Photoelectric conversion device and photoelectric conversion system

Abstract

The present invention includes: a photoelectric conversion unit; a light value holding unit that holds a light value based on signal charges generated during a first exposure period and a second exposure period, the second exposure period being different from the first exposure period in terms of start timing and / or end timing; a comparison unit that compares the light value based on the signal charges generated during the first exposure period with the light value based on the signal charges generated during the second exposure period; and a control unit that performs control based on the comparison result of the comparison unit to set a third exposure period and a fourth exposure period, the fourth exposure period being different from the third exposure period in terms of start timing and / or end timing. The third exposure period and the fourth exposure period are shorter than the first exposure period and / or the second exposure period.

Description

Technical Field

[0001] The present invention relates to a photoelectric conversion device and a photoelectric conversion system. Background Art

[0002] TOF (Time of Flight) technology is generally used to measure the distance to an object to be measured. According to TOF technology, light is emitted from a light source, and the reflected light reflected by the object to be measured is detected. Thereafter, in TOF technology, the distance to the object to be measured is measured by measuring the time difference between the timing of the emitted light and the timing of the detected reflected light.

[0003] PTL 1 describes a TOF range finder using an SPAD (Single Photon Avalanche Diode), in which the optical charge caused by a single photon causes avalanche multiplication in the PN junction region of the semiconductor region constituting the photoelectric conversion unit. In addition, PTL 1 describes distance measurement based on a time-gated method, in which the mode of detecting a photon signal incident on the SPAD (exposure mode) and the mode of not detecting a photon signal (non-exposure mode) are switched at high speed by a pulse signal having a width on the order of picoseconds to microseconds.

[0004] Citation List

[0005] Patent Document

[0006] PTL 1: U.S. Patent Application Publication No. 2017 / 0052065 Summary of the Invention

[0007] Technical Problem

[0008] However, according to PTL 1, in order to accurately measure the time distribution of the detected light, it is necessary to scan the relative difference in time-gated timing with respect to the light emission timing at fine intervals within the time range corresponding to a predetermined distance measurement range. For this reason, the time required for one distance measurement increases, making it difficult to accelerate the measurement of the distance from the photoelectric conversion device to the object to be measured.

[0009] According to one embodiment, a photoelectric conversion device includes: a photoelectric conversion unit; a light value holding unit configured to hold a light value based on signal charges generated during a first exposure period and a second exposure period, at least one of a start timing and an end timing of the second exposure period being different from that of the first exposure period; a comparison unit configured to compare the light value based on the signal charges generated during the first exposure period with the light value based on the signal charges generated during the second exposure period; and a control unit configured to set a third exposure period and a fourth exposure period based on a comparison result of the comparison unit, at least one of a start timing and an end timing of the fourth exposure period being different from that of the third exposure period, wherein the third exposure period and the fourth exposure period are less than at least one of the first exposure period and the second exposure period.

[0010] According to one embodiment, a photoelectric conversion device includes: a photoelectric conversion unit; a light value holding unit configured to hold a light value based on signal charges obtained when light is incident during a first exposure period and a second exposure period, at least one of a start timing and an end timing of the second exposure period being different from that of the first exposure period; a comparison unit configured to compare the light value obtained during the first exposure period with the light value obtained during the second exposure period; and a control unit configured to control a third exposure period and a fourth exposure period based on a comparison result of the comparison unit.

[0011] According to the present invention, it is possible to measure the distance from the photoelectric conversion device to the object to be measured at a higher speed than in PTL 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic diagram of an example of the photoelectric conversion device according to Embodiment 1.

[0013] Figure 2 is a timing chart illustrating exposure patterns according to a comparative example and Embodiment 1.

[0014] Figure 3 is a block diagram of a unit pixel according to Embodiment 1.

[0015] Figure 4 is a timing chart of pixel driving according to Embodiment 1.

[0016] Figure 5 is a block diagram of a unit pixel according to Embodiment 2.

[0017] Figure 6 is a timing chart of pixel driving according to Embodiment 2.

[0018] Figure 7 is a block diagram of a modified unit pixel according to Embodiment 2.

[0019] Figure 8 It is a block diagram of a unit pixel according to Embodiment 3.

[0020] Figure 9 It is a block diagram of a unit pixel according to Embodiment 4.

[0021] Figure 10 It is a timing diagram of pixel driving according to Embodiment 4.

[0022] Figure 11 It is a timing diagram illustrating an exposure pattern according to Embodiment 5.

[0023] Figure 12 It is a timing diagram illustrating an exposure pattern according to Embodiment 6.

[0024] Figure 13 It is a block diagram of a photoelectric conversion system according to Embodiment 7.

[0025] Figure 14 It is a block diagram of a photoelectric conversion system according to Embodiment 8.

[0026] Figure 15 It is a block diagram of a photoelectric conversion system according to Embodiment 9. Detailed implementation manners

[0027] The embodiments described below are used to implement the technical concept of the present invention and are not intended to limit the present invention. For the sake of clarity in description, the dimensions and positional relationships of the components shown in the drawings may be exaggerated. In the following description, the same configurations may be identified by the same reference numerals, and the description of such configurations may be omitted.

[0028] (Embodiment 1)

[0029] Reference Figures 1 to 4 Describe Embodiment 1. Figure 1 It is a block diagram of a photoelectric conversion device 100 of this embodiment. The photoelectric conversion device 100 includes a pixel unit 101, a control pulse generation unit 115, a horizontal scanning circuit unit 111, a readout circuit 112, a signal line 113, and a vertical scanning circuit unit 110. In the pixel unit 101, a plurality of pixels 104 are arranged in a two-dimensional array (matrix). Each of the pixels 104 is composed of a photoelectric conversion unit 102 including an avalanche photodiode (hereinafter referred to as "APD") and a pixel circuit 103. Note that at least APDs in the pixel unit 101 are required to be arranged in a two-dimensional array. The photoelectric conversion unit 102 converts light into an electrical signal. The pixel circuit 103 outputs the electrical signal converted by the photoelectric conversion unit 102 to the signal line 113.

[0030] The vertical scanning circuit unit 110 receives control pulses supplied from the control pulse generation unit 115 and supplies the control pulses to each pixel. Logic circuits such as a shift register and an address decoder are used in the vertical scanning circuit unit 110.

[0031] Signals output from the photoelectric conversion units 102 of each pixel are processed by the pixel circuits 103. The pixel circuits 103 include a counter circuit and / or a memory. Hereinafter, the pixel circuit 103 including a memory will be described. The memory holds digital values.

[0032] The horizontal scanning circuit unit 111 inputs control pulses for sequentially selecting each column to the pixel circuits 103 to read signals from the memories of the pixels holding digital signals.

[0033] For the selected row, signals from the pixel circuits 103 of the pixels 104 selected by the vertical scanning circuit unit 110 are output to the signal line 113.

