Photodetector circuit and distance measuring device

Abstract

[Problem] To provide an optical detection circuit by which distance measurement performance can be improved. [Solution] An optical detection circuit according to one embodiment of the present disclosure is provided with: an avalanche photodiode; a charging circuit that supplies a voltage to the avalanche photodiode; an input amplifier including a comparison circuit in which the voltage level of an output terminal is changed in accordance with a result of comparison between a reference voltage and the voltage of an input terminal connected to the avalanche photodiode, and a voltage control circuit that changes the electric potential of the reference voltage; and a state detection circuit that, on the basis of a detection result of the voltage level, sets a timing for causing the voltage control circuit to change the electric potential of the reference voltage.

Description

[Technical Field]

[0001] The present disclosure relates to a photodetector circuit and a distance measuring device. [Background technology]

[0002] The ToF (Time of Flight) method is used to measure the distance to a subject. In the ToF method, light emitted from a light source is detected when it is reflected by the subject. The distance to the subject is then measured based on the time between the emission of light and the detection of the reflected light.

[0003] Distance measuring devices using the ToF method generally include a photodetection circuit that detects the reflected light. The photodetection circuit detects the voltage change of the photodetector element when a photon is incident. The reference voltage for detecting this voltage change is generally fixed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-81254 Summary of the Invention [Problem to be solved by the invention]

[0005] If the reference voltage is low, the variation in the characteristics of the photodetector element may result in a large distance measurement error, so in order to reduce this distance measurement error, it is desirable to have a high reference voltage.

[0006] However, if the reference voltage is high, the dead time, which is the period during which photons cannot be detected, becomes long, and distance measurement accuracy may decrease.

[0007] The present disclosure provides a photodetector circuit and a distance measuring device that can improve distance measurement performance. [Means for solving the problem]

[0008] A photodetection circuit according to an embodiment of the present disclosure includes an input amplifier including an avalanche photodiode, a charging circuit that supplies a voltage to the avalanche photodiode, a comparison circuit in which the voltage level of an output terminal changes depending on a comparison result between a voltage at an input terminal connected to the avalanche photodiode and a reference voltage, and a voltage control circuit that changes the potential of the reference voltage, and a state detection circuit that sets a timing for changing the potential of the reference voltage in the voltage control circuit based on the detection result of the voltage level.

[0009] The comparison circuit includes an inverter circuit, The voltage control circuit may include a switching element connected to the inverter circuit and switching in response to the output voltage of the state detection circuit, and a resistance element or a current source connected in parallel with the switching element.

[0010] The comparison circuit includes an operational amplifier circuit, The voltage control circuit may include a switch circuit that switches the reference voltage between a first reference voltage and a second reference voltage different from the first reference voltage, depending on the output voltage of the state detection circuit.

[0011] The comparison circuit includes an inverter circuit, The voltage control circuit may include a current source connected to the inverter circuit and having an output current value that changes in accordance with the output voltage of the state detection circuit.

[0012] The state detection circuit may include an odd number of inverter stages connected in series with each other.

[0013] The input amplifier may include a first input amplifier that outputs the comparison result to a signal processing circuit, and a second input amplifier that outputs the comparison result to the state detection circuit.

[0014] The first input amplifier may have the same circuit configuration as the second input amplifier.

[0015] The circuit configuration of the first input amplifier may be different from the circuit configuration of the second input amplifier.

[0016] The avalanche photodiode, the charging circuit, the input amplifier, and the state detection circuit may be provided on a single semiconductor substrate.

[0017] The avalanche photodiode may be provided on a first semiconductor substrate, and the charging circuit, the input amplifier, and the state detection circuit may be provided on a second semiconductor substrate joined to the first semiconductor substrate.

[0018] The photodiode may further include a quench circuit connected to the avalanche photodiode and the input terminal of the input amplifier, for controlling the potential of the input terminal.

[0019] The cathode of the avalanche photodiode may be connected to the input terminal of the input amplifier.

[0020] The anode of the avalanche photodiode may be connected to the input terminal of the input amplifier.

[0021] A distance measuring device according to an embodiment of the present disclosure includes any one of the above-described photodetection circuits and a signal processing circuit that processes an output signal of the photodetection circuit.

[0022] The signal processing circuit a TDC (Time to Digital Converter) that converts the output signal into a digital value; a histogram generating circuit that measures the number of times the digital value is acquired; The image capturing device may further include a distance determining section that determines the distance from the light detection circuit to a subject based on the measurement result of the histogram generating circuit. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a block diagram showing an example of the configuration of an imaging system using a photodetector circuit and a distance measuring device according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing an example of the configuration of a photodetection circuit and a signal processing circuit. [Figure 3A] FIG. 2 is a circuit diagram showing the configuration of an input amplifier according to the first embodiment. [Figure 3B] FIG. 10 is a circuit diagram showing a configuration of a first modified example of an input amplifier. [Figure 4] FIG. 10 is a circuit diagram showing a configuration of a second modified example of the input amplifier. [Figure 5] FIG. 10 is a circuit diagram showing a configuration of a third modified example of the input amplifier. [Figure 6A] FIG. 10 is a circuit diagram showing a configuration of a fourth modified example of the input amplifier. [Figure 6B] FIG. 10 is a circuit diagram showing a configuration of a fifth modified example of an input amplifier. [Figure 7] FIG. 2 is a circuit diagram showing a configuration of a state detection circuit. [Figure 8] 10 is a graph showing an example of voltage characteristics of a plurality of photodetector elements. [Figure 9] 10 is a graph showing an example of voltage characteristics of a single photodetector element. [Figure 10] 10 is a graph showing the voltage characteristics of a photodetector element and the reference voltage characteristics of an input amplifier. [Figure 11] FIG. 10 is a perspective view showing the structure of a distance measuring device according to a modified example. [Figure 12] FIG. 10 is a block diagram showing an example of the configuration of a distance measuring device according to a second embodiment. [Figure 13] 10 is a graph showing the voltage characteristics of a photodetector element and the reference voltage characteristics of an input amplifier. [Figure 14] 1 is a block diagram showing an example of a schematic configuration of a vehicle control system; [Figure 15] FIG. 2 is an explanatory diagram showing an example of the installation positions of an outside-vehicle information detection unit and an imaging unit. DETAILED DESCRIPTION OF THE INVENTION

