Light detection device and distance measuring device

Abstract

To provide a photodetection device and a ranging device which correctly detect whether a photodetector ignites.SOLUTION: A photodetection device includes: a photodetector; an initialization circuit for setting one end of the photodetector at a predetermined initialization voltage; an ignition detection circuit for detecting ignition of the photodetector by comparing the voltage at the one end of the photodetector or a current flowing through the one end with a threshold; a monitor circuit for monitoring an output signal of the ignition detection circuit; and a threshold control circuit for controlling the threshold on the basis of the monitor output of the monitor circuit.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] One embodiment of the present invention relates to a light detection device and a distance measurement device.

Background Art

[0002] A LiDAR (Light Detecting And Ranging) device that measures the distance of an object non - contact is an important key part in autonomous driving technology. LiDAR receives reflected light reflected by an object with a plurality of photoelectric conversion elements arranged in a two - dimensional array. For example, a SPAD (Single Photon Avalanche Diode) is used as the photoelectric conversion element. When a SPAD detects a photon, the output voltage or output current of the SPAD changes. The state in which a SPAD detects a photon is called firing. By comparing the output voltage or output current of the SPAD when it fires with a predetermined threshold value, it is possible to detect whether the SPAD has received reflected light from an object.

[0003] However, the output voltage or output current when each SPAD arranged in a two - dimensional array fires may vary for each SPAD. Therefore, if the threshold values of all SPADs in the LiDAR device are set uniformly, it becomes impossible to correctly detect whether each SPAD has fired.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, one embodiment of the present invention provides a light detection device and a distance measurement device that can correctly detect whether a light detection element has fired.

Means for Solving the Problems

[0006] To solve the above problems, according to one embodiment of the present invention, a photodetector element and An initialization circuit that sets one end of the photodetector to a predetermined initialization voltage, A fire detection circuit that detects the firing of the photodetector by comparing the voltage at one end of the photodetector or the current flowing through one end of the photodetector with a threshold value, A monitoring circuit that monitors the output signal of the ignition detection circuit, The system includes a threshold control circuit that controls the threshold based on the monitor output of the monitor circuit, A light detection device is provided. [Brief explanation of the drawing]

[0007] [Figure 1A] A block diagram showing the schematic configuration of a photodetector with an active quench circuit. [Figure 1B] A block diagram showing the schematic configuration of a photodetector with a passive quench circuit. [Figure 2] A graph showing the relationship between the threshold value of the fire detection circuit and the occurrence rate of dark pulses detected by the fire detection circuit. [Figure 3A] A diagram showing the relationship between threshold voltage and dark count rate. [Figure 3B] Waveform diagram of the cathode voltage of the photodetector and the output current of the fire detection circuit. [Figure 4A] A diagram showing the relationship between threshold voltage and dark count rate. [Figure 4B] Waveform diagram of the cathode voltage of the photodetector and the output current of the fire detection circuit. [Figure 5A] A diagram showing the relationship between threshold voltage and dark count rate. [Figure 5B] Waveform diagram of the cathode voltage of the photodetector and the output current of the fire detection circuit. [Figure 6A] A diagram showing the relationship between threshold voltage and dark count rate. [Figure 6B] Waveform diagram of the cathode voltage of the photodetector and the output current of the fire detection circuit. [Figure 7]Flowchart showing a first example of the processing operation of the photodetection device according to the first embodiment. [Figure 8] Flowchart showing a second example of the processing operation of the photodetection device according to the first embodiment. [Figure 9A] Diagram explaining the reason for setting the minimum value of the control range of the threshold within which the amount of variation in the dark count rate is within a predetermined amount as the threshold. [Figure 9B] Diagram explaining the reason for setting the minimum value of the control range of the threshold within which the amount of variation in the dark count rate is within a predetermined amount as the threshold. [Figure 10] Block diagram of the photodetection device according to the first specific example in which the ignition detection circuit is embodied. [Figure 11] Block diagram of the photodetection device according to the second specific example in which the ignition detection circuit is embodied. [Figure 12] Block diagram showing a specific example of the monitor circuit in FIG. 11. [Figure 13] Block diagram showing the schematic configuration of the photodetection device according to the second embodiment. [Figure 14] Block diagram showing the schematic configuration of the photodetection device according to a modification of FIG. 13. [Figure 15] Block diagram showing the schematic configuration of the distance measurement device including the photodetection device according to the third embodiment. [Figure 16] Block diagram showing the schematic configuration of the distance measurement device according to the first modification of the third embodiment. [Figure 17] Block diagram showing the schematic configuration of the distance measurement device according to the second modification of the third embodiment.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the photodetection device and the distance measurement device will be described with reference to the drawings. Hereinafter, the description will focus on the main components of the photodetection device and the distance measurement device, but there may be components and functions that are not shown or described in the photodetection device and the distance measurement device. The following description does not exclude components and functions that are not shown or described.

[0009] (First Embodiment) Figures 1A and 1B are block diagrams illustrating the schematic configuration of the light detection device 1 according to the first embodiment. The light detection circuit in Figures 1A and 1B is a circuit that receives reflected light that is reflected by an object after light has been projected onto the object.

[0010] The photodetector 1 shown in Figures 1A and 1B comprises a photodetector 2, a reverse bias circuit 3, a fire detection circuit 4, a monitor circuit 5, and a threshold control circuit 6.

