion D1 also functions as a charge accumulating portion D3. Further, a region E4 where the charge holding portion D4 is formed is arranged on the side of the region E2 where the sensitivity control electrodes (17E to 17h) are provided.

In the region E3 where the charge separating portion D2 and the charge accumulating portion D3 are formed, the acceptance electrode 14f is formed adjacent to the sensitivity control electrode 17a of the photoelectric converting portion D1. When the potential well formed under the acceptance electrode 14f has a larger depth than the potential well formed under the sensitivity control electrode 17a, the electric charges collected in the potential well formed under the sensitivity control electrode 17a can be received from the photoelectric converting portion D1.

In the region E3, the separation electrode 14a, the barrier control electrode 14c, and the accumulation electrode 14b are provided on the side of the sensitivity control electrodes (17b, 17c, 17d), respectively. In the drawing, only the barrier control electrode 14c is shown to have a small size. However, the present embodiment is not limited to this dimensional relationship.

On the other hand, in the region E4 where the charge holding portion D4 is formed, the gate electrode 14E is formed adjacent to the sensitivity control electrodes (17E to 17g) of the photoelectric converting portion D1. When the potential well formed under the gate electrode 14e has a larger depth than the potential well formed under the sensitivity control electrode 17f, the electric charges collected in the potential well formed under the sensitivity control electrode 17f can be received from the photoelectric converting portion D1.

In the region E4, the holding electrode 14D is formed such that the photoelectric conversion portion D1 is arranged on one side of the gate electrode 14E, and the holding electrode 14D is arranged on the other side of the gate electrode 14E. Therefore, as in the second and third embodiments, when a potential well is formed under the holding electrode 14d and the potential under the gate electrode 14e is appropriately adjusted, the electric charges collected in the potential well under the sensitivity control electrode 17f can flow into the potential well under the holding electrode 14 d.

After the electric charges move into the potential well under the holding electrode 14D, i.e., the electric charge holding portion D4, the potential of the barrier control electrode 14c is determined by the amount held in the electric charge holding portion D4. That is, the height of the potential barrier formed under the barrier control electrode 14c is determined. A drain (overflow drain) 23 is formed adjacent to the well 12 (fig. 1) in the device formation layer 11.

Referring to fig. 14, the operation of the present embodiment is explained. As in the third embodiment, the pause period of the light emission source is set. In the case of using the photodetector of the present embodiment, first, a positive voltage is applied to the sensitivity control electrodes (17e to 17h) of the photoelectric converting portion D1 for the rest period (S1), and the sensitivity control electrodes (17a to 17D) are held at the reference potential. Alternatively, a negative voltage may be applied to the electrodes (17a-17 d). Then, the reference potential state may be replaced with a state in which a negative voltage is applied. In addition, the separation electrode 14a, the accumulation electrode 14b, the holding electrode 14d, the gate electrode 14E, and the acceptance electrode 14f formed in the region (E3, E4) are also held at the reference potential.

Through the above-described process, electrons corresponding to the received-light amount of the ambient light are collected into the region E2 corresponding to the sensitivity control electrodes (17E to 17h) of the photoelectric converting portion D1 (S2). Subsequently, a positive voltage is applied only to the sensitivity control electrode 17f, and the remaining sensitivity control electrodes (17a to 17e, 17g, 17h) are held at the reference potential. By this operation, electrons corresponding to the received-light amount of the ambient light are collected into the potential well corresponding to the sensitivity control electrode 17 f.

Next, a positive voltage is applied to the gate electrode 14e to form a channel under the gate electrode 14 e. So that electrons can be transferred from the potential well under the sensitivity control electrode 17f to the charge holding portion D4 under the holding electrode 14D (S3). When the electrons are transferred to the charge holding portion D4, the potential of the holding electrode 14D becomes a potential corresponding to the received-light amount of the ambient light, and the potential of the barrier control electrode 14c also becomes the same potential. That is, the height of the potential barrier formed under the barrier control electrode 14c is determined.

Next, a light emission period in which light is projected from the light emission source is started (S4). In the light emission period, after the signal light intensity-modulated by the modulation signal is projected, the following operation is performed to individually take out the received-light output corresponding to the received-light amount of the phase zone (P0, P2). In the present specification, electrons corresponding to the received-light amount of the phase zone P0 are collected in the region E1, and electrons corresponding to the received-light amount of the phase zone P2 are collected in the region E2.

First, a set of operations of applying a positive voltage to each of the sensitivity control electrodes (17a to 17d) of the region E1 and the sensitivity control electrode 17f of the region E2 and holding the residual sensitivity control electrodes (17E, 17g, 17h) of the region E2 at the reference potential (S5), and an operation of applying a positive voltage to the sensitivity control electrode 17b of the region E1 and the sensitivity control electrodes (17E to 17h) of the region E2 and holding the remaining sensitivity control electrodes (17a, 17c, 17d) of the region E1 at the reference potential (S6) are performed once or more times at a cycle synchronized with the modulation signal. Thus, the electrons corresponding to the received-light amount of the phase zone P0 are collected in the potential well corresponding to the sensitivity control electrode 17b, and the electrons corresponding to the received-light amount of the phase zone P2 are collected in the potential well corresponding to the sensitivity control electrode 17 f.

Next, an operation of separating unnecessary electric charges from the electrons corresponding to the received-light amount of each phase zone (P0, P2) and taking out effective electric charges is performed. Since the electrons corresponding to the received-light amount of the phase zone P0 are collected in the potential well corresponding to the sensitivity control electrode 17b, the electrons are transferred to the potential well corresponding to the sensitivity control electrode 17a by applying a positive voltage to the sensitivity control electrode 17a and holding the sensitivity control electrode 17b at the reference potential. Further, the electrons are transferred to the potential well under the acceptance electrode 14f by applying a positive voltage to the acceptance electrode 14f and holding the sensitivity control electrode 17a at the reference potential. That is, the electrons corresponding to the received-light amount of the phase zone P0 collected in the region E1 are transferred to the region E3 (S7).

The electrons transferred to the region E3 flow from the potential well corresponding to the acceptance electrode 14f into the charge separating portion D2 formed at the region corresponding to the separation electrode 14 a. At this point, since the height of the potential barrier between the charge separating portion D2 and the charge accumulating portion D3 has been determined, a constant amount of undesired electric charges remain in the charge separating portion D2, and the remaining electrons flow into the charge accumulating portion D3. The undesired electric charges in the charge separating portion D2 are discharged through the drain electrode 23. Therefore, the amount of the undesired electric charges is removed from the electrons corresponding to the received-light amount of the phase zone P0, and the effective electric charges are taken out (S8).

As described above, the effective electric charges thus obtained are transferred to the potential well formed under the sensitivity control electrode 17d adjacent to the accumulation electrode 14 b. That is, the effective electric charges obtained by separating the undesired electric charges corresponding to the received-light amount of the environmental light from the electrons corresponding to the received-light amount of the phase zone P0 are transferred from the region E3 to the region E1 (S9).

Similarly, it is desirable to separate out the undesired charge with respect to the electrons collected in region E2. In the region E2, electrons corresponding to the received-light amount of the phase zone P2 are collected in the potential well corresponding to the sensitivity control electrode 17 f. To transfer the electrons to the region E3, the electrons are first transferred from the potential well corresponding to the sensitivity control electrode 17f to the potential well corresponding to the sensitivity control electrode 17 a. At this time, in order to prevent the transferred electrons from being mixed with the effective electric charges obtained from the received-light amount of the phase zone P0, the electric charges transferred to the region E1 at step S9 are transferred in the vertical direction. That is, electrons (i.e., effective charges of the phase zone P0) are transferred from the potential well under the sensitivity control electrode 17d to the potential well under the sensitivity control electrode 17g of the adjacent cell 1. On the other hand, the electrons (i.e., the electrons of the phase zone P2) are transferred from the potential well under the sensitivity control electrode 17f to the potential well under the sensitivity control electrode 17a (S10).

