SPAD working overvoltage calibration circuit and calibration method

Abstract

According to the SPAD working overvoltage calibration circuit and calibration method provided by the invention, the detected maximum voltage value is compared with the withstand voltage of the first MOS tube, whether the output voltage of the charge pump needs to be adjusted or not is automatically judged, and the output voltage of the charge pump only needs to be adjusted once under the condition that adjustment is judged to be needed, so that the working voltage of the SPAD is accurately controlled. According to the scheme, the first terminal voltage (namely the voltage during avalanche breakdown) of the SPAD in the working process can be monitored in real time, the maximum value of the first terminal voltage can be captured, quick response and adjustment can be performed under the condition that breakdown voltage excursion is caused by working condition change or device aging, and potential damage of overvoltage to the SPAD and subsequent circuits is effectively avoided. According to the scheme, through built-in real-time detection and automatic calibration functions, the need of manual intervention is reduced, and the maintenance cost and complexity of the system are reduced.

Description

Technical Field

[0001] The present application relates to the technical field of single photon avalanche diodes, and in particular to a SPAD operating overvoltage calibration circuit and calibration method. Background Art

[0002] The single-photon avalanche diode (SPAD) and its key quenching circuit work together in an environment supported by a charge pump (adjustable voltage pump). The voltage pump precisely regulates and provides the necessary operating voltage for the SPAD, which is composed of the SPAD's inherent breakdown voltage (BV) plus a carefully designed overvoltage to ensure that the SPAD operates stably in Geiger mode. When the SPAD captures a photon and triggers an avalanche breakdown effect, the Vex node voltage will surge instantly. At this time, the quenching circuit quickly intervenes to adjust the voltage across the SPAD back to the BV level, thereby effectively cutting off the avalanche current. Subsequently, the MN0 circuit starts and slowly releases the voltage of the Vex node to 0V smoothly, fully preparing for the next photon detection.

[0003] Currently, the industry mostly adopts the method of directly monitoring the SPAD breakdown voltage and superimposing a fixed value, or using a single / multiple reference voltages to compare with Vex to avoid damage to the quenching circuit due to overvoltage. However, direct detection of BV is not only complicated, but also requires gradual adjustment of the charge pump voltage and monitoring of the SPAD response, which is time-consuming and affects the efficiency of ranging operations; the multi-channel comparator solution may cause inaccurate Vex peak detection due to input offset, bandwidth limitation and insufficient response speed, and it also requires multiple voltage adjustments to trigger the comparator flip, which increases the time cost. Summary of the invention

[0004] The purpose of the embodiments of the present application is to provide a SPAD working overvoltage calibration circuit and calibration method to solve the technical problems of inaccurate overvoltage detection, complex process and high time cost of existing SPADs.

[0005] A SPAD working overvoltage calibration circuit provided in an embodiment of the present application includes: a charge pump, a SPAD, a first MOS tube and a control module; The output end of the charge pump is connected to the second end of the SPAD, the first end of the SPAD is connected to the drain of the first MOS tube, the source of the first MOS tube is grounded, the input end of the control module is connected to the first end of the SPAD, and the output end of the control module is connected to the input end of the charge pump; The control module is used to detect the maximum value of the voltage at the first end of the SPAD when an avalanche breakdown occurs, and compare the maximum value with the withstand voltage of the first MOS tube. If the maximum value is greater than the withstand voltage of the first MOS tube, a control signal instructing the charge pump to reduce the output voltage of the charge pump is output to the charge pump.

[0006] In the above technical solution, by comparing the maximum detected voltage with the withstand voltage of the first MOS tube, and automatically judging whether the output voltage of the charge pump needs to be adjusted, if it is judged that adjustment is needed, the output voltage of the charge pump only needs to be adjusted once, so as to achieve precise control of the working voltage of the SPAD. This solution can monitor the first terminal voltage of the SPAD in real time during operation (i.e., the voltage at the time of avalanche breakdown) and capture its maximum value. It can also respond quickly and make adjustments when the breakdown voltage shifts due to changes in working conditions or aging of the device, effectively avoiding potential damage to the SPAD and subsequent circuits caused by overvoltage. This solution reduces the need for manual intervention and reduces the maintenance cost and complexity of the system through built-in real-time detection and automatic calibration functions. In addition, by precisely controlling the operating voltage of the SPAD, this solution helps to optimize the response speed and sensitivity of the SPAD, thereby improving its performance in applications such as light detection and photon counting.