[0011] The photodetector element 2 is, for example, a SPAD (Single Photon Avalanche Diode). The SPAD operates an APD (Avalanche Photo-Diode) in Geiger mode and can output an electrical signal obtained by photoelectric conversion of a single photon received. As will be described later, a pixel array section may be provided in which multiple photodetectors 2 are arranged in one or two dimensions, or a single photodetector element 2 may be provided within the photodetector device 1. In this specification, the two terminals of the photodetector element 2 are referred to as the anode and cathode.

[0012] The reverse bias circuit 3 is an initialization circuit that sets one end (e.g., the cathode) of the photodetector 2 to a predetermined initialization voltage. In this specification, the detection (reception) of a photon by the photodetector 2 is referred to as ignition. When the photodetector 2 ignites, the voltage at one end of the photodetector 2 (cathode voltage) decreases. When the photodetector 2 ignites and the cathode voltage of the photodetector 2 decreases, the reverse bias circuit 3 performs an operation to restore the cathode voltage to its original initialization voltage. The reverse bias circuit 3 may restore the cathode voltage of the photodetector 2 to the initialization voltage based on the output signal of the ignition detection circuit 4, which will be described later, or it may restore the cathode voltage of the photodetector 2 to the initialization voltage independently of the output signal of the ignition detection circuit 4.

[0013] The ignition detection circuit 4 detects ignition of the photodetector 2 by comparing the voltage at one end (cathode) of the photodetector 2 or the current flowing through one end with a threshold value. Figure 1A shows an active quench circuit in which the reverse bias circuit 3 restores one end of the photodetector 2 to its initial voltage based on the output signal of the ignition detection circuit 4. In contrast, Figure 1B shows a passive quench circuit in which the reverse bias circuit 3 restores one end of the photodetector 2 to its initial voltage independently of the output signal of the ignition detection circuit 4.

[0014] Thus, the ignition detection circuit 4, monitor circuit 5, and threshold control circuit 6 according to the first embodiment are applicable to both active quench circuits and passive quench circuits.

[0015] The ignition detection circuit 4 detects ignition of the photodetector element 2. It detects ignition of the photodetector element 2 in the event of spontaneous ignition under conditions where it is shielded from light, or when light is incident on the photodetector element 2.

[0016] The photodetector element 2 may spontaneously fire and generate pulses independent of the amount of incident light, which are called dark pulses. Dark pulses can be detected by appropriately setting the threshold of the fire detection circuit. In addition, the photodetector element 2 fires and generates pulses in response to ambient light such as sunlight. Fire pulses caused by ambient light can also be detected by appropriately setting the threshold of the fire detection circuit. Whether the fire detection circuit 4 can detect the fire of the photodetector element 2 depends on the threshold setting of the fire detection circuit 4.

[0017] The monitor circuit 5 monitors the output signal of the ignition detection circuit 4. For example, the monitor circuit 5 counts the number of times the ignition detection circuit 4 has detected an ignition and outputs the counted number as a monitor output. The monitor circuit 5 monitors ignitions based on dark pulses or ambient light detected by the ignition detection circuit 4. Specifically, the monitor circuit 5 counts the number of times the ignition detection circuit 4 has detected an ignition based on dark pulses or ambient light.

[0018] The threshold control circuit 6 controls the threshold of the ignition detection circuit 4 based on the monitor output of the monitor circuit 5. For example, the threshold control circuit 6 controls the threshold so that the ignition detection rate in the ignition detection circuit 4 is maximized.

[0019] Figure 2 is a graph showing the relationship between the threshold of the ignition detection circuit 4 and the number of dark pulses detected per unit time by the ignition detection circuit 4 (hereinafter referred to as the dark count rate, DCR). In Figure 2, the horizontal axis is the threshold setting value and the vertical axis is the dark count rate. In Figure 2, the threshold of the ignition detection circuit 4 is classified into three ranges (1st to 3rd threshold ranges) in order of magnitude: TR1, TR2, and TR3. The threshold increases in the order of the 1st threshold range TR1, the 2nd threshold range TR2, and the 3rd threshold range TR3. When the threshold of the ignition detection circuit 4 is within the 1st threshold range TR1, the dark count rate by the ignition detection circuit 4 increases as the threshold increases and becomes almost zero when the threshold decreases. When the threshold of the ignition detection circuit 4 is within the 2nd threshold range TR2, the dark count rate by the ignition detection circuit 4 maintains its maximum value. When the threshold of the ignition detection circuit 4 is within the third threshold range TR3, the dark count rate by the ignition detection circuit 4 decreases as the threshold increases, and becomes almost zero when the threshold is high.

[0020] The threshold control circuit 6 may have a function to search for the optimal threshold by continuously or intermittently changing (sweeping) the threshold of the ignition detection circuit 4. The optimal threshold lies within the second threshold range TR2 where the dark count rate is maximized. More specifically, the threshold control circuit 6 may continuously or intermittently change the threshold of the ignition detection circuit 4 and control the threshold so that the count value of the counter in the monitor circuit 5 falls within a predetermined rate of fluctuation. Within the predetermined rate of fluctuation means the dark count rate within the second threshold range TR2 where the dark count rate is approximately at its maximum value, which is within the dashed box 11 in Figure 2.

[0021] Furthermore, the threshold control circuit 6 may set the threshold to the median value of the threshold control range in which the counter's count value falls within a predetermined rate of change. Alternatively, the threshold control circuit 6 may set the threshold to the minimum value of the threshold control range in which the counter's count value falls within a predetermined rate of change. In other words, the threshold is set to the median or minimum value within the dashed box 11 in Figure 2.

[0022] The ignition detection circuit 4 can detect ignition based on the result of comparing the cathode voltage of the photodetector 2 with the threshold voltage output from the threshold control circuit 6.

