Photodetector and light detection device

Abstract

A photodetector 1 includes a light detection element 22, a comparison unit 9, a time measurement unit 11, and an energy monitor unit 12. The light detection element 22 includes a plurality of APDs 4 which operate in a non-linear region and are connected in parallel with each other. The comparison part 9 includes a plurality of comparators 16. The threshold values of the plurality of comparators 16 are different from each other. The time measurement unit 11 outputs, on the basis of one output signal SC among a plurality of output signals SC respectively outputted from the plurality of comparators 16, first information A1 indicating a time from a predetermined timing to when the one output signal SC is inputted. The energy monitor unit 12 generates second information A2 indicating the magnitude of the energy of the light pulse incident on the light detection element 22 on the basis of the plurality of output signals SC.

Description

Photodetectors and photodetection devices

[0001] This application claims priority to Japanese Patent Application No. 2023-223160, filed December 28, 2023, and incorporates by reference the entire contents of said Japanese application.

[0002] Patent Document 1 discloses a distance measurement system using light. In the system described in Patent Document 1, output signals from an avalanche photodiode (APD) operating in a linear region are input to multiple comparators. The multiple comparators each have a different threshold value. The output signals from all the comparators are input to a time measurement unit (time-to-digital converter: TDC). The TDC calculates the time of flight of light based on the multiple output signals.

[0003] International Publication No. 2017 / 095817

[0004] There are known devices that calculate distance based on the time of flight of light. Such devices use a photodetector element to detect light that is emitted from a light source and then reflected by an object, and calculate the time difference between when the light is emitted from the light source and when the light is incident on the photodetector element. However, in addition to the light mentioned above, ambient light and stray light also enter the photodetector element. It is desirable to accurately determine the timing of light incidence by suppressing the effects of such ambient light and stray light.

[0005] In the system described in Patent Document 1, as described above, all signals output from the multiple comparators are input to the time measurement unit, which increases the number of data items that the time measurement unit must process, resulting in a problem of a heavy computational load on the time measurement unit.

[0006] The present disclosure aims to provide a photodetector and a photodetecting device that can generate information for accurately identifying the timing of light incidence while reducing the computational load on a time measurement unit.

[0007] [1] A photodetector according to one aspect of the present disclosure includes a photodetector element, a comparison unit, a time measurement unit, and an energy monitor unit. The photodetector element receives light and outputs an electrical signal corresponding to the energy of the light. The photodetector element has multiple cell units connected in parallel, each of which includes an avalanche photodiode operating in a nonlinear region and a quenching resistor connected in series with the avalanche photodiode. The comparison unit includes multiple comparators that receive an electrical signal from the photodetector element or a signal based on the electrical signal. The multiple comparators each have a different threshold. The time measurement unit outputs first information indicating the time from a predetermined timing to the input of one output signal based on one of multiple output signals output from the multiple comparators. The energy monitor unit receives multiple output signals from the multiple comparators and generates second information indicating the magnitude of the energy of light incident on the photodetector element based on the multiple output signals.

[0008] In the photodetector of [1] above, the time measurement unit outputs first information based on one output signal from the multiple output signals output from the multiple comparators. Therefore, compared to when the first information is output based on all output signals, the number of data items is reduced, and the computational load on the time measurement unit is suppressed. Additionally, the energy monitor unit generates second information indicating the magnitude of the energy of light incident on the photodetector element based on the multiple output signals from the multiple comparators. Knowing the magnitude of the light energy makes it possible to accurately distinguish between ambient light, stray light, and light. Therefore, the photodetector of [1] above can generate information for accurately identifying the timing of light incidence.

[0009] [2] The photodetector of [1] may further include a data processing unit that creates a histogram based on the first information and the second information. In this case, the timing of light incidence can be identified with high accuracy from the histogram.

[0010] [3] The photodetector of [1] or [2] above may further include a switch that selectively connects the time measurement unit to one of a plurality of comparators. In this case, the threshold voltage of the comparator connected to the time measurement unit can be easily switched.

[0011] [4] The photodetector according to [1] or [2] may further include a logical OR circuit having an output terminal and a plurality of input terminals, each of which may be connected to a corresponding one of the plurality of comparators, and the output terminal of which may be connected to the time measurement unit.