[0024] (First embodiment) Fig. 1 is a block diagram showing an example of the configuration of an imaging system using a photodetector circuit and a distance measuring device according to the first embodiment. The imaging system 101 shown in Fig. 1 is a system that captures distance images using the ToF method, and includes an illumination device 111 and an imaging device 112.

[0025] The lighting device 111 includes a lighting control unit 121 and a light source 122. The lighting control unit 121 controls the pattern in which the light source 122 emits illumination light based on the control of the control unit 132 of the imaging device 112. Specifically, the lighting control unit 121 controls the pattern in which the light source 122 emits illumination light in accordance with an illumination code included in an illumination signal supplied from the control unit 132. For example, the illumination code consists of two values, "1" (High) and "0" (Low). The lighting control unit 121 turns on the light source 122 when the value of the illumination code is "1", and turns off the light source 122 when the value of the illumination code is "0".

[0026] The light source 122 emits light (irradiation light) in a predetermined wavelength range under the control of the illumination control unit 121. The light source 122 is, for example, an infrared laser diode. The type of light source 122 and the wavelength range of the irradiation light can be set arbitrarily depending on the application of the imaging system 101, etc.

[0027] The imaging device 112 receives the reflected light that is the irradiated light reflected by the subject 102 and the subject 103. The imaging device 112 includes a distance measuring device 131, a control unit 132, a display unit 133, and a storage unit .

[0028] The distance measuring device 131 includes a lens 141, a photodetection circuit 142, and a signal processing circuit 143. The lens 141 forms an image of incident light on the photodetection circuit 142. The lens 141 may have any configuration, and for example, the lens 141 may be configured using a group of multiple lenses.

[0029] The photodetection circuit 142 captures images of the subject 102, the subject 103, etc. under the control of the control unit 132. The photodetection circuit 142 also outputs a signal obtained by capturing the image to the signal processing circuit 143.

[0030] The signal processing circuit 143 processes the output signal of the light detection circuit 142 based on the control of the control unit 132. For example, the signal processing circuit 143 detects the distance to the subject based on the output signal of the light detection circuit 142, and generates a distance image indicating the distance to the subject.

[0031] The control unit 132 is configured by a control circuit, a processor, etc., such as an FPGA (Field Programmable Gate Array) or a DSP (Digital Signal Processor). The control unit 132 controls the illumination control unit 121, the photodetection circuit 142, and the signal processing circuit 143.

[0032] The display unit 133 is, for example, a panel-type display device such as a liquid crystal display device or an organic EL (Electro Luminescence) display device.

[0033] The storage unit 134 can be configured with any storage device or storage medium, and stores distance images and the like.

[0034] FIG. 2 is a block diagram showing an example of the configuration of the photodetection circuit 142 and the signal processing circuit 143. As shown in FIG.

[0035] The photodetection circuit 142 includes a photodetection element 151, a charging circuit 152, a quenching circuit 153, an input amplifier 154, and a state detection circuit 155. These are provided on a single semiconductor substrate. Note that the photodetection circuit 142 shown in FIG. 2 is a unit circuit corresponding to one pixel, and therefore the distance measuring device 131 has multiple photodetection circuits 142 according to the number of pixels.

[0036] The photodetector element 151 is a photodiode typified by an APD (Avalanche Photo Diode) or a SPAD (Single Photon Avalanche Diode). The cathode of the photodetector element 151 is connected to the charging circuit 152 and the input terminal of the input amplifier 154. The anode of the photodetector element 151 is set to a negative voltage VRL by a negative power supply (not shown).

[0037] The charging circuit 152 is configured, for example, with a current source and a resistor connected in series. The charging circuit 152 supplies a positive voltage to the cathode of the photodetector element 151. As a result, when a reverse voltage equal to or greater than the breakdown voltage is applied between the anode and cathode of the photodetector element 151, the photodetector element 151 is set to the Geiger mode. When a photon is incident on the photodetector element 151 set to the Geiger mode, avalanche multiplication occurs, and a current flows through the photodetector element 151.

[0038] The quench circuit 153 is configured, for example, with an N-channel MOS transistor 156. The drain of the N-channel MOS transistor 156 is connected to the cathode of the photodetector element 151 and the input terminal of the input amplifier 154, and the source is grounded. When an external signal APDEN is input to the gate of the N-channel MOS transistor 156, the cathode voltage Vc is forcibly set to ground potential. In this case, the photodetection function of the photodetector element 151 is reduced. This makes it possible to avoid erroneous detection such as afterpulses, in which avalanche multiplication occurs again even when no photons are incident on the photodetector element 151. Note that the quench circuit 153 is not limited to the N-channel MOS transistor 156, as long as it is configured to forcibly set the cathode voltage Vc to a potential that reduces the photodetection function of the photodetector element 151.