[0007] In some optional implementations, the control module includes: an ADC, a pulse shaping circuit, a delay unit, and an MCU; The delay unit is used to output a start conversion signal to the ADC and MCU after a delay time for the voltage signal at the first end of the SPAD; The ADC is used to start working when receiving a start conversion signal, sample the voltage signal of the first terminal of the SPAD and convert it into a digital signal, and output the digital signal to the MCU; The MCU is used to output different delay times to the delay unit and receive digital signals corresponding to different delay times obtained by ADC sampling; determine the maximum value of the digital signal based on the digital signals corresponding to all delay times, and use the maximum value of the digital signal as the maximum value of the first terminal voltage of the SPAD.

[0008] In the above technical solution, the analog voltage signal at the first end of the SPAD can be converted into a digital signal with high precision by sampling using the ADC. This enables the MCU to process and analyze the voltage data more accurately, thereby more accurately judging the overvoltage situation and making corresponding adjustments. The delay unit allows the conversion of the voltage signal to start after a certain delay time after the avalanche breakdown of the SPAD. As the control core, the MCU can receive and process digital signals corresponding to different delay times from the ADC. By comparing these signals, the MCU can accurately determine the maximum value of the voltage at the first end of the SPAD, thereby more accurately controlling the output voltage of the charge pump.

[0009] In some optional embodiments, the first end of the ADC is connected to the first end of the SPAD, the second end of the ADC is connected to the MCU, and the third end of the ADC is connected to the second end of the delay unit; the first end of the delay unit is connected to the first end of the SPAD, the second end of the delay unit is connected to the MCU, and the third end of the delay unit is connected to the MCU.

[0010] In some optional embodiments, the control module further comprises: a pulse shaping circuit; The pulse shaping circuit is used to widen the voltage signal of the first terminal of the SPAD; The delay unit is used to output the start conversion signal to the ADC and MCU after the stretched signal has been delayed.

[0011] In the above technical solution, the pulse shaping circuit widens the voltage signal at the first end of the SPAD, which helps to improve the waveform and quality of the signal. When the SPAD undergoes avalanche breakdown, the generated voltage signal is often very steep and changes rapidly. Directly sampling such a signal may cause the ADC to be unable to accurately capture its peak value. By widening the signal, the pulse shaping circuit makes the waveform of the signal smoother, which is conducive to more stable and accurate sampling by the ADC.

[0012] In some optional embodiments, the first end of the ADC is connected to the first end of the SPAD, the second end of the ADC is connected to the MCU, and the third end of the ADC is connected to the second end of the delay unit; the first end of the pulse shaping circuit is connected to the first end of the SPAD, and the second end of the pulse shaping circuit is connected to the first end of the delay unit; the second end of the delay unit is connected to the MCU, and the third end of the delay unit is connected to the MCU.

[0013] In some optional implementations, the control module further includes: a second MOS tube and a current source; The first end of the SPAD is connected to the gate of the second MOS tube, the drain of the second MOS tube is connected to the power supply VDD, the source of the second MOS tube is connected to the current source and then to the ground, and the source of the second MOS tube is connected to the ADC and the pulse shaping circuit.

[0014] In the above technical solution, by introducing a source tracker, the source follower has the characteristics of low output impedance and high input impedance, and it can transmit the SPAD anode voltage to the ADC with less distortion. This solution avoids the introduction of excessive capacitance before the ADC sampling point, ensuring that the dead time of the quenching circuit is not changed. Among them, the dead time is the time required for the quenching circuit to recover to a re-triggerable state after the SPAD avalanche breakdown, which is crucial for the stable operation and accurate measurement of the SPAD. Avoiding the influence of capacitance on the dead time helps to maintain the stable performance of the quenching circuit and ensure that the SPAD maintains high efficiency and accuracy in high-speed, continuous photon detection. In addition, by introducing a source follower, the solution effectively isolates the high voltage between the ADC sampling circuit and the SPAD anode, reducing the anode voltage to a safe level that the ADC can withstand, which not only protects the ADC from high voltage damage, but also ensures the safety and reliability of sampling.

[0015] In some optional implementations, the control module further includes: a second MOS tube and a third MOS tube; The first end of the SPAD is connected to the gate of the second MOS tube, the drain of the second MOS tube is connected to the power supply VDD, the source of the second MOS tube is connected to the drain of the third MOS tube, the drain of the third MOS tube is connected to the gate of the third MOS tube, the source of the third MOS tube is grounded, and the source of the second MOS tube is connected to the ADC and the pulse shaping circuit.

