A lidar time discrimination system

Abstract

The present invention discloses a lidar time discrimination system, which includes a lidar receiving module, an automatic gain control module, a first leading-edge time discrimination module, a second leading-edge time discrimination module, a logic determination module, and a time measurement fitting module; the lidar receiving module is respectively connected to the automatic gain control module and the second leading-edge time discrimination module, the automatic gain control module is connected to the first leading-edge time discrimination module, the first leading-edge time discrimination module is connected to the logic determination module, the second leading-edge time discrimination module is connected to the logic determination module, and the logic determination module is connected to the time measurement fitting module. The present invention adopts a two-stage leading-edge time discrimination and logic determination scheme to solve the problem of noise mis-triggering. By using four fitting curves to perform different degrees of fitting on signals with different gains in real time, the problems of time compensation and linear influence can be solved simultaneously, and high-precision ranging with a ranging error accuracy of less than 3 cm can be achieved.

Description

Technical Field

[0001] The present invention belongs to the field of active remote sensing, and particularly relates to a lidar time discrimination system. Background Art

[0002] Lidar technology has advantages such as high precision, strong anti-interference ability, and wide detection range. With the continuous development of laser technology, lidar often works in a large distance range, resulting in a large echo dynamic range. However, general laser rangefinders can only give the ranging accuracy within a specified range. How to reduce the walking error and improve the ranging accuracy is a problem that needs to be solved.

[0003] Existing lidars mainly convert the received laser from an optical signal into an electrical signal through an avalanche photodiode APD, and use a variable transconductance amplifier TIA for I / V conversion to obtain a received pulse and transmit it to the subsequent time discrimination system. According to existing research results, there are mainly three typical signal time discrimination systems: leading-edge time discrimination method, zero-crossing time discrimination method, and constant fraction timing discrimination method. The amplitude change of the received pulse in the leading-edge time discrimination method will produce a non-negligible ranging walk error, affecting the ranging accuracy; the zero-crossing time discrimination method is affected by the slope near the pulse peak point, and the pulse width size will also bring measurement errors; in the constant fraction timing discrimination system, the design of a high-precision delay system has certain difficulties, there are problems of signal attenuation and long delay lines, and it is impossible to reduce the time jitter error generated by a large dynamic range input signal, and a non-negligible ranging walk error will be generated.

[0004] In order to better reduce the dynamic range, the lidar system introduces an automatic gain control system AGC. For existing automatic gain control systems, mainly the large signal change range is compressed into a small signal change range, and then corresponding signal processing is carried out. According to different signal processing mechanisms, currently two schemes of feedforward automatic gain and feedback automatic gain are adopted.

[0005] The first is feedforward automatic gain. The working principle of feedforward AGC is to detect the amplitude of the input signal of the detection circuit and adjust the gain. Since there is no feedback loop formed and there is no requirement for stability, it can process large signal changes without changing the settling time. The settling time of feedforward AGC only depends on the signal detection branch (the signal detection branch has a filtering link and a large RC delay), so there is no trade-off between stability and dynamic range. The detection range of the feedforward AGC structure usually needs to cover the entire input signal dynamic range, and the circuit has no feedback guarantee, so the requirement for linearity is higher.

[0006] The second is feedback automatic gain. The working principle of feedback AGC is to detect the amplitude of the output signal of the detection circuit and adjust the gain. Due to stability limitations, the dynamic range of the feedback AGC circuit will not be very high. Therefore, the feedback AGC circuit has low requirements for the detection range of the peak detector, only needing to meet the gain control requirements. Its linearity will be higher due to the feedback structure. However, when the input signal changes too much, deep negative feedback will make stability a problem. To ensure stability, the feedback loop also has requirements for the maximum bandwidth of the signal, which in turn poses a minimum requirement for the loop settling time.

