阅读说明：本技术 光检测器 (Light detector ) 是由 东谦太 尾崎宪幸 柏田真司 木村祯祐 高井勇 松原弘幸 太田充彦 平塚诚良 于 2018-04-09 设计创作，主要内容包括：光检测器具备：受光部(2),具备构成为响应光子的入射的SPAD(4),并构成为若SPAD作出响应则受光部输出脉冲信号；以及脉冲率控制电路(20),构成为控制受光部的灵敏度,以使来自受光部的脉冲信号的每单位时间的输出数亦即脉冲率成为预先设定的设定值、包含该设定值的设定范围内、该设定值以上、或者该设定值以下。(The photodetector includes: a light receiving unit (2) which is provided with a SPAD (4) configured to respond to the incidence of photons and is configured to output a pulse signal when the SPAD responds; and a pulse rate control circuit (20) configured to control the sensitivity of the light receiving unit so that the pulse rate, which is the number of outputs per unit time of the pulse signal from the light receiving unit, is within a preset set value, a set range including the set value, the set value or more, or the set value or less.)

1. A photodetector includes:

a light receiving unit (2) which is provided with a SPAD (4) configured to respond to the incidence of photons and is configured to output a pulse signal when the SPAD responds; and

and a pulse rate control circuit (20) configured to control the sensitivity of the light receiving unit so that the pulse rate, which is the number of outputs per unit time of the pulse signal from the light receiving unit, is within a preset set value, a set range including the set value, the set value or more, or the set value or less.

2. The light detector of claim 1,

the pulse rate control circuit is configured to measure the pulse rate by counting the output of the pulse signal from the light receiving unit.

3. The light detector of claim 1 or 2,

the light receiving unit is provided with a plurality of light receiving parts,

the pulse rate control circuit is configured to control the sensitivities of the plurality of light receiving units such that the average of the pulse rates of the pulse signals output from the plurality of light receiving units is equal to or greater than the set value, within the set range, or equal to or less than the set value.

4. The light detector of claim 3,

a discrete output switch (40) configured to select a light receiving unit that outputs a pulse signal from among the plurality of light receiving units,

the pulse rate control circuit is configured to control the sensitivities of the plurality of light receiving units by changing the number of light receiving units that output the pulse signal via the discrete output switches.

5. A photodetector includes:

a plurality of light receiving units (2) which are provided with SPADs (4) configured to respond to the incidence of photons and are configured to output pulse signals when the SPADs respond;

a threshold determination circuit (30) configured to output a detection signal when the number of pulse signals output from the plurality of light receiving units reaches a threshold; and

and a pulse rate control circuit (20) configured to control at least one of the sensitivity of the plurality of light receiving units and the threshold value of the threshold value determination circuit so that the pulse rate, which is the number of outputs per unit time of the detection signal from the threshold value determination circuit, is within a preset set value, a set range including the set value, the set value or more, or the set value or less.

6. The light detector of claim 5,

a variable threshold value determination circuit (32) which is provided with a plurality of threshold value determination circuits for setting the threshold values to different values and is configured to select and output one of the detection signals output from the plurality of threshold value determination circuits,

the pulse rate control circuit is configured to measure the pulse rate by counting detection signals output from the plurality of threshold value determination circuits provided in the variable threshold value determination circuit, respectively, and to set the threshold value determination circuit selected by the variable threshold value determination circuit based on the measurement result.

7. The photodetector of any one of claims 1 to 3, 5, and 6,

the pulse rate control circuit is configured to control the sensitivity of the light receiving unit by changing a reverse bias voltage applied to the SPAD.

8. The light detector of claim 5 or 6,

a discrete output switch (40) configured to select a light receiving unit that outputs a pulse signal to the threshold determination circuit from among the plurality of light receiving units,

the pulse rate control circuit is configured to control the sensitivity of the light receiving unit by changing the number of light receiving units that output pulse signals to the threshold determination circuit via the discrete output switches.