After the electrons corresponding to the received-light amount of the phase zone P2 are transferred to the potential well under the sensitivity control electrode 17a, they are further transferred from the region E1 to the region E3. The undesired electric charges are separated from the transferred electrons, and the effective electric charges are accumulated in the charge accumulating portion D3 (S11-S13). That is, by performing the same operations as steps S7-S9, it is possible to take out the effective charge of the phase zone P2. The obtained effective electric charges are transferred to the potential well under the sensitivity control electrode 17 d. Therefore, the effective charge returns from the region E3 to the region E1 (S14).

According to the above-described procedure, when the effective charges of each phase zone (P0, P2) are obtained, they are transferred in the vertical direction and returned once to the region corresponding to the sensitivity control electrode (17b, 17f) (S15). After this operation is repeated a prescribed number of times in the light emission period (S16), the electrons remaining in the potential well corresponding to the sensitivity control electrode (17b, 17f) are finally taken out as the received-light output (S17).

In the present embodiment, the drain electrode 14g is formed between the separation electrode 14a and the drain electrode 23, and the drain electrode 14h is formed between the holding electrode 14d and the drain electrode 23. Unnecessary electric charges can be discharged every time electric charges are transferred from the region E1 to the region E3 by controlling the voltage applied to the discharge electrode 14 g. In addition, the electrons corresponding to the received-light amount of the ambient light held in the charge holding portion D4 can be discharged each time the electric charges are transferred from the region E2 to the region E4 by controlling the voltage applied to the discharge electrode 14 h. Other configurations and operations are the same as those in the above-described embodiment.

(fifth embodiment)

As shown in fig. 15, the present embodiment is characterized in that a region E3 capable of separating unnecessary electric charges and a region (E1, E2) forming the photoelectric conversion portion D1 are provided in the vertical direction.

That is, the sensitivity control electrodes (17a to 17f) are formed with respect to one cell 1. Regions (E1, E2) for collecting electric charges corresponding to the received-light amounts in the phase zones (P0, P2) are provided by the three sensitivity control electrodes (17a-17c) and the three sensitivity control electrodes (17d-17f), respectively. Further, a region E3 for separating undesired electric charges is formed between the adjacent cells 1 in the vertical direction. A region E4 for holding electric charges corresponding to the received-light amount of the ambient light is also formed on one side of the region E3 (i.e., a position distant from the region E3 in the horizontal direction).

That is, the acceptance electrode 14f is arranged in a region adjacent to the sensitivity control electrode 17f of the cell 1. The separation electrode 14a, the barrier control electrode 14c, and the accumulation electrode 14b are arranged in order adjacent to the acceptance electrode 14f in the vertical direction. That is, the acceptance electrode 14f is disposed between the sensitivity control electrode 17f and the separation electrode 14a, and the accumulation electrode 14b is disposed between the barrier control electrode 14c and the sensitivity control electrode 17a of the adjacent other cell 1.

In addition, the gate electrode 14E is formed such that the acceptance electrode 14f, the separation electrode 14a, and the barrier control electrode 14c of the region E3 are arranged on one side of the gate electrode 14E. In addition, a holding electrode 14d is disposed on the other side of the gate electrode 14 e. In this regard, the barrier control electrode 14c is electrically connected to the holding electrode 14d through the connection line 22. The drain 23 is formed to extend along the periphery of the region (E1, E2, E3, E4). In addition, a discharge electrode 14g is disposed between the holding portion D4 corresponding to the holding electrode 14D and the drain electrode 23. Each of the above-described electrodes is arranged on the surface of the n-type well 12 formed on the p-type device formation layer 11.

The operation of the present embodiment is substantially the same as the fourth embodiment. That is, a positive voltage is applied to the sensitivity control electrodes (17D to 17f) of the region E2 corresponding to the photoelectric converting portion D1 for the rest period, and the sensitivity control electrodes (17a to 17c) of the region E1 are held at the reference potential. In addition, the separation electrode 14a, the accumulation electrode 14b, the barrier control electrode 14c, the holding electrode 14d, the gate electrode 14e, and the receiving electrode 14f are held at a reference potential. Therefore, electrons corresponding to the received-light amount of the ambient light are collected in the region E2 of the photoelectric converting portion D1. Subsequently, a positive voltage is applied to only one of the sensitivity control electrodes (17a to 17f) (i.e., the sensitivity control electrode 17f) of the region (E1, E2), so that the collected electrons are collected in the potential well corresponding to the sensitivity control electrode 17 f.

The electrons collected in the potential well corresponding to the sensitivity control electrode 17f are transferred to the holding portion D4 under the holding electrode 14D through the acceptance electrode 14f and the gate electrode 14 e. At this stage, the height of the potential barrier formed under the barrier control electrode 14c is set according to the ambient light.

Next, a lighting period in which light is projected from the light emission source is started. At least one set of an operation of applying a positive voltage to the sensitivity control electrodes (17a-17c, 17e) and holding the sensitivity control electrodes (17d, 17f) at the reference potential and an operation of applying a positive voltage to the sensitivity control electrodes (17b, 17d-17f) and holding the sensitivity control electrodes (17a, 17c) at the reference potential are performed at a period synchronized with the modulation signal so as to be associated with a phase zone (P0, P2) synchronized with the modulation signal. According to these operations, the electrons corresponding to the received-light amount in the phase zone P0 are collected in the potential well under the sensitivity control electrode 17b, and the electrons corresponding to the received-light amount in the phase zone P2 are collected in the potential well under the sensitivity control electrode 17 e.

At this point, when the electrons collected in the potential well under the sensitivity control electrode 17e are transferred in the vertical direction and are also transferred to the potential well formed as the charge separating portion D2 under the separating electrode 14a, the unnecessary charges are separated according to the barrier height under the barrier control electrode 14c, and only the effective charges are accumulated in the charge accumulating portion D3 under the accumulating electrode 14 b. That is, the effective electric charge corresponding to the phase zone P2 is accumulated in the electric charge accumulating portion D3. On the other hand, the undesired electric charges left in the charge separating portion D2 are discharged through the drain 23 by a predetermined route (not shown).

In fig. 15, the drain electrode 23 is continuously formed from the upstream side toward the downstream side of the separation electrode 14 a. In this regard, it is assumed that electrons are transferred from the upper side to the lower side of fig. 15. Alternatively, the drain electrode 23 formed on the upstream side of the separation electrode 14a may be separated from the drain electrode 23 formed on the downstream side thereof. In this case, the undesired electric charges are transferred to a region under one of the sensitivity control electrodes (17a to 17f, for example, the sensitivity control electrode 17e) adjacent to the drain electrode 23 on the upstream side. Then, a voltage (for example, +15V) for attracting electrons is applied to the drain 23, and a voltage (for example, -5V) for ejecting electrons is applied to the sensitivity control electrode 17e corresponding to the region having the transferred undesired electric charges. A voltage for ejecting electrons is also applied to the sensitivity control electrodes (17c, 17d, 17f, 17g) adjacent to the sensitivity control electrode 17e to which the undesired electric charges are transferred. According to these operations, the unnecessary electric charges can be discharged through the drain 23 without flowing to the sensitivity control electrodes (17c, 17d, 17f, 17 g).

Next, the electrons corresponding to the received-light amount of the phase zone P0 collected in the potential well formed under the sensitivity control electrode 17b are transferred in the vertical direction, and are also transferred into the potential well formed under the separation electrode 14a as the charge separating portion D2. At this time, the effective electric charges of the phase zone P2 accumulated in the electric charge accumulating portion D3 under the accumulating electrode 14b are transferred in the vertical direction, and are temporarily held at the potential well formed under the sensitivity control electrode 17b of the vertically adjacent cell 1.