[0012] [5] In any one of the photodetectors [1] to [4] above, the threshold value of at least one of the multiple comparators may be changeable. In this case, the threshold value of the comparator can be easily adjusted depending on the application and usage environment of the photodetector, etc.

[0013] [6] In any one of the photodetectors [1] to [5] above, the photodetector may further include a memory unit that inputs first information from the time measurement unit and second information from the energy monitoring unit, and stores the first information and the second information.

[0014] [7] In the photodetector of any one of [1] to [6] above, the electrical signal may be a current signal. The photodetector may further include a current-voltage converter that converts the current signal into a voltage signal and provides the voltage signal to the comparator.

[0015] [8] A photodetection device according to one aspect of the present disclosure includes a plurality of photodetectors, each of which is the photodetector described in any one of [1] to [7] above. Each of the plurality of photodetectors further includes a bias application unit that selectively applies to the avalanche photodiode either a first bias voltage for operating the avalanche photodiode in a nonlinear region or a second bias voltage for operating the avalanche photodiode in a linear region or stopping the operation. In this photodetection device, for example, when light is incident on a certain spot, the avalanche photodiode of the photodetector within the spot can be operated in a nonlinear region, and the avalanche photodiode of the photodetector outside the spot can be operated in a linear region or stopped. When operating in the linear region, the magnitude of the output signal from the avalanche photodiode is extremely small compared to when operating in the nonlinear region. This allows for reduced power consumption.

[0016] According to the present disclosure, it is possible to provide a photodetector and a photodetecting device that can generate information for accurately identifying the timing of incidence of light while reducing the calculation load on the time measurement unit.

[0017] FIG. 1 is a plan view of a photodetector according to an embodiment of the present disclosure. FIG. 2 is a plan view of a photodetector element. FIG. 3 is a diagram illustrating the internal configuration of each photodetector element and the connection relationship between multiple cell units. FIG. 4 is a circuit diagram illustrating the configuration of a photodetector according to an embodiment of the present disclosure. FIG. 5 is a graph illustrating an example of the time waveform of a voltage signal input to a comparison unit. FIG. 6 is a graph illustrating an example of switch operation. FIG. 7 is a diagram illustrating an example of a histogram. FIG. 8 is a graph illustrating a comparison between a case where an APD operates in a nonlinear region and a case where an APD operates in a linear region, showing the time waveform of a voltage signal in each case. FIG. 9 is a diagram illustrating the configuration of a photodetector according to a comparative example. FIG. 10 is a diagram illustrating an example of a histogram. FIG. 11 is a diagram illustrating the configuration of a modified example.

[0018] Hereinafter, embodiments of a photodetector and a photodetection device according to the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0019] FIG. 1 is a plan view of a light detection device 20 according to an embodiment of the present disclosure. As shown in FIG. 1, the light detection device 20 includes a light receiving surface 21. A light pulse is incident on the light receiving surface 21. The light pulse is, for example, a light pulse emitted from a light source and then reflected by an object. The light detection device 20 is used, for example, in a LiDAR (Light Detection and Ranging) system. The light receiving surface 21 has a plurality of light detection elements 22. The plurality of light detection elements 22 are two-dimensionally arranged across a plurality of rows and a plurality of columns.

[0020] 2 is a plan view of each photodetector element 22. Each photodetector element 22 has a plurality of cell units 23. The plurality of cell units 23 are arranged two-dimensionally across a plurality of rows and a plurality of columns. While the figure illustrates an example of three cell units 23 arranged in three rows and three columns, the number of rows and columns of the cell units 23 is not limited to this.

[0021] FIG. 3 illustrates the internal configuration of each photodetector element 22 and the interconnections of multiple cell units 23. As shown in FIG. 3, each cell unit 23 includes an avalanche photodiode (APD) 4 and a quenching circuit 6. The APD 4 is connected in series with the quenching circuit 6. While FIG. 3 illustrates an example in which the quenching circuit 6 is connected to the cathode of the APD 4, the quenching circuit 6 may also be connected to the anode of the APD 4. The APD 4 operates in the nonlinear region (Geiger mode) when subjected to a bias voltage exceeding its breakdown voltage. This allows each cell unit 23 to detect a single photon event as a digital on / off signal. Each cell unit 23 is also referred to as a single photon avalanche diode (SPAD).