[0034] The signals output to the signal line 113 are output to an external recording unit or a signal processing unit of the photoelectric conversion device 100 via the output circuit 114.

[0035] In Figure 1 , the pixel unit 101 includes pixels 104 arranged in a two-dimensional array. The pixel unit 101 may include a plurality of pixels 104 arranged in a one-dimensional manner. Alternatively, the pixel unit 101 may include only a single pixel instead of an array.

[0036] It is not necessarily required to provide the functions of the pixel circuit 103 for each pixel 104. For example, one pixel circuit 103 may be shared by a plurality of pixels 104, and signal processing may be performed sequentially. The photoelectric conversion device may use a layered sensor in which a first substrate having a photoelectric conversion unit and a second substrate having a pixel circuit are stacked and bonded to achieve high sensitivity and high functionality. In this case, the photoelectric conversion unit and the pixel circuit are electrically connected via connection wirings provided for each pixel.

[0037] Next, Figure 2 the principle of improving the distance measurement speed, which is an effect of the present invention, will be described.

[0038] Figure 2 (i) is a diagram of a comparative example and illustrates a linear search method for finding the timing of reflected light in the time-gated TOF technique. Figure 2 (ii) illustrates a binary search method for searching the timing of reflected light according to the present embodiment. In Figure 2(i), the range shown in white in each sub-frame represents the exposure period of pixel 104, and the range shown in black represents the non-exposure period.

[0039] According to this embodiment, the term "exposure period" refers to, for example, the period during which the photoelectric conversion unit 102 is active and the signal from the photoelectric conversion unit 102 can be read out by the counter circuit and / or register circuit. The term "non-exposure period" refers to the period during which no signal is read out by the counter circuit and / or register circuit from the photoelectric conversion unit 102. In the following description, the exposure period is defined as the period during which a reverse bias potential capable of causing avalanche multiplication is applied to the APD, the gating element is turned on, and the signal from the APD can be read out by the counter circuit and / or register circuit. In addition, the non-exposure period is defined as the period during which the signal from the APD is not read out via the gating element. The non-exposure period is not limited to this.

[0040] For example, the non-exposure period can be defined as the period during which the potential difference applied to the APD is reduced so that no avalanche multiplication occurs in the APD, and the exposure period can be defined as the period during which a potential difference causing avalanche multiplication in the APD is applied. Alternatively, the non-exposure period can be defined as the period during which the control counter circuit and / or register circuit is not driven, and the exposure period can be defined as the period during which the control counter circuit and / or register circuit is driven.

[0041] In Figure 2 (i) and Figure 2 (ii), for easy understanding, the sub-frames are arranged from the emitted light. Actually, driving is performed so that the light amount is measured for the first sub-frame at the time of the first emitted light. Thereafter, the second emitted light is emitted at the same timing as the first emitted light, and the light amount is measured for the second sub-frame at the time of the second emitted light. Thereafter, the light amount is measured for the Nth sub-frame at the time of the Nth emitted light.

[0042] In the comparative example, while shifting the start timing and end timing of the exposure period with respect to the light emission timing of the light source, the light amount is measured N times. That is, while gradually shifting the start timing of the exposure period little by little, the reflected light is measured. When the timing of the exposure period is linearly scanned step by step within a predetermined distance measurement range, the time resolution of the reflected light detection or the distance measurement accuracy increases in proportion to the number of steps N of the linear scan. However, when the number of steps increases and thus the number of sub-frames increases, it takes a long time to measure the distance.

[0043] As a comparison, according to this embodiment, for the first sub-frame, the period corresponding to the emission light is time-divided into two or more exposure periods. For example, the period is time-divided into exposure period A and exposure period B, the light intensity in each exposure period is measured independently, and the light intensities in exposure period A and exposure period B are compared. In the shown figure, since the reflected light is included in exposure period A, the amount of light signal in exposure period A is greater than that in exposure period B. Based on the comparison result, assuming that the reflected light is included in exposure period A, exposure period A is further divided into two within the length of exposure period A of the first sub-frame, and two exposure periods A and B for the second sub-frame are determined. In this way, by comparing the light amounts in two or more exposure periods in each sub-frame and successively repeating the determination of the exposure pattern, especially the determination of the timing and period of repeated exposure, the accuracy of estimating the timing of the reflected light is improved. Therefore, linear search requires N light amount measurements, while binary search can reduce the number of light amount measurements to Log2(N). This can accelerate the distance measurement.

[0044] Although in Figure 2 (i), only one light emission and only one exposure period are illustrated for each sub-frame, the light signals obtained by repeatedly repeating each sub-frame can be added. Therefore, the accuracy of light signal measurement can be improved. In this case, according to the comparative embodiment, the time resolution of reflected light detection or the distance measurement accuracy increases proportionally to the number of steps N of linear scanning.

[0045] Therefore, the effect of improving the distance measurement speed by applying this embodiment is significant.

[0046] Note that Figure 2 (ii) illustrates an example of dividing the exposure period into two equal parts as an example of the binary search method. The following description of the drawings is given based on the method of dividing the exposure period into two equal parts. However, the term "binary search method" is not limited to dividing the exposure period into two equal parts. Even if the exposure period is divided into three or more equal parts for searching, this method is also called the binary search method. That is, the binary search method is the name of a method different from the linear scanning method and is not limited to dividing the exposure period into two equal parts. In addition, the lengths of the two exposure periods A and B in one sub-frame can be different. Furthermore, in the comparison step, instead of comparing the signal amounts in exposure period A and exposure period B, signals A' and B' obtained by performing a predetermined arithmetic process or correction process on the corresponding signals can be compared.

[0047] Figure 3 is an example of the block diagram of a unit pixel according to this embodiment. As described above, the pixel has a photoelectric conversion unit and a pixel circuit. In Figure 3In this case, APD 301 serves as a photoelectric conversion unit. The pixel circuit includes a quenching element 302, a gating element 303 (switch), a light value holding unit 31, a comparator circuit (comparison unit) 312, a register circuit 313, and a pulse generation circuit 314. The light value holding unit 31 includes a counter circuit 310 and a register circuit 311.

[0048] APD 301 is connected to the quenching element 302 that controls the avalanche current. The photon detection signal output from APD 301 is temporally controlled by the gating signal GATE input to the gating element 303. The output of the gating element 303 is input to the light value holding unit 31 including the counter circuit 310 and the register circuit 311. The photon signal that has passed through the gating element 303 is counted by the counter circuit 310, and the count value is written to the register circuit 311 according to the trigger signal RTRG. That is, the register circuit 311 serves as a recording circuit. Once the enable signal COEN is received, the comparator circuit 312 compares the output values of the counter circuit 310 and the register circuit 311, and records the comparison result in the register circuit 313. Once the hold signal, the clock signal CLK, and the enable signal PGEN of the register circuit 313 are received, the pulse generation circuit 314 generates the gating signal GATE that defines the exposure pattern. The reset signals RES1, RES2, and RES3 initialize the hold signals held in the counter circuit 310, the register circuit 311, and the register circuit 313, respectively.