As described above, when electrons corresponding to the received-light amount of the phase zone P0 are transferred to the charge separating portion D2, unnecessary electric charges are separated, and effective electric charges of the phase zone P0 are accumulated in the charge accumulating portion D3.

The effective electric charges of the phase zone P0 accumulated in the charge accumulating portion D3 and the effective electric charges of the phase zone P2 accumulated in the potential well formed under the sensitivity control electrode 17b are transferred in the vertical direction toward the upper side of fig. 15. By controlling the voltage applied to the accumulation electrode 14b, the effective charge accumulated in the charge accumulation portion D3 can cross the potential barrier formed under the barrier control electrode 14 c. Therefore, by transferring the effective charges in the opposite directions, the effective charges of the phase zones (P0, P2) can be accumulated in the potential wells under the sensitivity control electrodes (14b, 14e), respectively.

After the above operation is repeated a predetermined number of times in the light emission period, the effective electric charges are taken out as the received-light output. In this embodiment, there is an advantage that the number of operations is less compared to the fourth embodiment. The other configuration and operation are the same as those of the first embodiment. In each of the second to fifth embodiments, the holding electrode 14d is arranged on the holding well 15 through the insulating layer 13. Alternatively, the holding electrode 14d may not be ohmically connected to the holding well 15 through the insulating layer 13.

(sixth embodiment)

The present embodiment is characterized in that a plurality of electrodes having the same width are provided, and substantially the same operation as in the case of using a plurality of electrodes having different widths can be achieved by using an appropriate combination of electrodes having the same width. In the present embodiment, the intensity of light projected from the light emission source is modulated by a sinusoidal modulation signal, as in the third embodiment. The photoelectric converting portion D1 also functions as a charge separating portion D2 and a charge accumulating portion D3. In addition, the charge holding portion D4 is not formed.

As shown in fig. 16, one cell 1 of the present embodiment has a plurality of control electrodes (18a to 18l) having the same width and equally spaced from each other, which are arranged on the well 12 on the main surface of the device formation layer 11 through the insulating layer 13. That is, one cell 1 includes twelve control electrodes (18a-18 l). In one cell 1, wirings are formed so that voltages applied to the control electrodes (18a to 18l) can be individually controlled.

The operation of the photoelectric converting portion D1 is basically the same as the operation using the sensitivity control electrodes (17a to 17h) of the third embodiment, except for the following points. In the present embodiment, electrons corresponding to the received-light amount in the phase zone P0 are collected by using the control electrodes (18a to 18i), and electrons corresponding to the received-light amount in the phase zone P2 are collected by using the control electrodes (18d to 18 l). These operations are explained with reference to fig. 17A to 17H. In fig. 17A to 17H, the control electrodes (18a to 18l) are represented as (a) to (l).

During the operation of the photoelectric conversion portion D1 in the light receiving period, as shown in fig. 17A, a positive voltage is applied to the control electrodes (18a to 18i) with respect to the phase zone P0, so that electrons are collected by the regions corresponding to the nine control electrodes (18a to 18 i). In addition, as shown in fig. 17B, a positive voltage is applied to the control electrodes (18d-18l) with respect to the phase interval P2, so that electrons are collected by the regions corresponding to the nine control electrodes (18d-18 l). The electrons collected with respect to each phase zone (P0, P2) are held at a region other than the region for collecting electrons. That is, in the phase zone P0 in which electrons are collected by the region corresponding to the control electrodes (18a to 18i), the electrons collected with respect to the phase zone P2 are held at the region corresponding to the control electrode 18 k. Similarly, in the phase zone P2 where electrons are collected in the region corresponding to the control electrode (18d-18l), the electrons collected with respect to the phase zone P0 are held at the region corresponding to the control electrode 18 b. By repeating the operation for the phase zone (P0, P2) a plurality of times, electrons of an amount corresponding to the received-light amount are held at the region corresponding to the control electrode (18k, 18b) in the well 12.

When the light receiving period ends such that the amount of electrons corresponding to the received-light amount in the phase zone P0 is collected in the region corresponding to the control electrode 18b, or the amount of electrons corresponding to the received-light amount in the phase zone P2 is collected in the region corresponding to the control electrode 18k, the weighing period is started to perform an operation for separating unnecessary electric charges to obtain effective electric charges.

For example, in the case where the undesired electric charges are separated from the electrons held at the region corresponding to the control electrode 18b, a negative voltage is applied to the control electrode 18a to form a potential barrier under the condition that the electrons collected in the phase zone P0 are held in the potential well formed at the region corresponding to the control electrode 18 b. In addition, as described below, in order to use the region corresponding to the control electrodes (18d, 18e) as the charge accumulating portion, the electrons collected in the phase zone P2 are transferred. That is, as shown in fig. 17C, potential barriers corresponding to the control electrodes (18C, 18d) are formed. Subsequently, as shown in fig. 17D, potential barriers corresponding to the control electrodes (18c to 18e) are formed. Further, as shown in fig. 17E, potential barriers corresponding to the control electrodes (18f to 18h) are formed. Therefore, the electrons collected in the phase zone P2 can be transferred.

In addition, as shown in fig. 17E, a positive voltage is applied to the control electrodes (18D, 18E) to form a potential well serving as the charge accumulating portion D3, while a potential barrier B3 having a predetermined height is formed by controlling the voltage applied to the control electrode 18 c. By this operation, undesired electric charges remain in the potential well corresponding to the control electrode 18B, and electrons flowing into the potential well corresponding to the control electrodes (18d, 18e) over the potential barrier B3 are used as effective electric charges.

Next, as shown in fig. 17F, the height of the potential barrier corresponding to the control electrode 18c is increased to prevent leakage of the effective charge corresponding to the phase zone P0. Meanwhile, the electrons collected in the phase zone P2 are collected into the potential well corresponding to the control electrode 18 k. In this state, a potential well is formed as the charge accumulating portion D3 in the region corresponding to the control electrodes (18g to 18i), and a potential barrier B4 is formed at the region corresponding to the control electrode 18 j.

As shown in fig. 17G, in order to separate unnecessary electric charges from the electric charges (electrons) held in the potential well corresponding to the control electrode 18k, the potential barrier B4 is lowered by controlling the voltage applied to the control electrode 18 j. The amount of undesired electric charges in the electrons collected in the phase zone P2 is determined by the height of the potential barrier B4. That is, the region corresponding to the control electrode 18k serves as the charge separating portion D2.

As shown in fig. 17H, after the undesired electric charges are separated, the height of the potential barrier corresponding to the control electrode 18j is increased to prevent leakage of the effective electric charges collected in the potential well corresponding to the control electrodes (18g to 18i) with respect to the region P2. On the other hand, the undesired electric charges remaining in the region corresponding to the control electrodes (18b, 18k) are discharged.

According to the above operation, the undesired electric charges are separated from the electrons generated by the light irradiation in the phase zone (P0, P2), and the effective electric charges are taken out. In the present embodiment, since the control electrodes (18a to 18l) are arranged in one column, electrons of effective charges can be transferred in the arrangement direction of the control electrodes (18a to 18l) by applying voltages to the control electrodes (18a to 18l) at appropriate timings, as in the case of the vertical transfer resistor of the conventional CCD image sensor. By taking out the electrons to the outside of the photodetector, a received-light output is obtained. That is, in the configuration of the present embodiment, the photoelectric converting portion D1 also functions as the charge separating portion D2, the charge accumulating portion D3, and the charge extracting portion. In addition, since the operation for separating the undesired electric charges from the electrons generated in the two phase zones (P0, P2) can be performed simultaneously, there is an advantage that the processing time required for separating the undesired electric charges can be shortened.