[0007] In summary, the existing lidar time discrimination system has the deficiency of large walking error leading to low ranging accuracy, and the existing automatic gain control system has problems such as high requirements for feedforward linearity and delay control and poor feedback stability. Summary of the Invention

[0008] The existing lidar time discrimination system has the deficiency of large walking error leading to low ranging accuracy, and the existing automatic gain control module has problems such as high requirements for feedforward linearity and delay control and poor feedback stability. The present invention aims to provide a lidar time discrimination system to solve the deficiencies of the existing design, and proposes a solution to improve the measurement accuracy of lidar ranging and achieve high-precision measurement.

[0009] The object of the present invention is achieved by the following technical solutions:

[0010] A lidar time discrimination system includes a lidar receiving module, an automatic gain control module, a first front-edge time discrimination module, a second front-edge time discrimination module, a logic determination module, and a time measurement fitting module; the lidar receiving module is respectively connected to the automatic gain control module and the second front-edge time discrimination module, the automatic gain control module is connected to the first front-edge time discrimination module, the first front-edge time discrimination module is connected to the logic determination module, the second front-edge time discrimination module is connected to the logic determination module, and the logic determination module is connected to the time measurement fitting module.

[0011] Preferably, the automatic gain control module includes a peak holding unit, an amplitude comparison unit, a main control unit, a numerically controlled attenuation unit, and a fixed gain amplification unit connected in sequence; the automatic gain control module divides the output pulse signal of the lidar receiving module into two paths, one of which passes through the peak holding unit, the amplitude comparison unit, and the main control unit in sequence, and finally enters the numerically controlled attenuation unit, and the other path directly enters the fixed gain amplification unit after passing through the numerically controlled attenuation unit.

[0012] More preferably, the peak holding unit includes a transconductance amplifier MAX436ESD, a Schottky diode BAT17, a holding capacitor, and a discharge resistor.

[0013] Preferably, the amplitude comparison unit includes a comparator LM311M and a variable resistor.

[0014] More preferably, the main control unit is an STM32F103ZET6 single-chip microcomputer; the attenuation unit is an HMC472ALP4 numerically controlled attenuation chip; and the fixed gain amplification unit is an OPA657 transimpedance amplifier.

[0015] Preferably, the first leading edge time discrimination module includes a first voltage follower unit, a first high-speed comparison unit, and a time discrimination STOP1 signal unit.

[0016] Preferably, the second leading edge time discrimination module includes a second voltage follower unit, a second high-speed comparison unit, and a time discrimination STOP2 signal unit.

[0017] Preferably, the logic determination module includes a logic AND gate unit and a time discrimination STOP signal unit.

[0018] Preferably, the time measurement fitting module includes a time discrimination START signal unit, a time-to-digital conversion unit, and a terminal fitting unit.

[0019] The present invention also has the following advantages over the prior art:

[0020] 1. The lidar time discrimination system of the present invention adopts a solution that combines four technologies: new automatic gain, two-stage leading edge time discrimination, logic determination, and automatic fitting to solve the problems existing in the prior art. In terms of new automatic gain, by abandoning the delay circuit and designing a "self-attenuation + fixed gain" solution, the problems of high delay requirements, high linearity requirements, and small input dynamic range are solved. And by using the characteristics of short pulse time intervals and small amplitude changes, the amplitude characteristics of the current signal are detected to select the gain, and the next incoming pulse signal is amplified by the gain, realizing a new processing method of detecting the current input and gaining the next input. In terms of two-stage leading edge time discrimination and logic determination, through "AGC signal + leading edge time discrimination", a smaller walking error is obtained, and logical determination is performed with "original received signal + leading edge time discrimination" to solve the situation where the high-speed comparator is mis-triggered due to received noise or system noise and the time measurement is incorrect. In terms of automatic fitting, an accurate fitting solution with different gains and different fitting functions is adopted to solve the time compensation problem and realize accurate automatic fitting ranging of the lidar.

