Signal Processing Of Multi-line Lidar Based On Avalanche Photodiode

In the automotive field,in order to improve safety and convenience,vehicle machine system needs to alert or assist drivers by analyzing data collected by sensing technologies such as cameras,millimeter wave radar,and lidar.Lidar is one of the most important sensing technologies,with the advantages of large measurement range,high speed,and high accuracy.Due to the need for complex scanning devices in a single line lidar,the system stability is low,which is difficult to apply in fields with high stability requirements such as automobiles.And using a multi-line scheme can effectively improve the stability of the system.This article has carried out research on the key technologies of multi-line lidar,and focused on the multi-channel signal processing system,including weak signal processing,data processing,and display.The main contents are as follows:Firstly,aiming at the problems of complex hardware structure and high noise in a multiline lidar system,the hardware circuit of the multi-line lidar system was designed and optimized,including a transmitting module,a receiving module,and a signal processing module.In the transmission module,it is proposed to use FPGA to output two synchronization signals:one is used to drive the laser,and the other is used to start the timing system,which can effectively simplify the circuit.The receiving module can convert optical pulse signals into electrical pulse signals,which can effectively improve the circuit signalto-noise ratio after optimization.The signal processing module converts electrical pulse signals into time data,enabling multi-channel rapid measurement,providing an experimental platform for subsequent signal processing tests.Secondly,aiming at the problems of low multi-channel measurement accuracy and complex display process in a multi-line lidar system,the control programs for the multi-ine lidar system were designed and optimized,including the control system program design based on FPGA and the host computer program design based on Labview.In FPGA programming,the overall framework of the system was first designed,and subsequent programs were optimized based on this framework.Then,a multi-channel timing program was designed and tested,and the flight time fluctuations of the four channels were all less than 247 ps.Finally,the host computer designed in Labview implements real-time processing,display,and storage of multi-channel data,which can be used for multi-channel time measurement in various scenarios.Thirdly,aiming at the problems of traditional automatic gain control systems such as peak attenuation,poor stability,and slow response speed,an improved automatic gain control system without a peak holding circuit was designed.A 250 MHz high-speed ADC was used to collect the peak value of the echo pulse,and peak holding was implemented in FPGA.Experiments show that the improved system can control the echo peak within a set range(0.76 V to 1.44 V),effectively reducing the measurement error caused by echo changes,and this scheme has the advantages of small peak attenuation,good stability,and fast response speed,which can reduce echo issues in LidarFourthly,in order to verify the functionality and feasibility of the design system,a simplified multi-line lidar system was built and experimental tests were conducted,including multi-channel feasibility testing and single channel accuracy testing.The feasibility test results of multiple channels show that the system can simultaneously measure the flight time of multiple pulses,and then calculate multiple distances.Finally,the upper computer can display and save the measured data in real time.The single channel accuracy test shows that the measurement accuracy error(RMSE)is within 1.5 cm within 2 m.The multi-channel signal processing technology studied in this work provides a good foundation for the subsequent optimization of multi-line lidar systems.