Light detection device and ranging system

Abstract

The present technology relates to a light detection device and a ranging system that enable ranging accuracy to be improved. This light detection device is provided with: a readout circuit that outputs detection signals indicating the timing at which a light-receiving element detected reflected light resulting from the reflection of emitted light by an object; a time to digital converter (TDC) that counts time on the basis of the detection signals output from the readout circuit; a histogram generation unit that generates a histogram on the basis of the output of the TDC based on the detection signals; a first multiplexer that inputs, into a signal path between the readout circuit and the TDC, measurement signals for measuring propagation delay of signals in at least a portion of the signal path in time units smaller than the temporal resolution of the TDC; a propagation delay measurement unit that measures propagation delay on the basis of the output of the TDC based on the measurement signals in time units smaller than the temporal resolution of the TDC; and a correction unit that, on the basis of measurement results from the propagation delay measurement unit, corrects the output of the TDC based on the detection signals or the output of the histogram generation unit. The present technology can be applied, for instance, to a direct ToF type ranging device.

Description

Light detection devices and ranging systems

[0001] The present technology relates to a light detection device and a distance measurement system, and more particularly to a light detection device and a distance measurement system that can improve distance measurement accuracy.

[0002] Distance measuring devices that measure the distance to an object based on ToF (Time of Flight) are known. ToF distance measuring devices generally fall into two categories: direct ToF distance measuring devices and indirect ToF distance measuring devices. For example, a direct ToF distance measuring device measures the distance to an object by measuring the time it takes from irradiating the object with light to receiving the light reflected by the object.

[0003] The distance measuring device has pixels including a light receiving element such as a SPAD (Single Photon Avalanche Diode) that detects photons, and a TDC (Time to Digital Converter) that measures the time from a predetermined timing until the light receiving element detects light and reacts.

[0004] In conventional ranging devices, signal propagation delays in the signal path from pixels to TDCs reduce ranging accuracy, so the propagation delays are corrected. Even when the propagation delays in the signal path from pixels to TDCs are corrected, errors due to skew (propagation delay time differences) between TDCs can still be included in ranging results. Therefore, as described in Patent Literature 1, for example, a technology has been proposed in which the skew between TDCs is measured using TDCs and the ranging results are corrected based on the skew measurement results.

[0005] Japanese Patent Application Laid-Open No. 2020-148682

[0006] However, with the technology described in Patent Document 1, the skew measurement result contains a quantization error of the TDC, and this quantization error remains in the distance measurement result as a correction error. Also, with the technology described in Patent Document 1, correction is performed on a histogram based on the time measured by the TDC, so if there is not a one-to-one correspondence between the TDC and the histogram, errors due to skew between the TDCs cannot be corrected.

[0007] The present technology has been made in view of such circumstances, and is intended to make it possible to improve distance measurement accuracy.

[0008] a histogram generating unit that generates a histogram based on an output of the TDC that is based on the detection signal; a first multiplexer that inputs a measurement signal to the signal path to measure a propagation delay of a signal in at least a portion of a signal path between the readout circuit and the TDC in time units that are less than the time resolution of the TDC; a propagation delay measuring unit that measures the propagation delay in time units that are less than the time resolution of the TDC based on the output of the TDC that is based on the measurement signal; and a correction unit that corrects the output of the TDC or the output of the histogram generating unit that is based on the detection signal, based on a measurement result by the propagation delay measuring unit.

[0009] a histogram generating unit that generates a histogram based on an output of the TDC that is based on the detection signal; a first multiplexer that inputs a measurement signal to the signal path to measure a propagation delay of a signal in at least a portion of a signal path between the readout circuit and the TDC in time units that are less than the time resolution of the TDC; a propagation delay measuring unit that measures the propagation delay in time units that are less than the time resolution of the TDC based on the output of the TDC that is based on the measurement signal; and a correction unit that corrects the output of the TDC that is based on the detection signal or the output of the histogram generating unit based on the measurement result by the propagation delay measuring unit.

[0010] In one aspect of the present technology, a readout circuit outputs a detection signal indicating the timing at which a light receiving element detects reflected light that is emitted from an object, a TDC counts time based on the detection signal output from the readout circuit, a histogram generation unit generates a histogram based on the output of the TDC that is based on the detection signal, a first multiplexer inputs a measurement signal to the signal path to measure a propagation delay of a signal in at least a portion of a signal path between the readout circuit and the TDC in time units that are less than the time resolution of the TDC, a propagation delay measurement unit measures the propagation delay in time units that are less than the time resolution of the TDC based on the output of the TDC that is based on the measurement signal, and a correction unit corrects the output of the TDC or the output of the histogram generation unit that is based on the detection signal based on the measurement result by the propagation delay measurement unit.

[0011] 1 is a block diagram showing an example configuration of an electronic device equipped with a photodetector to which the present technology is applied. FIG. 2 is a diagram showing an example detailed configuration of the photodetector. FIG. 3 is a block diagram showing an example configuration of a measurement signal generation unit. FIG. 4 is a diagram showing an example circuit configuration of a delay adjustment circuit. FIG. 5 is a diagram showing another example circuit configuration of a delay adjustment circuit. FIG. 6 is a diagram explaining the flow of signals during an exposure period. FIG. 7 is a diagram explaining the flow of signals during a propagation delay measurement period. FIG. 8 is a block diagram showing an example configuration of an arithmetic circuit. FIG. 9 is a block diagram showing an example configuration of a propagation delay measurement unit and a correction value calculation unit when a correction value is calculated using an accumulator. FIG. 10 is a timing chart explaining the operation flow of the photodetector when a correction value is calculated using an accumulator. FIG. 11 is a block diagram showing an example configuration of a propagation delay measurement unit and a correction value calculation unit when a correction value is calculated using a histogram. FIG. 12 is a diagram showing an example method for calculating a correction value based on the centroid value of a histogram. FIG. 13 is a block diagram showing an example configuration of a correction unit. FIG. 14 is a diagram showing examples of the integer part and decimal part of an actual correction value. FIG. 15 is a diagram showing an example configuration of a pixel. FIG. 16 is a diagram showing a first modified example of the configuration of the photodetector. FIG. 17 is a diagram explaining an example arrangement of active pixels corresponding to various light source devices. FIG. 18 is a diagram showing a second modified example of the configuration of the photodetector. FIG. 19 is a diagram showing an example configuration of a pixel when a first MUX is provided inside a pixel readout circuit. 1 is a diagram showing another example of the configuration of a pixel when the first MUX is provided inside the pixel readout circuit. FIG. 2 is a diagram showing a third modified example of the configuration of the photodetector. FIG. 3 is a diagram showing an example of the configuration of a propagation delay measurement unit and a correction value calculation unit of an arithmetic circuit when correcting the propagation delay of a signal inside the second MUX. FIG. 4 is a block diagram showing an example of the configuration of a photodetector when correction of an error caused by skew between TDCs is performed after histogram generation. FIG. 5 is a perspective view showing an example of the configuration of a substrate of a photodetector. FIG. 6 is a perspective view showing another example of the configuration of a substrate of a photodetector. FIG. 7 is a diagram showing a fourth modified example of the configuration of the photodetector. FIG. 8 is a diagram explaining the flow of a signal during an exposure period when measurement pixels are provided in a pixel array unit. FIG. 9 is a diagram explaining the flow of a signal during a propagation delay measurement period when measurement pixels are provided in a pixel array unit. FIG. 10 is a diagram showing an example of the configuration of a arithmetic circuit when measurement pixels are provided in a pixel array unit. FIG. 11 is a diagram showing an example of the relationship between signal propagation delays in each signal path. FIG. 12 is a diagram showing an example of the configuration of a fifth modified example of the configuration of the photodetector.FIG. 10 is a diagram showing a sixth modified example of the configuration of the photodetector. FIG. 11 is a diagram showing a seventh modified example of the configuration of the photodetector. FIG. 12 is a diagram showing an eighth modified example of the configuration of the photodetector. FIG. 13 is a diagram showing an example of the configuration of a measurement pixel. FIG. 14 is a diagram explaining wiring of a tree-type circuit network and a pixel array unit. FIG. 15 is a block diagram showing an example of the configuration of a photodetector in the case where correction of errors caused by skew between signal paths of detection signals is performed at a subsequent stage of histogram generation.

[0012] Hereinafter, embodiments of the present technology will be described in the following order: 1. Configuration example of electronic device 2. Configuration example of photodetector 3. Modification

[0013] 1. Configuration Example of Electronic Device FIG. 1 is a block diagram showing a configuration example of an electronic device 1 equipped with a photodetector to which the present technology is applied.

[0014] As shown in FIG. 1, the electronic device 1 includes a distance measuring device 11 and an application unit 12 .

[0015] The distance measuring device 11 measures the distance to a target object Obj using a direct ToF method and outputs distance information as a distance measurement result to the application unit 12. The distance information is configured, for example, as a depth image in which a depth value indicating the distance to the object Obj is stored as the pixel value of each pixel.

[0016] The application unit 12 is realized by running a program on a CPU (Central Processing Unit), for example, and requests the distance measuring device 11 to perform distance measurement and obtains distance information from the distance measuring device 11 .

[0017] The electronic device 1 may be, for example, a smartphone, a tablet terminal, a wearable device, a camera, or a device mounted on a moving object. The camera may be an in-vehicle camera, a digital still camera, a digital video camera, etc. The moving object may be, for example, a vehicle such as an automobile, a drone, etc.

[0018] The distance measuring device 11 is configured as a distance measuring system including a control unit 21, a light source device 22, and a photodetector device 23. The control unit 21 includes control circuits and processors such as a field programmable gate array (FPGA) and a digital signal processor (DSP), and controls the overall operation of the distance measuring device 11. For example, the control unit 21 generates a reference clock signal that serves as a reference for clock signals used by each unit of the distance measuring device 11, and supplies the reference clock signal to the light source device 22 and the photodetector device 23. In addition, in response to a distance measurement execution request from the application unit 12, the control unit 21 instructs the photodetector device 23 to execute distance measurement, obtains distance information from the photodetector device 23, and supplies the information to the application unit 12.

[0019] The light source device 22 includes a light-emitting element that emits light with a wavelength in the infrared region, for example, and a drive circuit that drives the light-emitting element. The light-emitting element that emits light with a wavelength in the infrared region can be, for example, an LED (Light Emitting Diode). The light-emitting element is not limited to this, and can also be, for example, a VCSEL (Vertical Cavity Surface Emitting Laser) in which multiple light-emitting elements are formed in an array. The light source device 22 outputs the irradiation light L1 based on a light-emission timing signal supplied from the photodetector 23. The light-emission timing signal is, for example, a pulse signal modulated into a rectangular wave with a predetermined duty ratio. Hereinafter, unless otherwise specified, "the light-emitting element of the light source device 22 emits light" will be expressed as "the light source device 22 emits light," etc.

[0020] The photodetector 23 includes a light-receiving element capable of detecting light with a wavelength in the infrared region, for example, and a signal processing circuit that outputs a signal corresponding to the light detected by the light-receiving element. A SPAD, for example, can be used as the light-receiving element included in the photodetector 23. Hereinafter, unless otherwise specified, "the light-receiving element of the photodetector 23 detects light" will be expressed as "the photodetector 23 receives light," etc.

[0021] The photodetector 23 executes distance measurement processing in response to a distance measurement instruction from the control unit 21. For example, the photodetector 23 generates a light emission timing signal indicating the timing at which the light source device 22 emits light, and supplies the signal to the light source device 22. The photodetector 23 also performs a light reception operation in synchronization with the light emission timing signal and acquires a count value that serves as the basis for calculating a depth value. The count value is a count value obtained by counting the time from when the light source device 22 outputs illumination light L1 to when the photodetector 23 receives reflected light L2 from the illumination light L1 reflected by the object Obj. The photodetector 23, for example, supplies the count value to the control unit 21 as distance information. Alternatively, the photodetector 23 calculates the distance D to the object Obj based on the count value, and supplies a depth image storing the distance D as a depth value to the control unit 21 as distance information. The depth image generation process based on the count value may be performed by the control unit 21.

[0022] The photodetector 23 has pixels including light-receiving elements and a TDC (Time to Digital Converter) that counts the count value.

[0023] Conventionally, in photodetection devices, signal propagation delay in the signal path from pixels to TDCs reduces ranging accuracy, so the propagation delay is corrected. Even if the propagation delay in the signal path from pixels to TDCs is corrected, errors due to skew (propagation delay time difference) between TDCs can still be included in ranging results. Therefore, as described in Patent Literature 1, for example, a technology has been proposed in which the skew between TDCs is measured using TDCs and the ranging results are corrected based on the skew measurement results.

[0024] However, with the technology described in Patent Document 1, the skew measurement result contains a quantization error of the TDC, and this quantization error remains in the distance measurement result as a correction error. Also, with the technology described in Patent Document 1, correction is performed on a histogram based on the count value counted by the TDC, so if there is not a one-to-one correspondence between the TDC and the histogram, errors due to skew between the TDCs cannot be corrected.

[0025] The present technology has been conceived with a focus on the above points, and makes it possible to improve the ranging accuracy of the photodetector 23 by providing the photodetector 23 with: a pixel readout circuit that outputs a detection signal indicating the timing at which a light receiving element detects reflected light L2 when illumination light L1 is reflected by an object Obj; a TDC that counts time based on the detection signal output from the pixel readout circuit; a histogram generation unit that generates a histogram based on the output of the TDC that is based on the detection signal; a first MUX (multiplexer) that inputs a measurement signal to the signal path to measure the propagation delay of a signal in at least a part of the signal path between the readout circuit and the TDC in time units that are less than the time resolution of the TDC; a propagation delay measurement unit that measures the propagation delay in time units that are less than the time resolution of the TDC based on the output of the TDC that is based on the measurement signal; and a correction unit that corrects the output of the TDC that is based on the detection signal or the output of the histogram generation unit based on the measurement result by the propagation delay measurement unit.