[0016] In the above technical solution, the second MOS tube and the third MOS tube form a voltage divider circuit to reduce the voltage input to the ADC, thereby protecting the ADC from damage by high voltage and ensuring the safety and reliability of sampling.

[0017] An embodiment of the present application provides a SPAD operating overvoltage calibration method, including: The MCU is used to send an initial control signal to the charge pump, where the initial control signal is used to indicate the charge pump output voltage VSPAD; wherein VSPAD is greater than the SPAD breakdown voltage; When avalanche breakdown occurs in SPAD, the voltage VEX at the first end of SPAD is widened by using a pulse shaping circuit; Using the delay unit, the stretched signal is delayed for a certain period of time to generate a start conversion signal; When the ADC receives the start conversion signal, it samples and outputs the digital signal to the MCU; By using MCU, the delay time is adjusted to obtain digital signals corresponding to different delay times; Using the MCU, according to the digital signals corresponding to all the delay times, a maximum value of the digital signal is determined, and the maximum value of the digital signal is used as the maximum value of the first terminal voltage of the SPAD; Using the MCU, the maximum value of the first-end voltage of the SPAD is compared with the withstand voltage of the first MOS tube. If the maximum value is greater than the withstand voltage of the first MOS tube, a control signal instructing the charge pump output voltage to be reduced is output to the charge pump; if the maximum value is less than or equal to the withstand voltage of the first MOS tube, a control signal instructing the charge pump output voltage to remain unchanged is output to the charge pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A SPAD working overvoltage calibration circuit provided in the first embodiment of the present application; Figure 2 A SPAD operating overvoltage calibration circuit provided in the second embodiment of the present application; Figure 3 A SPAD operating overvoltage calibration circuit provided in the third embodiment of the present application; Figure 4 A SPAD operating overvoltage calibration circuit provided in the fourth embodiment of the present application; Figure 5 A SPAD operating overvoltage calibration circuit provided in the fifth embodiment of the present application; Figure 6 A flow chart of the steps of a SPAD working overvoltage calibration method provided in an embodiment of the present application; Figure 7 A schematic diagram of a start conversion signal waveform provided in an embodiment of the present application. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0021] Please refer to Figure 1 , Figure 1 A SPAD operating overvoltage calibration circuit provided in the first embodiment of the present application includes: a charge pump, a SPAD, a first MOS tube M0 and a control module.

[0022] Among them, the output end of the charge pump is connected to the second end of the SPAD, the first end of the SPAD is connected to the drain of the first MOS tube M0, the source of the first MOS tube M0 is grounded, the input end of the control module is connected to the first end of the SPAD, and the output end of the control module is connected to the input end of the charge pump; the control module is used to detect the maximum value of the voltage at the first end of the SPAD when an avalanche breakdown occurs in the SPAD, and compare the maximum value with the withstand voltage of the first MOS tube M0. If the maximum value is greater than the withstand voltage of the first MOS tube M0, the control signal indicating to reduce the output voltage of the charge pump is output to the charge pump.

[0023] In the embodiment of the present application, by comparing the detected maximum voltage with the withstand voltage of the first MOS tube M0, and automatically judging whether the output voltage of the charge pump needs to be adjusted, if it is judged that adjustment is needed, the output voltage of the charge pump only needs to be adjusted once, so as to achieve precise control of the working voltage of the SPAD. This solution can monitor the first terminal voltage of the SPAD in real time during operation (i.e., the voltage at the time of avalanche breakdown) and capture its maximum value. It can also respond quickly and make adjustments when the working conditions change or the device ages, causing the breakdown voltage to shift, effectively avoiding potential damage to the SPAD and subsequent circuits caused by overvoltage. This solution reduces the need for manual intervention and reduces the maintenance cost and complexity of the system through built-in real-time detection and automatic calibration functions. In addition, by precisely controlling the operating voltage of the SPAD, this solution helps to optimize the response speed and sensitivity of the SPAD, thereby improving its performance in applications such as light detection and photon counting.

[0024] Please refer to Figure 2 , Figure 2 The structure diagram of the SPAD working overvoltage calibration circuit provided for the second embodiment of the present application, the control module of this embodiment includes: ADC, pulse shaping circuit, delay unit and MCU. The first end of the ADC is connected to the first end of the SPAD, the second end of the ADC is connected to the MCU, and the third end of the ADC is connected to the second end of the delay unit; the first end of the delay unit is connected to the first end of the SPAD, the second end of the delay unit is connected to the MCU, and the third end of the delay unit is connected to the MCU.

