A system for determining the optimal gain point of APD based on laser ranging and its implementation method

Abstract

The present invention discloses a system for determining the optimal gain point of an APD based on laser ranging and an implementation method thereof, wherein the system comprises a laser transmitter, a photoelectric receiver, a local oscillator signal driver, an I-V converter, an intermediate frequency filter amplifier, an intermediate frequency echo output buffer, a low-pass filter, a noise sampling buffer, a linear high-voltage controller, a DC high-voltage generator, a high-voltage sampling buffer and a sampling controller. The present invention changes the traditional setting method of fixed gain point by experience to determining the optimal gain point by observing the optimal signal-to-noise ratio, so that the optimal optimal gain point voltage can be found by calibration for different APDs, greatly improving the performance, stability and consistency of the entire ranging system and the product yield.

Description

Technical Field

[0001] The present invention relates to the technical field of laser ranging, and in particular to a system for determining an optimal gain point of an APD based on laser ranging and a method for realizing the system. Background Art

[0002] In the phase method ranging system, the distance between the laser source and the reflecting target is indirectly measured by observing the phase difference between the local oscillator signal and the laser echo signal. In a complex measurement environment, different target reflection surfaces and measuring distances will often cause the echo signal of the laser rangefinder to be weakened and the echo signal is more likely to be submerged by the noise signal. At this time, the photoelectric receiver (hereinafter referred to as APD), the core device for detecting the reflected signal, plays a vital role. When using APD, it is necessary to add a suitable DC bias voltage to ensure that the APD can convert the laser signal received into a large enough photocurrent to facilitate further processing of the subsequent circuit. This external DC bias voltage determines the photosensitivity of the APD to the laser signal, and also determines the size of the output noise, so it involves the determination of the optimal signal-to-noise ratio of the APD output signal. There are consistency issues for different APD devices, which is mainly reflected in the different APD breakdown voltages at different temperatures. Therefore, at the same temperature and DC bias voltage, the gains of different APD outputs are not the same and the signal-to-noise ratios are also different. Therefore, if the APD is to work in the best state, the same DC bias voltage cannot be uniformly set to ensure that all APDs work in the same state. Instead, a calibration calculation method is required.

[0003] The selection of the optimal gain point voltage of traditional APDs is often uniformly selected and set based on empirical values, that is, the gain point voltage is selected and fixedly set between 85% and 90% of the breakdown voltage through batch test and analysis of the gain point experiment of APDs. This may lead to large differences in APD gain, large differences in noise, APD oversaturation, etc. For example, when the voltage is set too low, the gain may be insufficient and a good effect cannot be produced on a reflective surface with low reflectivity or when measuring at a long distance. When the voltage is set too high, the APD noise may increase and the circuit system may not be able to resist, resulting in a decrease in ranging accuracy or APD oversaturation on a reflective surface with good reflectivity, or even the disappearance of the echo signal and the inability to measure the distance normally. This can easily lead to inconsistent performance of the entire ranging system and a low factory yield. Summary of the invention

[0004] The purpose of the present invention is to provide a system for determining the optimal gain point of an APD based on laser ranging and an implementation method thereof, which changes the traditional setting method of fixed gain point by experience to the optimal gain point determined by optimal signal-to-noise ratio observation, so that the optimal optimal gain point voltage can be found for different APDs through calibration, greatly improving the performance, stability and consistency of the entire ranging system and the product yield.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a system for determining the optimal gain point of an APD based on laser ranging, comprising a laser transmitter, a photoelectric receiver, a local oscillator signal driver, an IV converter, an intermediate frequency filter amplifier, an intermediate frequency echo output buffer, a low-pass filter, a noise sampling buffer, a linear high-voltage controller, a DC high-voltage generator, a high-voltage sampling buffer and a sampling controller;

