Photodetector and light detection device

Abstract

To provide a photodetector and a light detection device that can generate information for accurately identifying light incident timing while suppressing computational load of a time measurement unit.SOLUTION: 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 unit 9 includes a plurality of comparators 16. 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 output from the plurality of comparators 16, respectively, first information A1 indicating a time from a predetermined timing to when the one output signal SC is input. The energy monitor unit 12 generates second information A2 indicating the magnitude of the energy of a light pulse incident on the light detection element 22 on the basis of the plurality of output signals SC.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a photodetector and a photodetection device.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Devices for calculating distance based on the flight time of light are known. Such a device detects light reflected by an object after being output from a light source with a photodetection element, and calculates the time difference between the timing when the light is output from the light source and the timing when the light enters the photodetection element. However, in addition to the above light, disturbance light and stray light also enter the photodetection element. It is desired to accurately identify the light incident timing while suppressing the influence of these disturbance light and stray light.

[0005] Note that, in the system described in Patent Document 1, as described above, all signals output from a plurality of comparators are input to the time measurement unit. In that case, there is a problem that the number of data to be processed by the time measurement unit increases, and the computational load of the time measurement unit becomes large.

[0006] An object of the present disclosure is to provide a photodetector and a photodetection device capable of generating information for accurately specifying the incident timing of light while suppressing the computational load of a time measurement unit. **Means for Solving the Problems**

[0007] [1] A photodetector according to one aspect of the present disclosure includes a photodetection element, a comparison unit, a time measurement unit, and an energy monitor unit. The photodetection element receives light and outputs an electrical signal corresponding to the energy of the light. The photodetection 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 resistor connected in series with the avalanche photodiode. The comparison unit includes a plurality of comparators that receive the electrical signal from the photodetection element or a signal based on the electrical signal. The thresholds of the plurality of comparators are different from each other. The time measurement unit outputs first information indicating the time from a predetermined timing until one output signal is input based on one output signal among the plurality of output signals respectively output from the plurality of comparators. The energy monitor unit receives a 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 photodetection element based on the plurality of output signals.

[0008] In the photodetector of [1] above, the time measurement unit outputs the first information based on one output signal among the plurality of output signals respectively output from the plurality of comparators. Therefore, compared with the case of outputting the first information based on all the output signals, the number of data is reduced and the computational load of the time measurement unit is suppressed. In addition, the energy monitor unit generates second information indicating the magnitude of the energy of the light incident on the photodetection element based on the plurality of output signals from the plurality of comparators. By knowing the magnitude of the energy of the light, it becomes possible to accurately distinguish between external light and stray light and the light. Therefore, according to the photodetector of [1] above, it is possible to generate information for accurately specifying the incident timing of the light.

[0009] [2] The photodetector of [1] above may further include a data processing unit that creates a histogram based on the first information and the second information. In that case, the incident timing of light can be accurately specified from the histogram.

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

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

[0012] [5] In any one of the photodetectors of [1] to [4] above, the threshold value of at least one of the plurality of comparators may be changeable. In that case, the threshold value of the comparator can be easily adjusted according to the use and the usage environment of the photodetector, etc.

[0013] [6] In any one of the photodetectors of [1] to [5] above, 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 may be further provided.

[0014] [7] In any one of the photodetectors of [1] to [6] above, the electric signal may be a current signal. The photodetector may further include a current-voltage conversion unit that converts the current signal into a voltage signal and provides the voltage signal to the comparison unit.

[0015] [8] The photodetection device according to one aspect of the present disclosure includes a plurality of photodetectors, each of which is one of the photodetectors in [1] to [7] above. Each of the plurality of photodetectors further includes a bias application unit that selectively applies either a first bias voltage for operating the avalanche photodiode in the non-linear region or a second bias voltage for operating or stopping the avalanche photodiode in the linear region to the avalanche photodiode. In this photodetection device, for example, when light is incident on a certain spot, the avalanche photodiode of the photodetector within that spot can be operated in the non-linear region, and the avalanche photodiode of the photodetector outside that spot can be operated in the 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 non-linear region. Therefore, power consumption can be reduced.

Effect of the Invention

[0016] According to the present disclosure, it is possible to provide a photodetector and a photodetection device capable of generating information for accurately specifying the light incidence timing while suppressing the calculation load of the time measurement unit.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

[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 reference numerals are assigned to the same elements, and redundant descriptions are omitted.