[0039] The source of the N-channel MOS transistor 156 may be connected to a negative potential instead of being grounded. In this case, there is a concern that the rise of the recharge (recovery) of the cathode voltage Vc may be delayed, lengthening the dead time. However, as will be described later, in this embodiment, the dead time can be shortened by optimizing the reference voltage of the input amplifier 154.

[0040] The input amplifier 154 compares the voltage at the input terminal, in other words, the cathode voltage Vc of the light detecting element 151, with a variable reference voltage. The voltage level at the output terminal of the input amplifier 154 changes depending on the comparison result. The circuit configuration of the input amplifier 154 will be described later.

[0041] The state detection circuit 155 detects the voltage level of the output terminal of the input amplifier 154 and sets the timing for changing the potential of the reference voltage. The configuration of the state detection circuit 155 will also be described later.

[0042] The signal processing circuit 143 includes a time to digital converter (TDC) 200, a histogram generating unit 201, and a distance determining unit 202. The time to digital converter (TDC) 200 converts the output signal of the input amplifier 154 into a digital value. Specifically, the TDC 200 converts the occurrence time of the transition timing of the voltage level of the output terminal of the input amplifier 154 into a digital value.

[0043] The histogram generating unit 201 counts the number of times the digital values ​​are acquired, that is, the number of times the photodetector element 151 reacts.

[0044] The distance determination unit 202 determines the distance from the light detection element 151 to the subjects 102 and 103 based on the measurement results of the histogram generation unit 201. The distance determination unit 202, for example, calculates an approximation curve for a normal distribution indicating the measurement results of the histogram generation unit 201 (so-called Gaussian fitting), and finds the distance using the approximation curve.

[0045] The circuit configuration of the input amplifier 154 will now be described.

[0046] 3A is a circuit diagram showing the configuration of an input amplifier according to this embodiment. The input amplifier 154 according to this embodiment includes an inverter circuit 161 and a voltage control circuit 162 connected to the inverter circuit 161. The inverter circuit 161 corresponds to a comparison circuit.

[0047] The inverter circuit 161 includes MOS transistors 170 to 173. The MOS transistors 170 and 172 are P-channel MOS transistors, and the MOS transistors 171 and 173 are N-channel MOS transistors. The MOS transistors 170 and 171 are connected in series. The MOS transistors 172 and 173 are connected in series.

[0048] The gates of the MOS transistors 170 and 171 are input terminals of the input amplifier 154. A cathode voltage Vc of the photodetector element 151 is input to each gate. The source of the MOS transistor 170 is connected to a positive power supply, and the source of the MOS transistor 171 is connected to the voltage control circuit 162. The drains of the MOS transistors 170 and 171 are connected to the gates of the MOS transistors 172 and 173, respectively. The source of the MOS transistor 172 is connected to a positive power supply, and the source of the MOS transistor 171 is grounded. The drains of the MOS transistors 172 and 173 are output terminals of the input amplifier 154, and are connected to the state detection circuit 155 and the signal processing circuit 143.

[0049] The voltage control circuit 162 includes a switching element 174 and a resistance element 175. The switching element 174 is, for example, an N-channel MOS transistor. The output voltage Vo of the state detection circuit 155 is input to the gate of the switching element 174. The drain is connected to the source of the MOS transistor 171. The source is grounded. On the other hand, the resistance element 175 is connected in parallel to the switching element 174.

[0050] In the inverter circuit 161 configured as described above, one of the MOS transistor 170 and the MOS transistor 171 is turned on and the other is turned off depending on the potential of the cathode voltage Vc of the light detecting element 151. When the MOS transistor 170 is turned on, the MOS transistor 173 is turned on and the MOS transistor 172 is turned off. In this case, the voltage level Vs becomes low. When the MOS transistor 171 is turned on, the MOS transistor 172 is turned on and the MOS transistor 173 is turned off. In this case, the voltage level Vs becomes high.

[0051] The threshold voltage at which the voltage level Vs is switched between high and low corresponds to the potential of the reference voltage. The potential of the reference voltage is changed by the voltage control circuit 162. When the switching element 174 of the voltage control circuit 162 is turned on, the potential of the reference voltage decreases. Conversely, when the switching element 174 is turned off, the potential of the reference voltage increases.

[0052] FIG. 3B is a circuit diagram showing the configuration of a first modified example of the input amplifier 154. Components similar to those of the input amplifier 154 shown in FIG. 3A are assigned the same reference numerals, and detailed description thereof will be omitted. The input amplifier 154 shown in FIG. 3B differs from the input amplifier 154 shown in FIG. 3A in the configuration of its voltage control circuit. Specifically, a voltage control circuit 162a according to this modified example is provided with a current source 175a instead of the resistance element 175. The current source 175a is an N-channel MOS transistor. The drain of this N-channel MOS transistor is connected to the drain of the switching element 174, and the source is grounded. A reference voltage is input to the gate. This reference voltage is set so that the on-resistance of the switching element 174 is lower than the on-resistance of the current source 175a.