[0021] 2. The novel automatic gain control module of the present invention can compress an input signal with a large dynamic range of 26.5 dB into a distortion-free signal with a small dynamic range of 9.5 dB, reducing the dynamic change of the pulse amplitude by 17 dB. Then, by using a two-stage leading-edge time discrimination system, time discrimination points STOP1 with small walking errors and the original received signal time discrimination point STOP2 are obtained, and the pulse reception time is recorded. Through logical determination by the logical determination module, the situation of noise mis-triggering is reduced, and a time discrimination STOP signal is generated. This signal and the time discrimination START signal are simultaneously input into the time-to-digital converter TDC to obtain measurement data. Finally, fitting with the real data is performed to obtain a fitting function, which is burned into the main control unit of the lidar to achieve automatic fitting ranging, and high-precision ranging with a ranging error accuracy of less than 3 cm is completed. Brief Description of the Drawings

[0022] The present invention will be further described with reference to the accompanying drawings. However, the embodiments in the drawings do not constitute any limitation to the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the following drawings.

[0023] Figure 1 It is a schematic diagram of the composition structure and working principle of the lidar time discrimination system according to the embodiment of the present invention;

[0024] Figure 2 It is a schematic diagram of the structure of the automatic gain control module according to the embodiment of the present invention;

[0025] Figure 3 It is a schematic diagram of the structure of the leading-edge fitting time discrimination module according to the embodiment of the present invention;

[0026] Figure 4 It is a schematic diagram of the flow of the algorithm design of the main control unit according to the embodiment of the present invention;

[0027] Figure 5 It is a schematic diagram of the time error generated by signals with different amplitudes at the same threshold according to the embodiment of the present invention. Detailed Embodiments

[0028] The following further describes a lidar time discrimination system in detail with specific embodiments. These embodiments are only for comparison and explanation purposes, and the present invention is not limited to these embodiments.

[0029] Embodiment

[0030] See the attached Figures 1 - 5, the lidar time discrimination system provided in this embodiment includes a lidar receiving module, an automatic gain control module, a first leading edge time discrimination module, a second leading edge time discrimination module, a logic determination module, and a time measurement fitting module; the lidar receiving module is respectively connected to the automatic gain control module and the second leading edge time discrimination module, the automatic gain control module is connected to the first leading edge time discrimination module, the first leading edge time discrimination module is connected to the logic determination module, the second leading edge time discrimination module is connected to the logic determination module, and the logic determination module is connected to the time measurement fitting module.

[0031] The automatic gain control module includes a peak holding unit, an amplitude comparison unit, a main control unit, a digital control attenuation unit, and a fixed gain amplification unit connected in sequence; the automatic gain control module divides the output pulse signal of the lidar receiving module into two paths, one of which passes through the peak holding unit, the amplitude comparison unit, and the main control unit in sequence, and finally enters the digital control attenuation unit, and the other path directly enters the fixed gain amplification unit after passing through the digital control attenuation unit.

[0032] More preferably, the peak holding unit includes a transconductance amplifier MAX436ESD, a Schottky diode BAT17, a holding capacitor, and a discharge resistor.

[0033] More preferably, the amplitude comparison unit includes a comparator LM311M and a variable resistor.

[0034] More preferably, the main control unit is an STM32F103ZET6 single-chip microcomputer; the attenuation unit is an HMC472ALP4 digital control attenuation chip; the fixed gain amplification unit is an OPA657 transimpedance amplifier.

[0035] Preferably, the first leading edge time discrimination module includes a first voltage follower unit, a first high-speed comparison unit, and a time discrimination STOP1 signal unit.

[0036] Preferably, the second leading edge time discrimination module includes a second voltage follower unit, a second high-speed comparison unit, and a time discrimination STOP2 signal unit.

[0037] Preferably, the logic determination module includes a logic AND gate unit and a time discrimination STOP signal unit.

[0038] Preferably, the time measurement fitting module includes a time discrimination START signal unit, a time-to-digital conversion unit, and a terminal fitting unit.