In the above configuration, the description has been made on the case where the same operation as that of the first embodiment is performed. Alternatively, the voltage applied to the control electrodes 18b, 18k may be controlled in accordance with the amount of electrons held by the charge holding portions D4 formed separately. In this case, as described in the second and third embodiments, it is possible to automatically adjust the amount of the undesired electric charges. Other configurations and operations are the same as those in the above-described embodiment.

Further, it is advantageous to take out the electric charges accumulated in the electric charge accumulating portion as the received-light output by the electric charge taking-out portion after the operation of generating the electric charges by the photoelectric converting portion and the operation of separating the unnecessary electric charges from the electric charges generated by the photoelectric converting portion and accumulating the effective electric charges in the electric charge accumulating portion are repeated a plurality of times. In this case, since unnecessary electric charges are repeatedly separated from the electric charges generated by the photoelectric conversion portion, it is possible to reduce the possibility of occurrence of saturation at the photoelectric conversion portion and achieve a reduction in size of the photoelectric conversion portion. In addition, when the size of the photoelectric conversion portion is reduced, the capacity of the charge extraction portion can also be reduced. As a result, it is possible to reduce the size of the photodetector as a whole.

(seventh embodiment)

This embodiment is the same as the sixth embodiment in the following respects: a plurality of control electrodes having the same width are provided. However, as shown in fig. 18, the present embodiment is characterized in that one cell 1 has nine control electrodes (19a to 19 i). As described in the sixth embodiment, six control electrodes are used to accumulate electrons corresponding to one phase zone of the modulation signal and separate unnecessary electric charges. Therefore, the operations of collecting electrons corresponding to the two phase zones of the modulation signal and separating unwanted electric charges therefrom cannot be performed separately at different regions by using nine control electrodes (19a to 19 i). That is, a part of the nine electrodes are used in an overlapping manner in the two phase intervals. In addition, in the sixth embodiment, the operation of separating the undesired electric charges from the electrons collected in the two compartments, respectively, may be performed simultaneously. On the other hand, in the present embodiment, since the partial control electrodes are used in an overlapping manner, the operation of separating the undesired electric charges from the electrons collected from one of the two phase zones is performed at a different time from the operation of separating the undesired electric charges from the electrons collected from the other phase zone.

Specifically, the operations shown in fig. 19A to 19O are performed. When the photoelectric converting portion D1 is used to collect electrons generated by receiving light from the object space, a period in which a negative voltage is applied to each control electrode (19g, 19i) as shown in fig. 19A and a period in which a negative voltage is applied to each control electrode (19A, 19c) as shown in fig. 19B are alternately set. These two periods are set in synchronization with the modulation signal. For example, the state of fig. 19A corresponds to the phase zone P0, and the state of fig. 19B corresponds to the phase zone P2. In fig. 19A to 19O, the control electrodes (19A to 19i) are represented as (a) to (i).

In the state of fig. 19A, the region corresponding to the control electrodes (19A to 19f) functions as the photoelectric converting portion D1 with respect to the phase zone P0. In the state of fig. 19B, the region corresponding to the control electrodes (19D to 19i) functions as the photoelectric converting portion D1 with respect to the phase zone P2. In addition, the electrons collected in the phase zone P0 are held in the region corresponding to the control electrode 19b in the phase zone P2. On the other hand, the electrons collected in the phase zone P2 are held in the region corresponding to the control electrode 19h in the phase zone P0.

After the states of fig. 19A and 19B are alternately repeated for a sufficiently long period of time, an operation of separating undesired electric charges from electrons held in the region corresponding to the control electrodes (19B, 19h) to obtain effective electric charges is performed. Since the region corresponding to the control electrode 19b is a region for effective charges, it also serves as the charge accumulating portion D3. As described above, the portion of the control electrode is shared by the two phase intervals of the modulation signal. In the period of separating the undesired electric charges, the potential barrier B5 is formed all the way in the region corresponding to the control electrode 19c to prevent the electrons collected in the two phase zones from mixing with each other. That is, a negative voltage is always applied to the control electrode 19 c.

In fig. 19A-19O, the undesired electric charges are first separated from the electrons collected in the phase zone P2, and then the undesired electric charges are separated from the electrons collected in the phase zone P0. Therefore, during the operation of separating the undesired electric charges from the electrons collected in the phase zone P2, the electrons collected in the phase zone P0 are held in the region corresponding to the control electrode 19 b.

After the photoelectric converting portion D1 collects the electrons generated by the light irradiation, as shown in fig. 19C, the electrons collected in the phase zone P0 are held in the potential well formed in the region corresponding to the control electrode 19 b. In addition, a negative voltage is applied to the control electrode 19a to form a potential barrier. This state is maintained until the undesired charge is separated from the electrons collected in phase interval P2 (i.e., over the range of fig. 19C-19I). On the other hand, in the state of fig. 19C, the electrons collected in the phase region P2 are held in the potential well formed in the region corresponding to the control electrodes (19d to 19 f). That is, electrons held in the region corresponding to the control electrodes (19d to 19i) in the phase zone P2 or electrons held in the region corresponding to the control electrode 19h in the phase zone P0 are collected in the region corresponding to the control electrodes (19d to 19 f).

As shown in fig. 19D, this operation is an operation performed previously to form a potential well free of electrons (empty) in a region corresponding to the control electrode 19 h. That is, in a stage where the operation of collecting electrons generated by light irradiation has ended, the electrons collected in the phase zone P2 exist in the region corresponding to the control electrode 19 h. Therefore, as shown in fig. 19C, after a negative voltage is applied to the control electrodes (19g to 19i), a potential well having no electrons is formed in the region corresponding to the control electrode 19h as shown in fig. 19D.

Next, as shown in fig. 19E and 19F, the electrons held in the region corresponding to the control electrodes (19d to 19F) are moved to the region corresponding to the control electrode 19 h. First, potential wells are formed in regions corresponding to the control electrodes (19f to 19h), and potential barriers are formed in regions corresponding to the control electrodes (19c to 19 e). Subsequently, a potential barrier is formed in a region corresponding to the control electrode 19f, and a potential barrier is also formed in a region corresponding to the control electrode 19 g. Therefore, electrons can be collected in the region corresponding to the control electrode 19 h. In this stage, empty potential wells are formed in regions corresponding to the control electrodes (19d to 19 f). Although there are a plurality of intermediate states between the state of fig. 19E and the state of fig. 19F, they are not shown in the drawings. On the other hand, regarding potential energy, the state of fig. 19F is the same as the state of fig. 19D. However, in the state of fig. 19D, electrons exist in the region corresponding to the control electrodes (19D to 19F), whereas in the state of fig. 19F, electrons exist in the region corresponding to the control electrode 19 h.

Through the above-described process, the electrons collected in the phase zone P2 are collected into the region corresponding to the control electrode 19 h. Next, as shown in fig. 19G, the potential barrier B6 corresponding to the control electrode 19G is lowered. This potential barrier B6 has the same function as the potential barrier B1 described in the first embodiment. An amount of electrons determined according to the height of the potential barrier B6 remains in the region corresponding to the control electrode 19h as the charge separating portion D2. The electrons in an amount exceeding the capacity of the charge separating portion D2 flow into the region corresponding to the control electrodes (19D to 19f), i.e., the charge accumulating portion D3, over the potential barrier B6.

After the electrons flow into the charge accumulating portion D3, as shown in fig. 19H, the height of the potential barrier B6 is increased by applying a negative voltage to the control electrode 19 g. The undesired electric charges in the charge separating portion D2 can be completely separated from the effective electric charges in the charge accumulating portion D3. As shown in fig. 19I, the undesired electric charges are discharged from the charge separating portion D2, and the effective electric charges are left in the regions corresponding to the control electrodes (19D to 19 f). The amount of effective electric charges corresponds to the received-light amount in the phase zone P2.