[0023] Figures 3A and 3B are characteristic diagrams of the ignition detection circuit 4 when the threshold voltage Vth is less than or equal to the first voltage V1. Figure 3A shows the relationship between the threshold voltage Vth and the dark count rate, and Figure 3B shows the waveform of the cathode voltage of the photodetector 2 and the output current of the ignition detection circuit 4.

[0024] As shown in Figure 3B, the cathode voltage of the photodetector 2 drops sharply to its lowest voltage when the photodetector 2 ignites, and then gradually increases back to its original initialization voltage. Since the first voltage is lower than the lowest voltage when the photodetector 2 ignites, the ignition detection circuit 4 does not detect ignition, as shown in Figure 3A, and almost no current flows through the cathode of the ignition detection circuit 4, as shown in Figure 3B.

[0025] Figures 4A and 4B are characteristic diagrams of the fire detection circuit 4 when the threshold voltage Vth is near the first voltage V1. Figure 4A shows the relationship between the threshold voltage Vth and the dark count rate, and Figure 4B shows the waveform of the cathode voltage of the photodetector 2 and the output current of the fire detection circuit 4.

[0026] Figure 4B shows the cathode voltage of the photodetector 2 when the reverse bias circuit 3 and the ignition detection circuit 4 constitute an active quench circuit. The active quench circuit performs initialization in two stages, as shown in Figure 4B. When the photodetector 2 ignites and the cathode voltage drops (time t1), the cathode voltage is kept below the breakdown voltage VBD (VBD-α) during the period from time t1 to t2. Then, during the period from time t2 to t3, the reverse bias circuit 3 performs the first stage of initialization. When the cathode voltage rises above the threshold voltage Vth (time t3), the reverse bias circuit 3 performs the second stage of initialization during the period from time t3 to t4. In the second stage of initialization, the cathode voltage of the photodetector 2 returns to the initialization voltage.

[0027] If the threshold voltage Vth is near the first voltage V1, as shown in Figure 4B, the threshold voltage Vth is about the same as the breakdown voltage of the photoluminescent element. Therefore, due to the influence of noise, the threshold voltage Vth may not be exceeded, and not all ignitions can be detected. As a result, although the dark count rate is higher than in Figure 3A, it is still below the maximum value.

[0028] Figures 5A and 5B are characteristic diagrams of the fire detection circuit 4 when the threshold voltage Vth is near the second voltage V2. Figure 5A shows the relationship between the threshold voltage Vth and the dark count rate, and Figure 5B shows the waveform of the cathode voltage of the photodetector 2 and the output current of the fire detection circuit 4.

[0029] If the threshold voltage Vth is near the second voltage V2, as shown in Figure 5B, the threshold voltage Vth will be at an appropriate voltage level, and all ignitions can be detected without being affected by noise, so the dark count rate will be maximized as shown in Figure 5A.

[0030] Figures 6A and 6B are characteristic diagrams of the fire detection circuit 4 when the threshold voltage Vth is equal to or greater than the initialization voltage. Figure 6A shows the relationship between the threshold voltage Vth and the dark count rate, and Figure 6B shows the waveform of the cathode voltage of the photodetector 2 and the output current of the fire detection circuit 4.

[0031] If the threshold voltage Vth is greater than or equal to the initialization voltage, the cathode voltage is constantly above the threshold voltage Vth. As a result, the ignition detection circuit 4 constantly detects ignition, and the output current remains constant. Therefore, it is not possible to detect ignition of the photodetector element 2.

[0032] Figures 3B, 4B, 5B, and 6B show the waveform of the output current of the fire detection circuit 4. The waveform of the output voltage of the fire detection circuit 4 also changes in accordance with the voltage level of the threshold voltage Vth, similar to the waveform of the output current. When a fire is detected, it outputs a pulsed voltage signal (hereinafter referred to as a pulse signal).

[0033] As can be seen from Figures 3A, 3B, 4A, 4B, 5A, 5B, 6A, and 6B, the dark count rate changes when the threshold control circuit 6 changes (sweeps) the threshold voltage Vth from the first voltage V1 to the initialization voltage. The dark count rate is maximum when the threshold voltage Vth of the fire detection circuit 4 is near the second voltage V2, at which point the fire detection circuit 4 outputs a pulse signal.

[0034] Figure 7 is a flowchart showing a first example of the processing operation of the photodetector 1 according to the first embodiment. The processing shown in the flowchart of Figure 7 is performed when the photodetector 2 is shielded from light, or when ambient light of uniform illuminance is incident on the photodetector 2.

[0035] First, the threshold of the ignition detection circuit 4 is set (step S1). The threshold is either a threshold voltage or a threshold current. The threshold control circuit 6 continuously or intermittently changes the threshold within a predetermined search range. The flowchart in Figure 7 illustrates an example in which the threshold control circuit 6 sequentially increases the threshold from the minimum value within the search range.

[0036] Next, the monitor circuit 5 detects the ignition status of the ignition detection circuit 4 (step S2). The ignition status indicates whether the ignition detection circuit 4 has detected an ignition or not, and is detected by the output signal of the ignition detection circuit 4. For example, when the ignition detection circuit 4 detects an ignition, it outputs a pulse signal. This pulse signal represents dark pulses with an occurrence rate corresponding to a threshold.

[0037] Next, the monitor circuit 5 counts the pulse signals output from the ignition detection circuit 4 and calculates the dark count rate (step S3). The dark count rate is calculated by the number of pulses in the pulse signal output from the ignition detection circuit 4 within a unit time.