[0039] In a specific embodiment, such as Figure 1As shown, the large-dynamic-range pulses received by the lidar receiving module undergo a three-way signal processing process. Two of them go through the gain processing of the automatic gain control module to attenuate large signals and amplify small signals, compress the dynamic range, and finally obtain the timing discrimination time point through the leading-edge timing discrimination module, generating the timing discrimination STOP1 signal. The third signal obtains the timing discrimination time point of the original received signal through the leading-edge timing discrimination module, generating the timing discrimination STOP2 signal. The two timing discrimination signals generate the timing discrimination STOP signal through the logic determination module, and input it and the timing discrimination START signal into the time-to-digital converter simultaneously to obtain measurement data. Finally, it is fitted with the real data to obtain the fitting function, which is burned into the lidar main control unit to achieve automatic fitting ranging. Since the dynamic range compression characteristic can provide the best input pulse amplitude for the leading-edge timing discrimination module, and the logic determination characteristic can prevent noise from triggering erroneously, high-accuracy signal timing discrimination of the pulse signal can be realized, reducing the time jitter and additional walk-off error in the ranging system.

[0040] The automatic gain control module divides the output pulse signal of the lidar receiving module into two paths. One path holds its peak for a microsecond-level time (the input pulse width is in the nanosecond level) through the peak hold module, and inputs the signal after peak hold into the amplitude comparison unit composed of three comparators with different thresholds, thereby outputting four different control levels, namely 000, 100, 110, and 111. Different control levels reflect the amplitude range of the input signal. The control levels are transmitted to the main control module composed of the STM32F103ZET6 single-chip microcomputer. The single-chip microcomputer writes a rising-edge capture program to capture the rising edge of the control levels. According to the captured rising-edge situation, new control levels are output correspondingly, namely 111111, 111011, 111101, and 111110. Different control levels reflect different gain selections; the other path of the signal undergoes different degrees of attenuation through the digital control attenuation module, and the gain selection is determined by the control level provided by the main control module. Finally, the attenuated signal is transmitted to the fixed-gain amplifier for amplification to achieve the output of a small-dynamic-range distortion-free signal.

[0041] The peak holding module includes a transconductance amplifier MAX436ESD, a Schottky diode BAT17, a holding capacitor, and a discharging resistor. MAX436ESD is a high-speed broadband transconductance operational amplifier with a positive differential high-impedance input terminal, which can provide stable and accurate current gain without any feedback. Its function is to convert voltage input into current output, and control the working current of the operational amplifier by applying an external bias voltage, so that its output current can vary within a large range. At the same time, its characteristics of high bandwidth and good stability make it suitable for processing nanosecond-level fast signals. The working principle of this module is that when the output signal Vout is less than the input signal Vin, the transconductance amplifier amplifies the differential voltage between the input and the output. The input voltage or current charges the holding capacitor through the diode. When the capacitor voltage is equal to the input voltage, the voltage output of the amplifier is reversed, and at this time the diode is cut off, and the capacitor discharges through the discharging resistor. The discharging speed is controlled by controlling the size of the resistor and capacitor. The most critical characteristics of the peak sampling circuit are its linearity and stability. The linearity of peak holding refers to the linear degree of the ratio of the output signal to the input signal, which is jointly determined by the amplifier, the diode, and the sampling holding capacitor. The larger the linear output range of the amplifier, the shorter the reverse recovery time of the diode, and the smaller the capacitance value of the capacitor, the better the linearity of the peak sampling output. The stability of peak holding refers to the floating situation of the sampling signal and the holding time length when the input signal remains unchanged, which is determined by the holding capacitor and the discharging resistor. The larger the capacitance value of the capacitor and the larger the resistance value of the resistor, the more stable the peak sampling and the longer the holding time. There is a contradiction between the linearity and stability of the peak sampling circuit, that is, the size of the capacitor. If it is too large, the linearity is not good; if it is too small, it is unstable. For a laser pulse signal with a rise time of about 15 ns, the holding capacitor is taken as 30 - 100 pF. Let I t be the charging current, T0 be the starting moment of charging, T c be the charging duration, C be the charging capacitance value, V i (t) and V o (t) be the input and output signal amplitudes, G represent the transconductance amplification factor, and Z be the equivalent impedance sum of the diode and the peak holding capacitor. The voltage V c across the holding capacitor and the charging current I t can be expressed as:

[0042]

[0043] I t =G(V i (t)-V o (t)) / Z

[0044] The amplitude comparison module includes an LM311M comparator and a variable resistor. By setting three different thresholds with the variable resistor, four different amplitude ranges can be obtained. The working principle of this module is that when the input signal Vin enters the three comparators simultaneously, according to its comparison with the comparator thresholds V A , V B , V C , it judges the amplitude range it is in and outputs control levels 000, 100, 110, 111 to the main control module.

[0045] The main control module includes an STM32F103ZET6 single-chip microcomputer. By writing an algorithm, signal rising edge capture and interrupt response are realized, and the algorithm flow is as Figure 4 shown. Its working principle is to transmit the control levels output by the amplitude comparison module to four pins of the STM32 single-chip microcomputer simultaneously to detect the pin states. At the same time, different interrupt priorities are set for each pin. Once a rising edge from low level to high level is detected, an interrupt response service is triggered according to the priority. To avoid incorrect control levels generated by the amplitude comparison module due to noise false triggering, during the interrupt response service, the states of the three pins are detected again to judge whether they conform to the control levels 100, 110, 111. When ensuring there is no error, it judges the amplitude range it is in according to the control levels input by each pin and selects different output levels 111011, 111101, 111110 to realize the selection of different gains. If no rising edge is detected, the output control level 111111 is output according to the default gain.

[0046] The numerically controlled attenuation module includes an HMC472ALP4 numerically controlled attenuation chip. This attenuation chip uses an external AC capacitor grounded to approximate DC operation. Its working frequency range is from DC to 3.8 GHz, the insertion loss is less than 2 dB, and the single-stage attenuation range is 31.5 dB, meeting the design requirements of this system. The bit width of its control signal is 6 bits (V1V2V3V4V5V6), and the step is 0.5 dB, which can achieve attenuations with gains of 0.5 dB, 1 dB, 2 dB, 4 dB, 8 dB, 16 dB, and 31.5 dB. In this design, four gain modes of 0 dB, 4 dB, 8 dB, and 16 dB are adopted, corresponding to the control levels 111111, 111011, 111101, 111110. The working principle of this module is that the original received signal output by the transimpedance amplifier TIA is transmitted to the attenuation module, and the attenuation module selects different gains through the control levels transmitted by the main control module to achieve different degrees of attenuation of the signal. Since the pre-circuit will cause a certain degree of attenuation and there is an insertion loss in the attenuation module, the actual gain will bring a gain change of about 0.5 dB on the original basis.

[0047] The fixed-gain amplification unit includes a transimpedance amplifier OPA657. The signal after pre-processing has changed from a large dynamic range to a small-signal with a small dynamic range. Amplifying the small signal at one stage can meet the input requirements of the subsequent time discrimination system.

[0048] The leading-edge time discrimination module is as Figure 3 shown, and includes a first leading-edge time discrimination module and a second leading-edge time discrimination module, both of which are composed of a high-speed comparator TLV3501, a voltage follower ADA4665, and a threshold adjustment circuit. The TLV3501 can be used to shape the waveform of the input signal and output a TTL-level signal. It has a fast propagation delay time of 4.5 ns, a relatively wide input signal frequency band, and can input signals from 0.1 Hz to 230 MHz, meeting the requirements of the present invention. The function of the ADA4665 rail-to-rail chip is to increase the input impedance. Since the output impedance of the external input part is small, in order to improve the accuracy of the threshold voltage, the input impedance must be increased. The working principle of this module is to set a certain threshold, input the small-dynamic-range signal after automatic gain and the original received signal into the leading-edge time discrimination system. When the amplitude of the input signal is greater than the set threshold, it will trigger the high-speed comparator to generate a response, and thus output the time discrimination STOP1 and STOP2 level signals.