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

[0020] FIG. 2 is a plan view of each photodetection element 22. Each photodetection element 22 has a plurality of cell units 23. The plurality of cell units 23 are two-dimensionally arranged in a plurality of rows and a plurality of columns. In the figure, 3 rows and 3 columns of cell units 23 are illustrated, but the number of rows and columns of the cell units 23 is not limited thereto.

[0021] FIG. 3 is a diagram showing the internal configuration of each photodetection element 22 and the connection relationship of a plurality of 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. Although an example in which the quenching circuit 6 is connected to the cathode of the APD 4 is shown in the figure, the quenching circuit 6 may be connected to the anode of the APD 4. The APD 4 operates in a non-linear region (Geiger mode) by receiving a bias voltage exceeding the breakdown voltage. Thereby, each cell unit 23 can detect a single photon event as a digital on / off signal. Each cell unit 23 is also called a single photon avalanche diode (SPAD).

[0022] The plurality of cell units 23 are connected in parallel with each other. In this way, the photodetection element 22 formed by connecting a plurality of cell units 23 which are SPADs in parallel is called a MPPC (Multi-Pixel Photon Counter, MPPC is a registered trademark) or a silicon photomultiplier (SiPM). The photodetection element 22 receives an optical pulse and outputs an electrical signal (current signal) corresponding to the energy of the optical pulse (in other words, the number of photons). For example, when one photon is incident on a certain cell unit 23 and one photon is incident on another cell unit 23, the photodetection element 22 outputs a current signal corresponding to two photons.

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

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

[0025] The current-voltage conversion part 8 is an example of a signal conversion part that converts or forms the output from the photodetection element 22 into an arbitrary signal. The current-voltage conversion part 8 has a signal input terminal and a signal output terminal. The signal input terminal of the current-voltage conversion part 8 is electrically connected to the cathode terminal of the photodetection element 22. A coupling capacitor may be provided between the signal input terminal of the current-voltage conversion part 8 and the cathode terminal of the photodetection element 22. The current-voltage conversion part 8 converts the current signal SJ output from the photodetection element 22 into a voltage signal SV and provides the voltage signal SV to the comparison part 9. In the figure, a transimpedance amplifier is shown as an example of the current-voltage conversion part 8, but the current-voltage conversion part 8 is not limited thereto. Also, since the photodetection element 22 which is a SiPM has a relatively high gain, a gain amplifier is not provided in the subsequent stage of the current-voltage conversion part 8 in the illustrated example. However, a gain amplifier may be provided in the subsequent stage of the current-voltage conversion part 8 as necessary. Note that a signal conversion part may not be arranged between the photodetection element 22 and each comparator 16.

[0026] The comparison unit 9 includes a plurality (four in the illustrated example) of comparators 16. Each comparator 16 has two input terminals. One input terminal of the plurality of comparators 16 is connected to each other and electrically connected to the signal output terminal of the current-voltage conversion unit 8. Note that a coupling capacitor may be provided between one input terminal of the plurality of comparators 16 and the signal output terminal of the current-voltage conversion unit 8. A voltage signal SV (a signal based on the current signal SJ) is input to one input terminal of each comparator 16. Threshold voltages ST1 to ST4 (where ST4 > ST3 > ST2 > ST1) having different magnitudes for each comparator 16 are input to the other input terminal of each comparator 16. The threshold voltages ST1 to ST4 input to each comparator 16 may be arbitrarily set by the user according to 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. Note that 1 pe is the amount of charge output by the photodetector 22 when one photon is detected. Each comparator 16 outputs a first logic signal (for example, a high-level signal) when the voltage signal SV exceeds the threshold voltage, and outputs a second logic signal (for example, a low-level signal) when the voltage signal SV does not exceed the threshold voltage. Note that when the comparator 16 is of the current input type, the arrangement of the current-voltage conversion unit 8 may be omitted, and in that case, the current signal SJ is input to one input terminal of each comparator 16. Each comparator 16 outputs a signal indicating whether or not the current signal SJ exceeds the threshold value.

[0027] The threshold voltage of at least one of the plurality of comparators 16 can be changed to an arbitrary magnitude according 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 an arbitrary magnitude.