9. The light detector of any of claims 1-8,

the pulse rate control circuit is configured to be able to set the set value in accordance with an external signal.

10. The light detector of any of claims 1-9,

the optical detector is provided with a performance monitoring circuit (50) which is configured to store a control value set by the pulse rate control circuit for controlling the pulse rate as data indicating the performance of the optical detector.

11. The light detector of any of claims 1-10,

the pulse rate control circuit is configured to determine a failure of the photodetector based on a result of the pulse rate control.

Technical Field

The present disclosure relates to a photodetector utilizing an avalanche effect.

Background

Conventionally, as a photodetector utilizing the avalanche effect, a photodetector is known in which an avalanche photodiode (hereinafter, APD) is operated in a geiger mode to detect light.

An APD operating in the geiger mode is called an SPAD and operates by applying a voltage higher than a breakdown voltage as a reverse bias voltage. In addition, SPAD is an abbreviation for Single Photon Avalanche Diode.

Since the SPAD breaks down by incidence of photons, such a photodetector is generally configured to detect a voltage change at the time of SPAD breakdown and output a digital pulse (hereinafter, pulse signal) having a predetermined pulse width.

However, since the pulse rate, which is the number of outputs per unit time of the pulse signal, changes according to the amount of ambient light, when very strong disturbance light or the like enters the photodetector, the pulse rate increases. Further, when the pulse rate is increased, a load is imposed on the processing circuit in the subsequent stage, and in some cases, the processing circuit exceeds the processing capacity of the processing circuit and becomes saturated.

Therefore, when such a photodetector is mounted on a vehicle and used in a distance measuring device, the distance measuring accuracy may be reduced as the pulse rate increases, and the distance measurement may be impossible in some cases.

Therefore, in such a photodetector, it is necessary to adjust the sensitivity of the light receiving section including the SPAD in an environment where the pulse rate is increased to lower the pulse rate, and as a device for this purpose, the technique described in patent document 1 has been proposed.

In other words, the distance measuring device described in patent document 1 is configured to adjust the sensitivity of the light receiving unit by measuring the light amount at the next distance measuring point in advance using the reference light receiving element and changing the reverse bias voltage or the like applied to the SPAD based on the measured light amount.

In the proposed apparatus, since the sensitivity of the light receiving unit is adjusted according to the measured light amount, the sensitivity of the light receiving unit can be lowered and the pulse rate of the pulse signal output from the light receiving unit can be suppressed when strong disturbance light enters the next distance measuring point.

Patent document 1 Japanese patent laid-open No. 2014-81254

However, as a result of detailed studies, the inventors have found that the device proposed above requires a reference light-receiving element to measure the light amount at the next distance measurement point for sensitivity adjustment of the light-receiving section, and therefore the device configuration becomes complicated.

In addition, since it is necessary to set a control value such as a reverse bias voltage in accordance with the light amount measured using the reference light receiving element in order to adjust the sensitivity, it is necessary to convert the data into the light amount-control value in order to set the control value. Therefore, there is also a problem that when designing a control unit for sensitivity adjustment, it is necessary to obtain light amount-control value conversion data in advance by actual measurement or the like, and the design of the control unit is troublesome.

Further, if there is a variation in the characteristics of the light receiving section, the control value obtained from the light amount-control value conversion data is deviated from the optimum value, and therefore, there is a problem that the variation in the characteristics of the light receiving section cannot be absorbed when the sensitivity of the light receiving section is adjusted by the proposed apparatus.

In the proposed apparatus, when strong disturbance light is incident on the light receiving unit, the sensitivity of the light receiving unit can be reduced, but the pulse rate cannot be controlled to a desired value according to the capability of the subsequent processing circuit. Therefore, the load on the processing circuit in the subsequent stage is increased, and the decrease in the distance measurement accuracy cannot be reliably prevented.