[0038] Next, it is determined whether the threshold has reached the maximum value of the search range (step S4). If the threshold has not reached the maximum value of the search range, the process from step S1 onwards is repeated. If the threshold has reached the maximum value of the search range, the threshold control circuit 6 detects a threshold control range in which the amount of variation in the dark count rate falls within a predetermined amount (step S5). The median value of the detected threshold control range is set as the threshold of the ignition detection circuit 4 (step S6).

[0039] For example, the dashed box 11 in Figure 2 represents the range where the variation in the dark count rate is within a predetermined amount. In step S5 of Figure 7, the threshold value of the ignition detection circuit 4 is set to the median value CT within the dashed box 11 in Figure 2. By setting the threshold value to the median value of the control range of the threshold where the variation in the dark count rate stays within a predetermined amount, even if the PVT (process, voltage, temperature) changes, there is no risk of the set threshold value falling outside the optimal range, and a robust threshold setting can be achieved.

[0040] Figure 8 is a flowchart showing a second example of the processing operation of the photodetector 1 according to the first embodiment. In Figure 8, the same step numbers are used for processes common to Figure 7, and the differences will be explained below. In the flowchart of Figure 8, steps S1 to S4 are processed in the same way as in Figure 7. If it is determined in step S4 that the threshold has reached the maximum value of the search range, the threshold control circuit 6 sets the threshold of the ignition detection circuit 4 to the minimum value of the threshold control range in which the amount of variation in the dark count rate stays within a predetermined amount (step S6a).

[0041] Thus, step S6a in Figure 8 differs from step S6 in Figure 7 in that it sets the threshold to the minimum value, rather than the median value, of the control range of the threshold that keeps the variation in the dark count rate within a predetermined amount. Figures 9A and 9B illustrate the reason why, in step S6a of Figure 8, the minimum value of the threshold control range that keeps the variation in the dark count rate within a predetermined amount is set as the threshold.

[0042] In an active quench circuit that performs initialization in two stages—a first-stage slow recharge and a second-stage fast recharge—to prevent thermal damage to the SPAD, the dead time during which the photodetector 2 cannot respond depends on the threshold voltage. Figure 9A shows an example where the threshold voltage is lower than in Figure 9B. In Figures 9A and 9B, the second-stage initialization operation begins when the cathode voltage of the photodetector 2 reaches the threshold voltage. The second-stage initialization operation involves a larger change in cathode voltage per unit time than the first-stage initialization operation. Therefore, starting the second-stage initialization operation at a lower threshold voltage level, as shown in Figure 9A, can further shorten the dead time.

[0043] Thus, from the perspective of further reducing dead time, it is preferable to set the minimum value of the control range of the threshold as the threshold, as shown in step S6a of Figure 8, rather than setting the median value of the control range of the threshold as the threshold, as shown in step S6 of Figure 7, because this further reduces the dead time.

[0044] In the flowcharts of Figures 7 and 8, the threshold was set based on the dark count rate, but the threshold may also be set based on the rate of fire ignition due to ambient light.

[0045] Furthermore, while the flowcharts in Figures 7 and 8 illustrate an example using a linear search method to set the optimal threshold by continuously or intermittently changing the threshold within the search range, the optimal threshold may also be set using a binary search method. By adopting a binary search method, the number of iterations required to set the optimal threshold can be reduced, allowing for a faster setting of the optimal threshold.

[0046] The flowcharts in Figures 7 and 8 show an example where the threshold of the firing detection circuit 4 is set to the median or minimum value of the threshold control range in which the variation in the dark count rate falls within a predetermined amount. However, the average value of the threshold control range may also be set as the threshold.

[0047] Figure 10 is a block diagram of a photodetector 1 relating to a first specific example that embodies the ignition detection circuit 4. The ignition detection circuit 4 in Figure 10 has a voltage comparator 4a. The voltage comparator 4a in Figure 10 compares the cathode voltage of the photodetector 2 with the threshold voltage controlled by the threshold control circuit 6 and outputs a signal indicating the comparison result. For example, the voltage comparator 4a outputs a high-level pulse signal when the cathode voltage of the photodetector 2 is less than or equal to the threshold voltage.

[0048] The monitor circuit 5 includes, for example, a counter 12. The counter 12 counts the pulse signals output from the voltage comparator 4a. The threshold control circuit 6 detects the frequency of pulse signals per unit time based on the count value of the counter 12, and controls the threshold voltage of the voltage comparator 4a according to the flowchart in Figure 7 or Figure 8 based on the detected frequency.

[0049] Figure 11 is a block diagram of a photodetector 1 relating to a second specific example that embodies the ignition detection circuit 4. The ignition detection circuit 4 in Figure 11 has a current comparator 4b. The current comparator 4b in Figure 11 compares the cathode current of the photodetector 2 with the threshold current controlled by the threshold control circuit 6 and outputs a signal indicating the comparison result. For example, the current comparator 4b outputs a high-level pulse signal when the cathode current of the photodetector 2 is less than or equal to the threshold current. The monitor circuit 5 counts the pulse signals output from the current comparator 4b and detects the occurrence rate of pulse signals per unit time. The threshold control circuit 6 controls the threshold current of the current comparator 4b based on the occurrence rate of pulse signals per unit time.

[0050] The monitor circuit 5 may be equipped with a counter 12 that counts the number of pulse signals output from the ignition detection circuit 4, as shown in Figure 10, or it may detect ignition in the ignition detection circuit 4 by other means.

[0051] Figure 12 is a block diagram showing a specific example of the monitor circuit 5. The monitor circuit 5 in Figure 12 is a VCO-based monitor circuit 13 and includes a current mirror circuit 14, a first current source 15, a second current source 16, a ring oscillator 17, and a frequency counter 18.