[0026] 2. Configuration Example of Photodetector> FIG. 2 is a diagram showing a detailed configuration example of the photodetector 23. As shown in FIG.

[0027] As shown in FIG. 2, the photodetector 23 is composed of a pixel array section 31, a measurement signal generator 32, N first MUXs 33-1 to 33-N, N TDCs 34-1 to 34-N, N arithmetic circuits 35-1 to 35-N, and N histogram generators 36-1 to 36-N.

[0028] Hereinafter, when there is no need to particularly distinguish between the first MUXes 33-1 to 33-N, they will simply be referred to as first MUXes 33, and when there is no need to particularly distinguish between the TDCs 34-1 to 34-N, they will simply be referred to as TDCs 34. When there is no need to particularly distinguish between the arithmetic circuits 35-1 to 35-N, they will simply be referred to as arithmetic circuits 35, and when there is no need to particularly distinguish between the histogram generation units 36-1 to 36-N, they will simply be referred to as histogram generation units 36.

[0029] The pixel array unit 31 is configured, for example, by two-dimensionally arranging a plurality of pixels 41 in a matrix. Each pixel 41 includes a SPAD, which is a light receiving element, and a pixel readout circuit (PFE: Pixel Frontend).

[0030] The SPAD detects incident light of a predetermined wavelength and outputs a detection signal indicating the timing at which the incident light is detected. The pixel readout circuit is a circuit that reads out and outputs the detection signal output from the SPAD.

[0031] For example, in the pixel array section 31, pixel drive lines (not shown) are wired along the column direction for each pixel column consisting of pixels arranged in the column direction, and horizontal signal lines are wired along the row direction for each pixel row consisting of pixels arranged in the row direction.

[0032] For example, a pixel drive unit (not shown) including a shift register, an address decoder, etc. supplies signals to each pixel via a plurality of pixel drive lines, thereby driving each pixel 41 (the pixel readout circuit of each pixel 41) of the pixel array unit 31 simultaneously or column by column. The detection signals output from each pixel 41 in the pixel column selected and scanned by the pixel drive unit are supplied to any of the first MUXes 33-1 to 33-N via the respective horizontal signal lines.

[0033] 2, a first MUX 33 is provided in one-to-one correspondence with each pixel row of the pixel array unit 31, and a series including a TDC 34, an arithmetic circuit 35, and a histogram generation unit 36 ​​is provided downstream of each first MUX 33. In other words, a signal path between a pixel row and a TDC 34, and a first MUX 33 that inputs a measurement signal to the signal path, are provided one for each of the N TDCs 34. For example, TDC 34-1 is connected to the output terminal of first MUX 33-1, TDC 34-2 is connected to the output terminal of first MUX 33-2, and TDC 34-N is connected to the output terminal of first MUX 33-N.

[0034] The measurement signal generation unit 32 generates measurement signals for measuring signal propagation delays in at least a portion of the signal path from the pixel 41 (pixel readout circuit) to the TDC 34, and inputs the measurement signals to the first MUXes 33-1 to 33-N. The measurement signal generation unit 32 also generates synchronization signals for synchronizing the operations of the TDCs 34-1 to 34-N, and inputs the synchronization signals to the TDCs 34-1 to 34-N.

[0035] The first MUX 33 switches the configuration of the pixel row of the pixel array unit 31 and the measurement signal generation unit 32 to be connected to an output terminal internally. In other words, the first MUX 33 supplies one of the detection signals output from the pixels 41 of one row of the pixel array unit 31 and the measurement signals input by the measurement signal generation unit 32 to the downstream TDC 34. The first MUX 33 functions as a MUX that inputs the measurement signals to the signal path from the pixels 41 to the TDC 34.

[0036] The TDC 34 counts a count value indicating the time from when the light source device 22 emits light to when the pixel 41 receives light, based on the light emission timing signal and the detection signal supplied from the first MUX 33. The TDC 34 also counts a count value indicating the signal propagation delay in at least a portion of the signal path from the pixel 41 to the TDC 34, based on the synchronization signal input from the measurement signal generation unit 32 and the measurement signal supplied from the first MUX 33. The TDC 34 supplies the count value to the calculation circuit 35 in the subsequent stage.

[0037] The arithmetic circuit 35 performs a correction process by adding or subtracting a correction value to the count value as the output of the TDC 34 based on the detection signal, the correction value correcting the error due to skew between the TDCs 34. The arithmetic circuit 35 supplies the corrected count value to the downstream histogram generation unit 36. The arithmetic circuit 35 also measures the skew between the TDCs 34 based on the count value as the output of the TDC 34 based on the measurement signal, and calculates a correction value correcting the error due to skew between the TDCs 34.

[0038] The histogram generation unit 36 ​​generates a histogram by counting up the frequency value of the bin corresponding to each count value based on the count value supplied from the arithmetic circuit 35. In direct ToF distance measurement, the light source device 22 emits light and each pixel 41 receives reflected light multiple times (for example, thousands to tens of thousands of times), and a histogram is generated for each pixel 41 by counting up the frequency value of the time (count value) until the reflected light is received.

[0039] For example, the histogram for each pixel generated by the histogram generating unit 36 ​​is supplied to the control unit 21 as distance information.

[0040] FIG. 3 is a block diagram showing an example of the configuration of the measurement signal generating section 32. As shown in FIG.

[0041] As shown in FIG. 3, the measurement signal generating section 32 is composed of a pulse generating circuit 61 and a delay adjusting circuit 62 .

[0042] The pulse generating circuit 61 generates, for example, a pulse signal having a predetermined duration and inputs it as a synchronization signal to each of the TDCs 34-1 to 34-N. The pulse generating circuit 61 also supplies the generated pulse signal to the delay adjusting circuit 62.

[0043] The delay adjustment circuit 62 generates a measurement signal by delaying the pulse signal supplied from the pulse generation circuit 61 by a predetermined delay amount relative to the synchronization signal input to the TDC 34. The delay adjustment circuit 62 inputs the generated measurement signal to each of the first MUXes 33-1 to 33-N.

[0044] If there is variation in the time at which the measurement signals arrive at each of the first MUXes 33-1 to 33-N, errors will be included in the skew measurement results obtained by the arithmetic circuits 35-1 to 35-N, so it is desirable that the measurement signals be transmitted by a transmission means that allows the signals output from the delay adjustment circuits 62 to arrive at each of the first MUXes 33 at approximately the same time. For example, the measurement signals may be transmitted within a tree-shaped circuit network formed by each of the measurement signal generators 32 and the first MUXes 33, or may be transmitted by low-resistance wiring such as global wiring.

[0045] The delay adjustment circuit 62 can adjust the delay amount of the measurement signal relative to the synchronization signal in time units less than the time resolution (the magnitude of 1 LSB (Least Significant Bit)) of the TDC 34. This reduces the quantization error of the TDC 34 included in the measurement result of the signal propagation delay in at least a portion of the signal path from the pixel 41 to the TDC 34, and enables the arithmetic circuit 35 to measure the skew between the TDCs 34 with high accuracy.

[0046] If the time resolution of the TDCs 34 is, for example, 1 ns, correcting the skew between the TDCs 34 based on the measurement result that includes the quantization error of the TDCs 34 may result in a ranging error of up to 15 cm. The photodetector 23 of the present technology reduces the quantization error of the TDCs 34 that is included in the skew measurement result, thereby reducing the correction error included in the final ranging result and improving ranging accuracy.

[0047] FIG. 4 is a diagram showing an example of the circuit configuration of the delay adjustment circuit 62. As shown in FIG.

[0048] In the example of FIG. 4, the delay adjustment circuit 62 is composed of four stages of delay elements 81-1 to 81-4 and a MUX 82.

[0049] The delay elements 81-1 to 81-4 are connected in series and gradually delay the pulse signal supplied from the pulse generating circuit 61. The output of each delay element is input to the MUX 82.

[0050] The MUX 82 outputs one of the pulse signals input by each of the delay elements 81-1 to 81-4 as a measurement signal. Here, the delay amount of the measurement signal relative to the synchronization signal is adjusted depending on which of the pulse signals input by each of the delay elements 81-1 to 81-4 is output as the measurement signal.

[0051] Although the delay adjustment circuit of FIG. 4 is provided with four stages of delay circuits, the number of stages is not limited to four.

[0052] FIG. 5 is a diagram showing another example of the circuit configuration of the delay adjustment circuit 62. In FIG.

[0053] In the example of FIG. 5, the delay adjustment circuit 62 is made up of four stages of delay elements 101-1 to 101-4, capacitive loads 102-1 to 102-3 for adjusting the loads of the delay elements 101-1 to 101-3, and switch circuits 103-1 to 103-3.

[0054] The delay elements 101 - 1 to 101 - 4 are connected in series and gradually delay the pulse signal supplied from the pulse generating circuit 61 .

[0055] The output terminal of delay element 101-1 is connected to one end of capacitive load 102-1, the other end of which is grounded, via switch circuit 103-1, and the output terminal of delay element 101-2 is connected to one end of capacitive load 102-2, the other end of which is grounded, via switch circuit 103-2. Furthermore, the output terminal of delay element 101-3 is connected to one end of capacitive load 102-3, the other end of which is grounded, via switch circuit 103-3.

[0056] Here, the delay amount of the measurement signal relative to the synchronization signal is adjusted by turning on / off each of the switch circuits 103-1 to 103-3.

[0057] Although the delay adjustment circuit of FIG. 5 is provided with four stages of delay circuits, the number of stages is not limited to four.

[0058] FIG. 6 is a diagram illustrating the flow of signals during an exposure period.

[0059] 6, during the exposure period of each pixel 41 (each light receiving element), detection signals output from the pixels 41 in one row of the pixel array unit 31 are input to the subsequent TDC 34 via each first MUX 33, and the TDC 34 counts a count value based on the detection signals. The count value based on the detection signals is supplied from the TDC 34 to the arithmetic circuit 35, and the arithmetic circuit 35 performs a correction process on the count value based on the detection signals.

[0060] FIG. 7 is a diagram illustrating the signal flow during the propagation delay measurement period.

[0061] 7, during the propagation delay measurement period before the exposure period, the measurement signals generated by the measurement signal generators 32 are input to the downstream TDCs 34 via the first MUXes 33, and the TDCs 34 count the count values ​​based on the measurement signals. The count values ​​based on the measurement signals are supplied from the TDCs 34 to the arithmetic circuit 35, and the arithmetic circuit 35 calculates the correction values ​​used in the correction process based on the count values ​​based on the measurement signals.

[0062] Methods for calculating the correction value include a method using an accumulator and a method using a histogram. When calculating the correction value using a histogram, it is necessary to provide the arithmetic circuit 35 with a relatively large circuit configuration, such as a histogram generation unit including a counter for multiple bins and a centroid calculation unit. Therefore, from the viewpoint of reducing the area of ​​the arithmetic circuit 35, the method of calculating the correction value using an accumulator is preferable to the method of calculating the correction value using a histogram.

[0063] FIG. 8 is a block diagram showing an example of the configuration of the arithmetic circuit 35.

[0064] As shown in FIG. 8, the arithmetic circuit 35 is made up of a propagation delay measurement unit 121 , a correction value calculation unit 122 , and a correction unit 123 .

[0065] The propagation delay measurement unit 121 measures the propagation delay of the signal in at least a part of the signal path from the pixel 41 to the TDC 34, based on a count value based on the measurement signal as an output of the upstream TDC 34. The propagation delay measurement unit 121 supplies the measurement result of the propagation delay to the correction value calculation unit 122.

[0066] The correction value calculation unit 122 calculates the skew between the TDC 34 in the upstream stage of the arithmetic circuit 35 and the reference TDC (hereinafter also referred to as the reference TDC) based on the measurement result of the propagation delay by the propagation delay measurement unit 121 and the measurement result of the signal propagation delay (hereinafter also referred to as the reference propagation delay) in at least a part of the signal path from the pixel 41 to the reference TDC 34. The correction value calculation unit 122 holds the calculation result of the skew between the TDCs as a correction value and supplies the correction value to the correction unit 123 at a predetermined timing during the exposure period.

[0067] The correction unit 123 performs correction processing by adding or subtracting the correction value supplied from the correction value calculation unit 122 to or from the count value based on the detection signal, which is the output of the preceding TDC 34. The correction unit 123 supplies the corrected count value to the following histogram generation unit 36.

[0068] In the photodetector 23 of the present technology, the correction units 123 are provided in one-to-one correspondence with the TDC 34. On the other hand, in the photodetector 23 of the present technology, the propagation delay measurement units 121 and the correction value calculation units 122 may be provided in one-to-one correspondence with the TDC 34, or, for the purpose of reducing the circuit scale, the propagation delay measurement units 121 and the correction value calculation units 122 may be provided in one-to-multiple correspondence with the TDC 34.

[0069] FIG. 9 is a block diagram showing an example of the configuration of the propagation delay measurement unit 121 and the correction value calculation unit 122 when the correction value is calculated using an accumulator.

[0070] 9, propagation delay measurement unit 121-1 is configured with accumulator 141-1 and divider 142-1, and correction value calculation unit 122-1 is configured with subtractor 151-1 and correction value holder 152-1. Furthermore, propagation delay measurement unit 121-(N-1) is configured with accumulator 141-(N-1) and divider 142-(N-1), and correction value calculation unit 122-(N-1) is configured with subtractor 151-(N-1) and correction value holder 152-(N-1). Furthermore, propagation delay measurement unit 121-N is configured with accumulator 141-N and divider 142-N, and correction value calculation unit 122-N is configured with subtractor 151-N and correction value holder 152-N.

