Design And Implementation Of TDC And Lidar System Based On FPG

Li DAR is a kind of sensor that can actively acquire the information of the surrounding environment.With its excellent ranging ability,Li DAR has been widely used in smart city,intelligent transportation,autonomous driving,UAV,robot and other fields.Compared with millimeter wave Radar,ultrasonic Radar,camera and other detection sensors,Li DAR has the advantages of strong anti-interference,long detection distance,high accuracy,acquiring environmental information in real-time with the transmission of high-speed laser pulse.For pulsed Li DAR,the accuracy of time of flight measurement needs to reach picosecond level.However,the traditional method of combining microcontroller and timing chip is limited by low chip life,long development cycle,non-repeatable configuration and high cost.In order to solve the above problems,this paper realizes high precision picosecond digital timing based on FPGA instead of timing chip.On this basis,a set of single-line Li DAR system is built completely through theoretical analysis and circuit design,and the overall performance of the system is verified by experimental tests.The main contents of the paper are as follows:(1)The ranging principle of Li DAR is analyzed,including the principle of laser ranging,time discrimination and time-of-flight interval measurement.The pulse laser ranging method is selected as the ranging scheme of this system to satisfy requirements of this paper.According to the principle of pulse laser ranging,the front-line time discrimination scheme and time-todigital converter(TDC)based on FPGA are used as the time interval measurement scheme.(2)The framework of the Li DAR system is studied,including designing the optical lens and the shell structure of the Li DAR system.The design of the collimating lens and focusing lens meets the requirements of the focal length and the size of the laser and photodetector.The three-dimensional structure of the Li DAR system is designed according to the volume and size of each module.The mirror,motor,main controller,driver and laser transceiver module are fixed in the shell.(3)The circuit of the Li DAR system is studied.The design process includes the analysis of design requirements,component selection,schematic design,PCB design and debugging.A high-power laser diode is used as a light source at Li DAR transmitter,and a high-power,narrow-pulse laser driving circuit is designed by using MOSFET and capacitance.The maximum power can reach 75 W.At the receiver,an echo signal receiving circuit is designed based on avalanche photodiode to realize a high-sensitivity signal receiving.(4)The realization of high-precision timing function based on FPGA is studied.The CARRY4 inside the FPGA chip is used to design delay line to realize the fine counter module,together with coarse counter module,encoder module,trigger signal generation module achieving a complete TDC timing function.The code density test method is used to verify and the function and the nonlinear error of TDC.(5)The design of control and communication for each module of the system are studied.The performance of the laser transceiver module,the timing effect of TDC and the data transmission function are tested.In order to verify the performance of the Li DAR system,different objects were scanned,and the position of each data point in two-dimensional space was calculated according to the rotation angle of the motor and the TDC timing data,and twodimensional imaging was realized in the upper computer.