Disclosure of Invention

In a photodetector for performing light detection using an SPAD, it is desirable in one aspect of the present disclosure that the sensitivity of the light receiving unit can be adjusted without using another detector for light amount measurement, and that the sensitivity adjustment can be appropriately performed according to the capability of a processing circuit in a subsequent stage.

A photodetector according to an aspect of the present disclosure includes a light receiving unit and a pulse rate control circuit, wherein the light receiving unit includes an SPAD configured to respond to incidence of photons, and is configured such that the light receiving unit outputs a pulse signal when the SPAD responds.

The pulse rate control circuit controls the sensitivity of the light receiving section so that the pulse rate, which is the number of outputs per unit time of the pulse signal from the light receiving section, is within a preset set value or a set range including the set value, or is greater than or equal to or less than the set value.

Therefore, even if the pulse rate of the pulse signal output from the light receiving unit changes due to external light such as sunlight, the sensitivity of the light receiving unit is feedback-controlled so that the pulse rate is equal to or greater than a set value or within a set range, or equal to or less than a set value.

Therefore, according to the photodetector of the present disclosure, it is possible to operate the light receiving unit at a desired pulse rate, and to suppress a problem that the processing circuit cannot normally operate due to an increase in load of the subsequent processing circuit or saturation of input to the subsequent processing circuit due to an increase in the pulse rate.

In addition, according to the photodetector of the present disclosure, since it is possible to suppress an abnormal increase in the pulse rate of the pulse signal output from the light receiving unit, it is also possible to suppress the light receiving unit itself from being saturated due to the strong light incident on the light receiving unit.

Further, according to the photodetector of the present disclosure, since it is not necessary to measure the light amount in advance and adjust the sensitivity of the light receiving unit, it is not necessary to set a reference light receiving element for measuring the light amount, and the device configuration can be simplified.

Further, since the sensitivity of the light receiving unit is adjusted based on the pulse rate of the pulse signal actually output from the light receiving unit, the sensitivity of the light receiving unit can be appropriately adjusted without being affected by variations in the characteristics of the light receiving unit.

Therefore, excessive control or insufficient control of the sensitivity of the light receiving section due to variations in the characteristics of the light receiving section does not occur. In addition, it is possible to automatically absorb variations in characteristics of the light receiving unit such as SPAD, performance degradation, and characteristic changes accompanying temperature changes.

Next, a photodetector according to another aspect of the present disclosure includes: a plurality of light receiving sections; a threshold determination circuit configured to output a detection signal when the number of pulse signals output from the plurality of light receiving units reaches a threshold; and a pulse rate control circuit.

The pulse rate control circuit controls at least one of the sensitivity of the plurality of light receiving units and the threshold value of the threshold value determination circuit so that the pulse rate, which is the number of outputs per unit time of the detection signal from the threshold value determination circuit, is equal to or greater than a preset value or within a set range including the preset value, or equal to or less than the preset value.

Therefore, according to the photodetector, the pulse rate of the detection signal output from the threshold value determination circuit can be controlled to a pulse rate at which the subsequent processing circuit can normally operate.

Therefore, similarly to the photodetector according to the above-described aspect, it is possible to suppress a problem that the load of the subsequent processing circuit increases due to an increase in the pulse rate, and the input to the subsequent processing circuit saturates, and the subsequent processing circuit cannot normally operate.

In the claims, the reference signs placed between parentheses indicate the correspondence with specific units described in the embodiments described below as one embodiment, and do not limit the scope of the technology of the present disclosure.

Drawings

Fig. 1 is an explanatory diagram illustrating a configuration of a photodetector according to the first embodiment.

Fig. 2 is a flowchart showing the operation of the pulse rate control circuit according to the first embodiment.

Fig. 3 is a block diagram showing an internal configuration of a pulse rate control circuit according to a second embodiment.

Fig. 4 is an explanatory diagram illustrating a configuration of a photodetector according to the third embodiment.

Fig. 5 is a block diagram showing an internal configuration of a pulse rate control circuit according to a third embodiment.