[0025] Among them, the delay unit is used to output a start conversion signal to the ADC and MCU for the voltage signal at the first end of the SPAD after a delay time; the ADC is used to start working when receiving the start conversion signal, sample the level of the voltage signal at the first end of the SPAD and convert it into a digital signal, and output the digital signal to the MCU; the MCU is used to output different delay times to the delay unit, and receive digital signals corresponding to different delay times obtained by ADC sampling; based on the digital signals corresponding to all delay times, the maximum value of the digital signal is determined, and the maximum value of the digital signal is used as the maximum value of the first end voltage of the SPAD.

[0026] In the embodiment of the present application, the analog voltage signal at the first end of the SPAD can be converted into a digital signal with high precision by sampling using an ADC. This enables the MCU to process and analyze the voltage data more accurately, thereby more accurately judging the overvoltage situation and making corresponding adjustments. The delay unit allows the conversion of the voltage signal to start after a certain delay time after the avalanche breakdown of the SPAD. As the control core, the MCU can receive and process digital signals corresponding to different delay times from the ADC. By comparing these signals, the MCU can accurately determine the maximum value of the voltage at the first end of the SPAD, thereby more accurately controlling the output voltage of the charge pump.

[0027] Please refer to Figure 3 , Figure 3 The structure diagram of the SPAD working overvoltage calibration circuit provided in the third embodiment of the present application, the control module of this embodiment includes ADC, pulse shaping circuit, delay unit, MCU and pulse shaping circuit. The first end of the ADC is connected to the first end of the SPAD, the second end of the ADC is connected to the MCU, and the third end of the ADC is connected to the second end of the delay unit; the first end of the pulse shaping circuit is connected to the first end of the SPAD, and the second end of the pulse shaping circuit is connected to the first end of the delay unit; the second end of the delay unit is connected to the MCU, and the third end of the delay unit is connected to the MCU.

[0028] Among them, the pulse shaping circuit is used to widen the voltage signal of the first end of the SPAD; the delay unit is used to output the start conversion signal to the ADC and MCU after the delay time for the widened signal. The ADC is used to start working when receiving the start conversion signal, sample the voltage signal of the first end of the SPAD and convert it into a digital signal, and output the digital signal to the MCU; the MCU is used to output different delay times to the delay unit, receive the digital signals corresponding to the different delay times obtained by ADC sampling; according to the digital signals corresponding to all the delay times, determine the maximum value of the digital signal, and use the maximum value of the digital signal as the maximum value of the voltage of the first end of the SPAD.

[0029] In the embodiment of the present application, the pulse shaping circuit widens the voltage signal at the first end of the SPAD, which helps to improve the waveform and quality of the signal. When the SPAD undergoes avalanche breakdown, the generated voltage signal is often very steep and changes rapidly. Direct sampling of such a signal may cause the ADC to be unable to accurately capture its peak value. By widening the signal, the pulse shaping circuit makes the waveform of the signal smoother, which is conducive to more stable and accurate sampling by the ADC.

[0030] Please refer to Figure 4 , Figure 4The SPAD working overvoltage calibration circuit structure diagram provided for the fourth embodiment of the present application is different from that of the third embodiment in that: the control module of this embodiment also includes a second MOS tube M1 and a current source; the first end of the SPAD is connected to the gate of the second MOS tube M1, the drain of the second MOS tube M1 is connected to the power supply VDD, the source of the second MOS tube M1 is connected to the current source and then to ground, and the source of the second MOS tube M1 is connected to the ADC and the pulse shaping circuit.

[0031] In the embodiment of the present application, by introducing a source tracker, the source follower has the characteristics of low output impedance and high input impedance, and it can transmit the SPAD anode voltage to the ADC with less distortion. This solution avoids the introduction of excessive capacitance before the ADC sampling point, ensuring that the dead time of the quenching circuit is not changed. Among them, the dead time is the time required for the quenching circuit to recover to a re-triggerable state after the SPAD avalanche breakdown, which is crucial for the stable operation and accurate measurement of the SPAD. Avoiding the influence of capacitance on the dead time helps to maintain the stable performance of the quenching circuit and ensure that the SPAD maintains high efficiency and accuracy in high-speed, continuous photon detection. In addition, by introducing a source follower, the solution effectively isolates the high voltage between the ADC sampling circuit and the SPAD anode, reducing the anode voltage to a safe level that the ADC can withstand, which not only protects the ADC from high voltage damage, but also ensures the safety and reliability of sampling.