[0022] The multiple cell units 23 are connected in parallel to each other. A photodetector element 22 formed by connecting multiple SPAD cell units 23 in parallel in this manner is called an MPPC (Multi-Pixel Photon Counter, MPPC is a registered trademark) or a silicon photomultiplier (SiPM). The photodetector element 22 receives a light pulse and outputs an electrical signal corresponding to the energy of the light pulse. The energy of the light pulse can also be expressed as the number of photons in the light pulse. The electrical signal is, for example, a current signal. For example, if one photon is incident on one cell unit 23 and one photon is incident on another cell unit 23, the photodetector element 22 outputs a current signal equivalent to two photons.

[0023] 4 is a circuit diagram showing a configuration of a photodetector 1 according to an embodiment of the present disclosure. The photodetector 1 includes one of the plurality of photodetection elements 22 described above. Therefore, the photodetection device 20 includes a plurality of photodetectors 1 corresponding to the plurality of photodetection elements 22, respectively.

[0024] The photodetector 1 includes a main body 2 and a data processing unit 3. In addition to a photodetecting element 22, the main body 2 includes a current-voltage conversion unit 8, a comparison unit 9, a switch (SW) 10, a time measurement unit (TDC: Time-to-Digital Converter) 11, an energy monitor unit 12, a storage unit (memory) 13, and a bias application unit 15. The data processing unit 3 includes a histogram creation unit 14. For simplicity of illustration, only one APD 4 and one quenching circuit 6 of the photodetecting element 22 are shown in FIG. 4 .

[0025] The current-voltage converter 8 is an example of a signal converter that converts or forms the output from the photodetector element 22 into an arbitrary signal. The current-voltage converter 8 has a signal input terminal and a signal output terminal. The signal input terminal of the current-voltage converter 8 is electrically connected to the cathode terminal of the photodetector element 22. A coupling capacitor may be provided between the signal input terminal of the current-voltage converter 8 and the cathode terminal of the photodetector element 22. The current-voltage converter 8 converts the current signal SJ output from the photodetector element 22 into a voltage signal SV and provides the voltage signal SV to the comparator 9. Although a transimpedance amplifier is shown in FIG. 4 as an example of the current-voltage converter 8, the current-voltage converter 8 is not limited thereto. Because the photodetector element 22, which is a SiPM, has a relatively high gain, a gain amplifier is not provided downstream of the current-voltage converter 8 in the illustrated example. However, a gain amplifier may be provided downstream of the current-voltage converter 8 if necessary. A signal conversion unit such as the current-voltage conversion unit 8 does not need to be disposed between the photodetector element 22 and the comparison unit 9 .

[0026] The comparison unit 9 includes multiple (four in the illustrated example) comparators 16. Each comparator 16 has two input terminals. One input terminal of each of the multiple comparators 16 is connected to each other and electrically connected to the signal output terminal of the current-voltage conversion unit 8. A coupling capacitor may be provided between one input terminal of each of the multiple comparators 16 and the signal output terminal of the current-voltage conversion unit 8. A voltage signal SV, which is a signal based on the current signal SJ, is input to one input terminal of each comparator 16. Threshold voltages ST1 to ST4, which vary in magnitude for each comparator 16, are input to the other input terminal of each comparator 16. However, the threshold voltages ST1 to ST4 satisfy the relationship ST4 > ST3 > ST2 > ST1. Each of the threshold voltages ST1 to ST4 input to each comparator 16 may be arbitrarily set by the user depending on one or both of the LiDAR optical system and the measurement environment. The threshold voltages ST1 to ST4 input to the four comparators 16 are, for example, 0.5 pe, 1.5 pe, 2.5 pe, and 3.5 pe, respectively. 1 pe is the amount of charge output by the photodetector element 22 when one photon is detected. Each comparator 16 outputs a first logic signal when the voltage signal SV exceeds the threshold voltage, and outputs a second logic signal when the voltage signal SV does not exceed the threshold voltage. The first logic signal is, for example, a high-level signal, and the second logic signal is, for example, a low-level signal. If the comparators 16 are of a current input type, the current-voltage conversion unit 8 may be omitted. In that case, a current signal SJ is input to one input terminal of each comparator 16. Each comparator 16 outputs a signal indicating whether the current signal SJ exceeds the threshold.