[0007] The laser transmitter transmits the optical signal carrying the carrier to the photoelectric receiver through the reflecting surface to be measured, and the local oscillator signal driver generates a fixed local oscillator frequency signal and transmits it to the photoelectric receiver; the photoelectric receiver is connected to the IV converter, and the IV converter is connected to the intermediate frequency filter amplifier and the low-pass filter; the intermediate frequency filter amplifier is connected to the intermediate frequency echo output buffer and the sampling controller in sequence; the low-pass filter is connected to the noise sampling buffer and the sampling controller in sequence; the linear high-voltage controller is connected to the DC high-voltage generator, the DC high-voltage generator provides gain for the photoelectric receiver, and the DC high-voltage generator is connected to the high-voltage sampling buffer and the sampling controller in sequence.

[0008] The present invention also provides a method for implementing a system for determining an APD optimal gain point based on laser ranging, comprising the following steps:

[0009] S1. Place the system in a constant high temperature environment to perform software high temperature calibration to obtain a first breakdown voltage and a first APD ambient temperature value; place the system in a constant low temperature environment to perform software low temperature calibration to obtain a second breakdown voltage and a second APD ambient temperature value;

[0010] S2, obtaining a linear relationship between the APD ambient temperature value and the breakdown voltage from the first breakdown voltage, the first APD ambient temperature value, the second breakdown voltage, and the second APD ambient temperature value;

[0011] S3. Based on the linear relationship between the APD ambient temperature value and the breakdown voltage, the system is calibrated at the optimal gain point under a reflective surface with a fixed reflectivity to obtain the APD optimal gain point voltage.

[0012] Preferably, the temperature difference between the constant high temperature environment and the constant low temperature environment is at least 10°C.

[0013] Preferably, the methods of software high-temperature calibration and software low-temperature calibration are the same, including: S11, placing the system in a constant high-temperature environment or a constant low-temperature environment, and the system performs program function initialization: initializing the laser transmitter to be off, setting the scanning initial voltage and the scanning end voltage, and the local oscillator signal driver outputs a fixed local oscillator frequency signal loaded onto the cathode pin of the photoelectric receiver; S12, the linear high-voltage controller controls the DC high-voltage generator to output the working voltage with the initial scanning voltage as the reference point until it increases to the scanning end voltage for multiple scans, and the sampling controller reads the voltage value of the high-voltage sampling buffer and the noise signal of the noise sampling buffer under each scan. signal and the temperature value of the photoelectric receiver, bind the three values ​​read each time into a key-value pair and store them in the buffer sequence of the sampling controller in the order of the scanning time; S13, record the multiple noise signals read in S12 as a continuous noise signal sequence, perform a first-order derivative of the noise signal sequence to obtain the minimum value of the noise signal, find out the voltage value and temperature value corresponding to the minimum value of the noise signal in the key-value pair, record the voltage value and temperature value found in the constant high temperature environment as the first breakdown voltage and the first APD ambient temperature value, respectively, and record the voltage value and temperature value found in the constant low temperature environment as the second breakdown voltage and the second APD ambient temperature value, respectively.

[0014] Preferably, the scanning initial voltage is 70V, and the scanning end voltage is 140V.

[0015] Preferably, S2 includes: S21, establishing a rectangular coordinate system; S22, constructing a first coordinate point with the first APD ambient temperature value as the first horizontal coordinate and the first breakdown voltage as the first vertical coordinate, and constructing a second coordinate point with the second APD ambient temperature value as the second horizontal coordinate and the second breakdown voltage as the second vertical coordinate; S23, obtaining a linear equation from the first coordinate point and the second coordinate point, and the linear equation is the linear relationship between the APD ambient temperature value and the breakdown voltage.