On the other hand, the amount of electrons held in the region corresponding to the control electrode 19b corresponds to the received-light amount in the phase zone P0. The undesired charge can be separated from the electrons by the process shown in fig. 19J-19O. The state in which the effective electric charges of the phase zone P2 are held in the region corresponding to the control electrodes (19d-19f) is maintained during this process. The present embodiment is characterized in that the region corresponding to the control electrode 19h has the function of the charge separating portion D2 for electrons collected in the phase zone P2 and the function of the charge separating portion D2 for electrons collected in the phase zone P0.

That is, after the undesired electric charges are discharged, as shown in fig. 19J and 19K, the electrons of the phase zone P0 held in the region corresponding to the control electrode 19b are moved into the region corresponding to the control electrode 19 h. At this time, the potentials of the regions corresponding to the control electrodes (19a, 19i) are first reduced so that the potentials of the regions corresponding to the control electrodes (19a, 19b, 19h, 19i) are equal to each other. Subsequently, the electrons are collected in the region corresponding to the control electrode 19 h. The intermediate state between fig. 19J and 19K is not shown in this figure. In short, the potential of the region corresponding to the control electrode 19b is first increased. Subsequently, the potential of the region corresponding to the control electrode 19a is increased, and then the potential of the region corresponding to the control electrode 19i is increased. After collecting electrons in the region corresponding to the control electrode 19h, the potential of the region corresponding to the control electrode (19a, 19b) is lowered.

According to the above operation, electrons of the phase zone P0 are held in the region corresponding to the control electrode 19h, and the region corresponding to the control electrode 19h serves as the charge separating portion D2. Next, as shown in fig. 19L, a potential barrier B7 is formed in a region corresponding to the control electrode 19 i. Electrons flowing into the region corresponding to the control electrode (19a, 19B) over the potential barrier B7 are effective charges. That is, the region corresponding to the control electrode (19a, 19b) serves as the charge accumulating portion D3.

Subsequently, as shown in fig. 19M, the potential barrier B7 corresponding to the control electrode 19i is raised. When electrons in the charge separating portion D2 are discharged as undesired electric charges in a state where the electrons in the charge separating portion D2 are isolated from the electrons in the charge accumulating portion D3, as shown in fig. 19N, electrons corresponding to the received-light amount in the phase zone P2 are held in the region corresponding to the control electrodes (19D, 19e, 19b), and electrons corresponding to the received-light amount in the phase zone P0 are held in the region corresponding to the control electrodes (19a, 19 b). After these electrons are taken out through the state of fig. 19O, the states shown in fig. 19A and 19B are reproduced to collect electrons generated by light irradiation.

Therefore, in the present embodiment, a plurality of control electrodes are provided as one unit, and electric charges are generated at different two timings (e.g., a0, a2) in the light reception period. The generated electric charges are temporarily collected in potential wells formed in regions corresponding to the different control electrodes of the one unit. On the other hand, in the weighing period, the charge separating portion, the charge accumulating portion, and the potential barrier formed with respect to the electric charge generated in one of the two timings are provided at positions different from the charge separating portion, the charge accumulating portion, and the potential barrier formed with respect to the electric charge generated in the other timing. It is thus possible to increase the area for collecting electric charges in the light receiving period. Also, in the weighing period, an undesired electric charge is separated from the electrons generated at each of the two different timings. That is, since the control electrode for separating the undesired electric charges from the electric charges generated at one of the two timings is different from the control electrode for separating the undesired electric charges from the electric charges generated at the other timing, it is possible to separate the undesired electric charges from the electric charges generated at each of the two different timings while preventing the electric charges generated at the two timings from being mixed with each other.

In addition, in the weighing period, the potential well for holding the electric charges generated at one of the two different timings can be used as the charge separating portion of the electric charges collected at the two timings. In fig. 19A to 19O, the control electrode (i) is shown at the right end. In practice, control electrodes (a) - (i) of adjacent cells are provided. Therefore, the potential well corresponding to the control electrode 19h functions as the charge separating portion D2 of the electrons collected in the phase zone P2. On the other hand, in the adjacent cell, as shown in fig. 19L, the potential well corresponding to the control electrode 19h also serves as the charge separating portion D2 of the electrons collected in the phase zone P0. At this time, a potential barrier for electrons collected at each timing is formed by using each control electrode adjacent to both sides of the control electrode 19h corresponding to the charge separating portion D2.

That is, when the effective charge is separated from the electrons collected in the phase zone P2, a potential barrier formed by applying a voltage to the control electrode 19g is used. On the other hand, when the effective charge is separated from the electrons collected in the phase zone P0, a potential barrier formed by applying a voltage to the control electrode 19i is used. Therefore, since the electrons collected at the two timings share the region serving as the charge separating portion, it is possible to reduce the number of control electrodes and reduce the occupied area of the control electrodes as a whole while maintaining the function of generating charges at the two timings, as compared with the electrode configuration of the sixth embodiment. As a result, the size of the photodetecting portion can be reduced. In addition, when the image pickup apparatus is configured such that a plurality of cells 1 are arranged and each cell 1 provides one pixel, there are the following advantages: the occupied area of one pixel is reduced and improvement in resolution is achieved. Other configurations and operations are the same as those in the above-described embodiment.

(eighth embodiment)

The present embodiment is characterized in that a prescribed constant amount of undesired electric charges are discharged from electric charges (electrons) generated by receiving light from a target space according to the following method.

That is, as shown in fig. 20, the drain well 25 formed on the main surface side of the device formation layer 11 is arranged at a position different from the well 12 serving as the photoelectric conversion portion D1. In addition, a drain gate electrode 26 is formed on the main surface of the device formation layer 11 through the insulating layer 13 and between the well 12 and the drain well 25. Also, the drain electrode 27 is ohmically connected to the drain well 25. The discarding well 25 has the same conductivity type as the well 12, and the impurity concentration of the discarding well 25 is higher than that of the well 12.

A positive constant voltage is applied all the way to the discharging electrode 27 so that the electrons collected in the discharging well 25 can be discharged through the discharging electrode 27. In addition, when a positive voltage is applied to the discarding gate electrode 26, a channel is formed so that electrons can move between the well 12 and the discarding well 25. The electrons in the well 12 move to the discharge well 25 through the channel. In this regard, when the voltages applied to the discarding gate electrode 26 and the discarding electrode 27 are kept constant, the electron mobility (electron mobility) from the well 12 to the discarding well 25 is almost constant.

After collecting electrons in the photoelectric converting portion D1 of the well 12 upon receiving light from the object space, a prescribed constant voltage is applied to the discarding gate electrode 26 for a predetermined period of time to move the electrons from the well 12 to the discarding well 25. As described above, since the electron mobility is constant, electrons of an amount determined in proportion to a period of time for which a voltage is applied to the drain gate electrode 26 may be moved to the drain well 25. That is, when the electrons moved from the well 12 to the discarding well 25 are undesired electric charges, and the residual electrons in the well 12 are used as effective electric charges, it means that a prescribed constant amount of the undesired electric charges can be removed from the electric charges generated in the well 12. The effective charge remaining in the well 12 is taken out as a received-light output.

According to the present embodiment, the amount of the undesired electric charges is determined by the voltages applied to the discarding gate electrode 26 and the discarding electrode 27 and the period of time for which the voltage is applied to the discarding gate electrode 26. On the other hand, as described above, since the voltages applied to the discarding gate electrode 26 and the discarding electrode 27 are kept constant, the amount of the undesired electric charges is expressed as a function of the period of time during which the voltage is applied to the discarding gate electrode 26. In addition, since the effective charges remain in the well 12, the well 12 of the present embodiment functions as the photoelectric converting portion D1 and also functions as the charge accumulating portion D3. The discarding well 25, the discarding gate electrode 26, and the discarding electrode 27 function as the charge separating part D2. Other configurations and operations are the same as those of the above-described embodiment.

