JP2017158178A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a sensitivity difference for each pixel group and further reduce the influence of electric charge generated during a period when imaging is not performed. An imaging device in which a plurality of imaging elements are arranged, the imaging element is a light receiving element that generates an electric charge from light received by photoelectric conversion, and a floating diffusion that converts the electric charge generated by the light receiving element into a voltage. It has a charge transfer switch that transfers charges from the light receiving element to the floating diffusion, a reset switch that resets the voltage of the floating diffusion, and a source follower that amplifies the voltage of the floating diffusion. During the acquisition period, the floating diffusion voltage is reset multiple times for each predetermined pixel group, and the charge transfer switch transfers the charge from the light receiving element to the floating diffusion for each predetermined pixel group during the one image data acquisition period. Do it multiple times. [Selection diagram] Fig. 2

Description

  The present invention relates to an imaging apparatus.

  An imaging device such as a CMOS linear image sensor reads out image data every predetermined period. For example, charges are accumulated in the photodiode of each pixel by photoelectric conversion, the accumulated charges are transferred to the floating diffusion at a predetermined timing, and the charges held in the floating diffusion are read as image data. For example, the following is disclosed as a pixel data reading technique in the imaging apparatus.

  For example, in Patent Document 1, the detection signal of each pixel of the solid-state image sensor is reset simultaneously for all rows, and then the exposure is started. A technique for sequentially reading out signals for each row is disclosed.

  Patent Document 2 discloses a technique for performing an operation of reading the reset level of the floating diffusion, and further performing an operation of reading out the electric charge transferred to the floating diffusion as a signal level to obtain a difference between the signal level and the reset level. Has been.

  Patent Document 3 discloses a technique for performing rolling shutter reset of a plurality of storage nodes so that each storage node is reset before charge is transferred from the photosensor.

  Patent Document 4 discloses a technique for evaluating the linearity of an electronic shutter before product shipment. In this technique, pixel data in which the exposure time is gradually extended from each row in the order of row alignment is output, and linearity evaluation is performed from the characteristics indicating the relationship between the exposure time of the pixel data and the output level of the pixel data.

  However, the conventional technique has not taken measures such as setting an accumulation period individually for each pixel group and keeping the floating diffusion state constant at the start of charge transfer. If charge transfer is performed in a state where the charge of the floating diffusion is not reset, the total amount of charge that can be held in the floating diffusion may be exceeded, and the charge generated by the photodiode may not be fully transferred. . In this case, a charge remains in the photodiode, and the charge is added to the charge amount obtained in the next accumulation period, which causes a problem that a deviation occurs between the actual subject and the captured image data.

  The present invention has been made in view of the above, and provides an imaging apparatus capable of correcting a sensitivity difference for each pixel group and further reducing the influence of charges generated during a period in which imaging is not performed. The purpose is to do.

  In order to solve the above-described problems and achieve the object, the present invention is an imaging device in which a plurality of imaging elements are arranged, and the imaging element generates a charge from light received by photoelectric conversion. A floating diffusion that converts the charge generated by the light receiving element into a voltage; a charge transfer switch that transfers the charge from the light receiving element to the floating diffusion; a reset switch that resets the voltage of the floating diffusion; A source follower that amplifies the voltage of the floating diffusion, and the reset switch resets the voltage of the floating diffusion a plurality of times for each predetermined pixel group during one image data acquisition period. The transfer switch And carrying out a plurality of times from the light receiving element during the data acquisition period for each of the predetermined group of pixels the transfer of charge to the floating diffusion.

  According to the present invention, it is possible to correct a difference in sensitivity for each pixel group, and further, it is possible to reduce the influence of charges generated during a period in which imaging is not performed.

FIG. 1 is a diagram illustrating a configuration example of an imaging apparatus according to the embodiment. FIG. 2 is a diagram illustrating a configuration example of the image sensor. FIG. 3 is a timing chart illustrating a first operation example of the imaging apparatus. FIG. 4 is a timing chart illustrating a second operation example of the imaging apparatus. FIG. 5 is a timing chart illustrating a third operation example of the imaging apparatus. FIG. 6 is a timing chart illustrating a fourth operation example of the imaging apparatus.