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

[0029] Based on one of the plurality of output signals SC respectively output from the plurality of comparators 16, the time measurement unit 11 outputs first information A1 indicating the time from a predetermined timing to the timing when 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 is input to one of the input terminals from switch 10. A signal ST indicating a predetermined timing is input to the other input terminal. The predetermined timing is, for example, the emission timing of the optical pulse from the light source in LiDAR. 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] FIG. 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. Also shown in the figure are a predetermined timing t0 and a timing t1 at which the voltage signal SV exceeds the threshold voltage ST1. When the switch 10 selects the output signal SC from the comparator 16 for which the threshold voltage ST1 is set, the time measurement unit 11 generates first information A1 indicating the time difference t between the predetermined timing t0 and the timing t1. Note that this is not limited to this example. When the switch 10 selects the output signal SC from the comparator 16 for which any of the threshold voltages ST2 to ST4 is set, the time measurement unit 11 generates first information A1 indicating the time difference between the timing at which the voltage signal SV exceeds the threshold voltage and the predetermined timing t0.

[0031] In the above example, the time difference between the timing at which the voltage signal SV exceeds the threshold voltage and the predetermined timing t0 is defined as the first information A1. However, the calculation method of the first information A1 is not limited to this. For example, the time difference between the timing at which the voltage signal SV falls below the threshold voltage after exceeding the threshold voltage and the predetermined timing t0 may be further obtained, and the first information A1 may be generated based on the time difference. In that case, the signal waveform of the voltage signal SV can be estimated with higher accuracy. Also, as in the above example, by setting only the time difference between the timing at which the voltage signal SV exceeds the threshold voltage and the predetermined timing t0 as the first information A1, the computational load on the time measurement unit 11 can be reduced.

[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, the period U1 is a period during which the comparator 16 to which the threshold voltage ST4 is set is connected to the time measurement unit 11. Similarly, each of the periods U2 to U4 is a period during which the comparator 16 to which the threshold voltages ST3 to ST1 are set, respectively, is connected to the time measurement unit 11. The line G1 shows the time change of the voltage signal SV. The line G2 shows the change of 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 enters the photodetector 22. Therefore, in the example shown in FIG. 6, the largest threshold voltage ST4 is applied during the period U1 when the elapsed time from the emission timing of the optical pulse is short, and thereafter the threshold voltage is gradually decreased as time elapses. Thereby, for example, the incidence timing of the reflected light from the short distance incident during the period U1 (pulse P2 in the figure), the incidence timing of the reflected light from the medium distance incident during the period U2 (pulse P3 in the figure), and the incidence timing of the reflected light from the long distance incident during the period U4 (pulse P4 in the figure) can be accurately detected. Further, false detection due to stray light (pulse P1 in the figure) in the LiDAR device incident during the period U1 can be prevented.

[0033] Referring to FIG. 4 again. The energy monitor unit 12 has the same number of input terminals as the comparator 16 and one output terminal. Each input terminal of the energy monitor unit 12 is electrically connected to the output terminal of the corresponding comparator 16. The energy monitor unit 12 inputs a plurality of output signals SC from a plurality of comparators 16. The energy monitor unit 12 generates second information A2 indicating the magnitude of the energy of the optical pulse (in other words, the number of photons) incident on the photodetector 22 based on the plurality of output signals SC. Specifically, when the energy monitor unit 12 receives a first logic signal (a signal indicating that the voltage signal SV has exceeded the threshold voltage) only from the comparator 16 with the smallest threshold voltage among the plurality of comparators 16, the energy monitor unit 12 generates second information A2 indicating the 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 the first logic signal only from 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, the energy monitor unit 12 generates second information A2 indicating a third energy level greater than the second energy level. In this way, the energy monitor unit 12 generates second information A2 indicating the energy level corresponding to the maximum threshold voltage of one or more comparators 16 that output the first logic signal. The energy monitor unit 12 outputs the second information A2 from the output terminal. The energy monitor unit 12 is configured by, for example, 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 inputs the first information A1 from the time measurement unit 11 and inputs 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 showing an example of a histogram. As shown in FIG. 7, the histogram divides the elapsed time from a predetermined timing (for example, in the case of LiDAR, the emission timing of the light pulse from the light source) for each unit time and integrates the energy level for each unit time. 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 figure represents one light incident event. The length in the vertical axis direction of each block B represents the energy level. The period T1 in the figure is the period in which the integrated value is the largest, and it is presumed to include the timing when the light pulse is incident on the photodetector 1. The period T2 in the figure is the period in which the integrated value is small, and it is presumed to include the timing when the stray light or the glare is incident. Therefore, based on such a histogram, it is possible to accurately specify the incident timing of the light pulse while eliminating the influence of the stray light and the glare.