[0052] The first current source 15 and the second current source 16 are connected in parallel to the current mirror circuit 14. The current flowing through the first current source 15 is controlled based on the output signal of the ignition detection circuit 4. When the current flowing through the first current source 15 changes, the power supply voltage supplied to the ring oscillator 17 changes, and the frequency of the oscillation signal generated by the ring oscillator 17 changes. The frequency counter 18 counts the frequency of the oscillation signal. As a result, the count value of the frequency counter 18 changes according to the comparison result of the ignition detection circuit 4.

[0053] Although the monitor circuit 5 in Figure 12 is larger in scale than the monitor circuit 5 in Figure 11, it can accurately detect the comparison results because it is also sensitive to the pulse width of the ignition detection circuit 4.

[0054] Thus, in the first embodiment, the threshold of the ignition detection circuit 4 is set based on the dark count rate or the rate of ignition due to ambient light detected by the ignition detection circuit 4. Specifically, the threshold is set based on the control range of the threshold within which the amount of variation in the dark count rate or the rate of ignition due to ambient light falls within a predetermined amount, so that the optimal threshold can be set according to the characteristics of the photodetector element 2.

[0055] (Second embodiment) The second embodiment involves arranging multiple photodetectors 2, similar to those in the first embodiment, in a one-dimensional or two-dimensional direction.

[0056] Figure 13 is a block diagram showing the schematic configuration of the photodetector 1 according to the second embodiment. The photodetector 1 in Figure 13 comprises a plurality of active quench circuits (AQ circuits) 21 arranged in one-dimensional or two-dimensional directions. Each active quench circuit 21 has the reverse bias circuit 3 and the ignition detection circuit 4 described above.

[0057] Figure 13 shows a configuration in which multiple active quench circuits 21 are arranged in a predetermined direction Y, but multiple active quench circuits 21 may also be arranged in a direction X that intersects the predetermined direction Y.

[0058] The output nodes of the multiple active quench circuits 21, which are arranged in a predetermined direction Y, are all connected to the input nodes of the monitor circuit 5. The output node of the threshold control circuit 6 is connected to the input nodes of the multiple active quench circuits 21.

[0059] As shown above, in the photodetector 1 of Figure 13, one monitor circuit 5 and one threshold control circuit 6 are provided in association with a plurality of active quench circuits 21. The number of active quench circuits 21 provided for each monitor circuit 5 and threshold control circuit 6 is arbitrary. In this specification, the monitor circuit 5 and threshold control circuit 6 corresponding to a plurality of active quench circuits 21 are referred to as the threshold detection circuit 22.

[0060] The output signals from each ignition detection circuit 4 within the multiple active quench circuits 21 are input to the monitor circuit 5 via a common signal wiring. The monitor circuit 5 then counts the pulse signals output from the corresponding multiple ignition detection circuits 4. The threshold control circuit 6 sets a common threshold for the corresponding multiple ignition detection circuits 4 based on the count value counted by the monitor circuit 5. This eliminates the need for a threshold detection circuit 22 consisting of a monitor circuit 5 and a threshold control circuit 6 for each active quench circuit 21, reducing the mounting area of ​​the threshold detection circuit 22 and allowing for a smaller optical detection device 1.

[0061] Since the multiple active quench circuits 21 arranged adjacent to each other have the same or similar electrical characteristics, mismatches do not pose a problem even if the threshold values ​​of each ignition detection circuit 4 within the multiple active quench circuits 21 are set to be the same.

[0062] Figure 14 is a block diagram showing a schematic configuration of a photodetector 1 according to one modified example of Figure 13. The photodetector 1 in Figure 14 comprises a SiPM (Silicon Photo-multiplier) array section 23 and a plurality of threshold detection circuits 22.

[0063] The SiPM array section 23 has a plurality of SiPMs 20 arranged along a first direction X and a second direction Y. Each SiPM constitutes a pixel. Each SiPM has one or more active quench circuits 21. Each active quench circuit 21 has a photodetector 2 and a fire detection circuit 4.

[0064] In the example shown in Figure 14, the photodetector 1 has a threshold detection circuit 22 for each group of active quench circuits 24, each having multiple active quench circuits 21 arranged along a first direction X. Multiple threshold detection circuits 22 are arranged along a second direction Y, and each threshold detection circuit 22 is provided for each corresponding group of active quench circuits 24.

[0065] Each threshold detection circuit 22 includes a monitor circuit 5, a threshold control circuit 6, and a pixel selection circuit 25. The input node of the monitor circuit 5 is connected to the output nodes of multiple active quench circuits 21 belonging to the corresponding active quench circuit group 24. More specifically, the input node of the monitor circuit 5 is connected to the output nodes of multiple ignition detection circuits 4 within the multiple active quench circuits 21.

[0066] The monitor circuit 5 within each threshold detection circuit 22 counts the pulse signals output from the fire detection circuit 4 within the active quench circuit 21 selected by the pixel selection circuit 25 from among multiple active quench circuits 21 belonging to the corresponding active quench circuit group 24. The threshold control circuit 6 within each threshold detection circuit 22 controls the threshold of the fire detection circuit 4 within the active quench circuit 21 selected by the pixel selection circuit 25 from among multiple active quench circuits 21 belonging to the corresponding active quench circuit group 24, based on the count value counted by the monitor circuit 5.

