HK1003076B - Device and method for the detection and demodulation of an itensity-modulated radiation field - Google Patents

Description

Apparatus and method for detection and demodulation of intensity modulated radiation fields

The invention relates to a device for detecting and demodulating a radiation field having an image sensor formed by a one-or two-dimensional arrangement of sensitive elements, wherein each sensitive element has a light-receiving section for converting a radiation signal into an electrical signal, and to a method in which successive signal charges corresponding to the intensity of the radiation field are generated, read out and stored in the light-receiving section of the sensitive element.

In addition, technically, the characteristics of many systems are studied with the aid of modulated signals. The system is then excited by a modulated signal, for example in the form of a sinusoid, in which the response of the system is measured. The modulation of the system response obtained is used as a characteristic value to determine the phase offset and the background signal level (offset) with respect to the excitation signal.

In the disclosed semiconductor image sensor, the light intensity of the two-dimensional distribution is converted into a two-dimensional photocurrent density distribution. The signal charges generated by the light are simultaneously integrated in the so-called pixels. A CCD image sensor is disclosed, for example, in DE 3909394C2, in which the charge pattern produced will shift laterally during exposure. Thus, the occurrence of motion blur should be avoided when capturing the relevant object moving relative to the image sensor.

For use in scanless, image-providing lidar 3D cameras, a method is disclosed in which modulated light is imaged on a conventional image sensor (lidar image without scanner, photon spectrum, pp.281994 month 4). The demodulation is effected by an image-retaining, short-time variable amplifier element between the imaging objective and the semiconductor sensor. The amplifier element is implemented as a microchannel plate (MCP), where it must operate at high pressures of 100-. The incident light is absorbed and modulated for a short time in the amplifier elements and then reaches the image sensor, where they only have the function of an integrator. In this case, it is possible to take three or more images, which must then withstand significant light leakage in the amplifier due to absorption. In addition, during shooting, an image must be completely read out from the image sensor.

Further, a CDD image sensor (h.level, h.aebersold, j.o.stenflo, "charge coupled device image sensor as a demodulator in a 2-D polarimeter with a piezo elastic modulator", applied optics, volume 29, page 1186 + 1190, 1990) for demodulating short time shifted polarized light is disclosed. Therefore, a modulator is arranged between the objective lens and the CCD image sensor, which converts the polarization of the light between two states in the adjusted continuous lens. The two images that have been generated for the two polarization states are accumulated and stored in the image sensor. Thus, one disclosed image sensor provides a strip mask that covers the optical density of every second image sensor scan line. In this way, one accumulates the images of each polarization state at the appropriate beat by pushing the image charge pattern up or down vertically.

The object of the invention is to provide a device and a method for detecting and demodulating intensity-modulated radiation fields, which ensure that a plurality of parameters of the modulated radiation fields are determined.

This object is achieved by the technical teaching of the device in that the clock generator (14) controls the electronic switch (22) in such a way that the signal charges generated in the light-receiving section (17) are transferred to the memory units (21, 26) in synchronism with the modulation signal emitted by the radiation source, and the measured values stored in the individual memory units (21, 26) for controlling the memory units (21, 26) are transmitted to the evaluation unit (15) for evaluating the measured values; and

by means of the technical teaching of the method that the radiation field is imaged by an optical system (12) on an image sensor (13, 23) consisting of one-or two-dimensionally arranged sensitive elements (16),

-a first phase in which a succession of signal charges corresponding to the intensity of the radiation field is generated in the light-receiving part (17) of the sensor (16), wherein the signal charges are integrated each time during an integration period (I),

-the signal charge integrated each time is transferred to the non-light receiving part (18) of the sensitive element (16) in synchronism with the modulation signal generated by the radiation source and is always stored in a storage unit (21, 26),

-the signal charge generated in the light-receiving section (17) is supplied from the light-receiving section of the sensor (16) to the respective memory cell (21, 26) via at least one electronic switch (22) assigned to the respective memory cell (21, 26) and stored.

-a second phase in which the measured values stored in the storage unit (21, 26) are read off continuously and supplied to the analysis unit (15)

The solution is carried out.

The advantages achieved by the invention are in particular that an image sensor is realized which extends in one or two dimensions and has a plurality of sensors which are always suitable and which detect modulated radiation on the one hand and perform demodulation as such on the other hand. A clock generator makes it possible to synchronize the demodulation always carried out in the sensor with the demodulated signal emitted from the radiation source, so that, after reading out the measured values from the device according to the invention, the parameters of the detected radiation field can be determined in a position-dependent manner.