[0049] APD 301 generates charge pairs according to incident light through photoelectric conversion. The cathode of APD 301 is supplied with a potential based on the potential VH that is higher than the potential VL supplied to the anode. At this time, the anode and cathode of APD 301 are provided with potentials such that a reverse bias is applied, so that photons incident on APD 301 are avalanche multiplied. By performing photoelectric conversion while being supplied with this reverse bias potential, avalanche multiplication of the charges generated by the incident light occurs, and an avalanche current is generated.

[0050] In the case where a reverse bias potential is supplied, if the potential difference between the anode and the cathode is greater than the breakdown voltage, the APD operates in the Geiger mode. Hereinafter, an APD that uses the Geiger mode operation to detect a weak signal at the single photon level at high speed is also referred to as an SPAD (single photon avalanche diode). According to this embodiment, it is desirable to use an SPAD for high-speed detection of weak signals. However, the APD can operate in the linear mode, in which charges are multiplied at a voltage lower than the breakdown voltage.

[0051] The quenching element 302 does not have to be a quenching element composed of a single transistor, and may be a quenching element composed of multiple transistors or a resistance element. When the photocurrent is multiplied by avalanche multiplication in the APD 301, the current obtained by multiplying the charges flows through the connection node between the APD 301 and the quenching element 302. The voltage drop caused by the current reduces the potential of the cathode of the APD 301, and the APD 301 no longer forms an electron avalanche. For this reason, the avalanche multiplication of the APD 301 stops. Thereafter, the potential VH of the power supply is supplied to the cathode of the APD 301 through the quenching element 302, so that the potential supplied to the cathode of the APD 301 returns to the potential VH. That is, the operation region of the APD 301 again becomes Geiger mode operation. In this way, the quenching element 302 serves as a load circuit (quenching element) and has a function of suppressing avalanche multiplication during charge multiplication caused by avalanche multiplication (quenching operation). In addition, the quenching element has a function of setting the operation region of the APD in Geiger mode again after suppressing avalanche multiplication (recharging operation).

[0052] As the gating element 303, a switching circuit or a logic circuit using multiple transistors can be used instead of a single transistor. In Figure 3 , the pixel exposure period is adjusted by controlling the on / off operation of the gating element 303. The term "exposure period" refers to the period during which the APD 301 can detect photons and the potential of the APD 301 is input to the optical value holding unit 31. In addition, the term "non-exposure period" of a pixel refers to the period during which the potential of the APD 301 is not input to the optical value holding unit 31. More specifically, the period during which the gating element 303 is turned on is the exposure period, and the period during which the gating element 303 is turned off is the non-exposure period. In Figure 3 , the gating element 303 is composed of a PMOS transistor. Therefore, when the signal input to the gating changes from the first level (high level) to the second level (low level), the gating element 303 is turned on. When the signal changes from the second level to the first level, the gating element 303 is turned off.

[0053] In the case where the gating element 303 is an NMOS transistor, the reverse is true. That is, when the signal input to the gating changes from the second level to the first level, the gating element 303 conducts, and when the signal changes from the first level to the second level, the gating element 303 turns off. The ON (conducting) state of the gating element is a state in which the APD 301 and the light value holding unit 31 are electrically connected, and the OFF (non-conducting) state of the gating element is a state in which the APD 301 and the light value holding unit 31 are not electrically connected. The gating element 303 can be replaced by an operation that temporarily switches between the enabled state and the disabled state of the operation performed by the counter, without providing a specific element between the APD 301 and the counter circuit 310. In this case, the state in which the operation performed by the counter is enabled is the exposure period, and the state in which the operation performed by the counter is disabled is the non-exposure period.

[0054] The counter circuit 310 can use a digital counter or an analog counter. The counter circuit 310 is connected to the register circuit 311 and the comparator circuit 312 such that the output signal output from the counter is input to the register circuit 311 and the comparator circuit 312. The register circuit 311 can hold the signal output from the counter circuit 310. The register circuit 311 is connected to the comparator circuit 312 such that the output of the register circuit 311 is input to the comparator circuit 312.

[0055] Some of the light value holding unit 31, the comparator circuit 312, the register circuit 313, and the pulse generation circuit 314 can be shared by multiple pixels.

[0056] The comparator circuit 312 is connected to compare the signal value output from the counter circuit 310 with the signal value output from the register circuit 311 and input the comparison result to the register circuit 313. The register circuit 313 is connected to the pulse generation circuit 314. The pulse generation circuit 314 is connected to the gating element, and the on / off state of the gating element is controlled based on the output signal output from the pulse generation circuit 314. According to the present embodiment, the exposure period is set by controlling the on / off state of the gating element. That is, the pulse generation circuit 314 serves as a control unit for controlling the exposure period.

[0057] The register circuit 313 is connected to output a signal to the signal line 113. The distance measurement can be performed based on the signal value output from the register circuit 313. Therefore, the number of the signal lines 113 is determined such that at least a signal equal in number to the output bits of the register circuit 313 can be output.

[0058] Note that in Figure 3In addition to the register circuit 313, the counter circuit 310 and the register circuit 311 are also connected to the signal line 113. By outputting the outputs from the counter circuit 310 and the register circuit 311 to the outside of the pixel via the signal line 113 in this way, the reliability of the distance measurement result can be improved. For example, the signal value output from the register circuit 311 and the signal value output from the counter circuit 310 are output on a frame-by-frame basis. Then, the output signal values are compared with each other. For a pixel on which reflected light is incident, there is a large difference between the signal value output from the register circuit 311 and the signal value output from the counter circuit 310. In contrast, for a pixel on which no reflected light is incident, only a signal based on noise or ambient light is detected. Therefore, there is almost no difference between the signal value output from the register circuit 311 and the signal value output from the counter circuit 310. By using the absolute value of such a signal value and the difference between the signal values, information on whether the pixel has received reflected light and data on the detected noise and ambient light can be obtained. Since this information can be used as information for determining the accuracy of the distance measurement, the reliability of the distance measurement result can be improved.

[0059] When the output values of each of the register circuit 313, the counter circuit 310, and the register circuit 311 are output to the signal line 113, the number of signal lines can be set so that signals from all the circuits can be output. Alternatively, the signal line 113 can be shared by the circuits. When the signal line 113 is shared, by shifting the output timings of the signals from the circuits with respect to each other, the signals output from the circuits can be detected outside the pixel.

[0060] Figure 4 is a timing chart illustrating the operations performed by the pixels of the photoelectric conversion device according to the present embodiment. During the period from time t1 to time t2, RES1, RES2, and RES3 are set to high level to initialize the hold signals (Count, Reg1, Reg2) of the counter circuit 310, the register circuit 311, and the register circuit 313.