  Hereinafter, embodiments of an imaging device will be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a configuration example of an imaging apparatus 1 according to the embodiment. The imaging apparatus 1 is, for example, a CMOS (Complementary MOS) color linear sensor, and includes an imaging element block 10, an AD (Analog to Digital) conversion circuit 12, a horizontal readout circuit 14, an image data processing circuit 16, and a control circuit 18. In the following description, the “imaging element” refers to any one of unit pixels configured in the imaging apparatus 1. A group of a plurality of image sensors, that is, a group of a plurality of unit pixels is referred to as a “pixel group”.

  The image sensor block 10 is an area where a plurality of image sensors 20 are arranged. FIG. 1 shows an example in which the imaging elements 20 are arranged in three rows. In the first row, the second row, and the third row of the image sensor block 10, the color filters 2r, 2g, and 2b are arranged in this order above the image sensors 20 (the front side in FIG. 1). That is, the image sensor block 10 includes a pixel group in the first row in which the color filter 2r is arranged, a pixel group in the second row in which the color filter 2g is arranged, and a pixel in the third row in which the color filter 2b is arranged. Having a group.

  Each pixel group receives light (R (red), G (green), and B (blue, respectively) through a color filter (any one of the color filters 2r, 2g, and 2b) disposed in association with the pixel group. ) Is received and charges generated by photoelectric conversion are accumulated. Each pixel group outputs a pixel signal that constitutes each pixel of the image data from each image sensor 20 based on the charge generated during the respective accumulation period. As will be described later, the “accumulation period” refers to a charge accumulation period in the light receiving element of each image sensor 20 corresponding to each pixel of image data.

  The AD conversion circuit 12 has a column configuration that AD-converts the voltages (pixel signals) output from the respective image sensors 20 in units of columns, and outputs the converted digital pixel signals of RGB colors to the horizontal readout circuit 14. To do. The horizontal readout circuit 14 performs parallel-serial conversion on digital pixel signals of RGB colors input from the AD conversion circuit 12 and outputs the converted signals to the image data processing circuit 16. The image data processing circuit 16 corrects the RGB digital signals (that is, image data) input from the horizontal readout circuit 14 and outputs the digital signals to the outside.

  A control circuit (an example of a control unit) 18 controls each unit constituting the imaging device 1. For example, the control circuit 18 outputs a control signal S to various switches SEL, TX, RT (see FIG. 2) of each image sensor 20, and controls switching between switch-on and switch-off. The control signal S includes SRTs 31, 33 and 35 (see FIG. 3) for controlling the RT 206, STXs 32, 34 and 36 (see FIG. 3) for controlling the TX 202, and SSEL 30 (see FIG. 3) for controlling the SEL 210. A signal is included. Each of these switches and controls will be described later.

  In addition, the control circuit 18 controls the AD conversion circuit 12, the horizontal readout circuit 14, the image data processing circuit 16, and the like. The control target by the control circuit 18 may be determined as appropriate.

  FIG. 2 is a diagram illustrating a configuration example of the image sensor 20. As an example of the imaging device 20, a photodiode (PD) 200, a charge transfer switch (TX) 202, a floating diffusion (FD) 204, a reset switch (RT) 206, a source follower circuit (SF) 208, and a selection A four-transistor configuration including a control switch (SEL) 210 is shown. The PD 200 is an example of a “light receiving element”, photoelectrically converts incident light to generate charges, and accumulates charges according to the amount of light. For example, it is an embedded photodiode. TX 202, RT 206, SF 208, and SEL 210 have a configuration of four transistors (for example, MOSFET (MOS Field Effect Transistor)). The connection relationship in the image sensor 20 is shown below.

  The PD 200 has an anode grounded and a cathode connected to the drain of the TX 202. TX 202 has a drain connected to the cathode of PD 200 and a source connected to FD 204. The RT 206 has a drain connected to the voltage VDD and a source connected to the FD 204. The SF 208 has a gate connected to the FD 204, a drain connected to the voltage VDD, and a source connected to the drain of the SEL 210. The SEL 210 has a drain connected to the source of the SF 208 and outputs a pixel signal (voltage) from the source to the AD conversion circuit 12 (see FIG. 1) side.