[0027] The threshold voltage of at least one of the multiple comparators 16 can be changed to any magnitude in response to a control input from outside the photodetector 1. In one example, the threshold voltages ST1 to ST4 of all the comparators 16 can be changed to any magnitude.

[0028] The switch 10 selectively connects the time measurement unit 11 to one of the plurality of comparators 16. Specifically, the switch 10 has the same number of input terminals as the number of comparators 16 and one output terminal. Each input terminal of the switch 10 is electrically connected to the output terminal of the corresponding comparator 16. The output terminal of the switch 10 is selectively connected to one of the plurality of input terminals of the switch 10 inside the switch 10. As a result, an output signal SC from one of the plurality of comparators 16 is output from the output terminal of the switch 10. The switch 10 may be configured as a mechanical switch or a semiconductor switch such as a transistor. The switch 10 may be operated by a user or may be controlled by a control circuit such as a computer (not shown).

[0029] The time measurement unit 11 outputs first information A1 based on one output signal SC among the multiple output signals SC output from the multiple comparators 16. The first information A1 indicates the time from a predetermined timing to the timing at which the one output signal SC is input to the time measurement unit 11. Specifically, the time measurement unit 11 has two input terminals and one output terminal. The output signal SC from the switch 10 is input to one input terminal. A signal ST indicating the predetermined timing is input to the other input terminal. In the case of LiDAR, for example, the predetermined timing is the emission timing of a light pulse from the light source. The time measurement unit 11 generates first information A1, which is information indicating the time difference between the input timing of the output signal SC and the input timing of the signal ST, and outputs the first information A1 from the output terminal.

[0030] 5 is a graph showing an example of the time waveform of the voltage signal SV input to the comparison unit 9. In FIG. 5, the vertical axis represents the signal voltage of the voltage signal SV, and the horizontal axis represents time. In FIG. 5, a predetermined timing t ０ and the timing t when the voltage signal SV exceeds the threshold voltage ST1. １ When the switch 10 selects the output signal SC from the comparator 16 to which the threshold voltage ST1 is set, the time measurement unit 11 ０ and timing t１ The present invention is not limited to this example. When the switch 10 selects the output signal SC from the comparator 16 to which one of the threshold voltages ST2 to ST4 is set, the time measurement unit 11 calculates the time difference t between the timing when the voltage signal SV exceeds the threshold voltage and the predetermined timing t ０ First information A1 indicating the time difference between the

[0031] In the above example, the timing when the voltage signal SV exceeds the threshold voltage and the predetermined timing t ０ However, the method of calculating the first information A1 is not limited to this. For example, the time difference between the timing when the voltage signal SV exceeds the threshold voltage and the timing when the voltage signal SV falls below the threshold voltage and the predetermined timing t ０ The time difference between the voltage signal SV and the predetermined timing t may be further calculated, and the first information A1 may be generated based on the time difference. In this case, the signal waveform of the voltage signal SV can be estimated with higher accuracy. Alternatively, as in the above example, the time difference between the timing at which the voltage signal SV exceeds the threshold voltage and the predetermined timing t ０ The first information A1 may be the time difference between the time and the time measured by the time measuring unit 11. This reduces the calculation load on the time measuring unit 11.