[0061] First, the driving performed in the first period of the first sub-frame of the k-th frame corresponding to the period from time t2 to time t7 will be described. At time t3, the light source emits pulsed light toward the object to be measured. The pulsed light is reflected by the object to be measured and reaches the light receiving surface of the photoelectric conversion device at time t4. During the period from time t3 to time t5, the gate signal GATE input to the gating element is set to low level so that the amount of light received by the APD 301 during the first exposure period A is measured.

[0062] That is, the first exposure period A starts by setting the gating signal GATE to a low level at the same timing as the light emission timing of the light source. According to this embodiment, since the gating element is composed of a PMOS transistor, the gating element conducts at a low level and turns off at a high level. During the period from time t5 to time t6, the gating signal GATE input to the gating element is set to a high level to set the photoelectric conversion device to a non-exposure mode in which the light signal is not measured. That is, the first exposure period A is a period in which exposure starts after a first delay time from the light emission timing of the light source. The first exposure period A terminates by setting the gating signal GATE to a high level after a predetermined period. At t4 included in the exposure period A, a reflected light pulse is detected, causing the count value Count of the counter circuit 310 to increase. By repeating the driving from time t2 to time t6 multiple times within the first period of the first sub-frame, the light signals accumulated during the exposure period A are obtained.

[0063] The driving performed during the period from time t7 to time t12 to record the signal held by the counter circuit 310 in the register circuit 311 is described below. During the period from time t7 to time t12, the enable signal PGEN of the pulse generation circuit 314 is set to a low level, so that the light detection signal from the APD 301 is not counted by the counter circuit 310. During the period from time t7 to t12, the gating signal GATE input to the gating element is at a high level. The trigger signal RTRG is set to a high level during the period from time t8 to t9, and the output of the counter circuit 310 is recorded in the register circuit 311. Therefore, the signal value Reg1 held in the register circuit 311 is changed. During the period from time t10 to time t11, the reset signal RES1 is set to a high level to initialize the held signal in the counter circuit 310.

[0064] The driving performed during the second period of the first sub-frame of the k-th frame corresponding to the period from time t12 to t16 is described below. The timing at which the gating signal GATE is set to a high level is different from that in the first period of the first sub-frame described above. In the second period of the first sub-frame, the period from time t14 to time t15 is the exposure period B, and the period from time t12 to time t14 is the non-exposure period. That is, the exposure period B is a period in which exposure starts after a second delay time from the light emission timing of the light source. The length of the second delay time is different from the length of the first delay time. The exposure period B terminates by setting the gating signal GATE to a high level after a predetermined period from the start of the exposure period B. Different from the driving performed in the first period of the first sub-frame described above, the reflected light reaches the light receiving surface at time t13. At this time, since the photoelectric conversion device is in the non-exposure period, the light signal is not counted.

[0065] The driving that is performed during the period from time t16 to t21 to compare the amounts of optical signals in exposure period A and exposure period B is described below. In a similar manner to the above, during the period from time t16 to t21, the enable signal PGEN of the pulse generation circuit 314 is set to a low level so that the optical detection signal from the APD 301 is not counted by the counter circuit 310. During the period from time t17 to t18, the enable signal COEN of the comparison circuit 312 is set to a high level. Then, the comparison result between the output of the register circuit 311 that holds the amount of signal corresponding to exposure period A and the output of the counter circuit 310 that holds the amount of signal corresponding to exposure period B is recorded in the register circuit 313 in the form of a digital signal. Accordingly, the hold signal Reg2 of the register circuit 313 is changed.

[0066] During the period from time t19 to time t20, RES1 and RES2 are set to a high level to initialize the hold signals of the counter circuit 310 and the register circuit 311.

[0067] Based on the comparison result, the first period of the second sub-frame of the k-th frame corresponding to the period from time t21 to time t24 has half the length of the exposure period A of the first sub-frame. Then, the pulse generation circuit 314 generates a gating signal GATE to set a new exposure period A defined by the period from time t21 to time t22. Here, one of the two exposure periods obtained by dividing the exposure period A with the larger signal accumulation amount in the first sub-frame into two equal parts is set as the new exposure period A. The remaining exposure period of the exposure period A in the first sub-frame and the exposure period B of the first sub-frame are set as non-exposure periods. In a similar manner to the above, the driving in the second period of the second sub-frame of the k-th frame continues after time t25. More specifically, in the two exposure periods obtained by dividing the exposure period A with the larger signal accumulation amount in the first sub-frame into two equal parts, the remaining period of the newly set exposure period A is set as the exposure period B.

[0068] In this way, the sequence of the exposure operation (A), the recording operation, the exposure operation (B), and the comparison operation is repeated a predetermined number of times, and a binary search is performed on the timing of the reflected light pulse to determine the distance to the object to be measured. This increases the measurement accuracy.

[0069] According to this embodiment, the driving in which the frequency of the clock signal CLK input to the pulse generation circuit 314 is doubled at time t21 when the first sub-frame is switched to the second sub-frame has been described. However, the driving is not limited thereto. A pulse generation circuit 314 capable of switching the exposure pattern interval of each sub-frame without changing the frequency can be used. Additionally, according to this embodiment, periodic pulsed light emission is used as the operation of the light source. However, the intensity and width of the emitted light and the temporal light emission pattern can be switched between different sub-frames.

[0070] Furthermore, in the above description, the signal value is output from the register circuit 313 after repeating the operation sequence a predetermined number of times. However, this embodiment is not limited thereto. For example, the signal value can be output from the register circuit 313 to the signal line 113 for each sub-frame or every few sub-frames. This enables obtaining a rough distance measurement result before the end of one frame period.

[0071] According to this embodiment, distance measurement can be performed at a higher speed compared to the comparative example.

[0072] (Embodiment 2)

[0073] Reference Figure 5 and Figure 6 describe Embodiment 2. Figure 5 is an example of a block diagram of a unit pixel according to this embodiment. This embodiment is different from Embodiment 1 in the following aspects. According to this embodiment, the optical value holding unit 31 is composed of two counter circuits 310a and 310b. The output terminal of the APD 301 is connected to two gating elements 303a and 303b deployed in parallel, and the outputs of the two gating elements 303a and 303b are respectively input to the counter circuits 310a and 310b. The comparator circuit 312 compares the outputs of the counter circuits 310a and 310b. The pulse generation circuit 314 generates independent gating signals GATE1 and GATE2 for the gating elements 303a and 303b, respectively. Hereinafter, the configurations different from those of Embodiment 1 are described, and the description of the configurations substantially the same as those of Embodiment 1 is not repeated.