  The control circuit 18 (see FIG. 1) operates the imaging device 20 by applying a pulse voltage as a control signal S (see FIG. 1) to the gate of TX 202, the gate of RT 206, or the gate of SEL 210.

  The basic operation of the image sensor 20 is as follows. First, the PD 200 performs photoelectric conversion to generate and store charges corresponding to the amount of incident light. The electric charge accumulated in the PD 200 is transferred from the PD 200 to the FD 204 when the TX 202 is switched on. The FD 204 converts the charge generated by the PD 200 into a voltage. Specifically, the FD 204 holds the signal charge transferred from the PD 200 via the TX 202. Further, the FD 204 converts the held signal charge into a voltage signal level and outputs it, and applies the signal level to the SF 208.

  The SF 208 operates as follows when the SEL 210 is switched on. The SF 208 amplifies the voltage of the signal level of the FD 204 and outputs it as a pixel signal (voltage) SFO. After outputting the signal level of the FD 204 to the SFO, the signal level of the FD 204 is reset by switching on the RT 206 and initialized to a predetermined level. The pixel signal SFO becomes image data through the AD conversion circuit 12, the horizontal readout circuit 14, and the like.

(First operation example)
Next, the operation of the imaging apparatus 1 will be described in detail. FIG. 3 is a timing chart illustrating a first operation example of the imaging apparatus 1. The SSEL 30 in FIG. 3 shows the switch-on and switch-off timings in the SEL 210 that are common to all rows including the row 1, the row 2, and the row 3. SRTs 31, 33, and 35 show the switch-on and switch-off timings in the RT 206 of row 1, row 2, and row 3, respectively. In STX 32, 34, and 36, the timing of switch-on and switch-off in TX 202 of row 1, row 2, and row 3, respectively is shown. In each timing, a high level indicates that the switch is on (hereinafter also referred to as “on”), and a low level indicates that the switch is off (hereinafter also referred to as “off”).

  Rows 1, 2, and 3 each include from the end of the previous image data acquisition period (the (n−1) th image data acquisition period) to the subsequent nth image data acquisition period. Show. Here, n is an integer of 2 or more.

  For example, in the row 1, the first pulse P11 of the SRT 31 indicates that the RT 206 is turned on in the (n−1) th image data acquisition period, and the first pulse P101 of the STX 32 is the same n−1th image data acquisition. Indicates that the period 202 is turned on. The second pulse P12 of the SRT 31 indicates that the RT 206 is turned on during the n-th image data acquisition period, and the second pulse P102 of the STX 32 indicates that the TX 202 is turned on during the same n-th image data acquisition period. Thus, in the first operation example, RT 206 and TX 202 are each turned on only once in the “one image data acquisition period”.

  The interval from immediately after readout of the pixel signal from the image sensor 20 to immediately after readout of the next pixel signal from the same image sensor 20 corresponds to an “image data acquisition interval”. In this specification, this period is referred to as “one image data”. This is called “acquisition period”. In FIG. 3, the period from the fall of the first pulse P101 to the fall of the second pulse P102 shown in STX 32 corresponds to the length of “one image data acquisition period”.

(Accumulation period)
Here, the accumulation period will be described. In the first pulse P11 of the SRT 31, the signal level of the FD 204 is reset. In the subsequent first pulse P101 of STX 32, all charges accumulated in the PD 200 are transferred to the FD 204. The signal level based on the charge transferred to the FD 204 is amplified by the SF 208 by the first pulse P1001 of the SSEL 30, and is output as the (n-1) th pixel signal. In FIG. 3, the (n−1) th image data G (n−1) shown in “image data” indicates the output timing of the image data configured based on the (n−1) th pixel signals. is there. Incidentally, the nth image data G (n) indicates the output timing of the image data configured based on each nth pixel signal.

  As described above, in the n-th image data acquisition period, the charge accumulation period by the PD 200 starts from the falling edge of the first pulse P101 of STX32, and the first one at the falling edge of the second pulse P102. The process ends when all the charges accumulated in the PD 200 are transferred to the FD 204 from the fall of the second pulse P101 to the fall of the second pulse P102. That is, the accumulation period T1 (n-th accumulation period) in the PD 200 in the n-th image data acquisition period is from the fall of the first pulse P101 to the fall of the second pulse P102. The accumulation period T1 is the same in each image data acquisition period. In the first operation example, the accumulation period T1 is applied to the entire “one image data acquisition period”.