(ninth embodiment)

The present embodiment is characterized in that the charge transfer portion is used as the charge accumulating portion D3 by controlling the voltage applied to the transfer control electrode 31 formed at the charge transfer portion for taking out the received-light output, without forming an electrode for controlling the movement of electrons at the charge separating portion D2 for separating undesired electric charges. That is, in each of the above-described embodiments, the electrode arrangement is the same as the electrode configuration of a frame-transfer type (frame-transfer type) CCD image sensor. In the present embodiment, the electrode arrangement is the same as the electrode configuration of an interline-transfer (IT) type CCD image sensor.

As shown in fig. 21, a p-type device formation layer 11 is formed on an n-type substrate 10. An n + type well 12 is formed on the main surface of the device formation layer 11 and on the side of the p + type well 33. In addition, an n-type transfer well 32 is formed on the opposite side of the p + -type potential well 33. The transfer well 32 has the same configuration as the IT-type CCD image sensor. The transfer control electrode is disposed on the main surface of the transfer well 32 through an insulating layer 34. The transfer well 32 is covered with a light shielding film 35. The plurality of transfer control electrodes 31 are arranged in a direction perpendicular to the page of fig. 21. In order to transfer electrons, the sequence of applying voltages to the transfer control electrodes 31 is controlled as in the conventional case. To separate unwanted charges, a drain electrode 36 ohmically connected to the substrate 10 is used in conjunction with the transfer control electrode 31. The well 12 is commonly used by the photoelectric converting portion D1 and the charge separating portion D2.

In the present embodiment, the well 12 has no electrode, and the device formation layer 11 has a different conductivity type from the well 12. Thus, as shown in fig. 22C, a potential well is formed in the well 12. Potential well 33 presents a potential barrier B8 between well 12 and transfer well 32. At this time, it is assumed that the transfer well 32 is in an electron-free state. In addition, no voltage is applied to the transfer control electrode 31, and a positive voltage (e.g., 5 volts) is applied to the drain electrode 35.

After electrons are generated by the light irradiation of the photoelectric conversion portion D1, a relatively large positive voltage (e.g., 10 volts) is applied to the transfer control electrode 31. As the voltage applied to the transfer control electrode 31 is larger, the potential of the potential barrier B8 decreases. When an appropriate voltage higher than the voltage applied in the case of transferring electrons is applied to the transfer control electrode 31, a part of the electrons collected in the well 12 flows into the transfer well 32 through the potential barrier B8, as shown in fig. 22D. Since the height of the potential barrier B8 is determined by the voltage applied to the transfer control electrode 31, a prescribed constant amount of electrons can remain in the well 12. That is, the well 12 functions as the charge separating portion D2, and the transfer well 32 functions as the charge accumulating portion D3.

When the undesired electric charges remain in the well 12 and the effective electric charges flow into the transfer well 32, the application of the voltage to the transfer control electrode 31 is stopped, and a relatively high positive voltage (e.g., 15 volts) is applied to the drain electrode 36. In this state, as shown in fig. 22E, the potential barrier B8 becomes high, and the potential well formed in the transfer well 32 becomes shallow. That is, the effective charges flowing into the transfer well 32 are held in the charge accumulating portion D3. In addition, the unnecessary electric charges remaining in the well 12 are discharged through the drain electrode 36.

According to the above operation, a predetermined constant amount of electrons are separated as unnecessary electric charges from the electrons generated by receiving light from the target space, and the effective electric charges remain in the transfer well 32. By controlling the voltage applied to the transfer control electrode 31 and performing an operation similar to that in the case of the vertical transfer resistor of the conventional CCD image sensor, it is possible to transfer effective charges in a direction perpendicular to the page of the figure. Other configurations and operations are the same as those of the above-described embodiment.

In addition, when the photodetector shown in fig. 21 of the present embodiment is used in combination with a light emission source for projecting light intensity-modulated by a modulation signal to detect information of a target space, it is necessary to extract the received-light amount between predetermined phase zones corresponding to the modulation signal. In this case, for example, as shown in fig. 23A, a relatively large positive voltage (for example, 15 volts) is applied to the transfer control electrode 31 for the light receiving period "T1" to form a deep potential well in the transfer well 32. Thus, electrons generated by the photoelectric converting portion D1 (well 12) can flow into the transfer well 32. On the other hand, as shown in fig. 23B, the voltage applied to the discarding electrode 36 is changed in two stages of high and low (e.g., 15V and 5V) in synchronization with the modulation signal, so that the state of discarding electrons and the state of flowing electrons into the potential well formed in the transfer well 32 are alternately repeated. When the voltage applied to the discharge electrode 36 is changed to a low voltage at the timing of taking out the electric charges serving as the received-light output from the electric charges generated by the photoelectric converting portion D1, the intended electric charges are allowed to flow into the transfer well 32. Changes in the potential well in the light receiving period "T1" are shown in fig. 22A and 22B.

After the voltage applied to the discharge electrode 36 is changed a plurality of times in the light receiving period in which the above-described operation is performed, the weighing period "T2" is started. In the weighing period "T2", a negative voltage (e.g., -5 volts) is applied to the transfer control electrode 31 so that the potential well of the transfer well 32 becomes shallow. In addition, the voltage applied to the discharge electrodes 36 is controlled to a relatively low voltage (e.g., 5 volts) so that electrons are not discharged from the well 12. According to this relationship, electrons can return from the transfer well 32 to the well 12. The charge weighing operation performed after the electrons return to the well 12 is the same as described above.

An object and feature of the present invention is to stably obtain effective electric charges required for detecting spatial information by preventing saturation without being affected by an increase or decrease in ambient light. Therefore, although details are not described in the preferred embodiment, the spatial information detected by using the effective charge as the received-light output includes: measuring a distance to an object in the target space by using a difference between received-light outputs detected at different timings synchronized with the plurality of phase zones of the modulation signal; generating an amplitude image having pixel values, each pixel value being provided by the difference; identifying a size or shape of the object from the amplitude image; and obtaining information such as the reflectivity of an object in the object space by eliminating the ambient light component.

Industrial applications

As described above, according to the present invention, the amount of electric charges flowing from the charge separating portion into the charge accumulating portion through the potential barrier is adjusted by controlling the voltage applied to the barrier control electrode to change the height of the potential barrier, and the undesired electric charges remaining in the charge separating portion are discharged. Therefore, it is possible to provide a spatial information detecting apparatus: which can reduce the size of a photoelectric conversion portion and reliably obtain effective charges by preventing a saturation phenomenon even in the case where a large amount of unnecessary charges are generated by receiving light from a subject space.

In particular, when the amount of electric charge separated as the undesired electric charges from the electric charges corresponding to the received-light amount in the light emission period is adjusted according to the amount of electric charges generated by the photoelectric conversion portion in the rest period, an appropriate amount of the undesired electric charges can be automatically discharged according to the change in the ambient light even when an increase or decrease in the ambient light occurs in the target space.

Therefore, since the spatial information detection apparatus of the present invention has the capability of accurately detecting information of the object space anywhere indoors and outdoors, it is expected that the application field of the conventional spatial information detection apparatus will be expanded.

The embodiment of the invention provides the following technical scheme.