[0071] Hereinafter, when there is no need to particularly distinguish between the accumulators 141-1 to 141-N, they will simply be referred to as accumulators 141, and when there is no need to particularly distinguish between the division units 142-1 to 142-N, they will simply be referred to as division units 142. Furthermore, when there is no need to particularly distinguish between the subtraction units 151-1 to 151-N, they will simply be referred to as subtraction units 151, and when there is no need to particularly distinguish between the correction value holding units 152-1 to 152-N, they will simply be referred to as correction value holding units 152.

[0072] In the example of FIG. 9, the TDC 34-N is a reference TDC, and the calculation circuit 35-N is a calculation circuit that measures a reference propagation delay (hereinafter also referred to as a reference calculation circuit).

[0073] The pulse generating circuit 61 of the measurement signal generating unit 32 repeatedly inputs a synchronization signal (pulse signal) to each TDC 34. The delay adjusting circuit 62 of the measurement signal generating unit 32 repeatedly inputs the measurement signal to each first MUX 33 while changing the delay amount of the measurement signal relative to the synchronization signal in time units less than the time resolution of the TDC 34.

[0074] The reference TDC 34-N counts a count value based on the measurement signal input by the delay adjustment circuit 62 via the first MUX 33-N, and supplies the count value to the accumulator 141-N.

[0075] The accumulator 141-N calculates the cumulative sum of the count values ​​output from the reference TDC 34-N, and supplies the cumulative sum of the count values ​​to a divider 142-N.

[0076] The divider 142-N divides the cumulative sum of the count values ​​supplied from the accumulator 141-N by the number of times the measurement signal is input to the first MUX 33-N by the measurement signal generator 32, to calculate the average value of the count values ​​(hereinafter also referred to as the reference average value). The divider 142-N supplies the reference average value to the subtractors 151-1 to 151-N.

[0077] The subtraction unit 151-N calculates the skew for the reference TDC 34-N by subtracting the reference average value from the average value of the count values ​​supplied from the division unit 142-N. Here, the skew for the reference TDC 34-N is set to 0 LSB. The subtraction unit 151-N supplies the skew for the reference TDC 34-N as a correction value to the correction value holding unit 152-N.

[0078] The correction value holding unit 152-N holds the correction value supplied from the subtraction unit 151-N.

[0079] The TDC 34-1 counts a count value based on the measurement signal input by the delay adjustment circuit 62 via the first MUX 33-1, and supplies the count value to the accumulator 141-1.

[0080] The accumulator 141-1 calculates the cumulative sum of the count values ​​output from the TDC 34-1, and supplies the cumulative sum of the count values ​​to the division unit 142-1.

[0081] The division unit 142-1 calculates the average value of the count values ​​by dividing the cumulative sum of the count values ​​supplied from the accumulator 141-1 by the number of times the measurement signal is input to the first MUX 33-1 by the measurement signal generation unit 32. The division unit 142-1 supplies the average value of the count values ​​to the subtraction unit 151-1.

[0082] The subtraction unit 151-1 calculates the skew between the TDC 34-1 and the reference TDC 34-N by subtracting the reference average value supplied from the division unit 142-N from the average value of the count values ​​supplied from the division unit 142-1. The subtraction unit 151-1 supplies the skew between the TDC 34-1 and the reference TDC 34-N as a correction value to the correction value holding unit 152-1.

[0083] The correction value holding unit 152-1 holds the correction value supplied from the subtraction unit 151-1.

[0084] The TDC 34-(N-1) counts a count value based on the measurement signal input by the delay adjustment circuit 62 via the first MUX 33-(N-1), and supplies the count value to the accumulator 141-(N-1).

[0085] The accumulator 141-(N-1) calculates the cumulative sum of the count values ​​output from the TDC 34-(N-1), and supplies the cumulative sum of the count values ​​to the divider 142-(N-1).

[0086] The divider 142-(N-1) calculates the average value of the count values ​​by dividing the cumulative sum of the count values ​​supplied from the accumulator 141-(N-1) by the number of times the measurement signal is input to the first MUX 33-(N-1) by the measurement signal generator 32. The divider 142-(N-1) supplies the average value of the count values ​​to the subtractor 151-(N-1).

[0087] The subtraction unit 151-(N-1) calculates the skew between the TDC 34-(N-1) and the reference TDC 34-N by subtracting the reference average value supplied from the division unit 142-N from the average value of the count values ​​supplied from the division unit 142-(N-1). The subtraction unit 151-(N-1) supplies the skew between the TDC 34-(N-1) and the reference TDC 34-N as a correction value to the correction value holding unit 152-(N-1).

[0088] The correction value holding unit 152-(N-1) holds the correction value supplied from the subtraction unit 151-(N-1).

[0089] FIG. 10 is a timing chart illustrating the flow of the operation of the photodetector 23 when the correction value is calculated using the accumulator.

[0090] As shown in Figure 10, first, a first synchronization signal is output by a pulse generation circuit 61, and a first measurement signal delayed from the first synchronization signal by the delay amount indicated by delay setting 1 is output by a delay adjustment circuit 62.

[0091] The first count value, which indicates the time from when the first synchronization signal arrives at the TDC 34-1 until when the first measurement signal arrives at the TDC 34-1, is counted by the TDC 34-1, and the cumulative sum of the count values ​​in the TDC 34-1 is calculated by the accumulator 141-1. In the example of Fig. 10, the first count value in the TDC 34-1 is 6 LSB, and the cumulative sum of the count values ​​is also 6 LSB.

[0092] Furthermore, the first count value, which indicates the time from when the first synchronization signal arrives at TDC 34-(N-1) to when the first measurement signal arrives at TDC 34-(N-1), is counted by TDC 34-(N-1), and the cumulative sum of the count values ​​at TDC 34-(N-1) is calculated by accumulator 141-(N-1). In the example of Fig. 10, the first count value at TDC 34-(N-1) is 7 LSB, and the cumulative sum of the count values ​​is also 7 LSB.

[0093] Furthermore, a first count value indicating the time from when the first synchronization signal reaches the reference TDC 34-N until when the first measurement signal reaches the reference TDC 34-N is counted by the reference TDC 34-N, and the cumulative sum of the count values ​​at the reference TDC 34-N is calculated by the accumulator 141-N. In the example of Fig. 10, the first count value at the reference TDC 34-N is 5 LSB, and the cumulative sum of the count values ​​is also 5 LSB.

[0094] Next, the second synchronization signal is output by the pulse generation circuit 61, and the second measurement signal delayed from the second synchronization signal by the delay amount indicated by delay setting 2 is output by the delay adjustment circuit 62.

[0095] The second count value, which indicates the time from when the second synchronization signal reaches the TDC 34-1 until when the second measurement signal reaches the TDC 34-1, is counted by the TDC 34-1, and the cumulative sum of the count values ​​in the TDC 34-1 is calculated by the accumulator 141-1. In the example of Fig. 10, the second count value in the TDC 34-1 is 7 LSB, and the cumulative sum of the count values ​​is 13 LSB.

[0096] Furthermore, a second count value indicating the time from when the second synchronization signal reaches TDC 34-(N-1) to when the second measurement signal reaches TDC 34-(N-1) is counted by TDC 34-(N-1), and the cumulative sum of the count values ​​at TDC 34-(N-1) is calculated by accumulator 141-(N-1). In the example of Fig. 10, the second count value at TDC 34-(N-1) is 7 LSB, and the cumulative sum of the count values ​​is 14 LSB.

[0097] Furthermore, a second count value indicating the time from when the second synchronization signal reaches the reference TDC 34-N until when the second measurement signal reaches the reference TDC 34-N is counted by the reference TDC 34-N, and the cumulative sum of the count values ​​at the reference TDC 34-N is calculated by the accumulator 141-N. In the example of Fig. 10, the second count value at the reference TDC 34-N is 6 LSB, and the cumulative sum of the count values ​​is 11 LSB.

[0098] Next, the third synchronization signal is output by the pulse generating circuit 61, and the third measurement signal delayed from the third synchronization signal by the delay amount indicated by delay setting 3 is output by the delay adjusting circuit 62.

[0099] The third count value, which indicates the time from when the third synchronization signal reaches the TDC 34-1 until when the third measurement signal reaches the TDC 34-1, is counted by the TDC 34-1, and the cumulative sum of the count values ​​in the TDC 34-1 is calculated by the accumulator 141-1. In the example of Fig. 10, the third count value in the TDC 34-1 is 7 LSB, and the cumulative sum of the count values ​​is 20 LSB.

[0100] Furthermore, a third count value indicating the time from when the third synchronization signal reaches TDC 34-(N-1) to when the third measurement signal reaches TDC 34-(N-1) is counted by TDC 34-(N-1), and the cumulative sum of the count values ​​at TDC 34-(N-1) is calculated by accumulator 141-(N-1). In the example of Fig. 10, the third count value at TDC 34-(N-1) is 8 LSB, and the cumulative sum of the count values ​​is 22 LSB.

[0101] Furthermore, a third count value indicating the time from when the third synchronization signal reaches the reference TDC 34-N until when the third measurement signal reaches the reference TDC 34-N is counted by the reference TDC 34-N, and the cumulative sum of the count values ​​at the reference TDC 34-N is calculated by the accumulator 141-N. In the example of Fig. 10, the third count value at the reference TDC 34-N is 6 LSB, and the cumulative sum of the count values ​​is 17 LSB.

[0102] Finally, the 128th synchronization signal is output by the pulse generation circuit 61, and the 128th measurement signal, delayed from the 128th synchronization signal by the delay amount indicated by the delay setting 128, is output by the delay adjustment circuit 62.

[0103] The 128th count value, which indicates the time from when the 128th synchronization signal reaches the TDC 34-1 until when the 128th measurement signal reaches the TDC 34-1, is counted by the TDC 34-1, and the cumulative sum of the count values ​​in the TDC 34-1 is calculated by the accumulator 141-1. In the example of Fig. 10, the 128th count value in the TDC 34-1 is 12 LSB, and the cumulative sum of the count values ​​is 1231 LSB.

[0104] Furthermore, the 128th count value, which indicates the time from when the 128th synchronization signal reaches TDC 34-(N-1) until when the 128th measurement signal reaches TDC 34-(N-1), is counted by TDC 34-(N-1), and the cumulative sum of the count values ​​at TDC 34-(N-1) is calculated by accumulator 141-(N-1). In the example of Fig. 10, the 128th count value at TDC 34-(N-1) is 13 LSB, and the cumulative sum of the count values ​​is 1344 LSB.

[0105] Furthermore, the 128th count value, which indicates the time from when the 128th synchronization signal reaches the reference TDC 34-N until when the 128th measurement signal reaches the reference TDC 34-N, is counted by the reference TDC 34-N, and the cumulative sum of the count values ​​at the reference TDC 34-N is calculated by the accumulator 141-N. In the example of Fig. 10, the 128th count value at the reference TDC 34-N is 12 SB, and the cumulative sum of the count values ​​is 1165 LSB.

[0106] Thereafter, the average value of the count values ​​in TDC 34-1 is calculated by divider 142-1, the average value of the count values ​​in TDC 34-(N-1) is calculated by divider 142-(N-1), and a reference average value is calculated by divider 142-N. The skew (correction value) between TDC 34-1 and reference TDC 34-N is calculated by subtractor 151-1, and the skew (correction value) between TDC 34-(N-1) and reference TDC 34-N is calculated by subtractor 151-(N-1). In the example of FIG. 10, the skew between TDC 34-1 and reference TDC 34-N is 1231 / 128-1165 / 128=0.52 [LSB], and the skew between TDC 34-(N-1) and reference TDC 34-N is 1344 / 128-1165 / 128=1.40 [LSB].

[0107] In this way, the correction value is expressed in time units less than the time resolution of the TDC 34 .

[0108] 11 is a block diagram showing an example of the configuration of the propagation delay measurement unit 121 and the correction value calculation unit 122 when calculating a correction value using a histogram. In Fig. 11, the same components as those in Fig. 9 are assigned the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0109] The arithmetic circuit 35 of FIG. 11 differs from the arithmetic circuit 35 of FIG. 9 in that the propagation delay measurement unit 121 is provided with histogram generation units 171 (171-1 to 171-N) and centroid calculation units 172 (172-1 to 172-N) instead of the accumulator 141 and division unit 142.

[0110] In the example of FIG. 11, the TDC 34-N is the reference TDC, and the arithmetic circuit 35-N is the reference arithmetic circuit.

[0111] The reference TDC 34-N counts a count value based on the measurement signal input by the delay adjustment circuit 62 via the first MUX 33-N, and supplies the count value to the histogram generation unit 171-N.

[0112] The histogram generator 171-N generates a histogram by counting up the frequency values ​​of the bins corresponding to the count values ​​based on the count values ​​output from the reference TDC 34-N. The histogram generator 171-N supplies the generated histogram to the center of gravity calculator 172-N.

[0113] The centroid calculation unit 172-N performs centroid calculation on the histogram supplied from the histogram generation unit 171-N to calculate the centroid value of the count value (hereinafter also referred to as the reference centroid value). The centroid calculation unit 172-N supplies the reference centroid value to the subtraction units 151-1 to 151-N.

[0114] The subtractor 151-N calculates the skew for the reference TDC 34-N by subtracting the reference center of gravity value from the center of gravity value of the count value supplied from the center of gravity calculation unit 172-N. Here, the skew for the reference TDC 34-N is set to 0 LSB.

[0115] The TDC 34-1 counts a count value based on the measurement signal input by the delay adjustment circuit 62 via the first MUX 33-1, and supplies the count value to the histogram generation unit 171-1.