[0016] Preferably, the S3 includes: S31, facing the system to a reflective surface with a fixed reflectivity, measuring the current APD ambient temperature value of the system and recording it as a calibrated APD ambient temperature value, obtaining the breakdown voltage corresponding to the calibrated APD ambient temperature value based on the linear relationship between the APD ambient temperature value and the breakdown voltage and recording it as the calibrated breakdown voltage; S32, initializing the system: setting 65% of the calibrated breakdown voltage as the starting scan voltage, 98% of the calibrated breakdown voltage as the ending scan voltage, turning on the laser transmitter to transmit a carrier-carrying optical signal to the reflective surface with a fixed reflectivity, and the local oscillator signal driver outputting a fixed local oscillator frequency signal to be loaded onto the cathode pin of the photoelectric receiver; S33, a linear high-voltage controller controls the starting scan voltage of the DC high-voltage generator as the reference point output working The bias voltage is scanned multiple times until it increases to the end scanning voltage, and the intermediate frequency signal of the intermediate frequency echo output buffer is sampled at multiple cycles at equal intervals during each scan through the sampling controller to obtain a serialized signal waveform, and the intermediate frequency signal in each serialized signal waveform is forward transformed by FFT and a signal-to-noise ratio is calculated, and the signal-to-noise ratio calculated each time and the ratio of the working bias voltage at that time to the calibrated breakdown voltage are bound to a key-value pair and stored in the buffer sequence of the sampling controller in the time order of the scan; S34, find the maximum value of the signal-to-noise ratio in the buffer sequence, and then find the ratio of the working bias voltage corresponding to the maximum value of the signal-to-noise ratio in the key-value pair to the calibrated breakdown voltage, and then obtain the corresponding working bias voltage based on the ratio, and record the current working bias voltage as the APD optimal gain point voltage.

[0017] Preferably, in S33, the sampling interval of the multi-period equally spaced sampling is determined by a preset sampling frequency.

[0018] Preferably, in S33, the calculation formula of the signal-to-noise ratio SNR is:

[0019] SNR=a(signal) / a(noise);

[0020] In the formula, a(signal) represents the amplitude corresponding to the fundamental frequency of the sampled intermediate frequency signal, and a(noise) represents the sum of the harmonic components of the sampled intermediate frequency signal within the sampling bandwidth;

[0021] The calculation formula of a(noise) is:

[0022] a(noise)=∑a(n);

[0023] Where a(n) represents the amplitude of each harmonic component of the sampled intermediate frequency signal within the sampling bandwidth, and n represents the order of the harmonic component.

[0024] Preferably, the optimal gain point voltage needs to satisfy the following constraints:

[0025] V(b)+V(m)≤V(k);

[0026] Where, V(b) represents the APD optimal gain point voltage, V(m) represents the swing amplitude of the local oscillator signal driver, and V(k) represents the calibrated breakdown voltage;

[0027] If V(b) does not satisfy the constraint condition, V(b) is adjusted until the constraint condition is satisfied, and the adjusted V(b) is the APD optimal gain point voltage.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention solves the problem of different APD parameters caused by the inability to accurately control the consistency of device parameters during production. For each APD, the corresponding optimal gain point voltage can be determined through the optimal signal-to-noise ratio, thereby improving the robustness of the APD and the system circuit, and greatly improving the performance, stability, consistency and product yield of the entire ranging system. While meeting the maximum gain of the APD, the noise caused by the APD is reduced as much as possible, the signal-to-noise ratio of the reflected signal is improved, and the signal interference is reduced, thereby also improving the ranging accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a system structure diagram of the present invention. DETAILED DESCRIPTION

[0031] Terminology explanation:

[0032] ‌I-V Converter:‌ A device that converts input current to output voltage, also known as a transimpedance amplifier.

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. In the description of the present invention, it should be noted that the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0034] like Figure 1 As shown, the present invention provides a system for determining the optimal gain point of APD based on laser ranging, including a laser transmitter, a photoelectric receiver, a local oscillator signal driver, an IV converter, an intermediate frequency filter amplifier, an intermediate frequency echo output buffer, a low-pass filter, a noise sampling buffer, a linear high-voltage controller, a DC high-voltage generator, a high-voltage sampling buffer and a sampling controller.