[0067] In the photodetector 1 shown in Figure 14, a threshold detection circuit 22 is provided for each active quench circuit group 24, which includes multiple active quench circuits 21 arranged in a first direction X. This eliminates the need to provide a threshold detection circuit 22 for each active quench circuit 21, thus reducing the mounting area of ​​the threshold detection circuit 22. Furthermore, since a pixel selection circuit 25 is provided within the threshold detection circuit 22, the threshold can be controlled individually for each firing detection circuit 4 within the active quench circuit 21 belonging to the active quench circuit group 24.

[0068] Thus, in the second embodiment, since multiple active quench circuits 21 share a single threshold detection circuit 22, it is no longer necessary to provide a threshold detection circuit 22 for each active quench circuit 21, reducing the mounting area of ​​the threshold detection circuit 22 and allowing the optical detection device 1 to be miniaturized. As a result, the active quench circuits 21 can be mounted at a higher density, increasing the number of pixels in the SiPM array section 23 and improving the resolution.

[0069] (Third embodiment) The third embodiment applies the light detection device 1 according to the first or second embodiment to a distance measuring device.

[0070] Figure 15 is a block diagram showing the schematic configuration of a distance measuring device 31 equipped with a light detection device 1 according to a third embodiment. The distance measuring device 31 in Figure 15 comprises a light detection device 1 and a distance measuring unit 32. The light detection device 1 in Figure 15 has a configuration similar to, for example, the light detection device 1 in Figure 15. The light detection device 1 in Figure 15 includes a threshold detection circuit 22 having a monitor circuit 5, a threshold control circuit 6, and a pixel selection circuit 25, whereas the light detection device 1 in Figure 15 integrates the monitor circuit 5 shown in Figure 1, etc., into the distance measuring unit 32.

[0071] The distance measuring unit 32 includes a light-emitting unit that projects light onto an object, a light-receiving unit that receives reflected light from the object, and a distance measuring unit that measures the distance to the object based on the time difference between the light projection timing and the light reception timing. The distance measuring unit 32 incorporates, for example, a counter that measures the number of received pulses, and this counter is reused in the monitor circuit 5. This eliminates the need for a dedicated counter 12 for the monitor circuit 5, and reduces the circuit size of the distance measuring device 31. In addition, even if a counter is not provided, the number of dark pulses can be estimated from the amplitude histogram of the AD conversion result of the output signal of the distance-measuring light detection device 1.

[0072] The SiPM array section 23, which has multiple SiPMs 20 arranged in a two-dimensional direction, and the pixel selection circuit 25 are arranged on, for example, the first semiconductor device 26. The distance measuring section 32, which has a monitor circuit 5, is arranged on, for example, the second semiconductor device 27. The second semiconductor device 27 is also called a measurement IC. The threshold control circuit 6 is arranged on the second semiconductor device 27 or on a third semiconductor device (not shown). Thus, the distance measuring device 31 of Figure 15 can be realized with at least two semiconductor devices, including the first semiconductor device 26 and the second semiconductor device 27.

[0073] Figure 16 is a block diagram showing the schematic configuration of a distance measuring device 31 according to a first modified example of the third embodiment. The optical detection device 1 in the distance measuring device 31 in Figure 16 has one pixel selection circuit 25 for a plurality of active quench circuit groups 24 arranged in the first direction X and second direction Y within the SiPM array section 23. For example, by using a control method such as I2C (Inter Integrated Circuit), the threshold of the selected pixel can be set sequentially. The pixel selection circuit 25 and the SiPM array section 23 are arranged in the first semiconductor device 26, but the number of pixel selection circuits 25 in the first semiconductor device 26 can be reduced compared to Figure 15, so the first semiconductor device 26 can be miniaturized and the SiPM array section 23 within the first semiconductor device 26 can be highly integrated, thereby improving the resolution.

[0074] Figure 17 is a block diagram showing the schematic configuration of a distance measuring device 31 according to a second modification of the third embodiment. The distance measuring device 31 in Figure 17 includes a storage device 33 in addition to the configuration in Figure 16. The storage device 33 stores the count value counted by the monitor circuit 5 in the second semiconductor device 27. The storage device 33 stores the pulse signal output from the ignition detection circuit 4 in the active quench circuit 21 selected by the pixel selection circuit 25, in association with the active quench circuit 21. The threshold control circuit 6 reads the count value corresponding to the active quench circuit 21 selected by the pixel selection circuit 25 from the storage device 33 and controls the threshold value to the ignition detection circuit 4 in the corresponding active quench circuit 21. The storage device 33 is located in the second semiconductor device 27 or in a third semiconductor device (not shown).

[0075] The monitor circuit 5 in the second semiconductor device 27 counts the pulse signals detected by the fire detection circuit 4 in the active quench circuit 21 selected by the pixel selection circuit 25 during blanking periods when the distance measuring unit 32 is not performing distance measurements, and stores the count value in the storage device 33. This allows the threshold control circuit 6 to read the count value from the storage device 33 just before the distance measuring unit 32 starts the distance measurement process, thereby controlling the threshold of the fire detection circuit 4 and enabling rapid distance measurement with the optimal threshold set for the fire detection circuit 4. Note that a storage device 33 similar to that in Figure 17 may be added to the distance measuring device 31 in Figure 15.

[0076] Thus, in the third embodiment, since the function of the monitor circuit 5 is provided within the second semiconductor device 27 having the distance measuring unit 32, it is not necessary to provide the monitor circuit 5 inside the first semiconductor device 26 having the SiPM array unit 23 and the pixel selection circuit 25, and the distance measuring device 31 can be miniaturized. Furthermore, by providing the threshold control circuit 6 in a semiconductor device other than the first semiconductor device 26, the first semiconductor device 26 can be miniaturized and the pixel resolution of the SiPM array unit 23 can be improved.