[0116] The histogram generator 171-1 generates a histogram by counting up the frequency values ​​of the bins corresponding to the count values ​​supplied from the reference TDC 34-1, and supplies the generated histogram to the center of gravity calculator 172-1.

[0117] The centroid calculation unit 172-1 calculates the centroid of the count value by performing centroid calculation on the histogram supplied from the histogram generation unit 171-1, and supplies the centroid value of the count value to the subtraction unit 151-1.

[0118] As shown in FIG. 12, the subtraction unit 151-1 calculates the skew between TDC 34-1 and the reference TDC 34-N (a correction value for the count value at TDC 34-1) by subtracting the reference center of gravity value supplied from the center of gravity calculation unit 172-N from the center of gravity value of the count value supplied from the center of gravity calculation unit 172-1.

[0119] Returning to Figure 11, the TDC 34-(N-1) counts a count value based on the measurement signal input by the delay adjustment circuit 62 via the first MUX 33-(N-1), and supplies the count value to the histogram generation unit 171-(N-1).

[0120] The histogram generator 171-(N-1) generates a histogram by counting up the frequency values ​​of the bins corresponding to the count values ​​based on the count values ​​output from the TDC 34-(N-1). The histogram generator 171-(N-1) supplies the generated histogram to the center of gravity calculator 172-(N-1).

[0121] The centroid calculation unit 172-(N-1) calculates the centroid of the count value by performing a centroid calculation on the histogram supplied from the histogram generation unit 171-(N-1). The centroid calculation unit 172-(N-1) supplies the centroid of the count value to the subtraction unit 151-(N-1).

[0122] The subtraction unit 151-(N-1) calculates the skew between the TDC 34-(N-1) and the reference TDC 34-N by subtracting the reference center of gravity value supplied from the center of gravity calculation unit 172-N from the center of gravity value of the count value supplied from the center of gravity calculation unit 172-(N-1).

[0123] Even when the correction value is calculated using a histogram, the correction value is expressed in time units less than the time resolution of the TDC 34 .

[0124] It should be noted that the histogram of the count values ​​based on the measurement signals may be generated by the histogram generation unit 46 instead of by the histogram generation unit 171 and supplied to the centroid calculation unit 172 .

[0125] FIG. 13 is a block diagram showing an example of the configuration of the correction unit 123.

[0126] As shown in FIG. 13, the correction unit 123 includes an adder 201 and an adder-subtractor 202 .

[0127] In the correction unit 123, the correction value expressed in time units less than the time resolution of the TDC 34 is not directly added to or subtracted from the count value, but rather the actual correction value expressed in time units the same as the time resolution of the TDC 34 is added to or subtracted from the count value.

[0128] In the direct ToF distance measuring device 11, light is emitted multiple times during an exposure period. The correction unit 123 utilizes the fact that light is emitted multiple times during the exposure period, in other words, that a count value based on a detection signal is output multiple times from the TDC 34, and dynamically changes the actual correction value so that the average value during the exposure period is equal to the correction value expressed in time units less than the time resolution of the TDC 34.

[0129] The actual correction value is composed of an integer part, which is a fixed value, and a decimal part, which changes dynamically during the exposure period. For example, if the correction value is 5.4 LSB, the integer part of the actual correction value is set as a fixed value of 5 LSB, and the decimal part of the actual correction value is set as a variable value that becomes +1 LSB or +0 LSB at a ratio of 2:3.

[0130] As described above, the decimal part of the actual correction value may be set as a variable value that becomes +1 LSB or +0 LSB at a predetermined ratio, or may be set as a variable value that becomes -1 LSB or +0 LSB at a predetermined ratio.

[0131] The adder 201 adds the integer part and the decimal part supplied from the correction value calculator 122 together to obtain an actual correction value, and supplies the result to the adder / subtractor 202 .

[0132] The adder / subtractor 202 performs a correction process by adding or subtracting the actual correction value supplied from the adder 201 to the count value output from the TDC 34 based on the detection signal, and supplies the corrected count value to the histogram generator 36.

[0133] FIG. 14 is a diagram showing an example of the integer part and the decimal part of the actual correction value.

[0134] As shown in the upper part of Figure 14, when the correction value is 5.4 LSB, the integer part is set to a fixed value of 5 LSB, and the decimal part is set to a variable value that becomes +1 LSB or +0 LSB in a ratio of 2:3 (variable value with an average value of 0.4 LSB).

[0135] For example, the decimal part of the first count during the exposure period will be +0 LSB, the decimal part of the second count will be +1 LSB, the decimal part of the third count will be +0 LSB, the decimal part of the fourth count will be +1 LSB, and the decimal part of the fifth count will be +0 LSB. Therefore, an actual correction value of 5 LSB is added to or subtracted from the first count value during the exposure period, an actual correction value of 6 LSB is added to or subtracted from the second count value, an actual correction value of 5 LSB is added to or subtracted from the third count value, an actual correction value of 6 LSB is added to or subtracted from the fourth count value, and an actual correction value of 5 LSB is added to or subtracted from the fifth count value.

[0136] As shown in the lower part of Figure 14, when the correction value is 5.625 LSB, the integer part is set to a fixed value of 5 LSB, and the decimal part is set to a variable value that becomes +1 LSB or +0 LSB at a ratio of 5:3 (variable value with an average value of 0.625 LSB).

[0137] For example, the decimal part of the first count during the exposure period will be +1 LSB, the decimal part of the second count will be +0 LSB, the decimal part of the third count will be +1 LSB, the decimal part of the fourth count will be +0 LSB, the decimal part of the fifth count will be +1 LSB, the decimal part of the sixth count will be +1 LSB, the decimal part of the seventh count will be +0 LSB, and the decimal part of the eighth count will be +1 LSB. Therefore, an actual correction value of 6 LSB is added to or subtracted from the first count value during the exposure period, an actual correction value of 5 LSB is added to or subtracted from the second count value, an actual correction value of 6 LSB is added to or subtracted from the third count value, and an actual correction value of 5 LSB is added to or subtracted from the fourth count value. An actual correction value of 6 LSB is added to or subtracted from the fifth count value, an actual correction value of 6 LSB is added to or subtracted from the sixth count value, an actual correction value of 5 LSB is added to or subtracted from the seventh count value, and an actual correction value of 6 LSB is added to or subtracted from the eighth count value.

[0138] As described above, the actual correction value added to or subtracted from the output of TDC 34 during the exposure period of the light receiving element can be said to be a fluctuating value that fluctuates so that the average value during the exposure period becomes equal to the correction value expressed in time units less than the time resolution of TDC 34.

[0139] During the exposure period, the correction unit 123 adds or subtracts such actual correction value to the output (count value) of the TDC 34, thereby being able to correct the output of the TDC 34 with an accuracy less than the time resolution of the TDC 34 when viewed as the histogram as a whole.

[0140] In the technology described in Patent Document 1, correction is performed on the histogram, so when a single histogram is generated based on the outputs of multiple TDCs, it is not possible to correct errors due to skew between the TDCs. If errors due to skew between the TDCs are not corrected, the peaks of the histogram will be dispersed, and the signal-to-noise (SN) ratio of the histogram will decrease.

[0141] On the other hand, in the present technology, correction is performed on the count value before it is counted up in the histogram, so even when one histogram is generated based on the outputs of multiple TDCs 34, errors caused by skew between TDCs 34 can be corrected.

[0142] FIG. 15 is a diagram showing an example of the configuration of the pixel 41.

[0143] As shown in FIG. 15, the pixel 41 includes a SPAD 221 , a constant current source 222 , and an input amplifier (inverter) 223 .

[0144] The cathode of the SPAD 221 is connected to the constant current source 222 and also to the input terminal of the input amplifier 223. The anode of the SPAD 221 is connected to the power supply voltage VSPAD.

[0145] The SPAD 221 is a photodiode that avalanches electrons generated when incident light is incident thereon, and outputs a cathode voltage signal. The power supply voltage VSPAD supplied to the anode of the SPAD 221 is set to, for example, a negative bias (negative potential) that is the same voltage as the breakdown voltage VBD of the SPAD 221.

[0146] The SPAD 221 has the property that when a large negative voltage that generates avalanche amplification is applied to the cathode, the electrons generated in response to the incidence of a single photon cause avalanche amplification, resulting in a large current flow. By utilizing this property of the SPAD 221, the incidence of a single photon can be detected with high sensitivity.

[0147] The constant current source 222 is configured, for example, with a P-type MOS (Metal Oxide Semiconductor) transistor that operates in the saturation region and performs passive quenching by acting as a quenching resistor. A power supply voltage VH (VH>0) is supplied to the constant current source 222. Note that a pull-up resistor or the like can also be used as the constant current source 222 instead of a P-type MOS transistor.

[0148] To detect photons with sufficient efficiency, a voltage (hereinafter referred to as excess bias) greater than the breakdown voltage VBD of the SPAD 221 is applied to the SPAD 221. By applying a reverse voltage greater than the breakdown voltage VBD to the SPAD 221, the SPAD 221 is set to Geiger mode. In this state, the cathode voltage of the SPAD 221 is the same as the power supply voltage VH.

[0149] When a photon is incident on the SPAD 221 set to the Geiger mode, avalanche amplification occurs, and a current flows through the SPAD 221. If avalanche amplification occurs and a current flows through the SPAD 221, the current flowing through the SPAD 221 also causes a current to flow through the constant current source 222, and a voltage drop occurs due to the resistance component of the constant current source 222.

[0150] When the cathode voltage of the SPAD 221 falls below 0 V, the anode-cathode voltage of the SPAD 221 falls below the breakdown voltage VBD, and avalanche amplification stops. Here, a current generated by avalanche amplification flows to the constant current source 222, causing a voltage drop. As a result of this voltage drop, the anode-cathode voltage of the SPAD 221 falls below the breakdown voltage VBD, and this operation, which stops avalanche amplification, is the quench operation.

[0151] When the avalanche amplification stops, the current flowing through the constant current source 222 gradually decreases, the cathode voltage returns to the original power supply voltage VH, and the next new photon can be detected (recharge operation).

[0152] The input amplifier 103 compares the cathode voltage of the SPAD 221 as an input signal with a threshold voltage Vth, and outputs a low detection signal when the cathode voltage is equal to or greater than the threshold voltage Vth, and outputs a high detection signal when the cathode voltage is less than the threshold voltage Vth.

[0153] <3. Modifications> Example in which a second MUX is provided between a pixel readout circuit and a TDC For the purposes of reducing the number of TDCs 34 provided in the photodetection device 23 and improving the degree of freedom in setting a region of interest (ROI), a second MUX that switches the connection between the pixel readout circuit (first MUX 33) and the TDC 34 may be provided in the photodetection device 23.

[0154] Fig. 16 is a diagram showing a first modified example of the configuration of the photodetector 23. In Fig. 16, the same components as those in Fig. 2 are denoted by the same reference numerals. Duplicate explanations will be omitted where appropriate.

[0155] 2 in that M (N>M) series including TDCs 34, arithmetic circuits 35, and histogram generators 36 are provided, and that a second MUX 251 is provided between first MUXes 33-1 to 33-N and TDCs 34-1 to 34-M. In the example of Fig. 16, at least one signal path between a pixel row and a TDC 34 and at least one first MUX 33 that inputs a measurement signal to the signal path are provided corresponding to each of the M TDCs 34.

[0156] The second MUX 251 connects the first MUX 33 corresponding to the active pixel to one of the TDCs 34-1 to 34-M in accordance with switching between active pixels and inactive pixels in the pixel array unit 31. In other words, the second MUX 251 supplies the detection signal output from the active pixel via the first MUX 33 to the TDC 34 corresponding to that first MUX 33.

[0157] The second MUX 251 also supplies the measurement signals input by the measurement signal generator 32 via the first MUX 33-1 to the first MUX 33-N to the TDCs 34 corresponding to the first MUX 33-1 to the first MUX 33-N, respectively.

[0158] The TDC 34 counts a count value indicating a signal propagation delay in the signal path from the input terminal of the second MUX 251 to the TDC 34, based on the synchronization signal input from the measurement signal generator 32 and the measurement signal supplied from the first MUX 33 via the second MUX 251. The TDC 34 supplies the count value to the arithmetic circuit 35 in the subsequent stage.

[0159] The calculation circuit 35 calculates the skew between the TDCs 34 that occurs during signal transmission from the input terminal of the second MUX 251 to the TDC 34 based on the count value based on the measurement signal supplied from the TDC 34, and calculates a correction value that corrects the error due to the skew between the TDCs 34 that is included in the count value based on the detection signal.

[0160] As described above, by providing the first MUX 33 on the input side of the second MUX 251, the calculation circuit 35 can calculate the skew between the TDCs 34 that occurs in signal transmission from the input terminal of the second MUX 251 to the TDC 34 during the propagation delay measurement period, and can correct the error due to the skew contained in the count value during the exposure period.

[0161] By providing a second MUX 251 between the pixel readout circuit (first MUX 33) and the TDC 34, it is possible to increase the number of pixels 41 that are simultaneously active pixels and to arrange the active pixels to correspond to various light source devices 22.

[0162] FIG. 17 is a diagram illustrating an example of an arrangement of active pixels corresponding to various light source devices 22. In FIG.

[0163] For example, when a spot light source is used as the light source device 22, a plurality of spot-shaped reflected light beams are incident on the pixel array unit 31, as shown by gray circles in A of Fig. 17. In this case, only the pixel 41 on which the spot-shaped reflected light beams are incident is set as an active pixel.

[0164] For example, when a flood light is used as the light source device 22, rectangular reflected light is incident on approximately the center of the pixel array section 31, as shown by the gray rectangle in Fig. 17B. In this case, only the pixel 41 at approximately the center of the pixel array section 31 on which the rectangular reflected light is incident is set as the active pixel.