[0053] 4 is a circuit diagram showing the configuration of a second modified example of input amplifier 154. Input amplifier 154a according to this modified example includes an inverter circuit 161a and a voltage control circuit 163 connected to inverter circuit 161a. Inverter circuit 161a is configured with MOS transistors 170a to 173a, similar to inverter circuit 161 shown in FIG. 3A, and therefore detailed description thereof will be omitted.

[0054] On the other hand, the voltage control circuit 163 includes a current source 176a, a switch 176b, a switch 176c, and an inverter element 176d. The current source 176a is an N-channel MOS transistor. The switches 176b and 176c are connected in parallel to the gate of this N-channel MOS transistor. The drain is connected to the source of the MOS transistor 171a. The source is grounded. The output current value of the current source 176a varies depending on the gate voltage of the N-channel MOS transistor. As the gate voltage decreases, the output current value decreases, and the reference voltage for switching the voltage level Vs of the inverter circuit 161a increases. Conversely, as the gate voltage increases, the output current value increases, and the reference voltage decreases. The switches 176b and 176c are turned on or off based on the output voltage Vo of the state detection circuit 155. A voltage obtained by inverting the potential of the output voltage Vo by the inverter element 176d is input to the switch 176c. Therefore, when one of the switches 176b and 176c is turned on, the other is turned off. When the switch 176b is turned on, the first reference voltage Vref1 is supplied to the current source 176a as the gate voltage. Conversely, when the switch 176c is turned on, the second reference voltage Vref2, which has a different potential from the first reference voltage Vref1, is supplied to the current source 176a as the gate voltage. Note that the inverter element 176d may be provided on the switch 176b side instead of the switch 176c side.

[0055] FIG. 5 is a circuit diagram showing the configuration of a third modified example of the input amplifier 154. The input amplifier 154b according to this modified example includes an operational amplifier circuit 164 and a switch circuit 165. The operational amplifier circuit 164 is an example of a comparison circuit and includes MOS transistors 177 to 180 and a current source 181. The MOS transistors 177 and 178 are P-channel MOS transistors and form a current mirror circuit. The MOS transistors 179 and 180 are N-channel MOS transistors having the same size and electrical characteristics and are connected in parallel to each other via the current mirror circuit. The gate of the MOS transistor 179 serves as the input terminal of the input amplifier 154b. The drains of the MOS transistors 178 and 180 serve as the output terminal of the input amplifier 154b. The current source 181 is connected to the sources of the MOS transistors 179 and 180.

[0056] The switch circuit 165 is a modified example of the voltage control circuit 162 and includes a switch 182, a switch 183, and an inverter element 184. The switches 182 and 183 are turned on or off based on the output voltage Vo of the state detection circuit 155. A voltage obtained by inverting the potential of the output voltage Vo by the inverter element 184 is input to the switch 183. Therefore, when one of the switches 182 and 183 is turned on, the other is turned off. When the switch 182 is turned on, a first reference voltage Vref1 is input to the gate of the MOS transistor 180. Conversely, when the switch 183 is turned on, a second reference voltage Vref2, which has a different potential from the first reference voltage Vref1, is input to the gate of the MOS transistor 180. Note that the inverter element 184 may be provided on the switch 182 side instead of the switch 183 side.

[0057] 6A is a circuit diagram showing the configuration of a fourth modified example of the input amplifier 154. This modified example includes a first input amplifier 154c and a second input amplifier 154d. Similar to the input amplifier 154 shown in FIG. 3A, the first input amplifier 154c includes MOS transistors 170c to 173c, a switching element 174c, and a resistor element 175c. In the first input amplifier 154c, the gate of the MOS transistor 170c serves as an input terminal, and the drains of the MOS transistors 172c and 173c serve as output terminals. These output terminals are connected to the signal processing circuit 143.

[0058] On the other hand, the second input amplifier 154d also has MOS transistors 170d to 173d, a switching element 174d, and a resistor element 175d, like the input amplifier 154. In the second input amplifier 154d, the gate of the MOS transistor 170d is an input terminal, and the drains of the MOS transistors 172d and 173d are output terminals. These output terminals are connected to the state detection circuit 155.

[0059] In this modification, the circuit configuration of the first input amplifier 154c is the same as the circuit configuration of the second input amplifier 154d, but may be different.

[0060] FIG. 6B is a circuit diagram showing the configuration of a fifth modified example of the input amplifier 154. Components similar to those in FIG. 6A are assigned the same reference numerals, and detailed descriptions thereof will be omitted. In this modified example, the configuration of a second input amplifier 154d differs from that shown in FIG. 6A. The second input amplifier 154d according to this modified example does not include a switching element 174d or a resistive element 175d, and the source of the MOS transistor 171d is grounded. In other words, the second input amplifier 154d does not perform reference voltage control based on the output voltage Vo of the state detection circuit 155. According to this modified example, the cathode voltage Vc input during operation of the state detection circuit 155 is constant, resulting in stable control.

[0061] The circuit configuration of the state detection circuit 155 will be described below.

[0062] Fig. 7 is a circuit diagram showing the configuration of state detection circuit 155. State detection circuit 155 shown in Fig. 7 can be applied to input amplifier 154 shown in Fig. 3A and Fig. 3B, input amplifier 154b shown in Fig. 5, and second input amplifier 154d shown in Fig. 6A and Fig. 6B. This state detection circuit 155 is made up of five stages of inverter elements 190 connected in series with each other.