[0077] Furthermore, since a storage device 33 is provided to store the count value counted by the monitor circuit 5 or the threshold value set by the threshold control unit, it is not necessary to perform the process of searching for the optimal threshold value each time distance measurement is performed, the frame rate can be increased, and power consumption can be reduced by decreasing the number of searches.

[0078] [Note] [Item 1] A light detection element, An initialization circuit that sets one end of the photodetector to a predetermined initialization voltage, A fire detection circuit that detects the firing of the photodetector by comparing the voltage at one end of the photodetector or the current flowing through one end of the photodetector with a threshold value, A monitoring circuit that monitors the output signal of the ignition detection circuit, The system includes a threshold control circuit that controls the threshold based on the monitor output of the monitor circuit, Light detection device. [Item 2] When the ignition detection circuit detects a fire, the initialization circuit restores one end of the photodetector to the initialization voltage based on the output signal of the ignition detection circuit. The light detection device described in item 1. [Item 3] When the ignition detection circuit detects a fire, the initialization circuit restores one end of the photodetector to the initialization voltage, regardless of the output signal of the ignition detection circuit. The light detection device described in item 1. [Item 4] The ignition detection circuit detects ignition of the photodetector element when the photodetector element is shielded from light or when ambient light of uniform illuminance is incident on the photodetector element. A light detection device as described in any one of items 1 to 3. [Item 5] The ignition detection circuit detects ignition caused by dark pulses or ambient light that have sensitivity to the threshold. The light detection device described in item 4. [Item 6] The ignition detection circuit includes a voltage comparator that compares the voltage at one end of the photodetector with a threshold voltage and outputs a binary signal indicating the comparison result. The monitoring circuit has a counter that monitors the number of signal changes of the binary signal, The threshold control circuit controls the threshold voltage based on the monitor output of the monitor circuit. A light detection device as described in any one of items 1 to 5. [Item 7] The ignition detection circuit includes a current comparator that compares the current flowing through one end of the photodetector with a threshold current. The threshold control circuit controls the threshold current based on the Monitor output of the Monitor circuit. A light detection device as described in any one of items 1 to 5. [Item 8] The ignition detection circuit outputs a signal corresponding to the comparison result between the signal from one end of the photodetector and the threshold value. The aforementioned monitoring circuit is An oscillator that outputs an oscillation signal with a frequency corresponding to the output signal of the ignition detection circuit, The system includes a frequency counter for detecting the frequency of the oscillation signal, The threshold control circuit controls the threshold based on the count value of the frequency counter. A light detection device as described in item 7 or 6. [Item 9] The ignition detection circuit outputs a pulse signal with an occurrence rate corresponding to the threshold, The threshold control circuit controls the threshold based on the generation rate of the pulse signal. A light detection device as described in any one of items 1 to 8. [Item 10] The threshold control circuit continuously or stepwise changes the threshold so that the amount of variation in the pulse signal generation rate falls within a predetermined amount, and sets the threshold to the firing detection circuit. The light detection device described in item 9. [Item 11] The threshold control circuit sets the threshold to the median value of the control range of the threshold such that the amount of variation in the generation rate of the pulse signal falls within a predetermined amount. The light detection device described in item 10. [Item 12] The threshold control circuit sets the threshold to the minimum value of the control range of the threshold such that the amount of variation in the generation rate of the pulse signal falls within a predetermined amount. The light detection device described in item 10. [Item 13] The pixel array section comprises a plurality of the aforementioned photodetectors arranged in a one-dimensional or two-dimensional direction, The monitor circuit and the threshold control circuit are shared by two or more of the photodetectors. The ignition detection circuit is provided for each of the plurality of photodetectors, The threshold control circuit controls the threshold of the two or more ignition detection circuits corresponding to the two or more shared photodetectors. A light detection device as described in any one of items 1 to 12. [Item 14] A group of photodetectors having a plurality of the photodetectors arranged in a predetermined direction, The system includes a selection circuit for selecting any of the photodetectors from the group of photodetectors, The ignition detection circuit, the monitoring circuit, and the threshold control circuit are provided in correspondence with the photodetector group, The monitoring circuit monitors the output signal of the ignition detection circuit corresponding to the photodetector selected by the selection circuit among the corresponding photodetector group, The threshold control circuit controls the threshold of the firing detection circuit corresponding to the photodetector selected by the selection circuit, based on the monitor output of the monitor circuit. A light detection device as described in any one of items 1 to 12. [Item 15] The light detection device described in item 14, It includes a distance measuring unit that projects light onto an object and receives reflected light from the object, and measures the distance to the object based on the time difference between the light projection timing and the light reception timing, The monitoring circuit uses the circuit of the distance measuring unit to monitor the output signal of the ignition detection circuit. Ranging device. [Item 16] The system includes a storage unit that stores control information for the threshold controlled by the threshold control circuit, The threshold control circuit reads the threshold control information stored in the storage unit when power is supplied or during initialization, and controls the threshold. The distance measuring device described in item 15. [Item 17] A first semiconductor device having the aforementioned photodetector group, the ignition detection circuit, and the selection circuit, A second semiconductor device having the distance measuring unit and the monitoring circuit, The distance measuring device described in item 15. [Item 18] A first semiconductor device having the aforementioned photodetector group, the ignition detection circuit, and the selection circuit, The device comprises the distance measuring device and the second semiconductor device having the monitoring circuit, The threshold control circuit and the memory unit are arranged in the second semiconductor device, or in a third semiconductor device separate from the first and second semiconductor devices. The distance measuring device described in item 16.