1. A spatial information detecting apparatus comprising:

a light emission source configured to project signal light intensity-modulated by a modulation signal to a target space;

a photodetection section configured to separate a constant amount of bias component from electric charges corresponding to the amount of received light detected from the object space at a timing synchronized with the modulation signal, thereby providing a received light output reflecting a fluctuation component of the signal light; and

a signal processing section configured to detect spatial information of the object space by using the received light output;

wherein the photodetecting section includes:

a photoelectric conversion portion configured to receive light from the object space to generate electric charges;

a charge separating section configured to separate a prescribed constant amount of undesired electric charges corresponding to the bias component from the electric charges generated by the photoelectric converting section, wherein the electric charges generated by the photoelectric converting section correspond to a sum of the constant amount of bias component that is not dependent on fluctuation of the signal light and the fluctuation component that varies according to fluctuation of the signal light;

a charge accumulating portion configured to accumulate residual charges obtained by separating the undesired charges from the charges generated by the photoelectric converting portion as effective charges; and

a charge extracting section configured to extract the effective charges accumulated in the charge accumulating section as the received-light output.

2. The spatial information detecting device according to claim 1, wherein the charge separating portion and the charge accumulating portion are potential wells formed in a semiconductor substrate, and the photodetecting portion further comprises a charge amount adjusting means configured to form a potential barrier between the charge separating portion and the charge accumulating portion, and to adjust an amount of the charges flowing from the charge separating portion into the charge accumulating portion through the potential barrier with respect to the charges generated by the photoelectric converting portion.

3. The spatial information detecting device according to claim 2, wherein the electric-charge amount adjusting means includes: a barrier control electrode disposed on the semiconductor substrate to form the potential barrier between the charge separating portion and the charge accumulating portion; and a control section configured to control a voltage applied to the barrier control electrode to change a height of the potential barrier.

4. The spatial information detecting device according to claim 2, wherein the electric-charge amount adjusting means includes: a separation electrode arranged at a position corresponding to the charge separation portion on the semiconductor substrate; and a control section configured to control a voltage applied to the separation electrode to change a depth of the potential well of the charge separation section.

5. The spatial information detecting device according to claim 1, further comprising a timing control section configured to determine operation timings of the photoelectric conversion section, the charge separation section, and the charge accumulation section in association with a light receiving period in which the photoelectric conversion section generates electric charges by receiving light from the subject space to which the intensity-modulated light is irradiated and a weighing period in which the unnecessary electric charges are separated from the electric charges generated by the photoelectric conversion section by using the charge separation section and the charge accumulation section.

6. The spatial information detecting device according to claim 1, further comprising a semiconductor layer of a first conductivity type; a well of a second conductivity type formed at a main surface of the semiconductor layer; a discharging portion to which the undesired electric charges are discharged from the charge separating portion; a plurality of electrodes disposed on the major surface of the well; and a control section configured to control a voltage applied to the electrode in association with a light receiving period in which the photoelectric conversion section generates electric charges by receiving light from the object space to which the intensity-modulated light is irradiated and a weighing period in which the unnecessary electric charges are separated from the electric charges generated by the photoelectric conversion section,

wherein the electrode comprises: a separation electrode for forming a potential well as the charge separating portion in the well; an accumulation electrode for forming a potential well in the well as the charge accumulation portion; and a barrier control electrode for forming a potential barrier between the charge separating portion and the charge accumulating portion.

7. The spatial information detecting device as set forth in claim 6, wherein said control section controls a voltage applied to at least one of said separating electrode and said barrier control electrode to change at least one of a height of said potential barrier and a depth of said potential well formed as said charge separating section, thereby adjusting an amount of electric charges flowing from said charge separating section to said charge accumulating section through said potential barrier.

8. The spatial information detecting apparatus according to claim 1, wherein the light emission source irradiates the light intensity-modulated by the modulation signal to the target space so as to have a light emission period in which the intensity-modulated light is projected from the light emission source to the target space and a pause period in which the intensity-modulated light is not projected to the target space, and

the photodetecting portion includes a charge amount adjusting device configured to adjust an amount of electric charges separated as the undesired electric charges from the electric charges corresponding to the received-light amount obtained in the light emission period, in accordance with an amount of electric charges generated by the photoelectric converting portion in the rest period.

9. The spatial information detecting device according to claim 8, wherein the charge amount adjusting means increases an amount of the undesired electric charges to be separated from the electric charges corresponding to the received-light amount obtained in the light emission period, when the amount of the electric charges generated by the photoelectric converting portion in the rest period increases.

10. The spatial information detecting device as set forth in claim 8, wherein said charge separating portion and said charge accumulating portion are potential wells formed in a semiconductor substrate,

arranging a barrier control electrode between the charge separating portion and the charge accumulating portion to form a potential barrier, an

The charge amount adjusting means controls the voltage applied to the barrier control electrode in accordance with the amount of charge generated by the photoelectric converting portion in the rest period to change the height of the potential barrier, thereby adjusting the amount of charge flowing from the charge separating portion into the charge accumulating portion through the potential barrier.

11. The spatial information detecting device as set forth in claim 10, wherein said electric-charge amount adjusting means has a charge holding portion which is a potential well formed in said semiconductor substrate to hold the electric charges generated by said photoelectric converting portion in said rest period, and

the charge amount adjusting means applies a voltage determined in accordance with the amount of charge held by the charge holding portion to the barrier control electrode.

12. The spatial information detecting device as set forth in claim 11, wherein said electric-charge amount adjusting means includes a holding electrode formed on said semiconductor substrate at a position corresponding to said electric-charge holding portion through an insulating layer and electrically connected to said barrier control electrode.

13. The spatial information detecting device as set forth in claim 11, wherein said barrier control electrode is electrically connected to a portion of said semiconductor substrate corresponding to a charge holding well formed as said charge holding portion.

14. The spatial information detecting device according to claim 11, further comprising a gate electrode formed on the main surface of the semiconductor substrate between the photoelectric converting portion and the charge holding portion and configured to control timing of transferring the electric charges generated by the photoelectric converting portion to the charge holding portion.

15. The spatial information detecting device as set forth in claim 8, wherein said charge separating portion and said charge accumulating portion are potential wells formed in a semiconductor substrate,

arranging a separation electrode at a position corresponding to the charge separation portion on the semiconductor substrate, an

The charge amount adjusting means controls the voltage applied to the separation electrode in accordance with the amount of charge generated by the photoelectric converting portion in the rest period to change the depth of a potential well formed as the charge separating portion, thereby adjusting the amount of charge flowing from the charge separating portion into the charge accumulating portion through the potential barrier.

16. The spatial information detecting device as set forth in claim 15, wherein said electric-charge amount adjusting means has a charge holding portion which is a potential well formed in said semiconductor substrate to hold the electric charges generated by said photoelectric converting portion in said rest period, and

the charge amount adjusting means applies a voltage determined in accordance with the amount of charge held by the charge holding portion to the separation electrode.

17. The spatial information detecting device according to claim 8, wherein the signal processing section increases the amount of the undesired electric charges separated in a next light emission period when an amount of electric charges generated in the light emission period reaches a predetermined saturation level.

18. The spatial information detecting device according to claim 8, wherein said photodetecting section has a plurality of photodetecting units, each of which corresponds to one pixel,

each of the photodetecting units includes: a semiconductor layer of a first conductivity type; a well of a second conductivity type formed in a main surface of the semiconductor layer; the photoelectric conversion section including an array of a plurality of sensitivity control electrodes formed on a prescribed region of the well of the second conductivity type through an insulating layer; a separation electrode for forming a potential well as the charge separating portion in the well; a barrier control electrode for forming the potential barrier in the well; an accumulation electrode for forming a potential well as the charge accumulation portion in the well; and a discharging portion to which the undesired electric charges are discharged from the electric charge separating portion,

wherein the electric-charge-amount adjusting means has a charge holding portion which is a potential well for holding electric charges generated by the photoelectric converting portion in the rest period, and

the charge amount adjusting means applies a voltage to at least one of the barrier control electrode and the separation electrode in accordance with the amount of charge held by the charge holding portion.

19. The spatial information detecting device as set forth in claim 18, wherein said separation electrode, said barrier control electrode, and said accumulation electrode are formed in said array of said sensitivity control electrodes, and said charge holding portion is formed adjacently in a direction perpendicular to said array of said sensitivity control electrodes.