[0074] The output from the gating element 303a is input to the counter circuit 310a. The output from the gating element 303b is input to the counter circuit 310b. The counter circuits 310a and 310b are connected such that their outputs are input to the comparator circuit 312. Note that in this document, the same reference numerals are used for elements having the same configuration but with letter characters such as a, b, or c attached, and the description of such elements can be omitted.

[0075] Figure 6 is a timing chart illustrating the pixel driving operation performed by the photoelectric conversion device according to this embodiment.

[0076] The reset signals RES1, RES2, and RES3 initialize the holding signals in the counter circuits 310a and 310b and the register circuit 313, respectively. Different from Embodiment 1 in which a sequence of a repeated exposure operation (A), a recording operation, an exposure operation (B), and a comparison operation is performed, in this embodiment, the sequence of the exposure operations (A, B) and the comparison operation can be repeatedly executed. The exposure period A defined by setting the gating signal GATE1 to a high level and the exposure period B defined by setting the gating signal GATE2 to a high level within the first sub-frame of the k-th frame corresponding to the period from time t3 to time t6 are complementary settings. According to this embodiment, each of the gating elements 303a and 303b is composed of an inverter circuit and a logic circuit. When avalanche multiplication occurs in the APDs 301a and 301b, the cathode potential drops. Then, if the threshold is exceeded in the inverter circuit included in the gating element 303a, the potential is inverted. When the potential is input to the AND circuit as the logic circuit, a high-level signal is output from each of the gating elements 303a and 303b. For example, the period from time t3 to time t4 is defined as the exposure period A. The counter circuit 310a counts the optical signals during this period, the period from time t4 to time t5 is defined as the exposure period B, and the counter circuit 310b counts the optical signals during this period.

[0077] Similar to Embodiment 1, during the period from time t6 to time t7, the output signals of the comparison counter circuit 310a and the counter circuit 310b are compared. Based on the comparison result, in the second sub-frame of the k-th frame corresponding to the period from time t7 to time t10, the exposure period A and the exposure period B are newly set. At this time, the new exposure period A and the exposure period B are set to two exposure periods obtained by dividing the exposure period A with a larger signal accumulation amount in the first sub-frame into two halves. Then, similar to the first sub-frame, the counter circuit 310a counts the amount of light during the newly set exposure period A, and the counter circuit 310b counts the amount of light during the exposure period B.

[0078] Similar to Embodiment 1, according to this embodiment, distance measurement can be performed at a higher speed compared to the comparative example. In addition, since the intensities of the optical signals in the exposure periods A and B can be obtained in parallel within a single sub-frame, the period from the exposure operation to the comparison operation can be reduced compared to Embodiment 1. Therefore, the measurement of the distance to the object to be measured can be accelerated. Furthermore, even when the object to be measured is moving, the lag time between the measurements of the optical signals in the exposure periods A and B can be reduced, which can improve the accuracy of distance measurement.

[0079] (Modification of Embodiment 2)

[0080] Reference Figure 7 Describe the modification of Example 2. Figure 7 is an example of a block diagram of a unit pixel according to the modification. Different from Example 2, according to the modification, two independent APDs 301a and 301b are respectively connected to two gating elements 303a and 303b. Since other configurations are substantially the same as those of Example 2 except for the configurations described below, the description of the configurations is not repeated. In addition, the driving method corresponding to this modification is based on the driving method according to Example 2.

[0081] As Figure 7 shown, the output from APD 301a is input to gating element 303a, and the output from APD 301b is input to gating element 303b. Therefore, counter circuit 310a counts the amount of light detected by APD 301a, and counter circuit 310b counts the amount of light detected by APD 301b.

[0082] According to this modification, similar to Example 2, distance measurement can be performed at a higher speed compared to the comparative example. In addition, by using two spatially adjacent APDs, the intensities of the optical signals during exposure period A and exposure period B can be obtained in parallel within a single sub-frame. Therefore, the period from the exposure operation to the comparison operation can be reduced, and thus the measurement of the distance to the object to be measured can be accelerated. In addition, even when the object to be measured is moving, the lag time between the optical signal measurements in exposure period A and exposure period B can be minimized, which can improve the accuracy of distance measurement.

[0083] (Example 3)

[0084] Reference Figure 8 Describe Example 3. Figure 8 is an example of a block diagram of a unit pixel according to this embodiment. Different from the modification of Example 2, according to this embodiment, the outputs from two independent APDs 301a and 301b and the outputs from two waveform shaping circuits 820a and 820b respectively connected to APD 301a and 301b are input to a simultaneous detection circuit 821, and the output of the simultaneous detection circuit 821 is connected to two gating elements 303a and 303b. Except for the configuration description below, other configurations are substantially the same as those of the modification of Example 2, and the description of the configurations is not repeated.

[0085] The waveform shaping circuits 820a and 820b have the function of shaping the waveforms of the outputs from the corresponding APDs, and are composed of, for example, an inverter circuit, a buffer circuit, or a monostable circuit that reduces the width of a pulse waveform. When a predetermined number or more of signals from multiple waveform shaping circuits are at a high level at the same timing or at a timing close thereto, the simultaneous detection circuit 821 outputs a pulse signal. Note that three or more APDs and waveform shaping circuits may be connected to one simultaneous detection circuit 821. According to the present embodiment, a driving method similar to the driving method of Embodiment 2 is adopted.

[0086] According to the present embodiment, similar to Embodiment 1, distance measurement can be performed at a higher speed compared to the comparative embodiment. In addition, photons that are temporally and spatially close due to reflected light can be selectively detected only, and randomly detected ambient light components and dark signals can be filtered out.

[0087] Therefore, the influence of ambient light and dark signals on the accuracy of distance measurement based on the ToF technology can be reduced.

[0088] (Embodiment 4)

[0089] Reference Figure 9 and Figure 10 describe Embodiment 4. Figure 9 is an example of a block diagram of a unit pixel according to the present embodiment. Different from Embodiment 1, in the present embodiment, a charge storage photodiode 901 is used instead of the APD 301, and an analog signal is input to the comparator circuit 312. Except for the configurations described below, other configurations are basically the same as those of Embodiment 1, and the description of the configurations will not be repeated.

[0090] When a control signal OFD is input to the overflow drain circuit 902, the optical charges accumulated in the photodiode 901 are released or input to the light amount holding unit 91.

[0091] The light amount holding unit 91 includes transfer gates 903a and 903b, holding units 910a and 910b, and transfer gates 905a and 905b. When a gate signal GATE1 or GATE2 is received, the optical charges photoelectrically converted by the photodiode 901 are transferred to the holding unit 910a or 910b via the transfer gate 903a or 903b. When the transfer gates 905a and 905b receive gate signals TX1 and TX2, respectively, the signals held in the holding unit are transferred to two floating diffusion (FD) regions FD1 and FD2. When the reset circuits 907a and 907b receive reset signals RES1 and RES2, respectively, the potentials VFD1 and VFD2 of the two FD regions are initialized.