[0036] Referring to FIG. 4 again, 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 for operating the APD 4 in a non-linear region (i.e., Geiger mode) or a second bias voltage for operating the APD 4 in a linear region or stopping it, to the APD 4. 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 22 via the switch 5. The second bias line 18 is electrically connected to the cathode terminal of the photodetector 22 via the switch 7. The anode terminal of the photodetector 22 is electrically connected to a third bias line 19. The potential of the first bias line 17 is higher 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 (first bias voltage) between the first bias line 17 and the third bias line 19 is applied to the APD 4 of the photodetector 22. When the switch 5 is in the off state and the switch 7 is in the on state, the potential difference (second bias voltage) between the second bias line 18 and the third bias line 19 is applied to the APD 4 of the photodetector 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 obtained by the photodetector 1 and the optical detection device 20 of the present embodiment having the above configuration will be described. In the photodetector 1 of the present embodiment, the time measurement unit 11 generates the first information A1 based on one of the plurality of output signals SC respectively output from the plurality of comparators 16. Therefore, compared with the case where the first information A1 is generated based on all the output signals SC, the number of data is reduced and the calculation load of the time measurement unit 11 is suppressed. In addition, the energy monitor unit 12 generates the second information A2 indicating the magnitude of the energy of the optical pulse incident on the photodetection element 22 based on the plurality of output signals SC from the plurality of comparators 16. By knowing the magnitude of the energy of the optical pulse, it becomes possible to accurately distinguish the external light and the stray light from the optical pulse. Therefore, according to the photodetector 1 of the present embodiment, it is possible to generate information for accurately specifying the incidence timing of the optical pulse. As a result, in LiDAR, it becomes possible to accurately measure the distance to the object.

[0038] As described above, the APD 4 of the present embodiment operates in the non-linear 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 showing a comparison between the case where the APD 4 operates in the non-linear region (FIG. 8(a)) and the case where it operates in the linear region (FIG. 8(b)), and shows the time waveforms 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 upon receiving the incidence of the optical pulse. That is, the time difference tb between the timing when the voltage signal SV exceeds a certain threshold voltage and the timing when the voltage signal SV exceeds another threshold voltage becomes relatively long. Therefore, in order to accurately detect the incidence timing of the optical pulse, as described in Patent Document 1, after accurately estimating the time waveform of the voltage signal SV by detecting the timing when the voltage signal SV exceeds the threshold voltage for each threshold voltage, it is necessary to obtain the incidence timing of the optical pulse from those timings. Therefore, the computational load of the time measurement unit increases. In contrast, as shown in FIG. 8(a), when the APD 4 operates in the non-linear region, the voltage signal SV rises steeply with the incidence of the optical pulse. That is, the time difference ta between the timing when the voltage signal SV exceeds a certain threshold voltage and the timing when the voltage signal SV exceeds another threshold voltage is extremely short. Therefore, by detecting the timing when the voltage signal SV exceeds any one of a plurality of threshold voltages, the incidence timing of the optical pulse can be detected almost accurately. Therefore, the computational load of the time measurement unit 11 can be reduced.

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

[0040] The data calculation unit 102 has a coincidence counting 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 counting 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 counting 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 considered at all. Therefore, as shown in FIG. 10, in the histogram created by the photodetector 100, the lengths in the vertical axis direction of the blocks B representing the light incident events are all the same. In this case, it is difficult to distinguish the optical pulse from ambient light and stray light. For this reason, the accuracy of specifying the incident timing of the optical pulse is reduced. On the other hand, as described above, the photodetector 1 of the present embodiment generates second information A2 indicating the magnitude of the energy of the optical pulse incident on the photodetection element 22 based on a plurality of output signals SC from the plurality of comparators 16. By knowing the magnitude of the energy of the optical pulse, as shown in FIG. 7, it becomes possible to accurately distinguish ambient light and stray light from the optical pulse. Therefore, it is possible to generate information for accurately specifying the incident timing of the optical pulse.

[0042] As in this embodiment, the photodetector 1 may include a histogram creation unit 14 (data processing unit 3) that creates a histogram based on the first information A1 and the second information A2. In that case, the incident timing of the optical pulse can be accurately specified 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 any one of a plurality of comparators 16. In that 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 has a plurality of cell units 23 connected in parallel to each other, and each of the plurality of cell units 23 may include an APD 4 and a quenching circuit 6 connected in series with the APD 4. Thus, the fact that the photodetector element 22 has a configuration as a SiPM is effective from the following viewpoints. That is, in each cell unit 23 (SPAD) constituting the SiPM, the rise of the output signal is much faster compared to the APD operating in the linear region. Therefore, the time difference in the signal outputs from the plurality of comparators 16 is small, and the variation in the first information A1 is small regardless of which comparator 16 the switch 10 selects among the plurality of comparators 16. In addition, although the amount of charge output is constant even if a plurality of photons are incident simultaneously in a single SPAD, in a SiPM having a plurality of SPADs, an amount of charge corresponding to the number of incident photons is output, so that the energy level can be suitably acquired in the energy monitor unit.

