Research On Laser Ranging System Based On Equivalent Pulse Counting Method

Laser ranging technology is a typical high-precision non-contact measurement technology.It has the advantages of long detection distance,precise pointing and strong anti-interference ability.It has been widely used in aerospace,military and environmental detection fields.The technology is gradually extended to satellite docking,aircraft mapping and missile guidance,etc.,which have high requirements on system volume,power,measurement speed and accuracy.How to improve the detection efficiency of laser ranging system,measurement speed and accuracy in the same laser intensity and system volume has become the key research direction in the field of laser ranging.Aiming at the low detection efficiency and slow response speed of linear photodetector in laser ranging system,this paper proposes a design method of laser receiving unit based on Multi-Pixel Photon Counter(MPPC).According to the internal structure and working characteristics of MPPC,the signal amplification,time identification and pulse shaping circuits are designed.The circuit performance is verified by Multisim,and the design and implementation of the laser receiving unit are finally completed.Compared to linear photodetectors,this design has higher detection efficiency and faster measurement speed at the same laser intensity.Aiming at the problem of high resource occupancy rate and small number of parallel measurement channels in Time-to-Digital Converter(TDC)design method,this paper proposes a TDC cell design method based on equivalent pulse counting method.According to the working principle of the equivalent pulse counting method,the MMCM module,the precision time measurement array and the data transmission module are built by FPGA,and the function of the module is verified by Modelsim,and finally the design and implementation of the high precision TDC unit based on FPGA is completed.The TDC unit design method proposed in this paper can achieve 16-channel high-precision timing,and has the advantages of saving design resources and high stability.In this paper,the main functional indexes of the laser ranging system are verified by experiments.The results show that the laser ranging system has 16 channels of high-precision parallel measurement capability.The theoretical measurement distance is 20 cm-3 km.The calibration accuracy after calibration is better than 20 cm.The standard deviation of the secondary measurement results is less than 0.6LSB,and the repeated measurement frequency can reach 2000 Hz.