[0092] Once the enable signal COEN is received, the comparator circuit 312 compares the magnitudes of the potentials VFD1 and VFD2 and records the comparison result in the register circuit 313. The pulse generation circuit 314 receives the hold signal of the register circuit 313, the clock signal CLK, and the enable signal PGEN, and generates the gate signals GATE1 and GATE2 that define the exposure pattern and the control signal OFD. The reset signal RES3 initializes the hold signal of the register circuit 313.

[0093] Figure 10 is a timing chart of the operations performed by the pixels of the photoelectric conversion device according to the present embodiment. During the period from time t1 to time t2, RES1, RES2, and RES3 are set to high level to initialize the potentials VFD1 and VFD2 of the two FD regions and the hold signal of the register circuit 313. During the period from time t2 to time t3, the control signal OFD is set to high level to reset the charge accumulated in the photodiode 901.

[0094] First, the driving performed in the first sub-frame of the k-th frame corresponding to the period from time t3 to time t8 is described. At time t3, the light source emits pulsed light toward the object to be measured. The pulsed light is reflected by the object to be measured and reaches the light receiving surface at time t4. By setting the gate signal GATE1 to high level during the period from time t4 to time t5, the optical charges received by the photodiode 901 during the first exposure period A corresponding to time t3 to t5 are transferred. In addition, by setting the gate signal GATE2 to high level during the period from time t6 to time t7, the optical charges received by the photodiode 901 during the second exposure period B corresponding to time t5 to time t7 are transferred. At this time, since a pulse of the reflected light is detected at t4 included in the exposure period A, the voltage value VM1 of the holding unit 910a changes. By repeatedly driving from time t3 to time t7 multiple times within the period of the first sub-frame, the optical signals accumulated in the exposure period A and the exposure period B are obtained.

[0095] The driving for comparing the holding signals of the holding units 910a and 910b during the period from time t8 to time t16 is described below. During the period from time t8 to time t16, the enable signal PGEN of the pulse generation circuit 314 is set to a low level so that the light detection signal from the photodiode 901 is not transferred to the holding units 910a and 910b. During the period from time t9 to time t10, RES1 and RES2 are set to a high level to reset the FD potentials VFD1 and VFD2. During the period from time t10 to time t11, the transfer signals TX1 and TX2 are set to a high level, and the signal charges held in the holding units 910a and 910b are respectively transferred to FD1 and FD2. During the period from time t12 to time t13, the enable signal COEN of the comparison circuit 312 is set to a high level. Then, the comparison result of the magnitude of VFD1 corresponding to the cumulative signal amount during the exposure period A and the magnitude of VFD2 corresponding to the cumulative signal amount during the exposure period B is recorded in the register circuit 313 in the form of a digital signal. During the period from time t14 to time t15, RES1 and RES2 are set to a high level to reset the FD potentials VFD1 and VFD2 again. During the period from time t15 to time t16, the control signal OFD is set to a high level to reset the charge accumulated in the photodiode 901.

[0096] In the second sub-frame of the k-th frame corresponding to the period from time t16 to time t20, a new exposure period A, a new exposure period B, and a non-exposure period are set based on the comparison result, and the pulse generation circuit 314 generates the gating signals GATE1 and GATE2 and the control signal OFD.

[0097] The length of the new exposure period A is half of the length of the exposure period A in the first sub-frame and is defined by the period from time t16 to time t17. The new exposure period B is defined by the period from time t17 to time t18. The non-exposure period is defined by the period from time t18 to time t19. Herein, the two exposure periods obtained by dividing the exposure period A with the larger signal cumulative amount in the first sub-frame into two halves are set as the new exposure period A and the exposure period B. In the same manner as described above, through the comparison operation from time t20 to time t21, the driving of the third sub-frame of the k-th frame continues after time t21.

[0098] In this way, the sequence of the exposure operations (A, B) and the comparison operation is repeated multiple times, and a binary search is performed on the timing of the reflected light pulse, so as to improve the measurement accuracy of the distance to the object to be measured.

[0099] Although this embodiment has been described by referring to an example of the "charge holding method" that uses a capacitor for holding an optical charge signal as a means for holding an optical signal, a "voltage holding method" may be employed, in which charge information is converted into voltage information via, for example, a transistor amplifier and the voltage signal is held.

[0100] According to this embodiment, similar to Embodiment 1, distance measurement can be performed at a higher speed compared to the comparative embodiment. In addition, by using a charge storage photodiode instead of an APD, the operating voltage can be reduced. Further, by using a capacitive element for holding charge or voltage instead of a counter circuit or a register circuit, miniaturization of the pixel can be achieved.

[0101] (Embodiment 5)

[0102] Reference Figure 11 Describe this embodiment. Figure 11 FIG. is an explanatory diagram of an example of an exposure pattern selection process according to this embodiment. Figure 11 (i) illustrates a case where reflected light reaches the photoelectric conversion device in the first half of the period corresponding to the light emission period, Figure 11 (ii) illustrates a case where reflected light reaches the sensor in the second half of the period corresponding to the light emission period.

[0103] Different from Embodiment 1, according to this embodiment, the exposure periods A and B of the first sub-frame do not cover the period corresponding to the light emission period. In the first sub-frame shown in Figure 11 (i), the amounts of optical signals in the exposure periods A and B are compared. At this time, if the signals in both exposure periods do not reach a certain threshold, then it is determined in the signal comparison that "no signal is included in either exposure period A or exposure period B". Then, the exposure periods A and B in the second sub-frame are set to not overlap with the exposure periods A and B in the first sub-frame and have the same lengths as the exposure periods A and B in the first sub-frame. In the second sub-frame, the timing of the reflected light is included in the exposure period B, and a signal amount exceeding the threshold is obtained. Therefore, in the signal comparison, it is determined that "the signal is included in the exposure period B", and the exposure periods A and B of the third sub-frame are determined by further dividing the exposure period B of the second sub-frame into two halves.

[0104] In contrast, in Figure 11 (ii), since the timing of the reflected light is included in the exposure period A of the first sub-frame, it is determined in the signal comparison that "the signal is included in the exposure period A". Then, the exposure periods A and B of the second sub-frame are determined by further dividing the exposure period A of the first sub-frame into two halves.

[0105] By using the binary search method according to the present embodiment, the distance measurement can be accelerated by preferentially searching for the period around the timing of the pre-estimated reflected light.

[0106] (Embodiment 6)

[0107] Reference Figure 12 Describe this embodiment. Figure 12 is an explanatory diagram of an example of distance measurement using binary search according to the present embodiment. Different from Embodiment 1, in Figure 12 (i), the pulse width of the emitted light is set to be substantially the same as the exposure periods A and B of the fourth sub-frame which is the final sub-frame.