[0032] Please refer to Figure 5 , Figure 5 The SPAD working overvoltage calibration circuit structure diagram provided for the fifth embodiment of the present application is different from that of the third embodiment in that: the control module of this embodiment also includes a second MOS tube M1 and a third MOS tube M2; the first end of the SPAD is connected to the gate of the second MOS tube M1, the drain of the second MOS tube M1 is connected to the power supply VDD, the source of the second MOS tube M1 is connected to the drain of the third MOS tube M2, the drain of the third MOS tube M2 is connected to the gate of the third MOS tube M2, the source of the third MOS tube M2 is grounded, and the source of the second MOS tube M1 is connected to the ADC and the pulse shaping circuit.

[0033] In the embodiment of the present application, the second MOS tube M1 and the third MOS tube M2 are used to form a voltage divider circuit to reduce the voltage input to the ADC, thereby protecting the ADC from damage by high voltage and ensuring the safety and reliability of sampling.

[0034] Please refer to Figure 6 , Figure 6 A flow chart of the steps of a SPAD working overvoltage calibration method provided in an embodiment of the present application specifically includes: Step S1, using MCU to send an initial control signal to the charge pump, the initial control signal is used to indicate the charge pump output voltage VSPAD, at this time the SPAD can work in Geiger mode; wherein VSPAD is greater than the SPAD breakdown voltage.

[0035] Among them, Geiger Mode, also known as avalanche mode, is a working mode of SPAD. In this mode, the operating voltage of SPAD is higher than its breakdown voltage (Vbreak). When a photon is absorbed by the depletion region of SPAD, an electron-hole pair is generated. Under the action of high electric field, this electron-hole pair will quickly split and accelerate, constantly collide and ionize, and produce more electron-hole pairs, thus triggering an avalanche-like multiplication effect. This multiplication effect enables SPAD to detect weak signals of single photons. The high sensitivity and time resolution of SPAD in Geiger mode make it a key component in lidar. By measuring the time of flight (ToF) of the light pulse, the distance and speed of the target object can be accurately calculated.

[0036] Step S2: When the SPAD undergoes avalanche breakdown, a pulse shaping circuit is used to widen the voltage VEX at the first end of the SPAD.

[0037] Among them, the pulse shaping circuit widens the voltage signal at the first end of the SPAD, which helps to improve the waveform and quality of the signal. When the SPAD undergoes avalanche breakdown, the generated voltage signal is often very steep and changes rapidly. Directly sampling such a signal may cause the ADC to be unable to accurately capture its peak value. By widening the signal, the pulse shaping circuit makes the waveform of the signal smoother, which is conducive to more stable and accurate sampling by the ADC.

[0038] Step S3: using a delay unit to generate a start conversion signal after the stretched signal has been delayed for a certain period of time.

[0039] Step S4: When the ADC receives the start conversion signal, the ADC samples and outputs the digital signal Dout to the MCU.

[0040] Step S5: Using the MCU to adjust the delay time to obtain digital signals corresponding to different delay times; Specifically, Figure 7 As shown, different start conversion signals are generated at different delay times, and the ADC is controlled to perform sampling according to the start conversion signals, so that different VEX values ​​can be obtained.

[0041] Step S6: using the MCU to determine the maximum value of the digital signal according to the digital signals corresponding to all the delay times, and using the maximum value of the digital signal as the maximum value of the first terminal voltage of the SPAD; Step S7, using the MCU, compare the maximum value of the first terminal voltage of the SPAD with the withstand voltage of the first MOS tube M0. If the maximum value is greater than the withstand voltage of the first MOS tube M0, output a control signal instructing the charge pump to reduce the output voltage of the charge pump to the charge pump; if the maximum value is less than or equal to the withstand voltage of the first MOS tube M0, output a control signal instructing the charge pump output voltage to remain unchanged to the charge pump.

[0042] In the embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some communication interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0043] In addition, the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0044] Furthermore, the functional modules in the various embodiments of the present application may be integrated together to form an independent part, or each module may exist separately, or two or more modules may be integrated to form an independent part.