Fig. 6 is a block diagram showing the configurations of a variable threshold value determination circuit and a pulse rate control circuit according to the fourth embodiment.

Fig. 7 is an explanatory diagram showing a discrete output switch according to a first modification.

Fig. 8 is an explanatory diagram showing a configuration of a performance monitoring circuit according to a second modification.

Fig. 9 is a flowchart showing an operation of the pulse rate control circuit according to the third modification.

Fig. 10 is an explanatory diagram showing a configuration of a photodetector according to a fourth modification.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[ first embodiment ]

As shown in fig. 1, the photodetector according to the present embodiment includes a plurality of light receiving portions 2, and the plurality of light receiving portions 2 include SPADs 4 that respond to the incidence of photons. The plurality of light receiving units 2 are arranged in a grid pattern in the longitudinal direction and the lateral direction to form a light receiving unit array 10, and the light receiving unit array 10 forms one pixel for light detection.

As shown in fig. 1, each light receiving unit 2 includes SPAD4, quenching resistor 6, and pulse output unit 8.

The SPAD4 is an APD capable of operating in the geiger mode as described above, and the quenching resistor 6 is connected in series to a current-carrying path to the SPAD 4.

The quenching resistor 6 applies a reverse bias voltage VB to the SPAD4, and when a photon is incident on the SPAD4 and the SPAD4 breaks down, geiger discharge of the SPAD4 is stopped due to a voltage drop caused by a current flowing through the SPAD 4.

The quenching resistor 6 is formed of a resistor element having a predetermined resistance value, a MOSFET capable of setting an on-resistance with a gate voltage, or the like.

The pulse output unit 8 is connected to a connection point between the SPAD4 and the quenching resistor 6. When the SPAD4 breaks down, a current flows through the quenching resistor 6, and a voltage equal to or higher than a threshold voltage is generated between both ends of the quenching resistor 6, the pulse output unit 8 outputs a digital pulse having a value of 1 as the pulse signal.

The light receiving unit 2 configured as described above outputs a pulse signal at a frequency responsive to the amount of ambient light. Therefore, when strong light such as sunlight enters the light receiving unit 2, the number of pulse signals output from the light receiving unit 2 per unit time, in other words, the pulse rate significantly increases.

Further, since the load on the processing circuit in the subsequent stage increases when the pulse rate increases and the processing circuit becomes saturated in some cases, for example, when the light receiving unit array 10 is used in a distance measuring device mounted on a vehicle, it is considered that the distance measuring operation cannot be normally performed.

Therefore, the photodetector of the present embodiment includes a pulse rate control circuit 20, and the pulse rate control circuit 20 controls the sensitivity of each light receiving unit 2 so that a pulse signal output from the light receiving unit 2 constituting the light receiving unit array 10 is obtained and the pulse rate becomes a desired pulse rate.

The pulse rate control circuit 20 controls the sensitivity of the light receiving section 2 in the process shown in fig. 2. Further, the pulse rate control circuit 20 is constituted by a logic circuit.

That is, the pulse rate control circuit 20 measures the pulse rate of the pulse signal output from the light receiving unit 2 in S100, and compares the measurement result with the set value that is the target value of the pulse rate in the next S200. Then, in the next step S300, the sensitivity of the light receiving unit 2 is controlled so that the difference between the measured pulse rate and the set value becomes zero or a predetermined value or less.

Further, the pulse rate of the pulse signal output from the light receiving unit 2 may not be controlled to be within a set value or a predetermined range centered on the set value, but may be controlled to be within a set range including the set value, or within a set range not lower than or equal to the set value.

In other words, the pulse rate output from the light receiving unit 2 may be controlled to a pulse rate at which the processing circuit can appropriately perform processing in accordance with the capability of the processing circuit in the subsequent stage by using the above-described set value.