The device of the invention comprises first of all a large number of sensitive cells, which extend in two dimensions. It can then advantageously be used to provide an image interferometry method, in which the modulated image signal appears shortly after the heterodyne method has been carried out when the image is captured. Secondly, the device of the invention may comprise a single sensing element and thus be measured in a point-wise manner.

Each sensor has at least one memory cell that accumulates charge detected at a light receiving portion of the sensor. Thus, measurement of a signal of smaller intensity can be ensured.

According to a preferred embodiment, a sinusoidal radiation is detected and demodulated. The background light of amplitude, phase and radiation field can be determined with a partial scan of four scans per cycle. As the scanning speed increases, further parameters of the detected radiation field may be obtained, e.g. determining fourier coefficients.

Embodiments of the invention are further illustrated by the following figures. The figure is as follows:

FIG. 1: block diagram of the apparatus according to the invention;

FIG. 2: a structure of an image sensor according to the first embodiment;

FIG. 3: a structure of an image sensor according to a second embodiment;

FIG. 4: short time courses of the detected, sinusoidally shaped modulation signal.

The invention is preferably used for distance measurement. The time delay of the modulated light pulses emitted from the radiation source, which are reflected by the measurement object and detected by the inventive device, can be determined by calculating the phase difference of the modulated light. The invention also provides the possibility of simultaneously recording image information of the measurement target. Automatic testing and robotics are therefore derived as a preferred field of application of the invention.

The embodiments described below are used to determine the phase, peak and signal level of the background light of the detected radiation field. The laser 10 serves as a radiation source for emitting a modulated signal, which is directed at the measurement target 11 (see fig. 1), and the radiation field reflected by the measurement target 11 is imaged by a conventional optical system 12 in a sensor 13 of the device. A beat generator 14 is provided for controlling the signals recorded in the image sensor 13, detecting and demodulating the signals in the image sensor 13 and directing them to an evaluation unit 15, in which evaluation unit 15 the measured values are calculated and directed to a display device provided with the introduction.

According to the first embodiment of fig. 2, the image sensor 13 comprises 9 identically constructed sensitive elements 16, which together form a 3 × 3 image sensor field. Each sensor comprises a light receiving portion 17, and the intensity modulated radiation field hits the light receiving portion 17 and generates a number of signal charges corresponding to the same intensity. The light receiving section 17 of the sensor 16 is constituted by a photodiode. Alternatively, the light receiving section 17 may be constituted by a MOS capacitor.

The sensor 16 furthermore has a non-light-receiving part 18 which comprises a memory area 19 and a switching area 20.

The memory area 19 and the switch area 20 each include the same number of memory cells 21 and electronic switches 22, wherein its number corresponds to the number of ray integrals performed per cycle in the light receiving section 17. The memory cells 21 may be respectively constituted by CCD pixels or CMOS capacitors. The electronic switch 22 is constituted by a transistor switch or a CCD gate.

The transfer of the electric charges integrated at the light receiving section 17 to the memory area 19 is realized by sequentially controlling the electronic switches 22. For this purpose, the beat generator 14 controls the electronic switch 22 in the following manner: the switch 22 is closed at a certain point in time. Accordingly, the contents of the light receiving section 17 are stored in the first storage unit 21. After the first switch is opened and after a short, determined time interval has elapsed, the second switch 22 is closed, so that the latest charge collection integrated in the light receiving section 17 can be transferred to the second memory cell. This switching process continues until the last switch is closed and opened again. Thereafter, the transfer of charge from the light receiving portion 17 to the memory cells 21 may start from the beginning, with the contents of each memory cell 21 being accumulated in time synchronization with the modulation signal emitted from the laser 10.

According to fig. 4, a sinusoidal radiation signal is detected. For this purpose, the charge is integrated four times in the light receiving section 17 in the period T of the radiation signal, each time in the integration period I. The integration periods are equalized and divided into intervals equal to each other. After the charge collection has been transferred sequentially to the memory unit 21 via the respective arranged switches 22 and after this has been repeatedly accumulated in the memory unit 21, the measured value of the charge ratio is further transferred from the memory area 20 to the evaluation unit 15, where the parameters of the detected radiation signal are calculated.