[0032] The switch 10 may switch the comparator 16 connected to the time measurement unit 11 over time. FIG. 6 is a graph showing an example of the operation of such a switch 10. In FIG. 6, period U1 is the period during which the comparator 16, to which the threshold voltage ST4 is set, is connected to the time measurement unit 11. Similarly, periods U2 to U4 are the periods during which the comparators 16, to which the threshold voltages ST3 to ST1 are set, are connected to the time measurement unit 11, respectively. Line G1 shows the change in the voltage signal SV over time. Line G2 shows the change in the threshold voltage applied to the voltage signal SV. In LiDAR, the closer the distance to the object to be measured, the stronger the reflected light incident on the photodetector element 22. Therefore, in the example shown in FIG. 6, the highest threshold voltage ST4 is applied during period U1, which is the shortest time elapsed since the emission of the light pulse, and the threshold voltage is subsequently gradually reduced over time. This allows for accurate detection of the timing of reflected light from a short distance (pulse P2 in the figure) that enters during period U1, the timing of reflected light from a medium distance (pulse P3 in the figure) that enters during period U2, and the timing of reflected light from a long distance (pulse P4 in the figure) that enters during period U4. Furthermore, it is possible to prevent erroneous detection due to stray light (pulse P1 in the figure) that enters during period U1 within the LiDAR device.

[0033] Referring again to FIG. 4 , the energy monitor unit 12 has the same number of input terminals as the comparators 16 and one output terminal. Each input terminal of the energy monitor unit 12 is electrically connected to the output terminal of a corresponding comparator 16. The energy monitor unit 12 receives multiple output signals SC from the multiple comparators 16. Based on the multiple output signals SC, the energy monitor unit 12 generates second information A2 indicating the magnitude of energy (in other words, the number of photons) of the optical pulse incident on the photodetector element 22. A signal indicating that the voltage signal SV has exceeded the threshold voltage is referred to as a first logic signal, and will be described in detail below. When the energy monitor unit 12 receives the first logic signal only from the comparator 16 with the smallest threshold voltage among the multiple comparators 16, the energy monitor unit 12 generates second information A2 indicating a first energy level. When the energy monitor unit 12 receives the first logic signal only from the comparator 16 with the smallest threshold voltage and the comparator 16 with the second smallest threshold voltage, the energy monitor unit 12 generates second information A2 indicating a second energy level greater than the first energy level. When the energy monitor unit 12 receives first logic signals from only the comparator 16 with the smallest threshold voltage, the comparator 16 with the second smallest threshold voltage, and the comparator 16 with the third smallest threshold voltage, it generates second information A2 indicating a third energy level that is greater than the second energy level. In this way, the energy monitor unit 12 generates second information A2 indicating an energy level corresponding to the maximum threshold voltage of the one or more comparators 16 that output the first logic signal. The energy monitor unit 12 outputs the second information A2 from its output terminal. The energy monitor unit 12 is configured, for example, by a combination of logic circuits.

[0034] The storage unit 13 is electrically connected to the output terminal of the time measurement unit 11 and the output terminal of the energy monitor unit 12. The storage unit 13 receives the first information A1 from the time measurement unit 11 and the second information A2 from the energy monitor unit 12. The storage unit 13 temporarily stores the first information A1 and the second information A2.

[0035] The histogram creation unit 14 creates a histogram based on the first information A1 and the second information A2. FIG. 7 is a diagram illustrating an example of a histogram. As illustrated in FIG. 7, the histogram divides the elapsed time from a predetermined timing into unit time periods and integrates the energy level for each unit time period. For example, in the case of LiDAR, the predetermined timing is the timing of emission of a light pulse from the light source. The elapsed time can be known based on the first information A1. The energy level can be known based on the second information A2. Each block B in the diagram represents a single light incident event. The length of each block B along the vertical axis represents the energy level. Period T1 in FIG. 7 is the period with the largest integrated value and is estimated to include the timing when a light pulse is incident on the photodetector 1. Period T2 in FIG. 7 is the period with the smallest integrated value and is estimated to include the timing when ambient light or stray light is incident. Therefore, based on such a histogram, the incident timing of a light pulse can be accurately identified while eliminating the effects of ambient light and stray light.