[0063] The state detection circuit 155 outputs the input signal after a predetermined time has elapsed. The predetermined time corresponds to the delay time between the input signal and the output signal. This delay time can be set based on the number of stages of the inverter elements 190. Therefore, the number of stages of the inverter elements 190 is not limited to five, but may be any odd number. By adjusting the number of stages of the inverter elements 190, the timing for changing the reference voltage of each input amplifier can be set.

[0064] FIG. 8 is a graph showing an example of the voltage characteristics of multiple photodetector elements 151. In the graph shown in FIG. 8, the horizontal axis represents time, and the vertical axis represents the cathode voltage Vc of the photodetector element. In a pixel array in which multiple photodetector elements 151 are arranged two-dimensionally, variations in on-resistance and parasitic capacitance may cause the drop characteristics of the cathode voltage Vc when a photon is incident on the photodetector element 151 to differ between the photodetector elements. In this case, as shown in FIG. 8, if the reference voltage Vref of the input amplifier is fixed to a low value, the timing for detecting the drop in the cathode voltage Vc may vary, which may cause distance measurement errors. To reduce this distance measurement error, it is desirable to set the reference voltage Vref to a high value.

[0065] FIG. 9 is a graph showing an example of the voltage characteristics of a single photodetector element 151. In the graph shown in FIG. 9, the horizontal axis also represents time, and the vertical axis represents the cathode voltage Vc of the photodetector element 151. When a photon is incident on the photodetector element 151, avalanche multiplication occurs, and a current flows through the photodetector element 151. This causes the cathode voltage Vc to drop. When the avalanche multiplication subsides, the cathode voltage Vc gradually recovers. During the dead time Tdead, which is the period from when the cathode voltage Vc drops to when it recovers, photons cannot be detected. Therefore, if the reference voltage Vref is fixed to a high value, the dead time Tdead becomes long, which may result in insufficient ranging performance. Therefore, in order to shorten the dead time Tdead, it is desirable to set the reference voltage Vref to a low value.

[0066] 10 is a graph showing the voltage characteristics of the photodetector element 151 and the reference voltage characteristics of the input amplifier 154. In the graph shown in FIG.

[0067] In the input amplifier 154 according to this embodiment, as described above, the voltage control circuit 162 can set two reference voltages. Furthermore, the state detection circuit 155 can set the timing for switching between the two reference voltages. Therefore, as shown in FIG. 10, a drop in the cathode voltage Vc can be detected using the high-potential first reference voltage Vref1, and a recovery of the cathode voltage Vc can be detected using the low-potential second reference voltage Vref2. In this embodiment, the state detection circuit 155 synchronizes the timing for switching from the first reference voltage Vref1 to the second reference voltage Vref2 with the timing of the rising and falling edges of the cathode voltage Vc. This allows for more accurate measurement of the drop and recovery of the cathode voltage Vc.

[0068] According to the present embodiment described above, the reference voltage for detecting a drop in the cathode voltage Vc of the photodetector element 151 can be set high, thereby reducing distance measurement errors due to variations in output timing among the multiple photodetector elements 151. Furthermore, the reference voltage for detecting the recovery of the cathode voltage Vc can be set low, thereby shortening the dead time. Therefore, it is possible to simultaneously satisfy the two contradictory requirements of early detection of a drop in the cathode voltage Vc and its recovery, thereby improving distance measurement performance.

[0069] (Variation) 11 is a perspective view showing the structure of a distance measuring device according to a modified example. Note that the same components as those in the distance measuring device 131 according to the first embodiment described above are given the same reference numerals, and detailed description thereof will be omitted.

[0070] 11 has a first semiconductor substrate 301 and a second semiconductor substrate 302. The first semiconductor substrate 301 and the second semiconductor substrate 302 are bonded and electrically connected by, for example, a copper pad.

[0071] A pixel array is formed by two-dimensionally arranging a plurality of photodetector elements 151 on the first semiconductor substrate 301. The surface on which the photodetector elements 151 are formed becomes the light receiving surface S of the distance measuring device 131a.

[0072] The second semiconductor substrate 302 has a region 312 facing the first semiconductor substrate 301 and a region 322 adjacent to the region 312. In the region 312, peripheral components of the photodetector element 151 of the photodetector circuit 142, namely, the charging circuit 152, the quenching circuit 153, the input amplifier 154, and the state detection circuit 155, are formed. On the other hand, in the region 322, the signal processing circuit 143 is formed.

[0073] Even with the structure of this modified example described above, similar to the first embodiment, it is possible to set separately the reference voltage for detecting a drop in the cathode voltage Vc of the photodetector element 151 and the reference voltage for detecting the recovery of the cathode voltage Vc, thereby improving distance measurement performance.

[0074] (Second embodiment) 12 is a block diagram showing an example of the configuration of a distance measuring device according to the second embodiment. Components similar to those of the distance measuring device 131 according to the first embodiment described above are given the same reference numerals, and detailed description thereof will be omitted. The distance measuring device according to this embodiment differs from the first embodiment in the configuration of the photodetection circuit. The photodetection circuit according to this embodiment will be described below.

[0075] 12, the anode of the photodetector element 151 is connected to the input terminal of the input amplifier 154, and the cathode is connected to the power supply. Therefore, the input amplifier 154 detects the rise and recovery of the anode voltage Va of the photodetector element 151 based on a comparison between the anode voltage Va and a reference voltage. Since the circuit configuration of the input amplifier 154 is the same as in the first embodiment, the reference voltage is switched based on the control of the state detection circuit 155.