[0049] The logic determination module includes a logical AND gate unit and a time discrimination STOP signal unit. In a feasible manner, it is a logical AND gate device SN74LVC1G08 and a filtering circuit. Its working principle is to perform logical discrimination on the two time discrimination STOP1 signals and STOP2 signals output by the two leading-edge time discrimination modules respectively. Only when both signals are at a high level can it trigger a response and output the time discrimination STOP signal. In order to better achieve the trigger response of the high-speed comparator, the set threshold is relatively low, so it is easy to cause the situation of mis-triggering the level signal due to noise. Therefore, the scheme of two-way leading-edge time discrimination can solve the problem of mis-triggering the high-speed comparator due to the received noise or the noise generated by the automatic gain system, resulting in incorrect time measurement, thereby improving the ranging accuracy of the lidar.

[0050] The time measurement fitting module identifies the START signal unit, the time-to-digital conversion unit, and the terminal fitting unit at all times. In a feasible manner, they are the time-to-digital converter GP22, the main control module, and the terminal fitting device. The time-to-digital converter uses the START signal emitted by the lidar as the start signal, and the time-discriminated STOP signal received and generated by the receiving end as the stop signal. Using the digital delay line technology of complementary metal-oxide-semiconductor gate delay inside the time-to-digital converter, after the start signal enters the time-to-digital converter delay system, it propagates along the delay line, and the number of delay units experienced between the start signal and the stop signal is calculated. Thus, the time difference between the transmitted pulse and the received pulse is calculated, and this time difference is stored in the main control module STM32 to provide high-precision time difference information for distance calculation in the lidar system.

[0051] The solution to the problems of high delay requirements and high linearity requirements of the feedforward AGC and the small dynamic range of the feedback AGC is essentially to abandon the delay part and adjust the peak-holding resistor-capacitor parameters to achieve correct detection of the signal amplitude in the dynamic range. Since the feedforward AGC needs to use a delay circuit or a delay line to ensure correct gain amplification of the signal, it is easy to cause signal distortion and lose the original signal characteristics. At the same time, if the delay time is set unreasonably, the signal cannot be gain-amplified. The traditional feedback AGC has a small input dynamic range and detects the amplitude of the output signal after gain, losing the amplitude characteristics of the original signal and causing the AGC to make incorrect gain judgments. Therefore, the present invention abandons the delay part and adjusts the holding capacitor and discharging resistor of the peak-holding module to optimize the linearity. Utilizing the characteristics of short pulse time intervals and small amplitude changes, the original received signal is processed in two paths. The amplitude characteristics of the current signal are used to select an appropriate gain to amplify the next incoming pulse signal, ensuring accurate processing of the original received signal. Finally, through the amplitude comparison module, any amplitude signal input can be classified into a specified amplitude range and the corresponding control sequence is output.

[0052] The principle of reducing the walking error is to reduce the large-range walking error caused by the input of a signal with a large dynamic range to a small-range walking error. As Figure 5 shown, different amplitude signals trigger a comparator at a fixed threshold. Due to the amplitude difference, there is a certain degree of difference in their trigger times, resulting in a walking error. The error time range is from t0 to tn. By using the present invention, an input signal with an amplitude of 150mv to 3000mv can be compressed into an output signal with an amplitude of 177mv to 530mv. The dynamic range is compressed from 26.5dB to 9.5dB, achieving a reduction of 17dB in the dynamic range, thereby reducing the error time range. The error time range is reduced to t0 to tk, where k << n, achieving the effect of reducing the walking error.