[0036] Referring again to FIG. 4 , the bias application unit 15 applies a bias voltage to the APD 4. The bias application unit 15 selectively applies either a first bias voltage or a second bias voltage to the APD 4. The first bias voltage is a voltage for operating the APD 4 in a nonlinear region (i.e., Geiger mode). The second bias voltage is a voltage for operating the APD 4 in a linear region or for stopping the operation. Specifically, the bias application unit 15 includes a switch 5, a switch 7, a first bias line 17, and a second bias line 18. The first bias line 17 is electrically connected to the cathode terminal of the photodetector element 22 via the switch 5. The second bias line 18 is electrically connected to the cathode terminal of the photodetector element 22 via the switch 7. The anode terminal of the photodetector element 22 is electrically connected to a third bias line 19. The potential of the first bias line 17 is greater than the potential of the second bias line 18. The potential of the third bias line 19 is lower than the potential of the second bias line 18. When the switch 5 is in the on state and the switch 7 is in the off state, the potential difference between the first bias line 17 and the third bias line 19 (first bias voltage) is applied to the APD 4 of the photodetector element 22. When the switch 5 is in the off state and the switch 7 is in the on state, the potential difference between the second bias line 18 and the third bias line 19 (second bias voltage) is applied to the APD 4 of the photodetector element 22. In one example, the potential of the first bias line 17 is 10 V, the potential of the second bias line 18 is 0 V, and the potential of the third bias line 19 is −40 V. In this case, the first bias voltage is 50 V, and the second bias voltage is 40 V.

[0037] The effects achieved by the photodetector 20 and photodetector 1 of this embodiment having the above configuration will be described. In the photodetector 1 of this embodiment, the time measurement unit 11 generates first information A1 based on one of the multiple output signals SC output from the multiple comparators 16. Therefore, compared to generating first information A1 based on all output signals SC, the number of data items is reduced, and the computational load on the time measurement unit 11 is suppressed. In addition, the energy monitor unit 12 generates second information A2 indicating the magnitude of the energy of the optical pulse incident on the photodetector element 22 based on the multiple output signals SC from the multiple comparators 16. Knowing the magnitude of the optical pulse energy makes it possible to accurately distinguish between ambient light, stray light, and optical pulses. Therefore, the photodetector 1 of this embodiment can generate information for accurately identifying the incidence timing of the optical pulse. As a result, in LiDAR, it is possible to accurately measure the distance to a target.

[0038] As described above, the APD 4 of this embodiment operates in the nonlinear region (Geiger mode). On the other hand, in the distance measurement system described in Patent Document 1, the APD operates in the linear region. FIG. 8 is a graph comparing the time waveform of the voltage signal SV when the APD 4 operates in the nonlinear region ( FIG. 8( a) ) and when it operates in the linear region ( FIG. 8( b) ). It shows the time waveform of the voltage signal SV in each case. As shown in FIG. 8( b) , when the APD 4 operates in the linear region, the voltage signal SV rises gently in response to the incidence of an optical pulse. That is, the time difference tb between the timing at which the voltage signal SV exceeds a certain threshold voltage and the timing at which the voltage signal SV exceeds another threshold voltage is relatively long. Therefore, to accurately detect the incidence timing of an optical pulse, as described in Patent Document 1, it is necessary to accurately estimate the time waveform of the voltage signal SV by detecting the timing at which the voltage signal SV exceeds a threshold voltage for each threshold voltage, and then determine the incidence timing of the optical pulse from these timings. This increases the computational load on the time measurement unit. In contrast, as shown in Figure 8(a), when the APD 4 operates in the nonlinear region, the voltage signal SV rises sharply upon the incidence of an optical pulse. In other words, the time difference ta between the timing at which the voltage signal SV exceeds a certain threshold voltage and the timing at which the voltage signal SV exceeds another threshold voltage is extremely short. Therefore, by detecting the timing at which the voltage signal SV exceeds one of multiple threshold voltages, the incidence timing of the optical pulse can be detected almost accurately. This reduces the computational load on the time measurement unit 11.

[0039] 9 is a diagram showing the configuration of a photodetector 100 according to a comparative example. The photodetector 100 includes a light receiving unit 101 and a data calculation unit (DSP: Digital Signal Processor) 102. The light receiving unit 101 includes multiple PQRCs (Passive Quenching and Recharge Circuits) 103 and an OR circuit 104. Each PQRC 103 includes a SPAD 105 and converts incident optical pulses into electrical pulse signals. The multiple PQRCs 103 are connected to the OR circuit 104, and when a pulse signal is output from any of the PQRCs 103, a pulse signal is output from the OR circuit 104.