  Furthermore, in the first operation example, the switch-on and switch-off timings of each row are aligned as shown in FIG. For this reason, charges are accumulated in the same period in each row (and hence all the image sensors 20). Therefore, the charge of light received at the same timing in all the image pickup devices 20 is output as a pixel signal, and the image data can be read out.

(Operation of control circuit)
In the first operation example shown in FIG. 3, the control circuit 18 operates as follows. As an example, the (n-1) th operation in row 1 will be described. The control circuit 18 initializes the FD 204 by outputting one pulse to the RT 206 (corresponding to the first pulse P11 of the SRT 31) and turning on the RT 206 in the (n-1) th image data acquisition period. Subsequently, the control circuit 18 outputs one pulse to the TX 202 (corresponding to the first pulse P101 of the STX 32) and turns on the TX 202, whereby the n−1th accumulation period (corresponding to the accumulation period T1). ), The charge generated in the PD 200 is transferred to the FD 204. Then, the control circuit 18 outputs one pulse (corresponding to the first pulse P1001 of the SSEL 30) to the SEL 210 in advance as shown in FIG.

  Accordingly, the control circuit 18 outputs a pixel signal obtained by amplifying the signal level of the FD 204 during a period in which the SEL 210 is on, and outputs image data of each pixel signal. Note that the control circuit 18 may output the pulse P1001 to the SEL 210 during the n-th accumulation period T1 (but before the output of the pulse P12).

  As described above, in the first operation example, light is sequentially converted into charges by the PD 200 over one image data acquisition period, and the accumulated charges are transferred from the PD 200 to the FD 204 when the TX 202 is turned on once. To do.

  Incidentally, there is a saturation level in the amount of charge generated in the PD 200 by photoelectric conversion. Therefore, in order to keep the amount of charge generated in the PD 200 during the period of receiving light below the saturation level, the PD 200 that receives the color with the highest sensitivity (in this example, R color) is stored so as not to reach the saturation level. It is desirable to set the period T1.

(Second operation example)
In the first operation example, it has been described that the amount of charge generated in the PD 200 during the period of receiving light needs to be suppressed to a saturation level or less. In addition, the FD 204 has a total amount of charge that can be held. When charges exceeding the total charge amount are transferred from the PD 200 to the FD 204, the corresponding charges remain in the PD 200. Therefore, it is necessary to reset the signal level of the FD 204 before the FD 204 reaches the total charge amount.

  FIG. 4 is a timing chart illustrating a second operation example of the imaging apparatus 1. In the second operation example, an example is shown in which both the number of resets and transfers are increased from one to a plurality of times in one image data acquisition period. Here, an example in which the number of resets and transfers is increased to two is shown as an example, but the number of resets and transfers is not limited to two but may be increased to three or four.

  In FIG. 4, the length of “one image data acquisition period” is the same as that of the first operation example in order to facilitate comparison. Therefore, in FIG. 4, the SSEL 40 is the same as the SSEL 30 (see FIG. 3). In this example, the length of the “one image data acquisition period” is a period from the falling edge of the first pulse P101 to the falling edge of the third pulse P103 shown in STX42. Note that the length of the “one image data acquisition period” is the same in other operation examples described later.

  In the second operation example, each of RT 206 and TX 202 is turned on twice in the “one image data acquisition period”. Both the first turn-on of RT 206 and TX 202 and the second turn-on are operations in which the signal level of FD 204 is reset and charges are transferred from PD 200 to FD 204. Among these, the first ON turns off the charges transferred to the FD 204 and the second ON turns on the charges transferred to the FD 204 and outputs them as pixel signals. That is, one image data acquisition period is composed of a first period of the first half in which charges are discarded and a second period of the second half in which charges are output as pixel signals.