The sensitivity of the light receiving unit 2 can be controlled by changing the reverse bias voltage VB applied to the SPAD4 from the breakdown voltage of the SPAD4 to the upper limit voltage allowed by the withstand voltage of the SPAD4, for example. Therefore, a control signal for adjusting the reverse bias voltage VB of each light receiving unit 2 is output from the pulse rate control circuit 20 to the light receiving unit array 10.

According to the photodetector of the present embodiment configured as described above, the pulse rate of the pulse signal output from each of the light receiving units 2 constituting the receiving unit array 10 is controlled to be within the above-described set value or set range.

Therefore, it is possible to suppress an increase in the load on the subsequent processing circuit due to an increase in the pulse rate of the pulse signal output from each receiving unit 2, and to suppress the subsequent processing circuit from becoming saturated. Therefore, when the light receiving unit array 10 is used in the distance measuring device, the distance measuring operation can be normally performed even if strong light enters the light receiving unit array 10.

In addition, according to the photodetector of the present embodiment, since it is possible to suppress an abnormal increase in the pulse rate of the pulse signal output from each light receiving unit 2, it is also possible to suppress the light receiving unit 2 itself from being saturated due to the strong light incident on the light receiving unit 2.

Further, according to the photodetector of the present embodiment, since it is not necessary to adjust the sensitivity of the light receiving unit 2 by measuring the light amount as described in patent document 1, it is not necessary to provide a reference light receiving element for measuring the light amount, and the device configuration can be simplified.

In the present embodiment, since the sensitivity of the light receiving unit 2 is adjusted based on the pulse rate of the pulse signal actually output from the light receiving unit 2, the sensitivity can be appropriately adjusted without being affected by variations in the characteristics of the light receiving unit 2.

Further, by this sensitivity adjustment, it is possible to control the pulse rate of the pulse signal output from the light receiving unit 2 to be within a set value or a set range while absorbing the influence of the performance degradation of the light receiving unit 2 or the characteristic change accompanying the temperature change.

In the above description, the sensitivity adjustment is performed for all the light receiving units 2 constituting the light receiving unit array 10, but the sensitivity adjustment may be performed for only a part of the light receiving units 2 arranged in a region where strong light is likely to enter, for example.

[ second embodiment ]

In the first embodiment, a description has been given of a mode in which the pulse rate control circuit 20 measures the pulse rate for each of the light receiving units 2 constituting the light receiving unit array 10, and adjusts the sensitivity of the corresponding light receiving unit 2 so that the pulse rate falls within a set value or a set range.

In contrast, in the present embodiment, as shown in fig. 3, the pulse rate control circuit 20 is configured by the adder circuit 22 and the control circuit 24, thereby adjusting the sensitivity of the entire light receiving unit array 10.

In other words, the adder circuit 22 shown in fig. 3 adds the number of pulse signals output from all the light receiving units 2 of the light receiving unit array 10 within a predetermined measurement time, thereby obtaining a value obtained by averaging the pulse rates of the pulse signals output from the light receiving units 2 of the light receiving unit array 10.

The control circuit 24 outputs a control signal to the light receiving unit array 10 so that the average value of the pulse rates obtained by the adder circuit 22 is a set value or falls within a set range, thereby adjusting the sensitivity of the light receiving unit array 10.

By configuring the pulse rate control circuit 20 in this manner, the sensitivity of the light receiving unit array 10 can be adjusted by measuring the pulse rate of the pulse signal output from the light receiving unit array 10, and it is not necessary to adjust the sensitivity for each light receiving unit 2, so that the configuration can be simplified.

Even if the pulse rate control circuit 20 is configured in this manner, the average of the pulse rates of the pulse signals output from the light receiving units 2 constituting the light receiving unit array 10 can be controlled to a desired pulse rate. Therefore, it is possible to suppress a significant increase in the pulse rate of the pulse signal input to the subsequent processing circuit, an increase in the load on the processing circuit, and a saturation of the processing circuit.