[0165] For example, when a line light source is used as the light source device 22, a strip of reflected light is incident on the pixel array unit 31, as shown by the vertically long gray rectangle in Fig. 17C. In this case, only the pixel 41 on which the strip of reflected light is incident is set as an active pixel.

[0166] - Example in which the first MUX is provided inside the pixel readout circuit Figure 18 is a diagram showing a second modified example of the configuration of the photodetector 23. In Figure 18, the same components as those in Figure 16 are assigned the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0167] The photodetector 23 in FIG. 18 differs from the photodetector 23 in FIG. 16 in that a first MUX 33 (not shown) is provided inside the pixel readout circuit.

[0168] In the example of FIG. 18, a tree-type circuit network is formed by the measurement signal generating unit 32 and the first MUX 33 in the pixel readout circuit, and the measurement signal is transmitted within this circuit network.

[0169] The second MUX 251 connects the active pixel to one of the TDCs 34-1 to 34-M in accordance with switching between active and inactive pixels in the pixel array unit 31. In other words, the second MUX 251 supplies the detection signal output from the active pixel to the TDC 34 corresponding to the pixel 41 that is set as the active pixel.

[0170] Furthermore, the second MUX 251 supplies the measurement signals input via the first MUX 33 inside each pixel readout circuit to the TDC 34 corresponding to each pixel 41 .

[0171] Fig. 19 is a diagram showing an example of the configuration of a pixel 41 when the first MUX is provided inside the pixel readout circuit. In Fig. 19, the same components as those in Fig. 15 are denoted by the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0172] The pixel 41 in FIG. 19 differs from the pixel 41 in FIG. 15 in that a first MUX 271 corresponding to the first MUX 33 is provided in the subsequent stage of the input amplifier 223 .

[0173] The first MUX 271 outputs the detection signal output from the input amplifier 223 during the exposure period, and outputs the measurement signal input by the measurement signal generator 32 during the propagation delay measurement period.

[0174] By providing the first MUX 271 after the input amplifier 223, the calculation circuit 35 can calculate the skew between the TDCs 34 in the signal transmission from the output terminal of the input amplifier 223 to the TDC 34 during the propagation delay measurement period, and can correct the error due to the skew contained in the count value during the exposure period. Since the range of the signal path for which skew is measured increases, it is expected that the variation in distance measurement accuracy will be further improved.

[0175] Fig. 20 is a diagram showing another example of the configuration of a pixel 41 when the first MUX is provided inside the pixel readout circuit. In Fig. 20, the same components as those in Fig. 15 are denoted by the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0176] The pixel 41 in FIG. 20 differs from the pixel 41 in FIG. 15 in that a transistor 291 and a first MUX 292 corresponding to the first MUX 33 are provided.

[0177] The drain of the transistor 291 is connected to the cathode of the SPAD 221, the constant current source 222, and the input terminal of the input amplifier 223, and the source is connected to a power supply voltage VS (Vth>VS). The gate of the transistor 291 is connected to the output terminal of the first MUX 292.

[0178] The first MUX 292 supplies a disable signal to the gate of the transistor 291 during the exposure period, and supplies the measurement signal input by the measurement signal generating unit 32 to the gate of the transistor 291 during the propagation delay measurement period.

[0179] During the exposure period, a disable signal is supplied to the gate of the transistor 291, so that the transistor 291 is set to off. During the propagation delay measurement period, a measurement signal is supplied to the gate of the transistor 291. When a high measurement signal is supplied to the gate of the transistor 291, the transistor 291 is set to on. As a result, the cathode voltage of the SPAD 221 becomes the same as the power supply voltage VS, and the input amplifier 103 outputs a high signal.

[0180] In this way, during the propagation delay measurement period, the input amplifier 223 outputs a signal synchronized with the measurement signal.

[0181] By providing the first MUX 292 in the stage preceding the input amplifier 223, the calculation circuit 35 can calculate the skew between the TDCs 34 in the signal transmission from the input terminal of the input amplifier 223 to the TDC 34 during the propagation delay measurement period, and can correct the error due to the skew contained in the count value during the exposure period. Since the range of the signal path for measuring skew is increased, it is expected that the variation in distance measurement accuracy will be further improved.

[0182] An example of performing a correction process to correct a propagation delay of a signal inside the second MUX 251. Fig. 21 is a diagram showing a third modified example of the configuration of the photodetector 23. In Fig. 21, the same components as those in Fig. 16 are assigned the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0183] The photodetector 23 of FIG. 21 differs from the photodetector 23 of FIG. 2 in that third MUXes 331-1 to 331-M that correspond one-to-one to the TDCs 34-1 to 34-M are provided after the second MUX 251.

[0184] Hereinafter, when there is no need to particularly distinguish between the third MUXes 331-1 to 331-M, they will be simply referred to as the third MUXes 331.

[0185] A measurement signal is input to the first MUX 33 from the measurement signal generator 32 via a signal line 312. The measurement signal originating from the first MUX 33 is a signal for measuring the propagation delay of a signal in a signal path from the input terminal of the second MUX 251 to the TDC 34. The first MUX 33 outputs the detection signal output from the pixel 41 during the exposure period, and outputs the measurement signal input from the measurement signal generator 32 during the propagation delay measurement period.

[0186] The second MUX 251 connects the first MUX 33 corresponding to the active pixel to one of the third MUXTDCs 311-1 to 311-M in accordance with switching between active pixels and inactive pixels in the pixel array unit 31. In other words, the second MUX 251 supplies the detection signal output by the active pixel via the first MUX 33 to the third MUX 311 in the preceding stage of the TDC 34 corresponding to that first MUX 33.

[0187] The second MUX 251 also supplies the measurement signal originating from the first MUX 33 to a third MUX 311 located in the preceding stage of the TDC 34 corresponding to the first MUX 33 .

[0188] A measurement signal is input to the third MUX 311 by the measurement signal generator 32 via a signal line 313. The measurement signal originating from the third MUX 311 is a signal for measuring the propagation delay of the signal in the signal path from the output terminal of the second MUX 251 to the TDC 34.

[0189] During the exposure period, the third MUX 311 supplies the detection signal supplied via the second MUX 251 to the downstream TDC 34. During the propagation delay measurement period, the third MUX 311 supplies the measurement signal supplied via the second MUX 241 or the measurement signal input by the measurement signal generator 32 to the downstream TDC 34.

[0190] The TDC 34 counts a count value indicating the time from when the light source device 22 emits light to when the pixel 41 receives light, based on the light emission timing signal and the detection signal supplied from the third MUX 311 .

[0191] In addition, the TDC 34 counts a count value indicating the signal propagation delay in the signal path from the input terminal of the second MUX 251 to the TDC 34 based on the synchronization signal supplied from the measurement signal generating unit 32 and the measurement signal originating from the first MUX 33 supplied from the third MUX 311.

[0192] Furthermore, the TDC 34 counts a count value indicating the signal propagation delay in the signal path from the output terminal of the second MUX 251 to the TDC 34 based on the synchronization signal and the measurement signal supplied from the third MUX 311 and originating from the third MUX 311.

[0193] The arithmetic circuit 35 performs a correction process to subtract from the count value based on the detection signal a correction value included in the count value that corrects the propagation delay of the signal inside the second MUX 251. Furthermore, the arithmetic circuit 35 calculates the propagation delay of the signal inside the second MUX 251 based on the count value based on the measurement signal originating from the first MUX 33-1 and the count value based on the measurement signal originating from the third MUX 33-3, both of which are supplied from the TDC 34, and calculates a correction value that corrects the propagation delay.

[0194] Fig. 22 is a diagram showing an example of the configuration of the propagation delay measurement unit 121 and the correction value calculation unit 122 of the arithmetic circuit 35 when correcting the propagation delay of a signal inside the second MUX 251. In Fig. 22, the same components as those in Fig. 9 are assigned the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0195] The arithmetic circuit 35 in FIG. 22 differs from the arithmetic circuit 35 in FIG. 9 in that measurement result holding units 351 and 352 are provided in front of the subtraction unit 151 in the correction value calculation unit 122 .

[0196] The TDC 34 counts a count value based on a measurement signal originating from the first MUX 33 and supplies the count value to the accumulator 141. The TDC 34 also counts a count value based on a measurement signal originating from the third MUX 331 and supplies the count value to the accumulator 141.

[0197] The accumulator 141 calculates the cumulative sum of the count values ​​based on the measurement signal originating from the first MUX 33 and the cumulative sum of the count values ​​based on the measurement signal originating from the third MUX 331 .

[0198] The divider 142 divides the cumulative sum of the count values ​​based on the measurement signals originating from the first MUX 33 by the number of times the measurement signal generator 32 has input the measurement signals originating from the first MUX 33, thereby calculating the average value of the count values ​​based on the measurement signals originating from the first MUX 33. The divider 142 supplies the average value of the count values ​​based on the measurement signals originating from the first MUX 33 to the measurement result holder 351.

[0199] The divider 142 also divides the cumulative sum of the count values ​​based on the measurement signals originating from the third MUX 331 by the number of times the measurement signal generator 32 has input the measurement signals originating from the third MUX 331, thereby calculating the average value of the count values ​​based on the measurement signals originating from the third MUX 331. The divider 142 supplies the average value of the count values ​​based on the measurement signals originating from the third MUX 331 to the measurement result holder 352.

[0200] The measurement result holding unit 351 holds the average value of the count values ​​based on the measurement signal, which is supplied from the division unit 142 and originates from the first MUX 33 .

[0201] The measurement result holding unit 352 holds the average value of the count values ​​based on the measurement signal, which is supplied from the division unit 142 and originates from the third MUX 331 .

[0202] The subtraction unit 151 obtains the average value of the count value based on the measurement signal starting from the first MUX 33 from the measurement result holding unit 351, and obtains the average value of the count value based on the measurement signal starting from the third MUX 331 from the measurement result holding unit 352.

[0203] The subtraction unit 151 calculates the propagation delay of the signal inside the second MUX 251 by subtracting the average value of the count values ​​based on the measurement signal originating from the first MUX 33 by the average value of the count values ​​based on the measurement signal originating from the third MUX 331. The subtraction unit 151 supplies the propagation delay of the signal inside the second MUX 251 to the correction value holding unit 152 as a correction value.

[0204] In the example of Figure 22, an example of calculating the correction value using an accumulator is described, but even when correcting the propagation delay of a signal inside the second MUX 251, it is possible to calculate the correction value using a histogram.

[0205] As described above, when correcting the propagation delay of a signal inside the second MUX 251, there is no need to calculate the skew between the TDCs 34, and therefore the calculation of the correction value can be completed within one arithmetic circuit 35. Therefore, there is no need to provide the photodetector 23 with a signal path that distributes the measurement result of the propagation delay to the reference TDC to multiple arithmetic circuits 35.

[0206] 23 is a block diagram showing an example of the configuration of the photodetector 23 when the correction of the error caused by the skew between the TDCs 34 is performed after the histogram generation. Note that Fig. 23 shows the configuration of the photodetector 23 after the TDC 34.

[0207] As shown in FIG. 23, the photodetector 23 includes a TDC 34 , a propagation delay measurement unit 121 , a correction value calculation unit 122 , a histogram generation unit 36 ​​, a depth calculation unit 371 , and a correction unit 123 .

[0208] The TDC 34 supplies a count value based on the measurement signal to the propagation delay measurement unit 121 and supplies a count value based on the detection signal to the histogram generation unit 36 ​​.

[0209] The propagation delay measurement unit 121 measures the propagation delay of the signal in at least a part of the signal path from the pixel 41 to the TDC 34, based on a count value based on the measurement signal as an output of the TDC 34. The propagation delay measurement unit 121 supplies the measurement result of the propagation delay to the correction value calculation unit 122.

[0210] The correction value calculation unit 122 calculates the skew between the TDC 34 and the reference TDC based on the measurement result of the propagation delay by the propagation delay measurement unit 121 and the measurement result of the reference propagation delay. Based on the calculation result of the skew between the TDC 34 and the reference TDC, the correction value calculation unit 122 calculates and stores a correction value for correcting the error due to the skew contained in the distance information, and supplies the correction value to the correction unit 123 at a predetermined timing during the exposure period.

[0211] The histogram generating unit 36 ​​generates a histogram for each pixel 41 based on the count value based on the detection signal as the output of the TDC 34 , and supplies the histogram for each pixel 41 to the depth calculating unit 371 .

[0212] The depth calculation unit 371 calculates the distance D to the object Obj for each pixel 41 based on the histogram supplied from the histogram generation unit 36. For example, the depth calculation unit 371 performs a centroid calculation on the histogram to calculate the centroid value of the count value, and calculates the distance D based on the centroid value of the count value. The depth calculation unit 371 supplies distance information indicating the distance D for each pixel to the correction unit 123.

[0213] The correction unit 123 performs correction processing to add or subtract the correction value supplied from the correction value calculation unit 122 to the distance information supplied from the depth calculation unit 371. The correction unit 123 supplies the corrected distance information to the control unit 21.

[0214] The depth calculation unit 371 and the correction unit 123 may be provided within a semiconductor chip that constitutes the photodetection device 23, or may be provided in the control unit 21 or application unit 12 downstream of the photodetection device 23. When the depth calculation unit 371 and the correction unit 123 are provided in the control unit 21 or application unit 12, the histogram and correction value are transmitted between the semiconductor chip and the control unit 21 or application unit 12.

[0215] As described above, it is possible to correct errors due to skew between TDCs 34 not only on the count values ​​output from TDCs 34 but also on the distance information calculated based on the histogram output from histogram generator 36.