As shown in fig. 4, the following parameters are measured according to the azimuth. The phase difference phi between the detected radiation signal and the emitted modulation signal is determined, so that the distance to the measurement object 11 can be inferred. Peak time t of the modulated signal_BUsed as a reference point in time. The peak a and background light signal level B may additionally be determined from the demodulated radiation signal.

According to the second embodiment of fig. 3, the image sensor 23 is constructed solely in CCD technology. The image sensor 23 includes a region consisting of 3 × 3 rear surface using MOS capacitors as light receiving portions of the image sensor 23. Between the light-receiving MOS capacitors 24, vertical CCD regions 25 are arranged, which are each formed by a memory cell 26. Each light-receiving MOS capacitor 24 is connected to four memory cells 26 via a transfer gate 27 as an electronic switch for four consecutive charges per cycle. A beat generator, not shown, controls the connection of signal charges from vertical CCD region 25 to MOS capacitor 24 and subsequently controls the transfer of signal charges from vertical CCD region 25 to horizontal CCD region 28. From there, the signal charge is fed to a division unit which determines the measured value.

Alternatively, the CCD area may be formed in the form of a circular arc, wherein the CCD area always contains the MOS capacitor 24.

Claims (10)

1. Apparatus for detecting and demodulating an intensity-modulated radiation field, having:

-one image sensor (13, 23) is formed by a one-dimensional or two-dimensional arrangement of sensitive elements (16),

-wherein each sensor (16) is formed by a light-receiving part (17) for converting a radiation signal into an electrical signal and a non-light-receiving part (18) with at least one electronic switch (22) and with at least one memory cell (21, 26) assigned to the switch (22),

-characterized in that the beat generator (14) controls the electronic switch (22) in such a way that the signal charges generated in the light-receiving section (17) are transferred to the memory units (21, 26) in synchronism with the modulation signal emitted by the radiation source, and the measured values stored in the respective memory units (21, 26) for controlling the memory units (21, 26) are transferred to the evaluation unit (15) for evaluating the measured values.

2. Device according to claim 1, characterized in that the image sensors (13, 23) are constructed in an integrated manner, wherein the sensitive elements (16) that are closely adjacent to each other form a one-dimensional or two-dimensional area.

3. Device according to claim 1 or 2, characterized in that the light receiving part (17) of the sensor (16) is constituted by a photodiode or by a MOS capacitor (24) of a predetermined voltage.

4. Device according to one or more of claims 1 to 3, characterized in that: the memory cell (21) is formed as a light-protected CCD pixel or as a MOS capacitor.

5. Device according to one or more of claims 1 to 4, characterized in that: the memory unit (26) forms a linear CCD region (25, 28), in particular a linear CCD region (25, 28), and the stored measurement data are transferred in succession from the memory unit to the evaluation unit.

6. Device according to one or more of claims 1 to 4, characterized in that: the memory cells (26) are arranged adjacent to each other in the following manner: they form a closed CCD region, in particular a ring-shaped CCD region.

7. Device according to one of claims 1 to 6, characterized in that: the electronic switch (22) is formed as a transistor switch or by a CCD transfer gate (27).

8. Method for detecting and demodulating an intensity-modulated radiation field, in which,

the radiation field is imaged by an optical system (12) on an image sensor (13, 23) consisting of one-or two-dimensionally arranged sensitive elements (16),

-a first phase in which a succession of signal charges corresponding to the intensity of the radiation field is generated in the light-receiving part (17) of the sensor (16), wherein the signal charges are integrated each time during an integration period (I),

-the signal charge integrated each time is transferred to the non-light receiving part (18) of the sensitive element (16) in synchronism with the modulation signal generated by the radiation source and is always stored in a storage unit (21, 26),

-the signal charge generated in the light-receiving section (17) is supplied from the light-receiving section of the sensor (16) to the respective memory cell (21, 26) via at least one electronic switch (22) assigned to the respective memory cell (21, 26) and stored,

-a second phase, in which the measured values stored in the storage unit (21, 26) are read out continuously and supplied to the analysis unit (15).

9. Method according to claim 8, characterized in that a periodic or pulse-shaped modulation signal generated by one or more radiation sources illuminates an object (11) and the radiation fields are imaged two-dimensionally as intensity-modulated on the image sensor (13) in the following manner: the information exists according to the shape and/or structure of the object.

10. A method according to claim 8 or 9, characterized in that: in each memory cell (21, 26), the signal charges are accumulated periodically.