In the pulse rate control circuit 20 shown in fig. 3, the control circuit 24 may compare the addition value with the set value using all bit data of the value added by the addition circuit 22. The added value and the set value may be compared with each other by using the upper bit data such as the highest bit of the added value.

Since the pulse rate control circuit 20 is only required to be able to adjust the sensitivity of the entire light receiving section array 10, the reverse bias voltage VB applied to all SPADs 4 constituting each light receiving section 2 may be adjusted in a lump by the control signal output to the light receiving section array 10. Further, the sensitivity of the light receiving unit array 10 may be adjusted by adjusting a parameter different from the reverse bias voltage VB.

As shown in fig. 3, the pulse rate control circuit 20 may be configured to be able to input a set value to the internal control circuit 24 by an external signal. In this way, the pulse rate of the pulse signal output from each light receiving unit 2 or the light receiving unit array 10 can be arbitrarily set from the outside.

[ third embodiment ]

When the light receiving unit array 10 is used in the distance measuring device, the pulse signal from each light receiving unit 2 of the light receiving unit array 10 may be input to the threshold value determining circuit 30 as shown in fig. 4.

Here, the threshold determination circuit 30 counts the number of pulse signals output substantially simultaneously from the plurality of light receiving units 2 constituting the light receiving unit array 10. When the count value is equal to or greater than the threshold value, the threshold value determination circuit 30 determines that light of a predetermined level or greater is incident on the light receiving section array 10, and outputs a detection signal indicating that light is incident.

Therefore, in the present embodiment, as shown in fig. 4, the detection signals output from the threshold value determination circuit 30 are input to the pulse rate control circuit 20, and the pulse rate control circuit 20 measures the pulse rate based on the number of the detection signals.

Specifically, as shown in fig. 5, the pulse rate control circuit 20 of the present embodiment includes a counter 26 and a control circuit 28.

The counter 26 counts the number of detection signals output from the threshold determination circuit 30, and the control circuit 28 measures the count value counted by the counter 26 for a predetermined measurement time as the pulse rate of the detection signal output from the threshold determination circuit 30.

The control circuit 28 adjusts the sensitivity of each light receiving unit 2 constituting the light receiving unit array 10 or the threshold of the threshold determination circuit 30 so that the measured pulse rate falls within a set value set in advance or in response to an external signal or a set range corresponding to the set value.

As in the above-described embodiment, the setting range may be within a predetermined range centered on the set value, may be within a setting range not smaller than the set value, or may be within a setting range not larger than the set value.

In other words, the pulse rate of the detection signal output from the threshold value determining circuit 30 can be controlled by adjusting the sensitivity of each light receiving unit 2 constituting the light receiving unit array 10, and the threshold value used for the determination by the threshold value determining circuit 30 can be controlled.

Therefore, in the present embodiment, the control circuit 28 controls the pulse rate of the detection signal output from the threshold value determining circuit 30 by adjusting at least one of the sensitivity of each light receiving unit 2 constituting the light receiving unit array 10 and the threshold value of the threshold value determining circuit 30.

As a result, according to the present embodiment, it is possible to suppress an increase in the pulse rate of the detection signal output from the threshold determination circuit 30 to the subsequent processing circuit, an increase in the load on the subsequent processing circuit, and a saturation of the subsequent processing circuit. Therefore, the photodetector of the present embodiment can also obtain the same effects as those of the first and second embodiments.

In the photodetector of the present embodiment, the pulse rate control circuit 20 only needs to measure the pulse rate of the detection signal output from the threshold value determination circuit 30 via 1 system of signal lines, and therefore the configuration of the pulse rate control circuit 20 can be simplified as compared with the first and second embodiments.

[ fourth embodiment ]

Next, in the third embodiment, the pulse rate of the detection signal output from the threshold value determining circuit 30 is controlled to be within a set value or a set range, so that the load increase of the subsequent processing circuit is suppressed and the subsequent processing circuit is brought into a saturated state.