  Specifically, line 1 will be described as an example. The first pulse P11 and pulse P101 of SRT41 and STX42 respectively represent the second turn-on of RT206 and TX202 in the (n-1) th image data acquisition period. That is, the charge transferred to the FD 204 after the FD 204 is reset is output as a pixel signal.

  The second pulse P12 and pulse P102 of SRT41 and STX42 respectively represent the first turn-on of RT206 and TX202 during the nth image data acquisition period. The period from the falling edge of the first pulse P101 of STX42 to the falling edge of the second pulse P102 corresponds to the first period. During this first period, the light received by the PD 200 is sequentially converted into charges, and all of the accumulated charges are transferred from the PD 200 to the FD 204 by the second pulse P12 and pulse P102 of RT206 and TX202. Is done.

  The third pulse P13 and pulse P103 of SRT41 and STX42 respectively represent the second turn-on of RT206 and TX202 in the n-th image data acquisition period. The period from the fall of the second pulse P102 of STX42 to the fall of the third pulse P103 corresponds to the second period. In the subsequent second period, the light received by the PD 200 is sequentially converted into electric charges and stored in the same manner as in the first period. Thereafter, all the charges in the first period held in the FD 204 are discarded by the pulse P13, and all charges accumulated in the second period are transferred from the PD 200 to the FD 204 by the subsequent pulse P103. This electric charge is output as a pixel signal by the pulse P1002 of the SSEL 40.

  In addition, although the description has been given by taking the line 1 as an example, the same applies to the lines 2 and 3. In each of the operation examples described later, unless there is a need to explain for each row, the explanation will be given by taking row 1 as an example.

(Accumulation period)
The accumulation period T2 in the second operation example is a second period from the fall of the second pulse P102 of the STX 42 to the fall of the third pulse P103. That is, a part of the “one image data acquisition period” is used as the accumulation period T2. Since the charge of the FD 204 is not reflected in the image data in the first period, this corresponds to a “period in which no imaging is performed”.

  The accumulation period T2 may be changed as appropriate by moving the timing of the second pulse P102 of the STX 42 within the range of the first pulse P101 and the third pulse P103 of the STX 42.

  When reset and transfer are performed a plurality of times in the first period, the accumulation period T2 starts from the falling edge of the STX42 pulse after the last reset of the SRT 41 in the first period.

  Further, in the second operation example, as in the first operation example, the timings of the accumulation periods T2 of the respective rows are aligned, so that it is possible to read the image data of the light received at the same timing in all the image pickup devices 20. become.

(Retention period)
All charges stored in the FD 204 in the first period are discarded by the pulse P13, and all charges stored in the second period are transferred from the PD 200 to the FD 204 by the subsequent pulse P103. The period from this transfer (multiple transfers during one image data acquisition period) to the rise of the next reset pulse corresponds to the “holding period”.

  In this example, the timing of the pulse P1002 of SSEL40 is overlapped with the timing of the pulse P103 of STX42. For this reason, it is possible to output all the charges held in the FD 204 as pixel signals before the next reset pulse rises, that is, within the holding period. The timing of the pulse P1002 of the SSEL 40 can be delayed until just before the rising edge of the next reset pulse.

(Operation of control circuit)
The control circuit 18 can increase the number of resets and transfers in one image data acquisition period by adding an output pulse in this period.

  As described above, as shown in the second operation example, the control circuit 18 suppresses the amount of charge generated in the PD 200 to a saturation level or less by outputting a pulse for performing transfer a plurality of times in one image data acquisition period. Is possible. Further, as shown in the second operation example, the control circuit 18 outputs a pulse for resetting a plurality of times in one image data acquisition period, so that the charge amount held by the FD 204 reaches the total charge amount. It is also possible to reset the signal level of the FD 204.

(Third operation example)
In general, when RGB three-color light is detected by the PD 200, the sensitivity decreases in the order of R, G, and B. For this reason, when photoelectric conversion is performed for the RGB three-color light in the same period, the amount of charge generated by the PD 200 in the order of R, G, and B decreases.

  When the accumulation period is set short so as not to saturate the PD 200 that receives R light, the charge generated in the PD 200 that receives B light with the lowest sensitivity is much less than the saturation level. Even if the PD 200 that receives light of R color can fully utilize the dynamic range, the PD 200 that receives light of B color may be insufficient. An operation example improved in this regard is shown below.