[0045] In this document, relational terms such as first and second, etc. are used merely to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0046] The above description is only an embodiment of the present application and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A SPAD working overvoltage calibration circuit, characterized in that: include: Charge pump, SPAD, first MOS tube and control module; The output end of the charge pump is connected to the second end of the SPAD, the first end of the SPAD is connected to the drain of the first MOS tube, the source of the first MOS tube is grounded, the input end of the control module is connected to the first end of the SPAD, and the output end of the control module is connected to the input end of the charge pump; The control module is used to detect the maximum value of the first terminal voltage of the SPAD when the SPAD undergoes avalanche breakdown, and compare the maximum value with the withstand voltage of the first MOS tube. If the maximum value is greater than the withstand voltage of the first MOS tube, a control signal instructing to reduce the output voltage of the charge pump is output to the charge pump.

2. The circuit according to claim 1, characterized in that The control module includes: ADC, pulse shaping circuit, delay unit and MCU; The delay unit is used to output a start conversion signal to the ADC and the MCU after a delay time for the first terminal voltage signal of the SPAD; The ADC is used to start working upon receiving a start conversion signal, sample the voltage level of the first terminal of the SPAD and convert it into a digital signal, and output the digital signal to the MCU; The MCU is used to output different delay times to the delay unit, and receive digital signals corresponding to different delay times obtained by ADC sampling; determine the maximum value of the digital signal based on the digital signals corresponding to all delay times, and use the maximum value of the digital signal as the maximum value of the first terminal voltage of the SPAD.

3. The circuit according to claim 2, characterized in that The first end of the ADC is connected to the first end of the SPAD, the second end of the ADC is connected to the MCU, and the third end of the ADC is connected to the second end of the delay unit; the first end of the delay unit is connected to the first end of the SPAD, the second end of the delay unit is connected to the MCU, and the third end of the delay unit is connected to the MCU.

4. The circuit according to claim 2, characterized in that The control module further includes: a pulse shaping circuit; The pulse shaping circuit is used to widen the voltage signal of the first terminal of the SPAD; The delay unit is used for outputting a start conversion signal to the ADC and the MCU after a delay time for the stretched signal.

5. The circuit according to claim 4, characterized in that The first end of the ADC is connected to the first end of the SPAD, the second end of the ADC is connected to the MCU, and the third end of the ADC is connected to the second end of the delay unit; the first end of the pulse shaping circuit is connected to the first end of the SPAD, and the second end of the pulse shaping circuit is connected to the first end of the delay unit; the second end of the delay unit is connected to the MCU, and the third end of the delay unit is connected to the MCU.

6. The circuit according to claim 4, characterized in that The control module further includes: a second MOS tube and a current source; The first end of the SPAD is connected to the gate of the second MOS tube, the drain of the second MOS tube is connected to the power supply VDD, the source of the second MOS tube is connected to the current source and then grounded, and the source of the second MOS tube is connected to the ADC and the pulse shaping circuit.

7. The circuit according to claim 4, characterized in that The control module further includes: a second MOS tube and a third MOS tube; The first end of the SPAD is connected to the gate of the second MOS tube, the drain of the second MOS tube is connected to the power supply VDD, the source of the second MOS tube is connected to the drain of the third MOS tube, the drain of the third MOS tube is connected to the gate of the third MOS tube, the source of the third MOS tube is grounded, and the source of the second MOS tube is connected to the ADC and the pulse shaping circuit.

8. A SPAD working overvoltage calibration method, characterized in that: include: Using the MCU to send an initial control signal to the charge pump, the initial control signal is used to indicate the charge pump output voltage VSPAD; wherein VSPAD is greater than the SPAD breakdown voltage; When avalanche breakdown occurs in SPAD, the voltage VEX at the first end of SPAD is widened by using a pulse shaping circuit; Using the delay unit, the stretched signal is delayed for a certain period of time to generate a start conversion signal; When the ADC receives the start conversion signal, it samples and outputs the digital signal to the MCU; By using MCU, the delay time is adjusted to obtain digital signals corresponding to different delay times; Using the MCU, according to the digital signals corresponding to all the delay times, a maximum value of the digital signal is determined, and the maximum value of the digital signal is used as the maximum value of the first terminal voltage of the SPAD; Using the MCU, the maximum value of the first-end voltage of the SPAD is compared with the withstand voltage of the first MOS tube. If the maximum value is greater than the withstand voltage of the first MOS tube, a control signal instructing the charge pump output voltage to be reduced is output to the charge pump; if the maximum value is less than or equal to the withstand voltage of the first MOS tube, a control signal instructing the charge pump output voltage to remain unchanged is output to the charge pump.

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