20. The spatial information detecting device as set forth in claim 18, wherein the separation electrode, the barrier control electrode, the accumulation electrode, and the charge holding portion are arranged in an array direction of the sensitivity control electrodes in a column adjacent to the array of the sensitivity control electrodes.

21. A spatial information detecting apparatus comprising:

a light emission source configured to irradiate light intensity-modulated by the modulation signal to the target space;

a photodetection portion configured to provide an electrical output in accordance with light received from the object space; and

a signal processing section configured to detect spatial information of the object space by using the electrical output;

wherein the photodetecting section includes:

a charge separating section configured to separate an amount of unnecessary electric charges determined according to an amount of electric charges generated by the photoelectric converting section in another section from electric charges generated by the photoelectric converting section in one of two sections of the modulation signal having different phase ranges;

a charge accumulating section configured to accumulate, as effective charges, residual charges obtained by separating the undesired charges from charges generated by the photoelectric converting section in the one of the two sections having different phases of the modulation signal; and

a charge extracting section configured to output the effective charge accumulated in the charge accumulating section as the electrical output.

22. The spatial information detecting device as set forth in claim 21, wherein said charge separating portion and said charge accumulating portion are potential wells formed in a semiconductor substrate,

the spatial information detection device includes: a barrier control electrode disposed on the semiconductor substrate to form a potential barrier between the charge separating portion and the charge accumulating portion; and a charge holding portion configured to hold a charge generated by the photoelectric conversion portion in the other of the two intervals having different phase ranges of the modulation signal,

applying a voltage to the barrier control electrode according to the amount of charge held by the charge holding portion to determine the amount of the undesired electric charges, an

Separating the amount of the undesired electric charges from the electric charges generated by the photoelectric converting portion in the one of the two sections of the modulation signal having different phase ranges by the electric charge separating portion.

23. A photodetector, comprising:

a photoelectric conversion portion configured to receive light from a subject space to generate electric charges;

a charge separating section configured to separate a prescribed constant amount of undesired electric charges corresponding to a bias component from the electric charges generated by the photoelectric converting section, the electric charges generated by the photoelectric converting section corresponding to a sum of the constant amount of the bias component and a fluctuation component varying with an increase or decrease in the received-light amount;

a charge accumulating portion configured to accumulate residual charges obtained by separating the unnecessary charges from the charges generated by the photoelectric converting portion as effective charges; and

a charge extracting section configured to extract the effective charges accumulated in the charge accumulating section as a received-light output.

24. The photodetector of claim 23, further comprising: a device formation layer made of a semiconductor of a first conductivity type; a well of a second conductivity type formed on a main surface of the device formation layer; a discharging portion to which the undesired electric charges are discharged from the charge separating portion; and a plurality of electrodes arranged on the major surface of the well, and the electrodes comprising: a separation electrode for forming a potential well as the charge separating portion in the well; an accumulation electrode for forming a potential well as the charge accumulation portion in the well; and a barrier control electrode for forming a potential barrier between the charge separating portion and the charge accumulating portion.

Claims

1. A spatial information detecting apparatus comprising:

a light emission source (2) configured to project signal light intensity-modulated by a modulation signal to a target space;

a photodetection section (1) configured to separate a constant amount of offset component from electric charges corresponding to the amount of received light detected from the object space at a timing synchronized with the modulation signal, thereby providing a received light output reflecting a fluctuating component of the signal light; and

a signal processing section (3, 4) configured to detect spatial information of the object space by using the received light output;

wherein the photodetection portion (1) comprises:

a photoelectric conversion portion (D1) configured to receive light from the object space to generate electric charges;

a charge separating section (D2) configured to separate a prescribed constant amount of undesired electric charges corresponding to the bias component from the electric charges generated by the photoelectric converting section corresponding to a sum of the constant amount of bias component not depending on the fluctuation of the signal light and the fluctuation component varying according to the fluctuation of the signal light;

a charge accumulating portion (D3) configured to accumulate, as effective charges, residual charges obtained by separating the undesired charges from the charges generated by the photoelectric converting portion (D1); and

a charge extracting section configured to extract the effective charges accumulated in the charge accumulating section (D3) as the received-light output,

wherein the photodetection portion (1) comprises:

a separation electrode (14a) arranged on a semiconductor substrate to form a potential well as the charge separating portion (D2) in the semiconductor substrate;

an accumulation electrode (14b) arranged on the semiconductor substrate to form a potential well as the charge accumulation portion (D3) in the semiconductor substrate;

a barrier control electrode (14c) arranged on the semiconductor substrate and between the separation electrode (14a) and the accumulation electrode (14B) to form a potential barrier (B1) between the charge separating portion (D2) and the charge accumulating portion (D3); and

an electric-charge-amount adjusting device configured to form a potential barrier (B1) between the charge separating portion (D2) and the charge accumulating portion (D3), and adjust an amount of electric charge flowing from the charge separating portion (D2) into the charge accumulating portion (D3) through the potential barrier (B1) with respect to the electric charge generated by the photoelectric converting portion (D1), and

wherein the charge amount adjusting device includes: a control section (4) configured to control a voltage applied to the barrier control electrode (14c) to change a height of the potential barrier (B1); or a control section (4) configured to control a voltage applied to the separation electrode (14a) to change a depth of the potential well of the charge separation section.

2. The spatial information detecting apparatus as set forth in claim 1, further comprising a timing control section (4) configured to determine operation timings of said photoelectric conversion section (D1), said charge separating section (D2), and said charge accumulating section (D3) in association with a light receiving period in which said photoelectric conversion section (D1) generates electric charges by receiving light from said subject space to which the intensity-modulated light is irradiated, and a weighing period in which said unnecessary electric charges are separated from the electric charges generated by said photoelectric conversion section (D1) by using said charge separating section (D2) and said charge accumulating section (D3).

3. The spatial information detecting device according to claim 1,

wherein the photodetection portion (1) comprises: the semiconductor substrate; a discharging portion to which the undesired electric charges are discharged from the charge separating portion; and a plurality of electrodes arranged in a matrix and,

wherein the control section (4) is configured to control the voltage applied to the electrodes in association with a light receiving period during which the photoelectric conversion section (D1) generates electric charges by receiving light from the subject space to which the intensity-modulated light is irradiated and a weighing period during which the undesired electric charges are separated from the electric charges generated by the photoelectric conversion section (D1),

wherein the semiconductor substrate comprises: a semiconductor layer (11) of a first conductivity type; and a well (12) of a second conductivity type formed in a main surface of the semiconductor layer (11),

wherein the plurality of the electrodes are arranged on the main surface of the well (12) and include the separation electrode (14a), the accumulation electrode (14b), and the barrier control electrode (14c),

wherein the separation electrode (14a) is configured to form the charge separation portion (D2) in the well (12), and

the accumulation electrode (14b) is configured to form the charge accumulation portion (D3) in the well (12).

4. The spatial information detecting device according to claim 1,

wherein the light emission source (2) irradiates the object space with light intensity-modulated by the modulation signal so as to have a light emission period in which the intensity-modulated light is projected from the light emission source (2) to the object space and a pause period in which the intensity-modulated light is not projected to the object space, and

wherein the charge amount adjusting means is configured to adjust an amount of electric charges separated as the undesired electric charges from the electric charges corresponding to the received-light amount obtained in the light emission period, in accordance with the amount of electric charges generated by the photoelectric converting portion (D1) in the rest period.

5. The spatial information detecting device as set forth in claim 4,

wherein when the amount of charge generated by the photoelectric conversion portion (D1) in the rest period increases, the charge amount adjustment means is configured to increase the amount of undesired electric charges to be separated from the electric charges corresponding to the received-light amount obtained in the light emission period.