[0216] Example of the substrate configuration of the photodetector 23 FIG. 24 is a perspective view showing an example of the substrate configuration of the photodetector 23.

[0217] The photodetector 23 is configured as a semiconductor substrate 400 (semiconductor chip), for example, as shown in FIG.

[0218] The semiconductor substrate 400 is formed with a pixel array section 31 in which a plurality of pixels 41 are arranged two-dimensionally in a matrix, as well as a measurement signal generating section 32, a MUX 33, a TDC 34, an arithmetic circuit 35, a histogram generating section 36, etc. (not shown).

[0219] FIG. 25 is a perspective view showing another example of the substrate configuration of the photodetector 23. In FIG.

[0220] 25A, the photodetector 23 is configured as a semiconductor chip having a stacked structure of two substrates, a pixel substrate 401 and a circuit substrate 411. The upper surface of the pixel substrate 401 is the light incident surface, and reflected light L2 is incident on the pixel substrate 401 from above.

[0221] A pixel array region 403 is formed on the pixel substrate 401, in which a plurality of pixels 402, each including a SPAD 221, are two-dimensionally arranged in a matrix.

[0222] A pixel array lower region 413 in which predetermined processing circuits 412 are two-dimensionally arranged is formed on the circuit substrate 411. The processing circuits 412 may or may not be provided in one-to-one correspondence with the pixels 402 on the pixel substrate 401. The processing circuits 412 are electrically connected to the pixels 402 above. There are no particular limitations on the type of circuit provided as the processing circuit 412 on the circuit substrate 411. In the pixel array lower region 413, part or all of the pixel readout circuit may be disposed, or components other than the pixel readout circuit, such as the measurement signal generator 32, MUX 33, TDC 34, arithmetic circuit 35, and histogram generator 36, may also be disposed.

[0223] The photodetector 23 may be configured as a semiconductor chip having a stacked structure of three or more substrates.

[0224] The photodetector 23 is configured as a semiconductor chip having a stacked structure of three substrates, with a pixel substrate 421 added between the pixel substrate 401 and the circuit substrate 411, as shown in FIG. 25B, for example.

[0225] A pixel array lower region 423 in which pixel readout circuits 422 are two-dimensionally arranged in a matrix is ​​formed on the pixel substrate 421. The pixel readout circuits 422 are provided in one-to-one correspondence with the pixels 41 of the pixel substrate 401 and are electrically connected to the pixels 41 above. The pixel readout circuits 422 are arranged in a region overlapping with the pixels 402 above in a planar view, and the pixel array lower region 423 is also a region overlapping with the pixel array unit 31 of the pixel substrate 401 in a planar view.

[0226] The processing circuits 412 on the circuit board 411 may or may not be provided in one-to-one correspondence with the pixel readout circuits 422 on the pixel board 421. The processing circuit 412 is electrically connected to the pixel readout circuit 422 above. A portion of the pixel readout circuit 422 corresponding to the pixel 402 may be disposed in the region 413 below the pixel array.

[0227] As described above, by configuring the photodetector 23 as a single semiconductor chip, it becomes possible to correct errors caused by skew between TDCs 34 on-chip in real time.

[0228] By configuring the photodetector 23 with a stacked structure of three substrates, there is more space for circuit layout on the pixel substrate 401, which makes it possible to reduce the chip area and extend the distance measurement range.In addition, it becomes possible to miniaturize pixels without increasing the chip area.

[0229] - Example in which the first MUX is provided inside the pixel readout circuit of the measurement pixel Figure 26 is a diagram showing a fourth modified example of the configuration of the photodetector 23. In Figure 26, the same components as those in Figure 18 are assigned the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0230] The photodetector 23 of FIG. 26 differs from the photodetector 23 of FIG. 18 in that a first MUX 33 (not shown) is provided inside the pixel readout circuit (measurement circuit) of the measurement pixel 501 .

[0231] The pixel array unit 31 is provided with a measurement pixel column 501A made up of measurement pixels 501 arranged in the column direction, for example. In the example of Fig. 26 , the measurement pixel column 501A is arranged at the far end of the pixel array unit 31, away from the second MUX 251 (TDC 34), and the measurement pixel 501 is connected to, for example, the far end of the horizontal signal line of the pixel array unit 31, away from the second MUX 251. In other words, the measurement pixel 501 is connected to the signal path from each pixel 41 to the TDC 34, at a stage preceding each pixel 41.

[0232] The measurement pixels 501 are configured by pixels including a light receiving element and a pixel readout circuit, dummy pixels including a pixel readout circuit, etc. The pixel readout circuit of the measurement pixels 501 includes a first MUX 33 that inputs a measurement signal to a signal path from each pixel 41 to the TDC 34. In the example of Fig. 26, the measurement signal is transmitted from the measurement signal generator 32 to the pixel readout circuit of each measurement pixel 501 via a tree-type circuit network 511.

[0233] FIG. 27 is a diagram for explaining the flow of signals during an exposure period when measurement pixels are provided in the pixel array section 31. In FIG.

[0234] 27 , detection signals output from the pixels 41 in one row of the pixel array unit 31 excluding the measurement pixels 501 are input to the TDC 34 corresponding to that pixel row via the second MUX 251, and the TDC 34 counts a count value based on the detection signals. Thereafter, the count value based on the detection signals is supplied from the TDC 34 to the arithmetic circuit 35, and the arithmetic circuit 35 performs a correction process on the count value based on the detection signals.

[0235] FIG. 28 is a diagram for explaining the flow of signals during the propagation delay measurement period when measurement pixels are provided in the pixel array section 31.

[0236] During a propagation delay measurement period before the exposure period, as indicated by the bold arrow in FIG. 28 , a measurement signal generated by the measurement signal generator 32 is input to the pixel readout circuit of the measurement pixel 501. The pixel readout circuit of the measurement pixel 501 then inputs the measurement signal to a signal path from the measurement pixel 501 to the TDC 34 corresponding to the pixel row including the measurement pixel 501, and the TDC 34 counts a count value based on the measurement signal. The count value based on the measurement signal is supplied from the TDC 34 to the arithmetic circuit 35, and the arithmetic circuit 35 calculates a correction value used in the correction process based on the count value based on the measurement signal. Here, a correction value is calculated for each pixel 41. Methods for calculating the correction value include a method using an accumulator and a method using a histogram.

[0237] FIG. 29 is a diagram showing an example of the configuration of the arithmetic circuit 35 when measurement pixels are provided in the pixel array section 31.

[0238] 29, the arithmetic circuit 35-1 is configured with a propagation delay measurement unit 121-1 and a correction value calculation unit 122-1, and the correction value calculation unit 122-1 is configured with a pixel-by-pixel propagation delay calculation unit 531-1, a subtraction unit 151-1, and a correction value holding unit 152-1. Also, the arithmetic circuit 35-(M-1) is configured with a propagation delay measurement unit 121-(M-1) and a correction value calculation unit 122-(M-1), and the correction value calculation unit 122-(M-1) is configured with a pixel-by-pixel propagation delay calculation unit 531-(M-1), a subtraction unit 151-(M-1), and a correction value holding unit 152-(M-1). Furthermore, the arithmetic circuit 35-M is composed of a propagation delay measurement unit 121-M and a correction value calculation unit 122-M, and the correction value calculation unit 122-M is composed of a pixel-by-pixel propagation delay calculation unit 531-M, a subtraction unit 151-M, and a correction value holding unit 152-M.

[0239] Hereinafter, when there is no need to particularly distinguish between the pixel-by-pixel propagation delay calculation units 531-1 to 531-M, they will simply be referred to as pixel-by-pixel propagation delay calculation units 531.

[0240] In the example of FIG. 29, the TDC 34-M is the reference TDC, and the calculation circuit 35-M is the reference calculation circuit.

[0241] The reference TDC 34-M counts a count value based on the measurement signal input via the measurement pixel 501 corresponding to the reference TDC 34-M and the second MUX 251, and supplies the count value to the propagation delay measurement unit 121-M.

[0242] The propagation delay measurement unit 121-M measures the propagation delay of the signal in the signal path from the measurement pixel 501 to the reference TDC 34-M based on a count value based on the measurement signal as an output of the reference TDC 34-M in the preceding stage. The propagation delay measurement unit 121-M supplies the measurement result of the propagation delay to the pixel-by-pixel propagation delay calculation unit 531-M.

[0243] Based on the measurement results of the signal propagation delay in the signal path from the measurement pixel 501 to the reference TDC 34-M by the propagation delay measurement unit 121-M, the pixel-by-pixel propagation delay calculation unit 531-M calculates the signal propagation delay in the signal path from each pixel 41 connected to the signal path, in other words, from each pixel 41 in the same pixel row as the measurement pixel 501 to the reference TDC 34-1.

[0244] 30 , the pixel-by-pixel propagation delay calculation unit 531 has information (e.g., a function or a table) indicating the relationship between the propagation delay Tpd in the signal path from the measurement pixel 501 to the TDC 34 and the propagation delay Tpd in the signal path from each pixel 41 in the same pixel row as the measurement pixel 501 to the TDC 34. In the example of Fig. 30 , the propagation delay Tpd from the measurement pixel 501 is proportional to the propagation delay Tpd from the pixel 41. The relationship between the propagation delay Tpd from the measurement pixel 501 and the propagation delay Tpd from the pixel 41 is determined in advance by simulation, testing before shipping from the factory, or the like.

[0245] For example, the pixel-by-pixel propagation delay calculation unit 531-M calculates the signal propagation delay in the signal path from each pixel 41 to the reference TDC 34-1 based on the propagation delay measurement results by the propagation delay measurement unit 121-M and information indicating the relationship between the propagation delay Tpd from the measurement pixel 501 and the propagation delay Tpd from the pixel 41.

[0246] The pixel-by-pixel propagation delay calculation unit 531 may calculate (estimate) the propagation delay of the signal on the signal path from each pixel 41 to the reference TDC 34-1 by inputting the measurement results of the propagation delay by the propagation delay measurement unit 121-M into a learning model obtained by machine learning. In this way, the pixel-by-pixel propagation delay calculation unit 531 functions as an estimation unit that estimates the propagation delay of the signal on the signal path from each pixel 41 to the TDC 34.

[0247] 29 , the pixel-by-pixel propagation delay calculation unit 531-M supplies the calculation results of the propagation delay in the signal path from each pixel 41 to the reference TDC 34-M to the subtraction unit 151-M. In addition, the pixel-by-pixel propagation delay calculation unit 531-M supplies the measurement results of the propagation delay in the signal path from the measurement pixel 51 to the reference TDC 34-1 (hereinafter also referred to as the reference propagation delay) to the subtraction units 151-1 to 151-M.

[0248] The subtraction unit 151-M calculates the skew between the signal path from each pixel 41 to the reference TDC 34-M and the signal path from the measurement pixel 501 to the reference TDC 34-M by subtracting the reference propagation delay from the propagation delay in the signal path from each pixel 41 to the reference TDC 34-M. The subtraction unit 151-M supplies the skew between the signal paths as a correction value to the correction value holding unit 152-M.

[0249] The correction value holding unit 152-M holds the correction value supplied from the subtraction unit 151-M.

[0250] The TDC 34-1 counts a count value based on the measurement signal input via the measurement pixel 501 corresponding to the TDC 34-1 and the second MUX 251, and supplies the count value to the propagation delay measurement unit 121-1.

[0251] The propagation delay measurement unit 121-1 measures the propagation delay of the signal in the signal path from the measurement pixel 501 to the TDC 34-1 based on a count value based on the measurement signal as an output of the preceding TDC 34-1. The propagation delay measurement unit 121-1 supplies the measurement result of the propagation delay to the pixel-by-pixel propagation delay calculation unit 531-1.

[0252] Based on the measurement result of the signal propagation delay in the signal path from the measurement pixel 501 to the TDC 34-1 by the propagation delay measurement unit 121-1, the pixel-by-pixel propagation delay calculation unit 531-1 calculates the signal propagation delay in the signal path from each pixel 41 connected to the signal path, in other words, from each pixel 41 in the same pixel row as the measurement pixel 501 to the TDC 34-1. The pixel-by-pixel propagation delay calculation unit 531-1 supplies the calculation result of the propagation delay in the signal path from each pixel 41 to the TDC 34-1 to the subtraction unit 151-1.

[0253] The subtraction unit 151-1 calculates the skew between the signal path from each pixel 41 to the TDC 34-1 and the signal path from the measurement pixel 501 to the reference TDC 34-M by subtracting the reference propagation delay from the propagation delay in the signal path from each pixel 41 to the TDC 34-1. The subtraction unit 151-1 supplies the skew between the signal paths as a correction value to the correction value holding unit 152-1.

[0254] The correction value holding unit 152-1 holds the correction value supplied from the subtraction unit 151-1.

[0255] The TDC 34-(M-1) counts a count value based on the measurement pixel 501 corresponding to the TDC 34-(M-1) and the measurement signal input via the second MUX 251, and supplies the count value to the propagation delay measurement unit 121-(M-1).

[0256] The propagation delay measurement unit 121-(M-1) measures the propagation delay of the signal in the signal path from the measurement pixel 501 to the TDC 34-(M-1) based on a count value based on the measurement signal as an output of the preceding TDC 34-(M-1). The propagation delay measurement unit 121-(M-1) supplies the measurement result of the propagation delay to the pixel-by-pixel propagation delay calculation unit 531-(M-1).

[0257] The pixel-by-pixel propagation delay calculation unit 531-(M-1) calculates the signal propagation delay in the signal path from the measurement pixel 501 to the TDC 34-(M-1) based on the measurement result of the signal propagation delay in the signal path from the measurement pixel 501 to the TDC 34-(M-1) by the propagation delay measurement unit 121-(M-1). The pixel-by-pixel propagation delay calculation unit 531-(M-1) supplies the calculation result of the propagation delay in the signal path from each pixel 41 to the TDC 34-(M-1) to the subtraction unit 151-(M-1).