[0040] The data calculation unit 102 has a coincidence circuit 106, a time measurement unit (TDC) 107, and a histogram creation unit 108. The pulse signal output from the OR circuit 104 is input to the coincidence circuit 106. The time measurement unit 107 measures the time difference between a predetermined timing and the input timing of the pulse signal based on the output from the coincidence circuit 106. The histogram creation unit 108 creates a histogram using the output data from the time measurement unit 107. FIG. 10 is a diagram showing an example of a histogram created by the histogram creation unit 108.

[0041] In this photodetector 100, the energy level of the incident optical pulse is not taken into consideration at all. Therefore, as shown in FIG. 10 , in the histogram created by the photodetector 100, all blocks B representing optical incident events have the same vertical length. In this case, it is difficult to distinguish optical pulses from ambient light and stray light. This reduces the accuracy with which the timing of the optical pulse incidence can be determined. In contrast, as described above, the photodetector 1 of this embodiment generates second information A2 indicating the magnitude of the energy of the optical pulse incident on the photodetector element 22 based on multiple output signals SC from multiple comparators 16. By knowing the magnitude of the optical pulse energy, it becomes possible to accurately distinguish between ambient light, stray light, and optical pulses, as shown in FIG. 7 . Therefore, information for accurately determining the timing of the optical pulse incidence can be generated.

[0042] As in the present embodiment, the photodetector 1 may include a histogram generator 14 (data processor 3) that generates a histogram based on the first information A1 and the second information A2. In this case, the incidence timing of the light pulse can be accurately identified from the histogram.

[0043] As in this embodiment, the photodetector 1 may include a switch 10 that selectively connects the time measurement unit 11 to one of a plurality of comparators 16. In this case, the threshold voltage of the comparator 16 connected to the time measurement unit 11 can be easily switched.

[0044] As in this embodiment, the photodetector element 22 includes multiple cell units 23 connected in parallel, and each of the multiple cell units 23 may include an APD 4 and a quenching circuit 6 connected in series with the APD 4. Having the photodetector element 22 configured as a SiPM is effective from the following perspective: In each cell unit 23 (SPAD) constituting the SiPM, the rise time of the output signal is significantly faster than that of an APD operating in the linear region. Therefore, the time difference between the signal outputs from the multiple comparators 16 is small, and the first information A1 varies little regardless of which of the multiple comparators 16 is selected by the switch 10. In addition, while a single SPAD outputs a constant amount of charge even when multiple photons are incident simultaneously, a SiPM with multiple SPADs outputs an amount of charge corresponding to the number of incident photons. This allows the energy monitor 12 to acquire the energy level appropriately.

[0045] As in the present embodiment, the threshold of at least one of the multiple comparators 16 may be changeable. In this case, the threshold of the comparator 16 can be easily adjusted depending on the application and usage environment of the photodetector 1, etc.

[0046] The photodetector 20 of this embodiment includes multiple photodetectors 1. Each of the multiple photodetectors 1 includes a bias application unit 15. The bias application unit 15 selectively applies to the APD 4 either a first bias voltage for operating the APD 4 in a nonlinear region or a second bias voltage for operating the APD 4 in a linear region or stopping it. In this photodetector 20, when an optical pulse is incident on a certain spot, for example, the APD 4 of the photodetector 1 within the spot can be operated in a nonlinear region, and the APD 4 of the photodetector 1 outside the spot can be operated in a linear region or stopped. When operating in the linear region, the magnitude of the output current from the APD 4 is extremely small compared to when operating in the nonlinear region. Therefore, power consumption can be reduced. Circuit design is easier when the magnitude of the second bias voltage is set to a value that causes the APD 4 to operate in the linear region rather than a value that causes the APD 4 to stop.