[0079] The aspects of this disclosure are not limited to the individual embodiments described above, but include various modifications that a person skilled in the art could conceive, and the effects of this disclosure are not limited to those described above. In other words, various additions, modifications, and partial deletions are possible, as long as they do not depart from the conceptual idea and spirit of this disclosure derived from the claims and their equivalents. [Explanation of symbols]

[0080] 1. Photodetector, 2. Photodetector element, 3. Reverse bias circuit, 4. Ignition detection circuit, 4a. Voltage comparator, 4b. Current comparator, 5. Monitor circuit, 6. Threshold control circuit, 12. Counter, 13. Current monitor circuit, 14. Current mirror circuit, 15. First current source, 16. Second current source, 17. Ring oscillator, 18. Frequency counter, 21. Active quench circuit, 22. Threshold detection circuit, 23. SiPM array section, 24. Active quench circuit group, 25. Pixel selection circuit, 26. First semiconductor device, 27. Second semiconductor device, 31. Distance measuring device, 32. Distance measuring section, 33. Memory device

Claims

1. A light detection element, An initialization circuit that sets one end of the photodetector to a predetermined initialization voltage, A fire detection circuit that detects the firing of the photodetector by comparing the voltage at one end of the photodetector with a threshold value, A monitoring circuit that monitors the output signal of the ignition detection circuit, The system includes a threshold control circuit that controls the threshold based on the monitor output of the monitor circuit, When the ignition detection circuit detects a fire, the initialization circuit restores the first end of the photodetector to the initialization voltage by different amounts of voltage change depending on whether the voltage at the first end exceeds the threshold. The ignition detection circuit outputs a pulse signal with an occurrence rate corresponding to the threshold, The threshold control circuit sets the threshold to the minimum value of the control range of the threshold such that the amount of variation in the generation rate of the pulse signal falls within a predetermined amount. Light detection device.

2. The initialization circuit restores the voltage at one end of the photodetector to the initialization voltage by making the voltage change when the voltage at the threshold exceeds the threshold larger than when the voltage at the one end of the photodetector does not exceed the threshold. The light detection device according to claim 1.

3. The ignition detection circuit detects ignition of the photodetector element when the photodetector element is shielded from light or when ambient light of uniform illuminance is incident on the photodetector element. The light detection device according to claim 1.

4. The ignition detection circuit detects ignition caused by dark count or ambient light, which has sensitivity to the threshold. The light detection device according to claim 3.

5. The ignition detection circuit includes a voltage comparator that compares the voltage at one end of the photodetector with a threshold voltage and outputs a binary signal indicating the comparison result. The monitoring circuit has a counter that monitors the number of signal changes of the binary signal, The threshold control circuit controls the threshold voltage based on the monitor output of the monitor circuit. The light detection device according to claim 1.

6. The ignition detection circuit outputs a signal corresponding to the comparison result between the signal from one end of the photodetector and the threshold value. The aforementioned monitoring circuit is An oscillator that outputs an oscillation signal with a frequency corresponding to the output signal of the ignition detection circuit, The system includes a frequency counter for detecting the frequency of the oscillation signal, The threshold control circuit controls the threshold based on the count value of the frequency counter. The light detection device according to claim 1.

7. The threshold control circuit continuously or stepwise changes the threshold so that the amount of variation in the pulse signal generation rate falls within a predetermined amount, and sets the threshold to the firing detection circuit. The light detection device according to claim 1.

8. The pixel array section comprises a plurality of the aforementioned photodetectors arranged in a one-dimensional or two-dimensional direction, The monitor circuit and the threshold control circuit are shared by two or more of the photodetectors. The ignition detection circuit is provided for each of the plurality of photodetectors, The threshold control circuit controls the threshold of the two or more ignition detection circuits corresponding to the two or more shared photodetectors. The light detection device according to claim 1.

9. A group of photodetectors having a plurality of the photodetectors arranged in a predetermined direction, The system includes a selection circuit for selecting any of the photodetectors from the group of photodetectors, The ignition detection circuit, the monitoring circuit, and the threshold control circuit are provided in correspondence with the photodetector group, The monitoring circuit monitors the output signal of the ignition detection circuit corresponding to the photodetector selected by the selection circuit among the corresponding photodetector group, The threshold control circuit controls the threshold of the firing detection circuit corresponding to the photodetector selected by the selection circuit, based on the monitor output of the monitor circuit. The light detection device according to claim 1.

10. The photodetector according to claim 9, It includes a distance measuring unit that projects light onto an object and receives reflected light from the object, and measures the distance to the object based on the time difference between the light projection timing and the light reception timing, The monitoring circuit uses the circuit of the distance measuring unit to monitor the output signal of the ignition detection circuit. Ranging device.

11. The system includes a storage unit that stores control information for the threshold controlled by the threshold control circuit, The threshold control circuit reads the threshold control information stored in the storage unit when power is supplied or during initialization, and controls the threshold. The distance measuring device according to claim 10.

12. A first semiconductor device having the photodetector group, the ignition detection circuit, and the selection circuit, A second semiconductor device having the distance measuring unit and the monitoring circuit, The distance measuring device according to claim 10.

13. A first semiconductor device having the photodetector group, the ignition detection circuit, and the selection circuit, The device comprises the distance measuring device and the second semiconductor device having the monitoring circuit, The threshold control circuit and the memory unit are arranged in the second semiconductor device, or in a third semiconductor device separate from the first and second semiconductor devices. The distance measuring device according to claim 11.

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