[0035] The laser transmitter transmits the optical signal carrying the carrier to the reflective surface to be measured, and the photoelectric receiver receives the reflected optical signal after being reflected by the reflective surface; the local oscillator signal driver generates a fixed local oscillator frequency signal and transmits it to the photoelectric receiver; the fixed local oscillator frequency signal and the reflected optical signal are mixed to obtain a difference frequency signal; the photoelectric receiver is connected to the IV converter, and the difference frequency signal is converted into a voltage signal through the IV converter. The IV converter connects the intermediate frequency filter amplifier and the low-pass filter; the intermediate frequency filter amplifier is connected to the intermediate frequency echo output buffer and the sampling controller in turn; the low-pass filter is connected to the noise sampling buffer and the sampling controller in turn; the linear high-voltage controller is connected to the DC high-voltage generator, which provides gain for the photoelectric receiver, and the DC high-voltage generator is connected to the high-voltage sampling buffer and the sampling controller in turn. The voltage signal output by the IV converter is processed by the intermediate frequency filter amplifier to obtain a single intermediate frequency signal, and the single intermediate frequency signal is input to the sampling controller through the intermediate frequency echo output buffer.

[0036] The present invention also provides a method for implementing a system for determining an APD optimal gain point based on laser ranging, which is based on the system for determining an APD optimal gain point based on laser ranging, and includes the following steps:

[0037] S1. Place the system in a constant high temperature environment to perform software high temperature calibration to obtain a first breakdown voltage and a first APD ambient temperature value; place the system in a constant low temperature environment to perform software low temperature calibration to obtain a second breakdown voltage and a second APD ambient temperature value;

[0038] S2, obtaining a linear relationship between the APD ambient temperature value and the breakdown voltage from the first breakdown voltage, the first APD ambient temperature value, the second breakdown voltage, and the second APD ambient temperature value;

[0039] S3. Based on the linear relationship between the APD ambient temperature value and the breakdown voltage, the system is calibrated at the optimal gain point under a reflective surface with a fixed reflectivity to obtain the APD optimal gain point voltage.

[0040] The present invention performs software high and low temperature to achieve preliminary calibration under a constant high and low temperature environment, and then performs optimal gain point calibration under a reflective surface with a fixed reflectivity to achieve the final result, so that the APD of each product can work in its own optimal state. The present invention mainly solves the influence of consistency caused by setting the same bias voltage in the traditional method, finds the working bias voltage of the APD under the best signal-to-noise ratio through calibration calculation and updates the setting of the optimal working bias voltage at different temperatures, and provides a solution for the correct use of APD.

[0041] Furthermore, the temperature difference between the constant high temperature environment and the constant low temperature environment is at least 10° C. Since the breakdown voltage is a linear calibration method, the temperature sensor has errors and the constant temperature environment used for calibration also has errors. The temperature difference between the high and low temperature environments should be as large as possible to avoid the calibration deviation affecting the slope, thereby causing the deviation to increase when working outside the two endpoints of the linear calibration.