[0108] Figure 12 (ii) is Figure 12 an enlarged view of the reflected light and the exposure pattern of the fourth sub-frame around the period from time t1 to t2 in (i). The case where the reflected light arrives at the timing delayed by Δt with respect to the start time t1 of the exposure pattern A will be discussed below. Since most of the reflected light is included in the exposure period A, the signal amount in the exposure period A is larger than the signal amount in the exposure period B. At this time, assuming that the pulse width of the reflected light is the same as the widths of the exposure periods A and B, then Δt can be given by the following equation using the internal division ratio for the signal amounts A and B:

[0109] Δt = T / 2 × B / (A + B)... Equation 1

[0110] In the above Equation 1, it is assumed that the influences of ambient light and dark signals are negligible. However, the ambient light and dark signals can be measured separately and subtracted from the signals A and B, and then Δt can be calculated using the above equation.

[0111] According to the present embodiment, a time resolution finer than the length of the exposure period of the final sub-frame can be achieved, which can improve the accuracy of distance measurement.

[0112] (Embodiment 7)

[0113] Figure 13 is a block diagram of the configuration of the photoelectric conversion system 1200 according to the present embodiment. The photoelectric conversion system 1200 according to the present embodiment includes a photoelectric conversion device 1204. At this time, any one of the photoelectric conversion devices described in the above embodiments can be used as the photoelectric conversion device 1204. The photoelectric conversion system 1200 can be used as, for example, an imaging system. Specific examples of the imaging system include a digital still camera, a digital video camera, a surveillance camera, etc. Figure 13 Illustrates an example of the photoelectric conversion system 1200 as a digital still camera.

[0114] Figure 13The photoelectric conversion system 1200 shown in the figure includes a photoelectric conversion device 1204, a lens 1202 for forming an optical image of an object on the photoelectric conversion device 1204, a diaphragm 1203 for changing the amount of light passing through the lens 1202, and a barrier 1201 for protecting the lens 1202.

[0115] The lens 1202 and the diaphragm 1203 are optical systems for focusing light onto the photoelectric conversion device 1204.

[0116] The photoelectric conversion system 1200 includes a signal processing unit 1205 that processes the output signal output from the photoelectric conversion device 1204. The signal processing unit 1205 performs signal processing operations to perform various corrections and compressions on the input signal as needed and outputs the signal. The photoelectric conversion system 1200 also includes a buffer memory unit 1206 for temporarily storing image data and an external interface unit (external I / F unit) 1209 for communicating with an external computer or the like.

[0117] The photoelectric conversion system 1200 also includes a recording medium 1211, such as a semiconductor memory, for recording or reading the captured image data, and a recording medium control interface unit (recording medium control I / F unit) 1210 for recording data onto the recording medium 1211 or reading data from the recording medium 1211. The recording medium 1211 can be built into the photoelectric conversion system 1200 or can be removable.

[0118] The communication between the recording medium control I / F unit 1210 and the recording medium 1211 and the communication between the external I / F unit 1209 and the recording medium control I / F unit 1210 can be performed wirelessly.

[0119] The photoelectric conversion system 1200 also includes an overall control / operation unit 1208 that performs various calculations and performs the overall control of the digital still camera, and a timing generation unit 1207 that outputs various timing signals to the photoelectric conversion device 1204 and the signal processing unit 1205. The timing signals and the like can be input from the outside, and the photoelectric conversion system 1200 only needs to include at least the photoelectric conversion device 1204 and the signal processing unit 1205 that processes the output signal output from the photoelectric conversion device 1204. As described in the fourth embodiment, the timing generation unit 1207 can be installed in the photoelectric conversion device. The overall control / operation unit 1208 and the timing generation unit 1207 can be configured to perform some or all of the control functions of the photoelectric conversion device 1204.

[0120] The photoelectric conversion device 1204 outputs an image signal to the signal processing unit 1205. The signal processing unit 1205 performs predetermined signal processing on the image signal output from the photoelectric conversion device 1204 and outputs image data. In addition, the signal processing unit 1205 generates an image using the image signal. The signal processing unit 1205 can perform distance measurement calculations on the signal output from the photoelectric conversion device 1204. Note that the signal processing unit 1205 and the timing generation unit 1207 can be installed in the photoelectric conversion device. That is, the signal processing unit 1205 and the timing generation unit 1207 can be provided on the substrate on which the pixels are arranged or can be provided on another substrate. By configuring an imaging system using the photoelectric conversion device according to any of the above embodiments, an imaging system capable of acquiring higher-quality images can be realized.

[0121] (Embodiment 8)

[0122] Figure 14 is a block diagram showing a configuration example of a distance image sensor (ToF system), which is an electronic device using the photoelectric conversion device described in the above embodiments.

[0123] As shown in Figure 14 the distance image sensor 401 includes an optical system 402, a photoelectric conversion device 403, an image processing circuit 404, a monitor 405, and a memory 406. The distance image sensor 401 receives light (modulated light or pulsed light) that is emitted from the light source device 411 to an object and reflected by the surface of the object, and thus can obtain a distance image according to the distance to the object.

[0124] The optical system 402 includes one or more lenses. The optical system 402 guides image light (incident light) from the object to the photoelectric conversion device 403 and forms an image on the light receiving surface (sensor unit) of the photoelectric conversion device 403.

[0125] As the photoelectric conversion device 403, the photoelectric conversion device according to any of the above embodiments is applied, and a distance signal indicating the distance obtained based on the received light signal output from the photoelectric conversion device 403 is supplied to the image processing circuit 404.

[0126] The image processing circuit 404 performs image processing based on the distance signal supplied from the photoelectric conversion device 403 to construct a distance image. The distance image (image data) obtained through image processing is supplied to the monitor 405 and displayed. In addition, the distance image is supplied to the memory 406 and stored (recorded).

[0127] In the distance image sensor 401 configured in this way, by applying the above photoelectric conversion device, for example, a more accurate distance image with improved pixel characteristics can be obtained.

[0128] (Example 9)

[0129] Reference Figure 15 Describe a photoelectric conversion system and a moving object according to this embodiment. Figure 15 It is a schematic illustration of a configuration example of a photoelectric conversion system and a moving object according to this embodiment. According to this embodiment, an example of an in-vehicle camera is described as the photoelectric conversion system.

[0130] Figure 15 An example of a vehicle system and a photoelectric conversion system installed therein for imaging is illustrated. According to this embodiment, two photoelectric conversion devices 1302 are deployed at the front of the vehicle 1300. More specifically, in order to obtain distance information between the vehicle 1300 and an object to be imaged and determine the possibility of a collision, it is desirable to consider the center line of the forward / backward driving direction or the shape of the vehicle 1300 (e.g., the width of the vehicle) as the axis of symmetry and place the two photoelectric conversion devices 1302 symmetrically with respect to the axis of symmetry. In addition, it is desirable that the photoelectric conversion devices 1302 be deployed so as not to obstruct the driver's view when the driver sitting in the driver's seat visually recognizes the external situation of the vehicle 1300. Note that additional photoelectric conversion devices 1302 can be deployed at the rear of the vehicle 1300 to issue an alarm when a following vehicle approaches.