[0076] 13 is a graph showing the voltage characteristics of the photodetector element 151 and the reference voltage characteristics of the input amplifier 154. In the graph shown in FIG.

[0077] In this embodiment, when a photon is incident on the photodetector element 151, the anode voltage Va rises. Thereafter, the anode voltage Va gradually drops (recovers). At this time, in the input amplifier 154, the voltage control circuit 162 switches between two reference voltages based on the control of the state detection circuit 155. Therefore, as shown in FIG. 13, it is possible to detect a rise in the anode voltage Va using the low-potential first reference voltage and a drop in the anode voltage Va using the high-potential second reference voltage Vref2. This reduces distance measurement errors due to variations in output timing among the multiple photodetector elements 151 and shortens the dead time Tdead.

[0078] According to the present embodiment described above, it is possible to separately set the reference voltage for detecting an increase in the anode voltage Va of the photodetector element 151 and the reference voltage for detecting a decrease in the anode voltage Va. This makes it possible to improve distance measurement performance.

[0079] <Application to moving objects> The technology according to the present disclosure (the present technology) can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of moving body, such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, or a robot.

[0080] FIG. 14 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile object control system to which the technology according to the present disclosure can be applied.

[0081] The vehicle control system 12000 includes a plurality of electronic control units connected via a communication network 12001. In the example shown in Fig. 14, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an outside-vehicle information detection unit 12030, an inside-vehicle information detection unit 12040, and an integrated control unit 12050. Also shown as functional components of the integrated control unit 12050 are a microcomputer 12051, an audio / video output unit 12052, and an in-vehicle network I / F (Interface) 12053.

[0082] The drivetrain control unit 12010 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 12010 functions as a control device for a drive force generating device for generating a drive force for the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting the drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, a braking device for generating a braking force for the vehicle, etc.

[0083] The body system control unit 12020 controls the operation of various devices equipped in the vehicle body according to various programs. For example, the body system control unit 12020 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as headlamps, backup lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves transmitted from a portable device that serves as a key or signals from various switches may be input to the body system control unit 12020. The body system control unit 12020 receives these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

[0084] The outside-vehicle information detection unit 12030 detects information outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the outside-vehicle information detection unit 12030. The outside-vehicle information detection unit 12030 causes the imaging unit 12031 to capture images outside the vehicle and receives the captured images. The outside-vehicle information detection unit 12030 may perform object detection processing or distance detection processing for people, cars, obstacles, signs, characters on the road surface, etc., based on the received images.

[0085] The imaging unit 12031 is an optical sensor that receives light and outputs an electrical signal according to the amount of light received. The imaging unit 12031 can output the electrical signal as an image, or as distance measurement information. The light received by the imaging unit 12031 may be visible light or invisible light such as infrared light.

[0086] The in-vehicle information detection unit 12040 detects information inside the vehicle. For example, a driver state detection unit 12041 that detects the state of the driver is connected to the in-vehicle information detection unit 12040. The driver state detection unit 12041 includes, for example, a camera that captures an image of the driver, and the in-vehicle information detection unit 12040 may calculate the degree of fatigue or concentration of the driver based on the detection information input from the driver state detection unit 12041, or may determine whether the driver is dozing off.

[0087] The microcomputer 12051 can calculate control target values ​​for the driving force generating device, steering mechanism, or braking device based on the information inside and outside the vehicle acquired by the outside-vehicle information detection unit 12030 or the inside-vehicle information detection unit 12040, and output control commands to the drivetrain control unit 12010. For example, the microcomputer 12051 can perform cooperative control aimed at realizing the functions of an ADAS (Advanced Driver Assistance System), including avoiding or mitigating collisions between vehicles, following based on the distance between vehicles, maintaining vehicle speed, warning of vehicle collisions, or warning of vehicle lane departure.

[0088] In addition, the microcomputer 12051 can perform cooperative control for the purpose of autonomous driving, which allows the vehicle to travel autonomously without relying on driver operation, by controlling the driving force generating device, steering mechanism, braking device, etc. based on information about the surroundings of the vehicle obtained by the outside vehicle information detection unit 12030 or the inside vehicle information detection unit 12040.

[0089] Furthermore, the microcomputer 12051 can output a control command to the body system control unit 12030 based on the information about the outside of the vehicle acquired by the outside information detection unit 12030. For example, the microcomputer 12051 can control the headlamps according to the position of a preceding vehicle or an oncoming vehicle detected by the outside information detection unit 12030, and perform cooperative control for the purpose of preventing glare, such as switching from high beams to low beams.

[0090] The audio / video output unit 12052 transmits at least one of audio and video output signals to an output device capable of visually or audibly notifying information to vehicle occupants or the outside of the vehicle. In the example of Fig. 14, an audio speaker 12061, a display unit 12062, and an instrument panel 12063 are exemplified as output devices. The display unit 12062 may include, for example, at least one of an on-board display and a head-up display.

[0091] FIG. 15 is a diagram showing an example of the installation position of the imaging unit 12031.

[0092] In FIG. 15, the imaging unit 12031 includes imaging units 12101, 12102, 12103, 12104, and 12105.