[0042] Furthermore, the methods of software high-temperature calibration and software low-temperature calibration are the same, including: S11, placing the system in a constant high-temperature environment or a constant low-temperature environment, and the system performs program function initialization: initializing the laser transmitter to be off, setting the scan initial voltage and the scan end voltage, and the local oscillator signal driver outputs a fixed local oscillator frequency signal loaded onto the cathode pin of the photoelectric receiver; S12, a linear high-voltage controller controls the DC high-voltage generator to output the working voltage with the initial scan voltage as the reference point until it increases to the scan end voltage for multiple scans, and the increase is a step increase, that is, it increases according to a fixed step size, and then the sampling controller reads the voltage value of the high-voltage sampling buffer, the noise signal of the noise sampling buffer and the temperature value of the photoelectric receiver under each scan, and binds the three values ​​read each time into a key-value pair and stores them in the buffer sequence of the sampling controller in the time order of the scan. , the corresponding temperature value and noise signal can be queried through the voltage value later; S13, the multiple noise signals read in S12 are recorded as a continuous noise signal sequence y=f(x), the background noise signal will become smoother after passing through the low-pass filter, so the multiple noise signals sampled by the noise sampling buffer must also be smooth and continuous signals. Therefore, the sampled noise signal sequence is also a continuous function, which has a first-order derivative function. The first-order derivative y′=f′(x) of the noise signal sequence is taken to obtain the minimum value of the noise signal, and the voltage value and temperature value corresponding to the minimum value of the noise signal in the key-value pair are found. The voltage value and temperature value found in the constant high temperature environment are respectively recorded as the first breakdown voltage and the first APD ambient temperature value, and the voltage value and temperature value found in the constant low temperature environment are respectively recorded as the second breakdown voltage and the second APD ambient temperature value.

[0043] Furthermore, the scan initial voltage is 70 V, and the scan end voltage is 140 V. These two values ​​are actually obtained by the breakdown voltage of the APD being not less than 70 V at a low temperature of -30°C and not more than 140 V at a high temperature of 50°C.

[0044] Further, the S2 includes: S21, establishing a rectangular coordinate system; S22, constructing a first coordinate point (x 1 ,y 1), the second coordinate point (x 2 ,y 2 ); S23, by the first coordinate point (x 1 ,y 1 ) and the second coordinate point (x 2 ,y 2 ) to obtain a linear equation such as , a and b are based on (x 2 ,y 2 ) and (x 2 ,y 2 ) is a constant calculated by the linear equation, and the linear equation is the linear relationship between the APD ambient temperature value x and the breakdown voltage y, that is, each APD ambient temperature value can obtain a correspondingly changing breakdown voltage.

[0045] Furthermore, the S3 includes: S31, facing the system to a reflective surface with a fixed reflectivity, measuring the current APD ambient temperature value of the system and recording it as a calibrated APD ambient temperature value, obtaining the breakdown voltage corresponding to the calibrated APD ambient temperature value based on the linear relationship between the APD ambient temperature value and the breakdown voltage and recording it as the calibrated breakdown voltage; S32, initializing the system: setting 65% of the calibrated breakdown voltage as the starting scan voltage, and 98% of the calibrated breakdown voltage as the ending scan voltage, turning on the laser transmitter to transmit a carrier-carrying optical signal to the reflective surface with a fixed reflectivity, and the local oscillator signal driver outputting a fixed local oscillator frequency signal loaded onto the cathode pin of the photoelectric receiver, and the fixed local oscillator frequency signal is the same as the fixed local oscillator frequency signal in S11; S33, a linear high-voltage controller controls the DC high-voltage generator to start The starting scanning voltage is used as the reference point to output the working bias voltage until it increases to the ending scanning voltage and performs multiple scans. The intermediate frequency signal of the intermediate frequency echo output buffer is sampled at multiple cycles at equal intervals during each scan through the sampling controller to obtain a serialized signal waveform. The intermediate frequency signal in each serialized signal waveform is subjected to FFT forward transformation and a signal-to-noise ratio is calculated. The signal-to-noise ratio calculated each time and the ratio of the current working bias voltage to the calibrated breakdown voltage are bound to a key-value pair and stored in the buffer sequence of the sampling controller in the order of the scanning time; S34, searching for the maximum value of the signal-to-noise ratio in the buffer sequence, and then finding the ratio of the working bias voltage corresponding to the maximum value of the signal-to-noise ratio in the key-value pair to the calibrated breakdown voltage, and then obtaining the corresponding working bias voltage based on the ratio, and recording the current working bias voltage as the APD optimal gain point voltage.