[0047] [Modification] Fig. 11 is a diagram showing the configuration of a modification of the above embodiment. As shown in Fig. 11, the switch 10 of the above embodiment may be replaced with a logical sum circuit (OR circuit) 24. The logical sum circuit 24 has an output terminal and multiple input terminals. Each of the multiple input terminals of the logical sum circuit 24 is electrically connected to the output terminal of each of the multiple comparators 16. The output terminal of the logical sum circuit 24 is electrically connected to one input terminal of the time measurement unit 11. As long as it is possible to input the output signal SC from any one of the multiple comparators 16 to the time measurement unit 11, a logic circuit other than the logical sum circuit may be arranged instead of the logical sum circuit 24.

[0048] The photodetector and photodetecting device according to the present disclosure are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above-described embodiments, the photodetector 1 includes the data processing unit 3 in addition to the main body unit 2, but the photodetector 1 may include only the main body unit 2. In the above-described embodiments, optical pulses are exemplified as the light incident on the photodetector, but the light does not have to be pulsed.

[0049] The signal conversion section disposed between the quenching circuit 6 and each comparator 16 is not limited to a current-voltage conversion circuit as long as it can convert or form the output from the photodetector element 22 into an arbitrary signal.

[0050] 1...photodetector, 2...main body, 3...data processing unit, 4...avalanche photodiode (APD), 5, 7...switch, 6...quenching circuit, 8...current-voltage conversion unit, 9...comparison unit, 10...switch, 11...time measurement unit, 12...energy monitor unit, 13...storage unit, 14...histogram creation unit, 15...bias application unit, 16...comparator, 17...first bias line, 18...second bias line, 19...third bias line, 20...photodetector, 21...light-receiving surface 22...photodetection element, 23...cell unit, 24...logical OR circuit, 100...photodetector, 101...light receiving unit, 102...data calculation unit, 103...PQRC, 104...logical OR circuit, 105...SPAD, 106...coincidence counting circuit, 107...time measurement unit, 108...histogram creation unit, A1...first information, A2...second information, B...block, SC...output signal, SJ...current signal, ST...signal, ST1 to ST4...threshold voltage, SV...voltage signal, T1, T2, U1 to U4...period.

Claims

1. A photodetector comprising: a photodetecting element that receives light and outputs an electrical signal corresponding to the energy of the light; a comparison unit including a plurality of comparators that receive the electrical signal from the photodetecting element or a signal based on the electrical signal, wherein threshold values of the plurality of comparators are different from each other; a time measurement unit that outputs first information indicating a time from a predetermined timing until one of the output signals among the plurality of output signals respectively output from the plurality of comparators is input, based on the one output signal; and an energy monitor unit that receives the plurality of output signals from the plurality of comparators and generates second information indicating the magnitude of the energy of the light incident on the photodetecting element, based on the plurality of output signals, wherein the photodetecting element has a plurality of cell units connected in parallel to each other, and each of the plurality of cell units includes an avalanche photodiode operating in a non-linear region and a quenching circuit connected in series with the avalanche photodiode.

2. The photodetector according to claim 1, further comprising a data processing unit that creates a histogram based on the first information and the second information.

3. The photodetector according to claim 1 or 2, further comprising a switch that selectively connects the time measurement unit to any one of the plurality of comparators.

4. The photodetector according to claim 1 or 2, further comprising an OR circuit having an output terminal and a plurality of input terminals, wherein each of the plurality of input terminals is connected to each of the plurality of comparators, and the output terminal is connected to the time measurement unit.

5. The photodetector according to any one of claims 1 to 4, wherein a threshold value of at least one of the plurality of comparators is changeable.

6. The photodetector according to any one of claims 1 to 5, further comprising a storage unit that inputs the first information from the time measurement unit and inputs the second information from the energy monitor unit, and stores the first information and the second information.

7. The photodetector according to any one of claims 1 to 6, wherein the electrical signal is a current signal, and further comprising a current-voltage conversion unit that converts the current signal into a voltage signal and provides the voltage signal to the comparison unit.

8. A photodetection device comprising a plurality of photodetectors which are the photodetectors according to any one of claims 1 to 7, wherein each of the plurality of photodetectors further comprises a bias application unit that selectively applies to the avalanche photodiode any one of a first bias voltage for operating the avalanche photodiode in a non-linear region and a second bias voltage for operating or stopping the avalanche photodiode in a linear region.

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