However, in order to suppress an increase in the load on the subsequent processing circuit, the pulse rate of the detection signal input to the subsequent processing circuit may be controlled, and it is not necessary to control the pulse rate of the detection signal output from one threshold determination circuit 30.

Therefore, in the present embodiment, as shown in fig. 6, the variable threshold determination circuit 32 is used, and the variable threshold determination circuit 32 includes 3 threshold determination circuits 30A, 30B, and 30C that set the threshold Σ to different values TH1, TH2, and TH 3.

Then, the detection signal output from any one of the 3 threshold value determination circuits 30A, 30B, and 30C is selected via the selection circuit 34 included in the variable threshold value determination circuit 32, and is output to the subsequent processing circuit.

In the present embodiment, the pulse rate control circuit 20 includes 3 counters 26A, 26B, and 26C, and the 3 counters 26A, 26B, and 26C count the detection signals output from the 3 threshold determination circuits 30A, 30B, and 30C of the variable threshold determination circuit 32, respectively.

The control circuit 29 provided in the pulse rate control circuit 20 measures the count value counted by each of the counters 26A, 26B, and 26C for a predetermined measurement time as the pulse rate of the detection signal output from each of the threshold determination circuits 30A, 30B, and 30C.

The control circuit 29 uses the measured pulse rate to specify a threshold determination circuit that outputs a detection signal at a pulse rate closest to the set value from among the 3 threshold determination circuits 30A, 30B, and 30C. The selection circuit 34 is switched so that the detection signal from the identified threshold value determination circuit is output to the subsequent processing circuit.

The control circuit 29 outputs a control signal to the light receiving section array 10 so that the pulse rate of the detection signal output from the threshold determination circuit selected by the selection circuit 34 is a set value or within a set range.

Therefore, even if the variable threshold determination circuit 32 and the pulse rate control circuit 20 of the present embodiment are provided in the photodetector of the third embodiment shown in fig. 4, the same effects as those of the third embodiment can be obtained.

In addition, when the pulse rate of the detection signal output from the threshold determination circuit selected by the selection circuit 34 is greatly deviated from the set value, the pulse rate of the detection signal output to the subsequent processing circuit can be brought close to the set value by switching the threshold determination circuit selected by the selection circuit 34.

Further, since the control circuit 29 can grasp the pulse rate of the detection signal output from the plurality of threshold value determination circuits 30A, 30B, and 30C constituting the variable threshold value determination circuit 32, the pulse rate after switching the threshold value determination circuit selected by the selection circuit 34 can be confirmed in advance.

Therefore, the pulse rate of the detection signal output to the processing circuit of the subsequent stage can be controlled within a set value or a set range in a short time, and the control accuracy can be improved.

The number of the threshold determination circuits 30 provided in the variable threshold determination circuit 32 may be plural, 2, or 4 or more.

While the present disclosure has been described with reference to the embodiments, the present disclosure is not limited to the embodiments described above, and various modifications can be made.

[ first modification ]

In the photodetectors according to the second to fourth embodiments, the reverse bias voltage applied to the SPAD4 or other parameters of the light receiving unit 2 are changed when the sensitivity of the pixel formed of the light receiving unit array 10 is adjusted.

On the other hand, as shown in fig. 7, a discrete output switch 40 for turning on or off the signal path may be provided for each light receiving unit 2 in the signal path for outputting the pulse signal from each light receiving unit 2 of the light receiving unit array 10 to the threshold value determining circuit 30.

In this way, the pulse rate control circuit 20 can control the pulse rate by increasing or decreasing the number of pulse signals output from the light receiving unit array 10 or the number of pulse signals input to the threshold value determination circuit 30 via the discrete output switch 40.

The pulse rate control circuit 20 may set a signal path to be cut off via the discrete output switch 40 in advance, or may cut off an arbitrary path.