[0046] In S31, there is a temperature sensor on the PCB board, which can be collected by the A / D converter. This is because the temperature sensor needs to be as close to the photoelectric receiver as possible, so that the local ambient temperature around the photoelectric receiver can be more accurately determined. Therefore, the APD ambient temperature value is obtained by the temperature sensor. Then, based on the linear relationship between the APD ambient temperature value and the breakdown voltage, the breakdown voltage corresponding to the current APD ambient temperature value is obtained, and the current APD ambient temperature value and breakdown voltage are recorded as the calibrated APD ambient temperature value and the calibrated breakdown voltage, respectively.

[0047] In S32, 65% of the calibrated breakdown voltage is set as the starting scan voltage, and 98% of the calibrated breakdown voltage is set as the ending scan voltage. The calibrated breakdown voltage means that it is just working in the breakdown state, and the gain is 0 at this time. In fact, when the APD works before the breakdown voltage, the higher the scan voltage, the higher the gain. When the scan voltage increases to near the breakdown voltage, the gain actually shows a gradual decline trend until it reaches 0, and the noise also increases rapidly at this stage. Therefore, 98% is an empirical value obtained from experiments. There is a difference frequency between the frequency of the local oscillator frequency signal output by the local oscillator signal driver and the frequency of the optical signal emitted by the laser transmitter.

[0048] In S33, the increment of the working bias voltage is also a step increment, that is, it is increased according to a fixed step length, and multiple scans are performed using multiple working bias voltages. The signal output by the intermediate frequency echo output buffer is sampled at multiple cycles at equal intervals by the sampling controller, and the sampling interval of the multiple cycles at equal intervals is determined by the sampling frequency f(s) of the photoelectric receiver. According to the Nyquist theorem, the sampling frequency is less than or equal to The frequency signal can be completely restored, so when calculating the noise signal, we only need to pay attention to the energy spectrum within the sampling bandwidth. Perform FFT forward transformation on the intermediate frequency signal in each serialized signal waveform and calculate a signal-to-noise ratio. The calculation formula of the signal-to-noise ratio SNR is:

[0049] SNR=a(signal) / a(noise);

[0050] In the formula, a(signal) represents the amplitude corresponding to the fundamental frequency of the sampled intermediate frequency signal, and a(noise) represents the sum of the harmonic components of the sampled intermediate frequency signal within the sampling bandwidth;

[0051] The calculation formula of a(noise) is:

[0052] a(noise)=∑a(n);

[0053] Where a(n) represents the amplitude of each harmonic component of the sampled intermediate frequency signal within the sampling bandwidth, and n represents the order of the harmonic component.

[0054] Finally, the signal-to-noise ratio calculated each time and the ratio of the working bias voltage to the calibrated breakdown voltage are bound into a key-value pair and stored in the buffer sequence of the sampling controller according to the scanning time sequence.

[0055] In S34, after the scan is completed, the maximum value of the signal-to-noise ratio in the buffer sequence is searched, and then the ratio of the working bias voltage corresponding to the maximum value of the signal-to-noise ratio in the key-value pair to the calibrated breakdown voltage is found, and then the corresponding working bias voltage is obtained based on the ratio, and the current working bias voltage is recorded as the APD optimal gain point voltage. However, since the local oscillator signal driver also has a fixed swing amplitude V(m), if its signal peak-to-peak value is V(p), , since the swing amplitude is superimposed on V(b), the actual optimal gain point voltage can reach V(b)+V(m), which may lead to the possibility that the actual operating voltage exceeds the calibrated breakdown voltage V(k). To this end, the optimal gain point voltage must meet the following constraints: V(b)+V(m)≤V(k). When the temperature is constant, V(k) is a constant and V(m) is also a constant. If V(b) does not meet the constraints, adjust V(b) until the constraints are met. The adjusted V(b) is the final APD optimal gain point voltage.