[0093] The imaging units 12101, 12102, 12103, 12104, and 12105 are provided, for example, at positions such as the front nose, side mirrors, rear bumper, back door, and the top of the windshield inside the vehicle cabin of the vehicle 12100. The imaging unit 12101 provided at the front nose and the imaging unit 12105 provided at the top of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 provided at the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 provided at the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The imaging unit 12105 provided at the top of the windshield inside the vehicle cabin is mainly used to detect preceding vehicles, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc.

[0094] 15 shows an example of the imaging ranges of the imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of the imaging unit 12101 provided on the front nose, imaging ranges 1211212113 indicate the imaging ranges of the imaging units 12102 and 12103 provided on the side mirrors, and imaging range 12114 indicates the imaging range of the imaging unit 12104 provided on the rear bumper or back door. For example, by overlaying the image data captured by the imaging units 12101 to 12104, a bird's-eye view image of the vehicle 12100 viewed from above can be obtained.

[0095] At least one of the imaging units 12101 to 12104 may have a function of acquiring distance information. For example, at least one of the imaging units 12101 to 12104 may be a stereo camera made up of multiple imaging elements, or may be an imaging element having pixels for phase difference detection.

[0096] For example, the microcomputer 12051 can calculate the distance to each three-dimensional object within the imaging ranges 12111 to 12114 and the change in this distance over time (relative speed with respect to the vehicle 12100) based on the distance information obtained from the imaging units 12101 to 12104, thereby extracting as a preceding vehicle, in particular, the three-dimensional object that is the closest three-dimensional object on the path of the vehicle 12100 and traveling in approximately the same direction as the vehicle 12100 at a predetermined speed (for example, 0 km / h or higher). Furthermore, the microcomputer 12051 can set a vehicle-to-vehicle distance to be maintained in advance in front of the preceding vehicle, and perform automatic braking control (including follow-up stop control), automatic acceleration control (including follow-up start control), etc. In this way, cooperative control can be performed for the purpose of automatic driving, which runs autonomously without relying on driver operation.

[0097] For example, the microcomputer 12051 classifies and extracts three-dimensional object data regarding three-dimensional objects into two-wheeled vehicles, ordinary vehicles, large vehicles, pedestrians, utility poles, and other three-dimensional objects based on distance information obtained from the imaging units 12101 to 12104, and can use the data for automatic obstacle avoidance. For example, the microcomputer 12051 distinguishes obstacles around the vehicle 12100 into obstacles that are visible to the driver of the vehicle 12100 and obstacles that are difficult to see. The microcomputer 12051 then determines the collision risk, which indicates the degree of risk of collision with each obstacle, and when the collision risk is equal to or greater than a set value and a collision is possible, the microcomputer 12051 can provide driving assistance for collision avoidance by outputting an alarm to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or avoidance steering via the drivetrain control unit 12010.

[0098] At least one of the image capturing units 12101 to 12104 may be an infrared camera that detects infrared rays. For example, the microcomputer 12051 can recognize a pedestrian by determining whether or not a pedestrian is present in the images captured by the image capturing units 12101 to 12104. The pedestrian recognition is performed, for example, by extracting feature points from the images captured by the image capturing units 12101 to 12104, which are infrared cameras, and then performing pattern matching on a series of feature points that indicate the outline of an object to determine whether or not the object is a pedestrian. When the microcomputer 12051 determines that a pedestrian is present in the images captured by the image capturing units 12101 to 12104 and recognizes the pedestrian, the audio / image output unit 12052 controls the display unit 12062 to superimpose a rectangular outline on the recognized pedestrian for emphasis. The audio / image output unit 12052 may also control the display unit 12062 to display an icon or the like indicating the pedestrian at a desired position.

[0099] An example of a vehicle control system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to, for example, the image capturing unit 12031 among the configurations described above. Specifically, the distance measuring devices 131 and 131a can be applied to the image capturing unit 12031. By applying the technology according to the present disclosure, it is possible to obtain captured images with higher distance measurement accuracy, thereby improving safety.

[0100] The present technology can be configured as follows: (1) an avalanche photodiode; a charging circuit that supplies a voltage to the avalanche photodiode; an input amplifier including a comparator circuit whose output terminal voltage level changes in response to a comparison result between a voltage at an input terminal connected to the avalanche photodiode and a reference voltage, and a voltage control circuit which changes the potential of the reference voltage; a state detection circuit that sets a timing for changing the potential of the reference voltage in the voltage control circuit based on the detection result of the voltage level; A photodetector circuit comprising: (2) the comparison circuit includes an inverter circuit; The photodetection circuit according to (1), wherein the voltage control circuit includes a switching element connected to the inverter circuit and switching in response to the output voltage of the state detection circuit, and a resistive element or a current source connected in parallel with the switching element. (3) the comparison circuit includes an operational amplifier circuit; The photodetection circuit of (1), wherein the voltage control circuit includes a switch circuit that switches the reference voltage to a first reference voltage or a second reference voltage different from the first reference voltage depending on the output voltage of the state detection circuit. (4) The comparison circuit includes an inverter circuit; The photodetection circuit according to (1), wherein the voltage control circuit includes a current source connected to the inverter circuit and having an output current value that changes in accordance with the output voltage of the state detection circuit. (5) The photodetection circuit according to (2) or (3), wherein the state detection circuit includes an odd number of inverter elements connected in series with each other. (6) The photodetection circuit according to any one of (1) to (5), wherein the input amplifier includes a first input amplifier that outputs the comparison result to a signal processing circuit and a second input amplifier that outputs the comparison result to the state detection circuit. (7) The photodetector circuit according to (6), wherein the circuit configuration of the first input amplifier is the same as the circuit configuration of the second input amplifier. (8) The photodetector circuit according to (6), wherein the circuit configuration of the first input amplifier is different from the circuit configuration of the second input amplifier. (9) The photodetection circuit according to any one of (1) to (8), wherein the avalanche photodiode, the charging circuit, the input amplifier, and the state detection circuit are provided on a single semiconductor substrate. (10) A photodetection circuit according to any one of (1) to (8), wherein the avalanche photodiode is provided on a first semiconductor substrate, and the charging circuit, the input amplifier, and the state detection circuit are provided on a second semiconductor substrate joined to the first semiconductor substrate. (11) The photodetection circuit according to any one of (1) to (10), further comprising a quench circuit connected to the avalanche photodiode and the input terminal of the input amplifier, for controlling the potential of the input terminal. (12) The photodetection circuit according to any one of (1) to (11), wherein the cathode of the avalanche photodiode is connected to the input terminal of the input amplifier. (13) The photodetection circuit according to any one of (1) to (11), wherein the anode of the avalanche photodiode is connected to the input terminal of the input amplifier. (14) The photodetection circuit according to any one of (1) to (13), a signal processing circuit that processes an output signal of the photodetection circuit. (15) The signal processing circuit a TDC (Time to Digital Converter) that converts the output signal into a digital value; a histogram generating circuit that measures the number of times the digital value is acquired; The distance measuring device according to (14), further comprising: a distance determining unit that determines the distance from the light detection circuit to the subject based on the measurement result of the histogram generating circuit. [Explanation of symbols]