  FIG. 5 is a timing chart illustrating a third operation example of the imaging apparatus 1. In the third operation example, each accumulation period is different for each pixel group (in this example, the pixel group in row 1, the pixel group in row 2, and the pixel group in row 3) divided according to the color of the color filter. Show.

  In the third operation example, the first ON timing of RT 206 and TX 202 in the “one image data acquisition period” is varied depending on the row (pixel group). Specifically, in order to receive R light in row 1, the second pulse P12 and pulse P102 of SRT 51 and STX 52 are moved backward as shown in FIG. As a result, the accumulation period T31 is the shortest of the three rows. In row 2, since light of G color is received, the second pulse P22 and pulse P202 of SRT 53 and STX 54 are moved slightly backward. As a result, the accumulation period T32 is the second shortest of the three rows. In row 3, since light of B color is received, the second pulse P32 and pulse P302 of SRT55 and STX56 are set as they are. As a result, the accumulation period T33 is the longest of the three rows.

  As in the first and second operation examples, the timing at which the TX 202 is turned on in the period in which the SEL 210 is turned on is the same for all rows, so that the image data is read at the same timing even if the accumulation period is different. It becomes.

(Accumulation period)
In the third operation example, as in the second operation example, in the row 1, the accumulation period (accumulation period) is from the falling edge of the second pulse P102 of STX52 to the falling edge of the third pulse P103 of STX52. T31). In row 2, the accumulation period (accumulation period T32) is from the fall of the second pulse P202 of STX54 to the fall of the third pulse P203 of STX54. In row 3, the accumulation period (accumulation period T33) is from the fall of the second pulse P302 of STX 56 to the fall of the third pulse P303 of STX 56.

  For example, in the row 1, for example, the same number of pulses between the second pulse P12 and the third pulse P13 of the SRT 51 and between the second pulse P102 and the third pulse P103 of the STX 52. Is added from the falling edge of the last pulse of STX52 during the period in which SEL210 is turned off (period from the falling edge of the first pulse P1001 of SSEL50 to the rising edge of the second pulse P1002). The accumulation period is the period until the falling edge of the third pulse of STX52 during the period in which SEL210 is turned on (the period of the second pulse P1002 of SSEL50).

(Operation of control circuit)
In the third operation example, the control circuit 18 turns on RT 206 and TX 202 twice in this order in one image data acquisition period. The control circuit 18 shifts the accumulation period for each color (for each pixel group) by shifting the first timing (the timing of the second pulses P102, P202, and P303) for turning on the TX 202 for each row. That is, the imaging apparatus 1 can set the accumulation period for each color by the control signal from the control circuit 18.

  As described above, even in the same image sensor 20, by setting the accumulation period in the control circuit 18 according to the color received by the PD 200, a high dynamic range can be achieved in each image sensor 20 without depending on the color received. It becomes possible to secure.

  Here, the control circuit 18 sets a short accumulation period T31 for the image sensor 20 that processes R color with high sensitivity, and sets a long accumulation period T33 for the image sensor 20 that processes B color with low sensitivity. As a result, the low sensitivity B color is converted into a larger amount of charge by setting the accumulation time longer, and a high dynamic range can be secured. Further, the R color with high sensitivity can suppress charge conversion to less than the saturation amount by setting the accumulation time short, and can secure a high dynamic range. Therefore, it is possible to correct so that the difference in sensitivity caused when the image pickup device 20 handles different colors becomes uniform.

(Fourth operation example)
In the fourth operation example, a case will be described in which the accumulation period is changed according to the color to be handled and the midpoints of the accumulation periods of the respective colors are aligned.

  FIG. 6 is a timing chart illustrating a fourth operation example of the imaging apparatus 1. Here, the accumulation periods of row 1, row 2, and row 3 are defined as accumulation period T41, accumulation period T42, and accumulation period T43, respectively, and the midpoint of each accumulation period (T41 / 2, T42 / 2, T43 / 2). The case where the timing is matched with the perpendicular line indicated by a broken line is shown.