[0056] Finally, it should be noted that the above embodiments are only preferred embodiments of the present invention to illustrate the technical solutions of the present invention, rather than limiting them, and certainly not limiting the patent scope of the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. In other words, any changes or modifications made to the main design concept and spirit of the present invention that have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention in other related technical fields is also included in the patent protection scope of the present invention.

Claims

1. A method for implementing a system for determining an APD optimal gain point based on laser ranging, characterized in that: The implementation method is based on a system, including a laser transmitter, a photoelectric receiver, a local oscillator signal driver, an IV converter, an intermediate frequency filter amplifier, an intermediate frequency echo output buffer, a low-pass filter, a noise sampling buffer, a linear high voltage controller, a DC high voltage generator, a high voltage sampling buffer and a sampling controller; The laser transmitter transmits the optical signal carrying the carrier to the photoelectric receiver through the reflective surface to be measured, and the local oscillator signal driver generates a fixed local oscillator frequency signal and transmits it to the photoelectric receiver; the photoelectric receiver is connected to the IV converter, and the IV converter is connected to the intermediate frequency filter amplifier and the low-pass filter; The intermediate frequency filter amplifier is connected to the intermediate frequency echo output buffer and the sampling controller in sequence; The low-pass filter is connected to the noise sampling buffer and the sampling controller in sequence; the linear high-voltage controller is connected to the DC high-voltage generator, the DC high-voltage generator provides gain for the photoelectric receiver, and the DC high-voltage generator is connected to the high-voltage sampling buffer and the sampling controller in sequence; The implementation method comprises the following steps: S1. Place the system in a constant high temperature environment to perform software high temperature calibration to obtain a first breakdown voltage and a first APD ambient temperature value; place the system in a constant low temperature environment to perform software low temperature calibration to obtain a second breakdown voltage and a second APD ambient temperature value; S2, obtaining a linear relationship between the APD ambient temperature value and the breakdown voltage from the first breakdown voltage, the first APD ambient temperature value, the second breakdown voltage, and the second APD ambient temperature value; S3, based on the linear relationship between the APD ambient temperature value and the breakdown voltage, the system is calibrated at the optimal gain point under a reflective surface with a fixed reflectivity to obtain the APD optimal gain point voltage; The methods of software high temperature calibration and software low temperature calibration are the same, including: S11, placing the system in a constant high temperature environment or a constant low temperature environment, and the system performs program function initialization: initializing the laser transmitter to be off, setting the scan initial voltage and the scan end voltage, and the local oscillator signal driver outputs a fixed local oscillator frequency signal loaded onto the cathode pin of the photoelectric receiver; S12, the linear high voltage controller controls the DC high voltage generator to output the working voltage with the initial scan voltage as the reference point until it increases to the scan end voltage for multiple scans, and the sampling controller reads the voltage value of the high voltage sampling buffer, the noise signal of the noise sampling buffer and The temperature value of the photoelectric receiver, binds the three values ​​read each time into a key-value pair and stores them in the buffer sequence of the sampling controller in the order of the scanning time; S13, records the multiple noise signals read in S12 as a continuous noise signal sequence, performs a first-order derivative on the noise signal sequence to obtain the minimum value of the noise signal, finds the voltage value and temperature value corresponding to the minimum value of the noise signal in the key-value pair, and records the voltage value and temperature value found in the constant high temperature environment as the first breakdown voltage and the first APD ambient temperature value, respectively, and records the voltage value and temperature value found in the constant low temperature environment as the second breakdown voltage and the second APD ambient temperature value, respectively.

2. The method for implementing a system for determining an APD optimal gain point based on laser ranging according to claim 1, characterized in that: The temperature difference between the constant high temperature environment and the constant low temperature environment is at least 10°C.

3. The method for implementing a system for determining an APD optimal gain point based on laser ranging according to claim 1, characterized in that: The scanning initial voltage is 70V, and the scanning end voltage is 140V.