[0258] The subtraction unit 151-(M-1) calculates the skew between the signal path from each pixel 41 to the TDC 34-(M-1) and the signal path from the measurement pixel 501 to the reference TDC 34-M by subtracting the reference propagation delay from the propagation delay in the signal path from each pixel 41 to the TDC 34-(M-1). The subtraction unit 151-(M-1) supplies the skew between the signal paths as a correction value to the correction value holding unit 152-(M-1).

[0259] The correction value holding unit 152-(M-1) holds the correction value supplied from the subtraction unit 151-(M-1).

[0260] As described above, it is possible to measure and correct skew between signal paths in real time by simply providing the first MUX inside the pixel readout circuit of the measurement pixel 501, without providing the first MUX inside the pixel readout circuit of each pixel 41. The measured skew includes regular skew in the signal path within the pixel array unit 31, skew due to manufacturing variations in the signal path from the second MUX 251 to the TDC 34, and the like. Note that the measured skew does not include skew due to manufacturing variations in the signal path from the measurement pixel 501 to the pixel 41.

[0261] If the skew between the signal paths of the detection signals can be measured and corrected, there is no need to design the pixel array unit 31 to reduce the skew between the signal paths of the detection signals. In other words, limitations on wiring resources are alleviated. This allows, for example, narrowing the wiring width of the horizontal signal lines that make up the signal paths of the detection signals. Narrowing the wiring width of the horizontal signal lines reduces the parasitic capacitance of the horizontal signal lines, making it possible to reduce read power. Furthermore, narrowing the wiring width of the horizontal signal lines makes it possible to perform complex wiring and reduce the number of wiring layers, thereby reducing chip costs.

[0262] Fig. 31 is a diagram showing a fifth modified example of the configuration of the photodetector. In Fig. 31, the same components as those in Fig. 26 are denoted by the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0263] The photodetector 23 of FIG. 31 differs from the photodetector 23 of FIG. 26 in that a binning circuit (AND / MUX) is provided in the pixel array section 31.

[0264] 31 , a measurement pixel block column 532A made up of measurement pixel blocks 532 arranged in the column direction is disposed at the far end of the pixel array section 31, away from the second MUX 251. The measurement pixel block 532 is made up of, for example, 2×2 measurement pixels 501.

[0265] The pixel array unit 31 is provided with a binning circuit that sums or multiplexes and outputs detection signals output from, for example, 2×2 pixels 41 that make up a pixel block 531, and each binning circuit is connected to a horizontal signal line that is wired for each column of the pixel block 531. The pixel array unit 31 is also provided with a binning circuit that sums or multiplexes and outputs measurement signals output from 2×2 measurement pixels 501 that make up a measurement pixel block 532, and each binning circuit is connected to a horizontal signal line that is wired for each column of the corresponding pixel block 531.

[0266] The measurement signal is transmitted from the measurement signal generator 32 via a tree-type circuit network 511 to the pixel readout circuit of at least one measurement pixel 501 that constitutes each measurement pixel block.

[0267] As described above, even when the horizontal signal lines (output wiring) are wired so as to perform pixel binning, the measurement signal can be input to the signal path of the detection signal via the first MUX of the measurement pixel 501, and the skew between the signal paths can be measured.

[0268] Fig. 32 is a diagram showing a sixth modified example of the configuration of the photodetector 23. In Fig. 32, the same components as those in Fig. 26 are denoted by the same reference numerals. Duplicate explanations will be omitted where appropriate.

[0269] The photodetector 23 of FIG. 32 differs from the photodetector 23 of FIG. 26 in that a measurement pixel column 501B made up of measurement pixels 501 arranged in the column direction is provided in the pixel array section 31.

[0270] In the example of Figure 32, the measurement pixel column 501B is arranged at the near end of the pixel array section 31 close to the second MUX 251 (TDC 34), and the measurement pixel 501 is connected to the signal path from each pixel 41 to the TDC 34 between each pixel 41 and the second MUX 251.

[0271] 32 , the measurement signal is transmitted from the measurement signal generation unit 32 to the pixel readout circuit of each measurement pixel 501 in the measurement pixel column 501A via a tree-type circuit network 511A. The measurement signal originating from the first MUX of the measurement pixel 501 in the measurement pixel column 501A is a signal for measuring the signal propagation delay in the signal path from the far end of the pixel array section 31, which is away from the second MUX 251, to the TDC 34. The measurement signal is also transmitted from the measurement signal generation unit 32 to the pixel readout circuit of each measurement pixel 501 in the measurement pixel column 501B via a tree-type circuit network 511B. The measurement signal originating from the first MUX of the measurement pixel 501 in the measurement pixel column 501B is a signal for measuring the signal propagation delay in the signal path from the near end of the pixel array section 31, which is close to the second MUX 251, to the TDC 34. Hereinafter, when there is no need to particularly distinguish between the tree-type circuit networks 511A and 511B, they will be simply referred to as the circuit network 511.

[0272] The second MUX 251 supplies the measurement signal originating from the first MUX of the measurement pixel 501 in the measurement pixel column 501A and the measurement signal originating from the first MUX of the measurement pixel 501 in the measurement pixel column 501B to the TDC 34 corresponding to the pixel row containing the measurement pixel.

[0273] The TDC 34 counts a count value indicating the signal propagation delay in the signal path from the far end of the pixel array unit 31 to the TDC 34 based on the synchronization signal supplied from the measurement signal generation unit 32 and the measurement signal supplied from the second MUX 251 and originating from the first MUX of the measurement pixel 501 in the measurement pixel column 501A.

[0274] In addition, the TDC 34 counts a count value indicating the signal propagation delay in the signal path from the near end of the pixel array section 31 to the TDC 34 based on the synchronization signal and the measurement signal originating from the first MUX of the measurement pixel 501 in the measurement pixel column 501B supplied from the second MUX 251.

[0275] The calculation circuit 35 calculates the signal propagation delay in the signal path from each pixel 41 in the pixel row corresponding to the preceding TDC 34 to the TDC 34 based on the count value based on the measurement signal supplied from the TDC 34 and starting from the first MUX of the measurement pixel 501 in the measurement pixel column 501A, and the count value based on the measurement signal starting from the first MUX of the measurement pixel 501 in the measurement pixel column 501A.

[0276] The arithmetic circuit 35 calculates the signal propagation delay on the signal path from each pixel 41 to the TDC 34 based on the signal propagation delay on the signal path from the far end of the pixel array unit 31 to the TDC 34 and the signal propagation delay on the signal path from the near end of the pixel array unit 31 to the TDC 34, thereby making it possible to calculate the propagation delay more accurately.

[0277] Fig. 33 is a diagram showing a seventh modified example of the configuration of the photodetector 23. In Fig. 33, the same components as those in Fig. 26 are denoted by the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0278] The photodetector 23 of FIG. 33 differs from the photodetector 23 of FIG. 26 in that the measurement pixel array 501A is not provided, but the measurement pixel array 501B is provided.

[0279] As shown in FIG. 33, the measurement pixels 501 may be provided only at the near end of the pixel array section 31 close to the second MUX 251 .

[0280] Fig. 34 is a diagram showing an eighth modified example of the configuration of the photodetector 23. In Fig. 34, the same components as those in Fig. 26 are denoted by the same reference numerals. Duplicate explanations will be omitted where appropriate.

[0281] The photodetector 23 of FIG. 34 differs from the photodetector 23 of FIG. 26 in that two horizontal signal lines are wired for each pixel row in the pixel array section 31.

[0282] 34 , a measurement pixel column 501C made up of measurement pixels 501 arranged in the column direction is disposed at the far end of the pixel array section 31, away from the second MUX 251. In addition, a measurement pixel column 501D made up of measurement pixels 501 arranged in the column direction is provided adjacent to the measurement pixel column 501C.

[0283] The pixel readout circuit of each pixel 41 is connected to one of two horizontal signal lines wired for each pixel row. The pixel readout circuit of each measurement pixel 501 constituting the measurement pixel column 501C is connected to one of the two horizontal signal lines wired for each pixel row, and the pixel readout circuit of each measurement pixel 501 constituting the measurement pixel column 501D is connected to the other horizontal signal line.

[0284] The measurement signal is transmitted from the measurement signal generating unit 32 via a tree-type circuit network 511 to the pixel readout circuits of the measurement pixels 501 that make up the measurement pixel column 501C and to the pixel readout circuits of the measurement pixels 501 that make up the measurement pixel column 501D.

[0285] As described above, even when multiple horizontal signal lines (output wiring) are wired for each pixel row, the measurement signal can be input to the signal path of the detection signal via the first MUX of the measurement pixel 501, and the skew between the signal paths can be measured.

[0286] FIG. 35 is a diagram showing an example of the configuration of the measurement pixel 501.

[0287] As shown in A of FIG. 35, the measurement pixel 501 is composed of, for example, a SPAD 551, a constant current source 552A, an input amplifier 553, and a first MUX 554.

[0288] The SPAD 551 corresponds to the SPAD 221 ( FIG. 19 ) of the pixel 41, and the constant current source 552 corresponds to the constant current source 222 of the pixel 41. The input amplifier 553 corresponds to the input amplifier 223 of the pixel 41, and the first MUX 554 corresponds to the first MUX 271 of the pixel 41.

[0289] 35B, the anode voltage of the SPAD 551 may be input as an input signal to the input amplifier 553. In this case, the cathode of the SPAD 551 is connected to the power supply voltage VSPAD, and the anode is connected to a constant current source 552 and an input terminal of the input amplifier 553. The power supply voltage VS is supplied to the constant current source 552.

[0290] Fig. 36 is a diagram showing another example of the configuration of the measurement pixel 501. In Fig. 36, the same components as those in Fig. 34 are denoted by the same reference numerals. Duplicate explanations will be omitted as appropriate.

[0291] 36 differs from the measurement pixel 501 in FIG. 34 in that the first MUX 554 is not provided, and the transistor 561A or the transistor 561B and the first MUX 562 are provided.

[0292] The transistor 561A corresponds to the transistor 291 (FIG. 20) of the pixel 41, and the first MUX 562 corresponds to the first MUX 292 of the pixel 41. The transistor 561A is configured, for example, by an n-type MOS transistor.

[0293] 36B, the anode voltage of the SPAD 551 may be input as an input signal to the input amplifier 553. In this case, the cathode of the SPAD 551 is connected to the power supply voltage VSPAD, and the anode is connected to the constant current source 552, the input terminal of the input amplifier 553, and the drain of the transistor 561B. The power supply voltage VS is supplied to the constant current source 552. The source of the transistor 561B is connected to the power supply voltage VH, and the gate of the transistor 561B is connected to the output terminal of the first MUX 562. The transistor 561B is configured, for example, as a p-type MOS transistor.

[0294] FIG. 37 is a diagram for explaining wiring between the tree-type circuit network 511 and the pixel array section 31.

[0295] As shown on the left side of Fig. 37, a tree-type circuit network 511 is configured by connecting, for example, two-way dividers in a tournament configuration. A plurality of inverters and level shifters connected in series are connected in front of the two-way dividers. Each two-way divider is provided with an inverter as needed.

[0296] For example, the wiring width of the tree-type circuit network 511 is formed wide so that the measurement signals reach each of the measurement pixels 501 at approximately the same time and are input to the horizontal signal line 631. Since the signal propagation delay in the tree-type circuit network 511 is small, it is possible to suppress the effects of temperature and voltage on the measurement signals.

[0297] 38 is a block diagram showing an example of the configuration of the photodetector 23 when the correction of errors caused by skew between signal paths of the detection signal is performed after the histogram generation. Note that Fig. 38 shows the configuration of the photodetector 23 after the TDC 34.

[0298] As shown in FIG. 38, the photodetector 23 includes a TDC 34 , a propagation delay measurement unit 121 , a correction value calculation unit 122 , a histogram generation unit 36 ​​, a depth calculation unit 371 , and a correction unit 123 .

[0299] The TDC 34 supplies a count value based on the measurement signal to the propagation delay measurement unit 121 and supplies a count value based on the detection signal to the histogram generation unit 36 ​​.

[0300] The propagation delay measurement unit 121 measures the propagation delay of the signal in the signal path from the measurement pixel 501 to the TDC 34, based on a count value based on the measurement signal as an output of the TDC 34. The propagation delay measurement unit 121 supplies the measurement result of the propagation delay of the signal in the signal path from the measurement pixel 501 to the TDC 34 to the correction value calculation unit 122.

[0301] The correction value calculation unit 122 (pixel-by-pixel propagation delay calculation unit 531) calculates the signal propagation delay on the signal path from each pixel to the TDC 34, based on the signal propagation delay on the signal path from the measurement pixel 501 to the TDC 34 measured by the propagation delay measurement unit 121. The correction value calculation unit 122 calculates the skew between the signal paths of the detection signal, based on the calculation result of the signal propagation delay on the signal path from each pixel to the TDC 34 and the measurement result of the reference propagation delay. The correction value calculation unit 122 calculates and stores a correction value for correcting an error due to the skew, which is included in the distance information, based on the calculation result of the skew between the signal paths, and supplies the correction value to the correction unit 123 at a predetermined timing during the exposure period.

[0302] The histogram generating unit 36 ​​generates a histogram for each pixel 41 based on the count value based on the detection signal as the output of the TDC 34 , and supplies the histogram for each pixel 41 to the depth calculating unit 371 .