[ second modification ]

In each of the above embodiments, the sensitivity of the light receiving unit array 10 or each light receiving unit 2 controlled by the pulse rate control circuit 20 or the threshold of the threshold determination circuit 30 changes depending on the usage environment such as the amount of ambient light, but changes depending on the characteristic degradation of the light receiving unit array 10 or the peripheral circuit.

Therefore, as shown in fig. 8, a performance monitoring circuit 50 may be provided which monitors control values such as a control signal and a threshold value output from the pulse rate control circuit 20 and periodically stores the control values in a memory 52.

In this way, the user can grasp the deterioration state of the performance of the photodetector from the time-series change of the control value stored in the memory 52, and can effectively use the performance monitoring circuit 50 for maintenance management of the photodetector, the distance measuring device using the photodetector, and the like.

[ third modification ]

In each of the above embodiments, the pulse rate control circuit 20 adjusts the sensitivity of the light receiving unit array 10 or each light receiving unit 2 constituting the light receiving unit array 10, or the threshold value determination circuit 30 so that the measured pulse rate becomes a set value or a set range.

If the pulse rate cannot be controlled by this pulse rate control, it can be determined that an abnormality has occurred in the photodetector itself.

Therefore, the pulse rate control circuit 20 may operate in the procedure shown in fig. 9 when operating in the diagnostic mode, such as at startup.

In other words, in the diagnosis mode, similarly to the pulse rate control shown in fig. 2, the sensitivity is adjusted so that the pulse rate is within the set value or the set range by the processing of S100 to S300, and then the process proceeds to S400. In S400, it is determined whether or not the pulse rate can be controlled by determining whether or not the pulse rate has changed or detecting whether or not at least a pulse is output.

If a decision is made in S400 that the pulse rate cannot be controlled, the photodetector does not operate normally, and the process proceeds to S500, where an abnormality in the photodetector is reported to the user or an external device.

In this way, the failure determination of the photodetector is performed based on the control result of the pulse rate, and when a failure occurs, it is possible to prohibit an external device such as a distance measuring device from performing control using the photodetector. In addition, it is possible to notify the user that the photodetector has failed, and to quickly take measures such as repair.

[ fourth modification ]

As described above, when the pulse rate control circuit 20 is configured such that the set values can be externally input to the control circuits 24, 28, and 29, the set values may be input from the post-processing unit 60 including a processing circuit that processes the detection signal from the threshold value determination circuit 30, as illustrated in fig. 10.

In other words, the post-stage processing unit 60 may be, for example, a time measuring unit that measures the time from the emission of the light for distance measurement to the reception of the reflected light by the light detecting unit using the distance measuring device, but the pulse rate requested may change due to external factors in the post-stage processing unit 60.

For example, when the ambient temperature rises, the post-stage processing unit 60 may need to reduce the processing load in order to suppress its own heat generation, or may need to reduce the processing load due to a factor different from the signal processing from the photodetector.

In such a case, if the set value can be specified to the pulse rate control circuit 20 by the subsequent stage processing unit 60, the pulse rate of the detection signal output from the photodetector to the subsequent stage processing unit 60 is temporarily lowered, and the processing load for the signal processing can be reduced.

Therefore, in the fourth modification, the set value of the pulse rate controlled by the pulse rate control circuit 20 can be changed in accordance with the instruction from the subsequent-stage processing unit 60, and the detection signal can be output at the pulse rate requested by the subsequent-stage processing unit 60. In addition, this can improve the convenience of use of the photodetector and enlarge its use.

The plurality of components may realize a plurality of functions of one component in the above embodiments or a plurality of components may realize one function of one component. Further, a plurality of functions provided by a plurality of components may be realized by one component, or one function realized by a plurality of components may be realized by one component. In addition, a part of the structure of the above embodiment may be omitted. In addition, at least a part of the structure of the above embodiment may be added to or replaced with the structure of the other above embodiment. All the aspects included in the technical idea defined only by the characters described in the claims are embodiments of the present disclosure.