4. The method for implementing a system for determining an APD optimal gain point based on laser ranging according to claim 1, characterized in that: The S2 includes: S21, establishing a rectangular coordinate system; S22, constructing a first coordinate point with the first APD ambient temperature value as the first horizontal coordinate and the first breakdown voltage as the first vertical coordinate, and constructing a second coordinate point with the second APD ambient temperature value as the second horizontal coordinate and the second breakdown voltage as the second vertical coordinate; S23, obtaining a linear equation from the first coordinate point and the second coordinate point, and the linear equation is the linear relationship between the APD ambient temperature value and the breakdown voltage.

5. The method for implementing a system for determining an APD optimal gain point based on laser ranging according to claim 1, characterized in that: The S3 includes: S31, facing the system to a reflective surface with a fixed reflectivity, measuring the current APD ambient temperature value of the system and recording it as a calibrated APD ambient temperature value, obtaining the breakdown voltage corresponding to the calibrated APD ambient temperature value based on the linear relationship between the APD ambient temperature value and the breakdown voltage and recording it as the calibrated breakdown voltage; S32, initializing the system: setting 65% of the calibrated breakdown voltage as the starting scan voltage, 98% of the calibrated breakdown voltage as the ending scan voltage, turning on the laser transmitter to transmit a carrier-carrying optical signal to the reflective surface with a fixed reflectivity, and the local oscillator signal driver outputting a fixed local oscillator frequency signal to be loaded onto the cathode pin of the photoelectric receiver; S33, a linear high-voltage controller controlling the starting scan voltage of the DC high-voltage generator as a reference point to output a working bias voltage The scanning voltage is scanned multiple times until it increases to the end, and the intermediate frequency signal of the intermediate frequency echo output buffer is sampled at multiple cycles at equal intervals during each scan through the sampling controller to obtain a serialized signal waveform, and the intermediate frequency signal in each serialized signal waveform is subjected to FFT forward transformation and a signal-to-noise ratio is calculated, and the signal-to-noise ratio calculated each time and the ratio of the current working bias voltage to the calibrated breakdown voltage are bound to a key-value pair and stored in the buffer sequence of the sampling controller in the order of the scanning time; S34, searching for the maximum value of the signal-to-noise ratio in the buffer sequence, and then finding the ratio of the working bias voltage corresponding to the maximum value of the signal-to-noise ratio in the key-value pair to the calibrated breakdown voltage, and then obtaining the corresponding working bias voltage based on the ratio, and recording the current working bias voltage as the APD optimal gain point voltage.

6. The method for implementing a system for determining an APD optimal gain point based on laser ranging according to claim 5, characterized in that: In S33, the sampling interval of the multi-period equally spaced sampling is determined by a preset sampling frequency.

7. The method for implementing a system for determining an APD optimal gain point based on laser ranging according to claim 5, characterized in that: In S33, the calculation formula of the signal-to-noise ratio SNR is: SNR=a(signal) / a(noise); In the formula, a(signal) represents the amplitude corresponding to the fundamental frequency of the sampled intermediate frequency signal, and a(noise) represents the sum of the harmonic components of the sampled intermediate frequency signal within the sampling bandwidth; The calculation formula of a(noise) is: a(noise)=∑a(n); Where a(n) represents the amplitude of each harmonic component of the sampled intermediate frequency signal within the sampling bandwidth, and n represents the order of the harmonic component.

8. The method for implementing a system for determining an APD optimal gain point based on laser ranging according to claim 5, characterized in that: The optimal gain point voltage must meet the following constraints: V(b)+V(m)≤V(k); Where, V(b) represents the APD optimal gain point voltage, V(m) represents the swing amplitude of the local oscillator signal driver, and V(k) represents the calibrated breakdown voltage; If V(b) does not satisfy the constraint condition, V(b) is adjusted until the constraint condition is satisfied, and the adjusted V(b) is the APD optimal gain point voltage.

Images