[0303] The depth calculation unit 371 calculates the distance D to the object Obj for each pixel 41 based on the histogram supplied from the histogram generation unit 36. For example, the depth calculation unit 371 performs a centroid calculation on the histogram to calculate the centroid value of the count value, and calculates the distance D based on the centroid value of the count value. The depth calculation unit 371 supplies distance information indicating the distance D for each pixel to the correction unit 123.

[0304] The correction unit 123 performs correction processing to add or subtract the correction value supplied from the correction value calculation unit 122 to the distance information supplied from the depth calculation unit 371. The correction unit 123 supplies the corrected distance information to the control unit 21.

[0305] The depth calculation unit 371 and the correction unit 123 may be provided within a semiconductor chip that constitutes the photodetection device 23, or may be provided in the control unit 21 or application unit 12 downstream of the photodetection device 23. When the depth calculation unit 371 and the correction unit 123 are provided in the control unit 21 or application unit 12, the histogram and correction value are transmitted between the semiconductor chip and the control unit 21 or application unit 12.

[0306] As described above, it is possible to correct errors due to skew between signal paths of the detection signal not on the count value output from the TDC 34 but on the distance information calculated based on the histogram output from the histogram generator 36.

[0307] In this specification, a system refers to a collection of multiple components (devices, modules (components), etc.), regardless of whether all of the components are contained in the same housing. Therefore, multiple devices housed in separate housings and connected via a network, and a single device with multiple modules housed in a single housing, are both systems.

[0308] The effects described in this specification are merely examples and are not limiting, and other effects may also be present.

[0309] The embodiments of the present technology are not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present technology.

[0310] Example of Combination of Configurations The present technology can also be configured as follows.

[0311] (1) A photodetector comprising: a readout circuit that outputs a detection signal indicating the timing at which a light receiving element detects reflected light that is irradiated by an object; a TDC that counts time based on the detection signal output from the readout circuit; a histogram generator that generates a histogram based on the output of the TDC that is based on the detection signal; a first multiplexer that inputs a measurement signal to the signal path to measure the propagation delay of a signal in at least a portion of the signal path between the readout circuit and the TDC in time units that are less than the time resolution of the TDC; a propagation delay measurement unit that measures the propagation delay in time units that are less than the time resolution of the TDC based on the output of the TDC that is based on the measurement signal; and a correction unit that corrects the output of the TDC or the output of the histogram generator that is based on the detection signal based on the measurement result by the propagation delay measurement unit. (2) The photodetector according to (1), wherein a plurality of the TDCs are provided, at least one of the signal path and the first multiplexer is provided corresponding to each of the plurality of TDCs, and further comprising a correction value calculation unit that calculates, based on a measurement result by the propagation delay measurement unit, a correction value for correcting an error due to skew between the TDCs included in the output of the TDC based on the detection signal or the output of the histogram generation unit, and the correction unit corrects the output of the TDC based on the detection signal or the output of the histogram generation unit using the correction value. (3) The photodetector according to (2), wherein the correction unit is provided in one-to-one correspondence with the TDC. (4) The photodetector according to (2) or (3), wherein the propagation delay measurement unit, the correction value calculation unit, and the TDCs are provided in one-to-one or one-to-multiple correspondence. (5) The photodetector according to any one of (2) to (4), wherein the correction value calculation unit calculates the correction value based on a calculation result of an accumulator that calculates a cumulative sum of the output of the TDC based on the measurement signal. (6) The photodetector according to any one of (2) to (4), wherein the correction value calculation unit calculates the correction value based on a histogram generated based on the output of the TDC based on the measurement signal.(7) The photodetector according to any one of (2) to (6), wherein the correction unit adds or subtracts an actual correction value expressed in time units equal to the time resolution of the TDC to the output of the TDC based on the detection signal, the actual correction value being a variable value that fluctuates so that an average value during an exposure period of the light receiving element becomes equal to the correction value expressed in time units less than the time resolution of the TDC. (8) The photodetector according to any one of (1) to (7), further comprising a measurement signal generation unit that inputs a pulse signal to the TDC and delays the pulse signal to generate the measurement signal and inputs it to the first multiplexer, wherein the measurement signal generation unit repeatedly inputs the measurement signal to the first multiplexer while changing an amount of delay of the measurement signal relative to the pulse signal in time units less than the time resolution of the TDC. (9) The photodetector according to (8), wherein the measurement signal generation unit inputs the measurement signal to a plurality of the first multiplexers substantially simultaneously. (10) The photodetector according to any one of (1) to (9), further comprising a second multiplexer that switches connections between the plurality of readout circuits and the TDC. (11) The photodetector according to (10), wherein the first multiplexer is provided inside the readout circuit. (12) The photodetector according to (11), wherein the readout circuit includes an input amplifier that outputs the detection signal in response to a signal output from the light-receiving element, and the first multiplexer is provided in a stage subsequent to the input amplifier. (13) The photodetector according to (11), wherein the readout circuit includes an input amplifier that outputs the detection signal in response to a signal output from the light-receiving element, and the first multiplexer is provided in a stage prior to the input amplifier. (14) The photodetector according to (10), wherein the first multiplexer inputs the measurement signal to the signal path between an input terminal of the second multiplexer and the TDC.(15) The photodetector according to (14), further comprising a third multiplexer that inputs the measurement signal to the signal path between the output terminal of the second multiplexer and the TDC, wherein the propagation delay measurement unit measures the propagation delay of the signal inside the second multiplexer based on an output of the TDC based on the measurement signal originating from the first multiplexer and an output of the TDC based on the measurement signal originating from the third multiplexer. (16) The photodetector according to any of (1) to (15), wherein the correction unit corrects the distance to the object calculated based on the output of the histogram generation unit based on the measurement result by the propagation delay measurement unit. (17) The photodetector according to any of (1) to (10), further comprising a measurement circuit arranged in an array unit in which the readout circuits are arranged in a matrix, and connected to the signal path between the readout circuits and the TDC, wherein the first multiplexer is provided inside the measurement circuit. (18) The photodetector according to (17), further comprising a propagation delay estimation unit that estimates a signal propagation delay in a signal path between the readout circuit and the TDC based on a measurement result of the signal propagation delay in the signal path between the measurement circuit and the TDC by the propagation delay measurement unit, wherein the correction unit corrects an output of the TDC or an output of the histogram generation unit based on the detection signal based on the estimation result by the propagation delay estimation unit. (19) The photodetector according to (17), wherein the measurement circuit is connected to the signal path between the readout circuit and the TDC at least either before the readout circuit or between the readout circuit and the TDC.(20) A ranging system comprising: a light source that outputs illumination light; a readout circuit that outputs a detection signal indicating the timing at which a light receiving element detects reflected light of the illumination light reflected by an object; a TDC that counts time based on the detection signal output from the readout circuit; a histogram generation unit that generates a histogram based on the output of the TDC based on the detection signal; a first multiplexer that inputs a measurement signal to the signal path to measure the propagation delay of a signal in at least a portion of the signal path between the readout circuit and the TDC in time units less than the time resolution of the TDC; a propagation delay measurement unit that measures the propagation delay in time units less than the time resolution of the TDC based on the output of the TDC based on the measurement signal; and a correction unit that corrects the output of the TDC based on the detection signal or the output of the histogram generation unit based on the measurement result by the propagation delay measurement unit.

[0312] 1 Electronic device, 11 Distance measuring device, 12 Application unit, 21 Control unit, 22 Light source device, 23 Light detection device, 31 Pixel array unit, 32 Measurement signal generation unit, 33 First MUX, 34 TDC, 35 Arithmetic circuit, 36 Histogram generation unit, 41 Pixel, 61 Pulse generation circuit, 62 Delay adjustment circuit, 121 Propagation delay measurement unit, 122 Correction value calculation unit, 123 Correction unit, 141 Accumulator, 142 Division unit, 151 Subtraction unit, 152 Correction value holding unit, 171 Histogram generation unit, 172 Center of gravity calculation unit, 202 Addition / subtraction unit, 221 SPAD, 222 Constant current source, 223 Input amplifier, 251 Second MUX, 271 First MUX, 291 transistor, 292 first MUX, 311 third MUX, 351, 352 measurement result holding unit, 371 depth calculation unit

Claims

1. A photodetection device comprising: a readout circuit that outputs a detection signal indicating the timing at which a light receiving element detects reflected light that is emitted from an object; a TDC that counts time based on the detection signal output from the readout circuit; a histogram generation unit that generates a histogram based on the output of the TDC that is based on the detection signal; a first multiplexer that inputs a measurement signal to the signal path to measure the propagation delay of a signal in at least a portion of the signal path between the readout circuit and the TDC in time units that are less than the time resolution of the TDC; a propagation delay measurement unit that measures the propagation delay in time units that are less than the time resolution of the TDC based on the output of the TDC that is based on the measurement signal; and a correction unit that corrects the output of the TDC or the output of the histogram generation unit that is based on the detection signal based on the measurement result by the propagation delay measurement unit.

2. The photodetector according to claim 1, wherein a plurality of the TDCs are provided, at least one of the signal path and the first multiplexer is provided corresponding to each of the plurality of TDCs, and the photodetector further comprises a correction value calculation unit that calculates a correction value based on the measurement result by the propagation delay measurement unit to correct an error due to skew between the TDCs included in the output of the TDC based on the detection signal or the output of the histogram generation unit, and the correction unit corrects the output of the TDC based on the detection signal or the output of the histogram generation unit using the correction value.

3. The photodetector according to claim 2, wherein the correction section is provided in one-to-one correspondence with the TDC.

4. The photodetector according to claim 2, wherein the propagation delay measurement section, the correction value calculation section, and the TDC are provided in a one-to-one or one-to-many correspondence.

5. The photodetector according to claim 2, wherein the correction value calculation section calculates the correction value based on the calculation result of an accumulator that calculates the cumulative sum of the output of the TDC based on the measurement signal.

6. The photodetector according to claim 2, wherein the correction value calculation section calculates the correction value based on a histogram generated based on the output of the TDC that is based on the measurement signal.

7. The optical detection device of claim 2, wherein the correction unit adds or subtracts an actual correction value expressed in the same time unit as the time resolution of the TDC to the output of the TDC based on the detection signal, and the actual correction value is a variable value that fluctuates so that the average value during the exposure period of the light receiving element becomes equal to the correction value expressed in the time unit less than the time resolution of the TDC.

8. The photodetector according to claim 1, further comprising a measurement signal generation unit that inputs a pulse signal to the TDC and delays the pulse signal to generate the measurement signal and inputs it to the first multiplexer, wherein the measurement signal generation unit repeatedly inputs the measurement signal to the first multiplexer while changing the amount of delay of the measurement signal relative to the pulse signal in time units that are less than the time resolution of the TDC.

9. The photodetector according to claim 8, wherein the measurement signal generator inputs the measurement signals to a plurality of the first multiplexers substantially simultaneously.

10. The photodetector device according to claim 1, further comprising a second multiplexer for switching the connection between the plurality of readout circuits and the TDC.

11. The photodetector device according to claim 10, wherein the first multiplexer is provided inside the readout circuit.

12. The photodetector according to claim 11, wherein the readout circuit includes an input amplifier that outputs the detection signal in response to a signal output from the light-receiving element, and the first multiplexer is provided in a stage subsequent to the input amplifier.

13. The photodetector according to claim 11, wherein the readout circuit includes an input amplifier that outputs the detection signal in response to a signal output from the light-receiving element, and the first multiplexer is provided in a stage preceding the input amplifier.

14. The photodetector device according to claim 10, wherein the first multiplexer inputs the measurement signal to the signal path between the input terminal of the second multiplexer and the TDC.

15. The photodetector device according to claim 14, further comprising a third multiplexer that inputs the measurement signal to the signal path between the output terminal of the second multiplexer and the TDC, wherein the propagation delay measurement unit measures the propagation delay of the signal inside the second multiplexer based on the output of the TDC based on the measurement signal originating from the first multiplexer and the output of the TDC based on the measurement signal originating from the third multiplexer.

16. The optical detection device according to claim 1, wherein the correction section corrects the distance to the object calculated based on the output of the histogram generation section based on the measurement result by the propagation delay measurement section.

17. The photodetector device according to claim 1, further comprising a measurement circuit arranged in an array section in which the readout circuits are arranged in a matrix, and connected to a signal path between the readout circuits and the TDC, wherein the first multiplexer is provided inside the measurement circuit.

18. The photodetector device of claim 17, further comprising a propagation delay estimation unit that estimates the propagation delay of a signal in a signal path between the readout circuit and the TDC based on the measurement result of the propagation delay of the signal in the signal path between the measurement circuit and the TDC by the propagation delay measurement unit, and the correction unit corrects the output of the TDC or the output of the histogram generation unit based on the detection signal based on the estimation result by the propagation delay estimation unit.

19. The photodetector device of claim 17, wherein the measurement circuit is connected to a signal path between the readout circuit and the TDC at least one of a stage preceding the readout circuit and a stage between the readout circuit and the TDC.

20. A ranging system comprising: a light source that outputs illumination light; a readout circuit that outputs a detection signal indicating the timing at which a light-receiving element detects light reflected from an object from the illumination light; a TDC that counts time based on the detection signal output from the readout circuit; a histogram generation unit that generates a histogram based on the output of the TDC that is based on the detection signal; a first multiplexer that inputs a measurement signal to the signal path to measure the propagation delay of a signal in at least a portion of the signal path between the readout circuit and the TDC in time units that are less than the time resolution of the TDC; a propagation delay measurement unit that measures the propagation delay in time units that are less than the time resolution of the TDC based on the output of the TDC that is based on the measurement signal; and a correction unit that corrects the output of the TDC or the output of the histogram generation unit that is based on the detection signal based on the measurement result by the propagation delay measurement unit.

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