[0045] As in this embodiment, the threshold value of at least one of the plurality of comparators 16 may be changeable. In that case, the threshold value of the comparator 16 can be easily adjusted according to the application and usage environment of the photodetector 1 and the like.

[0046] The optical detection device 20 of this embodiment includes a plurality of photodetectors 1. Each of the plurality of photodetectors 1 includes a bias application unit 15 that selectively applies either a first bias voltage for operating the APD 4 in a non-linear region or a second bias voltage for operating or stopping the APD 4 in a linear region to the APD 4. In this optical detection device 20, for example, when an optical pulse is incident on a certain spot, the APD 4 of the photodetector 1 within that spot can be operated in a non-linear region, and the APD 4 of the photodetector 1 outside that 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 non-linear region. Therefore, power consumption can be reduced. Note that it is preferable to set the magnitude of the second bias voltage to be the magnitude at which the APD 4 operates in the linear region rather than the magnitude at which the APD 4 stops, as this facilitates the circuit design.

[0047] [Modification Example] 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 24. The logical sum circuit 24 has an output terminal and a plurality of input terminals. Each of the plurality of input terminals of the logical sum circuit 24 is electrically connected to the output terminal of each of the plurality of comparators 16. The output terminal of the logical sum circuit 24 is electrically connected to one input terminal of the time measurement unit 11. Note that if it is possible to input the output signal SC from any one of the plurality of comparators 16 to the time measurement unit 11, a logical circuit other than the logical sum circuit (OR circuit) may be arranged instead of the logical sum circuit 24.

[0048] The photodetector and the optical detection 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 embodiment, the photodetector 1 includes a data processing unit 3 in addition to the main body unit 2, but the photodetector 1 may include only the main body unit 2. Also, in the above embodiment, an optical pulse is exemplified as the light incident on the photodetector, but the light may not be pulsed.

[0049] Also, the signal conversion unit disposed between the quenching circuit 6 and each comparator 16 only needs to be able to convert or form the output from the photodetection element 22 into an arbitrary signal, and is not limited to a current-voltage conversion circuit.

Explanation of Signs

[0050] 1…Photodetector, 2…Main body part, 3…Data processing part, 4…Avalanche photodiode (APD), 5, 7…Switches, 6…Quenching circuit, 8…Current-voltage conversion part, 9…Comparison part, 10…Switch, 11…Time measurement part, 12…Energy monitor part, 13…Memory part, 14…Histogram creation part, 15…Bias application part, 16…Comparator, 17…First bias line, 18…Second bias line, 19…Third bias line, 20…Photodetection device, 21…Light receiving surface, 22…Photodetection element, 23…Cell unit, 24…Logical sum circuit, 100…Photodetector, 101…Light receiving part, 102…Data arithmetic part, 103…PQRC, 104…Logical sum circuit, 105…SPAD, 106…Simultaneous counting circuit, 107…Time measurement part, 108…Histogram creation part, A1…First information, A2…Second information, B…Block, SC…Output signal, SJ…Current signal, ST…Signal, ST1~ST4…Threshold voltage, SV…Voltage signal, T1, T2, U1~U4…Periods.

Claims

1. A photodetector that receives light and outputs an electrical signal corresponding to the energy of the light, including a plurality of comparators that receive the electrical signal from the photodetector or a signal based on the electrical signal, and a comparison unit in which the thresholds of the plurality of comparators are different from each other, a time measurement unit that outputs first information indicating the time from a predetermined timing until the one output signal is input, based on one output signal among the plurality of output signals respectively output from the plurality of comparators, 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 photodetector, based on the plurality of output signals, comprising, the photodetector has a plurality of cell units connected in parallel to each other, each of the plurality of cell units is a photodetector including 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. further comprising an OR circuit having an output terminal and a plurality of input terminals, 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. The photodetector according to claim 1 or 2.

5. The photodetector according to claim 1 or 2, wherein the threshold of at least one of the plurality of comparators is changeable.

6. The photodetector according to claim 1 or 2, 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 electrical signal is a current signal, The photodetector according to claim 1 or 2, 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. comprising a plurality of photodetectors that are the photodetectors according to claim 1 or 2, 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 non-linear region or a second bias voltage for operating or stopping the avalanche photodiode in a linear region, a photodetection device.

Images