[0053] Measurement data fitting scheme. In the present invention, by using the CFTOOL toolbox of Matlab software, the power approximation function model f = a * x is called b + c, where f is the fitted data, a is the weight of the measurement data x, and c is the compensation constant. The measurement data is obtained by lidar ranging, and the real data is obtained by standard lidar ranging. Since the present invention uses four kinds of gains, four fitting curves are used to fit the measurement data to obtain the theoretical fitting function. Finally, the fitting function is input into the main control module to realize the automatic fitting and accurate ranging of the lidar system. To better reflect the ranging performance of the system, the ranging accuracy is introduced as a performance index. The ranging accuracy is used to estimate the systematic error of the lidar ranging system. Generally, the average value of the difference between the measured value and the true distance value is used as the accuracy of the system. Let E acu be the accuracy, R j be the measured value, R true be the true value, and its expression is as follows:

[0054]

[0055] For the lidar time discrimination system provided in the above embodiment of the present invention, in terms of the automatic gain hardware design, the present invention uses a digital control attenuator to attenuate the signal, and uses a fixed gain amplifier to amplify it. The peak holding and amplitude comparison two units are used to realize the input of the large dynamic range of the signal amplitude range; in terms of the automatic gain algorithm design, the rising edge capture and capture interrupt response methods are used to realize the output of different control levels, and the noise mis-triggering algorithm is designed to avoid the wrong judgment caused by noise mis-triggering; in terms of the time discrimination and ranging scheme, AGC is used to realize different gains of the signal, reducing the walking error. The two-stage front edge time discrimination and logic determination scheme is used to solve the noise mis-triggering. By using four fitting curves to fit the signals with different gains in real time, not only the time compensation problem is solved, but also the linear influence problem is solved, realizing high-precision ranging with a ranging error accuracy of less than 3 cm.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lidar time discrimination system, characterized in that, It includes a lidar receiving module, an automatic gain control module, a first leading-edge time discrimination module, a second leading-edge time discrimination module, a logic determination module, and a time measurement and fitting module; the lidar receiving module is respectively connected to the automatic gain control module and the second leading-edge time discrimination module, the automatic gain control module is connected to the first leading-edge time discrimination module, the first leading-edge time discrimination module is connected to the logic determination module, the second leading-edge time discrimination module is connected to the logic determination module, and the logic determination module is connected to the time measurement and fitting module; the automatic gain control module includes a peak hold unit, an amplitude comparison unit, a main control unit, a numerically controlled attenuation unit, and a fixed gain amplification unit connected in sequence; the automatic gain control module divides the output pulse signal of the lidar receiving module into two paths, one of which passes through the peak hold unit, the amplitude comparison unit, and the main control unit in sequence, and finally enters the numerically controlled attenuation unit, and the other path directly enters the fixed gain amplification unit after passing through the numerically controlled attenuation unit.

2. The lidar time discrimination system according to claim 1, wherein The peak hold unit includes a transconductance amplifier MAX436ESD, a Schottky diode BAT17, a holding capacitor, and a discharge resistor.

3. The lidar time discrimination system according to claim 1, characterized in that, The amplitude comparison unit includes a comparator LM311M and a variable resistor.

4. The lidar time discrimination system according to claim 1, wherein, The main control unit is an STM32F103ZET6 single-chip microcomputer; the attenuation unit is an HMC472ALP4 numerically controlled attenuation chip; the fixed gain amplification unit is an OPA657 transimpedance amplifier.

5. The lidar time discrimination system according to claim 1, wherein The first leading-edge time discrimination module includes a first voltage follower unit, a first high-speed comparison unit, and a time discrimination STOP1 signal unit.

6. The lidar time discrimination system according to claim 1, wherein The second leading-edge time discrimination module includes a second voltage follower unit, a second high-speed comparison unit, and a time discrimination STOP2 signal unit.

7. The lidar time discrimination system according to claim 1, wherein The logic determination module includes a logical AND gate unit and a time discrimination STOP signal unit.

8. The lidar time discrimination system according to claim 1, wherein, The time measurement and fitting module includes a time discrimination START signal unit, a time-to-digital conversion unit, and a terminal fitting unit.

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