  Further, compared with the third operation example, the ON timing of the SEL 210 in each row is also adjusted to a different timing for each row. For example, for row 1, the falling timing of the pulse P1002 of SSEL60 is matched with the falling timing of the third pulse P103 of STX62. For row 2, the falling timing of the pulse P1002 of SSEL63 is matched to the falling timing of the third pulse P203 of STX65. For the row 3, the falling timing of the pulse P1002 of the SSEL 66 is matched with the falling timing of the second pulse P302 of the STX 68. Therefore, the timing of the SEL 210 is different for each row.

  In this example, pixel signals are output in the order of row 1, row 2, and row 3 due to the timing relationship of the SEL 210 in each row. For this reason, the image data G (n−1) and the image data G (n) are output after the output of the row 3.

(Operation of control circuit)
The control circuit 18 controls the switch-on operation timings of the SELs 210, RT206, and TX202, for example as shown in FIG.

  Note that the timings of SSEL60, SSEL63, and SSEL66 are merely examples, and are not limited to these timings.

  As described above, by aligning the midpoints of the accumulation periods of the pixels in each row (that is, each color), it becomes possible to include more data of light received at the same timing in each pixel of the image data.

  In this case, for example, when the original image is reproduced by stitching together the successively captured RGB images, the relative positional relationship of the RGB image data can be matched, and image processing during reproduction is possible. The load can be reduced.

  The first to fourth operations described above are examples, and may be appropriately modified within the scope of application of the present embodiment. The following is an example of the modification.

  The signal level of the FD 204 is reset immediately before the charge is transferred from the PD 200, and the charge transfer from the PD 200 is performed after the reset of the signal level of the FD 204 is completed. For example, taking row 1 shown in FIG. 4 as an example, each pulse P11, P12, P13 of SRT41 is arranged immediately before each pulse P102, P102, P103 of STX42. By doing so, the control circuit 18 always performs initialization of the FD 204 by the RT 206 immediately before the charge transfer by the TX 202, so that the signal level of the FD 204 is always in a reset state immediately before the charge transfer from the PD 200. If the FD 204 is in the reset state, all of the charge of the PD 200 can be transferred, so that the residual charge in the PD 200 can be eliminated.

  In addition, in the case where the charge of the first period remains in the PD 200 at the start of the second period, reset and transfer may be performed a plurality of times before the start of the second period. That is, the operation of transferring the accumulated charge of the PD 200 to the FD 204 and discarding the charge by resetting is repeated a plurality of times within the first period. Taking row 1 shown in FIG. 4 as an example, a plurality of sets of reset pulses and transfer pulses are added between the pulse P12 of SRT41 and the pulse P102 of STX42. If the first period can be shortened, a plurality of reset pulses are added between the pulse P12 and the pulse P13 of the SRT 41, and the reset pulse added to the SRT 41 is supported between the pulse P102 and the pulse P103 of the STX 42. Add a transfer pulse. In this case, the fall of the transfer pulse immediately before the pulse P103 among the added transfer pulses is the start of the accumulation period.

  Further, the positional relationship of SSEL pulses with respect to SRT and STX is merely an example, and may be modified as appropriate. Taking the row 1 shown in FIG. 4 as an example, the first pulse P1001 of the SSEL 40 is from the falling timing of the first pulse P101 of the STX 42 to the time before the rising of the second pulse P12 of the SRT 41. What is necessary is just to be arrange | positioned between.

  Further, the TX 202 may be always turned on outside the accumulation period. If TX 202 remains on, the charge generated in PD 200 can always be transferred to FD 204. However, if there is a possibility that charges exceeding the total charge amount that can be transferred to the FD 204 may be generated in the PD 200, charges that could not be transferred to the FD 204 may remain in the PD 200. Therefore, in that case, the charge held in the FD 204 is discarded by performing initialization of the FD 204 by the RT 206 before the charge exceeding the total charge amount is transferred to the FD 204.

  For example, the control circuit 18 may set the image data acquisition interval longer, set the accumulation period shorter, and transfer the charges accumulated in the PD 200 outside the accumulation period to the FD 204 in a plurality of times.

  Further, the SF 208 may be configured in multiple stages. The SEL 210 is shown as an example of a “control switch”. In addition, as long as it is a constant current circuit, it may be changed to another configuration.

