Research On Laser Ranging System Based On High Precision TDC Of FPGA

Laser ranging technology is a kind of precision measurement technology developed with the progress of The Times.It is widely used in military,civil,aerospace and other fields because of its long working distance and strong anti-interference ability.This paper makes a comprehensive analysis of the factors affecting the measurement accuracy of laser ranging system,including low detection efficiency,complex structure and low time interval measurement accuracy,so as to improve the ranging accuracy,simplify the circuit structure and improve the stability of the system.The paper analyzes and understands several common laser ranging methods and the corresponding advantages and disadvantages,then choose a simple pulse method.According to the laser ranging process,the overall structure of the system is designed and the FPGA control module is used to complete the coordinated control of each unit of work in the system.According to the performance requirements of the ranging system,the specific design schemes of the laser transmitting module,laser receiving module and FPGA timing control module are developed.Firstly,the power of the pulse ranging system is analyzed,and the Q-switched laser with 1064 nm wavelength is selected and its driving circuit is designed.Secondly,when the laser ranging system is measured in the dynamic range,aiming at the defects of low detection efficiency,low responsiveness and complex peripheral control circuit of the photodetector working in linear mode,the high-sensitivity Multi-Pixel Photon Counter(MPPC)working in geiger mode is used as the detector to carry out the echo photon signal accumulative output to realize the photoelectric conversion.According to the characteristics of MPPC,the signal amplifying circuit,the time discrimination circuit and the pulse shaping circuit are designed,and the photon level laser receiving module of non cooperative target is designed.To overcome of the disadvantages of time to digital converter(TDC),such as low measurement resolution and few parallel measurement channels,combined with the system application requirements,a high precision time interval measurement scheme is designed on FPGA platform.After a thorough study of various commonly used time interval measurement methods,the precise measurement of laser flight time is completed by using the strict delay chain measurement method.The integrated design of TDC module reduces the complexity and power consumption of the circuit system.The TDC design scheme proposed in this paper can achieve 16 channel high-precision timing and high flexibility.It can extend its dynamic measurement range according to the performance requirements of the ranging system,thus increasing the working distance of the laser ranging system.A laser ranging experiment platform was built,and high-speed oscilloscopes were used to test the transmitting module and receiving module circuits inside the system,and the whole system was tested at different working distances.Theoretical analysis and experimental results show that the distance measurement system has the capability of 16 channels parallel measurement,and the accuracy of distance measurement is better than ±30cm at the same time for target detection at different distances.It is proved that the system designed in this paper can achieve the desired effect.