[0101] 142: Photodetector circuit 143: Signal processing circuit 151: Photodetector element 152: Charging circuit 153: Quench circuit 154, 154a, 154b: Input amplifier 154c: 1st input amplifier 154d: Second input amplifier 155: Status detection circuit 161, 161a: inverter circuit 162: Voltage control circuit 163: Voltage control circuit 164: Op-amp circuit 165: Switch circuit 174: Switching element 175: Resistor element 175a: Current source 190: Inverter element 191: Operational amplifier 200:TDC 201: Histogram generation unit 202: Distance determination unit 301: First semiconductor substrate 302: Second semiconductor substrate

Claims

1. an avalanche photodiode; a charging circuit that supplies a voltage to the avalanche photodiode; an input amplifier including: a comparator circuit that changes the voltage level of an output terminal in accordance with a comparison result between a voltage of an input terminal connected to the anode or cathode of the avalanche photodiode and a reference voltage; and a voltage control circuit that changes the potential of the reference voltage in a lower direction when the cathode is connected to the input terminal, and changes the potential of the reference voltage in a higher direction when the anode is connected to the input terminal; a state detection circuit that sets a timing for changing the potential of the reference voltage in the voltage control circuit based on a result of detecting the state of the change in the voltage level; A photodetector circuit comprising:

2. the comparison circuit includes an inverter circuit, 2. The photodetection circuit according to claim 1, wherein the voltage control circuit includes: a switching element connected to the inverter circuit and switching in response to the output voltage of the state detection circuit; and a resistive element or a current source connected in parallel with the switching element.

3. the comparison circuit includes an operational amplifier circuit; 2. The photodetection circuit according to claim 1, wherein the voltage control circuit includes a switch circuit that switches the reference voltage to a first reference voltage or a second reference voltage different from the first reference voltage in accordance with an output voltage of the state detection circuit.

4. the comparison circuit includes an inverter circuit, 2. The photodetection circuit according to claim 1, wherein the voltage control circuit includes a current source connected to the inverter circuit and having an output current value that changes in accordance with the output voltage of the state detection circuit.

5. the state detection circuit includes an odd number of inverter elements connected in series with each other; 3. The photodetector circuit according to claim 2, wherein the timing is set in accordance with a delay time based on the number of stages of the inverter elements.

6. 2. The photodetection circuit according to claim 1, wherein the input amplifier includes: a first input amplifier that outputs the comparison result to a signal processing circuit connected to the photodetection circuit; and a second input amplifier that outputs the comparison result to the state detection circuit.

7. 7. The photodetector circuit according to claim 6, wherein the circuit configuration of the first input amplifier is the same as the circuit configuration of the second input amplifier.

8. 7. The photodetector circuit according to claim 6, wherein the first input amplifier has a different circuit configuration from the second input amplifier.

9. 2. The photodetector circuit according to claim 1, wherein the avalanche photodiode, the charging circuit, the input amplifier, and the state detection circuit are provided on a single semiconductor substrate.

10. 2. The photodetection circuit according to claim 1, wherein the avalanche photodiode is provided on a first semiconductor substrate, and the charging circuit, the input amplifier, and the state detection circuit are provided on a second semiconductor substrate bonded to the first semiconductor substrate.

11. 2. The photodetector circuit according to claim 1, further comprising a quench circuit connected to the avalanche photodiode and the input terminal of the input amplifier, for controlling the potential of the input terminal.

12. a photodetector circuit according to claim 1; a signal processing circuit that processes an output signal of the photodetection circuit.

13. The signal processing circuit a TDC (Time to Digital Converter) that converts the output signal into a digital value; a histogram generating circuit that measures the number of times the digital value is acquired; 13. The distance measuring device according to claim 12, further comprising: a distance determining unit that determines the distance from said light detection circuit to the subject based on the measurement result of said histogram generating circuit.

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