  In addition, the imaging apparatus may be capable of setting the accumulation period in units of pixels or may be capable of setting the accumulation period for each predetermined pixel group. As an example, a configuration in which an accumulation period is set for each row (pixel group) is shown, but an accumulation period may be set for each pixel. Moreover, although the RGB row of the linear sensor is shown as an example of the pixel group, the pixel group is not limited to this. For example, a pixel group may be formed by classifying each pixel in the Bayer array by color.

  In addition, although the configuration of the pixel group when the pixels are classified by color is shown, the pixel group may be classified by the photoelectric conversion characteristics of the PD 200 of each pixel without being limited by color. For example, a pixel having a photoelectric conversion characteristic better than a predetermined standard is classified as a first pixel group, and a pixel having a photoelectric conversion characteristic worse than a predetermined standard is classified as a second pixel group.

  In addition, by arranging different color filters on the image sensor, the image sensor is classified into a pixel group that makes R light incident, a pixel group that makes G light incident, and a pixel group that makes B light incident. In addition, any one of RGB colors separated from white light may be directly incident on each image sensor.

  As described above, in the operations shown in the first operation example to the fourth operation example, and all the deformation operations included in this technical idea, and the configuration including the deformation operations, the sensitivity difference can be corrected for each pixel group. Furthermore, there is an effect that it is possible to reduce the influence of electric charges generated during a period in which imaging is not performed.

DESCRIPTION OF SYMBOLS 1 Imaging device 10 Imaging element block 18 Control circuit (control part)
20 Image sensor 200 Photodiode (PD: light receiving element)
202 Charge transfer switch (TX)
204 Floating diffusion (FD)
206 Reset switch (RT)
208 Source follower circuit (SF)
210 Selection control switch (SEL)

JP 2006-191236 A JP 2013-106231 A International Publication No. 2007/111854 JP 2011-66852 A

Claims (9)

An imaging device in which a plurality of imaging elements are arranged,
The image sensor is
A light receiving element that generates electric charge from light received by photoelectric conversion;
Floating diffusion for converting the charge generated by the light receiving element into a voltage;
A charge transfer switch for transferring the charge from the light receiving element to the floating diffusion;
A reset switch for resetting the voltage of the floating diffusion;
A source follower for amplifying the voltage of the floating diffusion;
Have
The reset switch is
The voltage of the floating diffusion is reset a plurality of times for each predetermined pixel group during one image data acquisition period,
The charge transfer switch
The imaging apparatus, wherein the charge transfer from the light receiving element to the floating diffusion is performed a plurality of times for each predetermined pixel group during the one image data acquisition period. The imaging apparatus according to claim 1, wherein the reset switch resets the voltage of the floating diffusion immediately before the charge transfer switch transfers the charge from the light receiving element to the floating diffusion. The plurality of image sensors are
Each of the light receiving elements is provided with a filter so as to receive light of any one color of red, blue, and green, and the pixel group is configured for each color of the received light. The imaging device according to claim 1 or 2. The control unit further controls a timing at which the reset switch resets the voltage of the floating diffusion and a timing at which the charge transfer switch transfers the charge from the light receiving element to the floating diffusion. The imaging device according to any one of 1 to 3. A control switch for turning on an operation of amplifying and outputting the voltage of the floating diffusion by the source follower;
The control switch performs the operation until the end of the holding period in which the charge transferred by a part of the plurality of transfers is held in the floating diffusion during the one image data acquisition period. The imaging apparatus according to any one of claims 1 to 4, wherein the imaging apparatus is turned on. The control unit further includes:
The imaging apparatus according to claim 5, wherein a timing at which the operation of the control switch is turned on is controlled. The holding period is a period from the transfer of the charge accumulated in the light receiving element during the accumulation period started after the plurality of transfers to the next reset after the transfer to the floating diffusion. The imaging device according to claim 5 or 6. The imaging apparatus according to claim 7, wherein the accumulation period is different for each pixel group. The controller is
9. The operation timing of the reset switch and the charge transfer switch is controlled so that the midpoints of the periods in which the light receiving elements each accumulate charges are aligned. 9. Imaging device.

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