[0131] In this way, the photoelectric conversion device can be applied to autonomous driving control, for example, for following another vehicle and maintaining a lane. In addition, the photoelectric conversion system 1301 can be applied not only to vehicles such as one's own vehicle, but also to moving objects (mobile devices) such as ships, airplanes, or industrial robots. In addition, the photoelectric conversion device can be applied not only to moving objects, but also to equipment that uses object recognition over a large range, such as an intelligent transportation system (ITS).

[0132] The photoelectric conversion device according to the present invention may also have a configuration capable of acquiring various types of information such as distance information.

[0133] (Other Embodiments)

[0134] Although the embodiments have been described above, the present invention is not limited to these embodiments, and various changes and modifications can be made. In addition, the embodiments are applicable to each other.

[0135] The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, the claims are attached to disclose the scope of the present invention.

[0136] This application claims the benefit of Japanese Patent Application No. 2020-176599, filed on October 21, 2020, which is hereby incorporated by reference in its entirety.

Claims

1. A photoelectric conversion device, comprising: a photoelectric conversion unit; a light value holding unit configured to hold a light value based on signal charges generated during a first exposure period and a second exposure period, at least one of a start timing and an end timing of the second exposure period being different from that of the first exposure period; a comparison unit configured to compare a light value based on signal charges generated during the first exposure period with a light value based on signal charges generated during the second exposure period; and a control unit configured to set a third exposure period and a fourth exposure period based on a result of the comparison performed by the comparison unit, at least one of a start timing and an end timing of the fourth exposure period being different from that of the third exposure period, wherein the light value holding unit includes a digital counter circuit configured to count signals based on an output from the photoelectric conversion unit, wherein the third exposure period and the fourth exposure period are less than at least one of the first exposure period and the second exposure period, and wherein the third exposure period and the fourth exposure period are set within a length of an exposure period having a larger light amount in a result of the comparison performed by the comparison unit among the first exposure period or the second exposure period.

2. The photoelectric conversion device according to claim 1, wherein the photoelectric conversion unit is an avalanche photodiode.

3. The photoelectric conversion device according to claim 2, wherein the light value holding unit includes a recording circuit that holds a count value of the digital counter circuit.

4. The photoelectric conversion device according to claim 2, wherein the digital counter circuit includes a first counter circuit and a second counter circuit, wherein the light value during the first exposure period is counted by the first counter circuit, and wherein the light value during the second exposure period is counted by the second counter circuit.

5. The photoelectric conversion device according to claim 2, wherein the photoelectric conversion unit includes a first avalanche photodiode and a second avalanche photodiode, wherein the digital counter circuit includes a first counter circuit and a second counter circuit, wherein the light value obtained from the first avalanche photodiode during the first exposure period is counted by the first counter circuit, and wherein the light value obtained from the second avalanche photodiode during the second exposure period is counted by the second counter circuit.

6. The photoelectric conversion device according to any one of claims 2 to 5, wherein the avalanche photodiode is an SPAD operating in Geiger mode.

7. The photoelectric conversion device according to claim 1, wherein the photoelectric conversion unit is a charge storage photodiode, and wherein the photoelectric conversion unit forms part of an overflow drain circuit, and controls the exposure period by controlling the on / off of the overflow drain circuit.

8. The photoelectric conversion device according to any one of claims 1 to 5, wherein the third exposure period and the fourth exposure period are less than the first exposure period and the second exposure period.

9. The photoelectric conversion device according to any one of claims 1 to 5, wherein if the light value during the first exposure period and the light value during the second exposure period do not reach a predetermined threshold in the result of the comparison performed by the comparison unit, then a period that does not overlap with either the first exposure period or the second exposure period is set as the third exposure period and the fourth exposure period.

10. The photoelectric conversion device according to any one of claims 1 to 5, wherein the length of the first exposure period is the same as the length of the second exposure period, and wherein the length of the third exposure period is the same as the length of the fourth exposure period.

11. The photoelectric conversion device according to any one of claims 1 to 5, wherein a switch is provided between the nodes of the photoelectric conversion unit and the light value holding unit, the switch being configured to control whether the nodes of the photoelectric conversion unit and the light value holding unit are connected to each other, and wherein the first exposure period, the second exposure period, the third exposure period, and the fourth exposure period are set by controlling the on / off of the switch.

12. The photoelectric conversion device according to claim 11, wherein the first exposure period starts by changing a control signal for the switch from a first level to a second level at a timing that is the same as the light emission timing of the light source or at a timing after a predetermined period has elapsed from the light emission timing, and ends by changing the control signal for the switch from the second level to the first level at a timing after a predetermined period has elapsed from the start of the first exposure period, and wherein the second exposure period starts by changing the control signal for the switch from the first level to the second level at a timing after a predetermined period has elapsed from the end of the first exposure period, and ends by changing the control signal for the switch from the second level to the first level at a timing after a predetermined period has elapsed from the start of the second exposure period.

13. The photoelectric conversion device according to claim 11, wherein the switch is composed of a PMOS transistor.

14. The photoelectric conversion device according to any one of claims 1 to 5, wherein after repeating the first exposure period, the second exposure period is repeated a plurality of times, wherein the light value obtained during the first exposure period is a value obtained by accumulating the light values obtained during a plurality of first exposure periods, and wherein the light value obtained during the second exposure period is a value obtained by accumulating the light values obtained during a plurality of second exposure periods.

15. The photoelectric conversion device according to claim 14, further comprising: a signal processing unit, wherein the light value obtained during the first exposure period and the light value obtained during the second exposure period are output to the signal processing unit.

16. The photoelectric conversion device according to claim 15, wherein the light value during each of the plurality of first exposure periods before accumulation is further output to the signal processing unit, and The light value during each of the plurality of second exposure periods before accumulation is further output to the signal processing unit.

17. The photoelectric conversion device according to any one of claims 1 to 5, wherein the photoelectric conversion unit is disposed on a first substrate, and the comparison unit is disposed on a second substrate, and wherein the first substrate and the second substrate are stacked and bonded.

18. The photoelectric conversion device according to any one of claims 1 to 5, wherein the photoelectric conversion device is configured to measure light emitted from a light source and reflected by a physical object, wherein the first exposure period is a period that starts exposure with a first lag time after the light emission timing of the light source, wherein the second exposure period is a period that starts exposure with a second lag time after the light emission timing of the light source, and wherein the length of the first lag time is different from the length of the second lag time.

19. A photoelectric conversion system, comprising: a light source; and the photoelectric conversion device according to any one of claims 1 to 18, wherein the light emitted from the light source and reflected by the physical object is measured by the photoelectric conversion device.

Images