Design Of Self-triggered Pulse Laser Ranging System Based On FPGA

As a non-contact measuring method,laser ranging system has the advantages of wide measuring range,fast speed,high precision and strong anti-interference ability.It is widely used in various fields,including aerospace,lunar surface survey,building surveying and mapping,transportation and so on.According to the type of laser emitter,laser ranging method can be divided into pulse method and phase method.Through the study and research of traditional laser ranging technology,based on FPGA chip and self-trigger principle,a laser ranging system with simple system structure,high measurement accuracy and strong anti-interference ability is designed.This paper first introduces the basic principle of laser ranging,selects pulse method as the system ranging method through comparative analysis and design expectation,and then introduces four commonly used time interval measurement methods.After comparative analysis,direct pulse counting method combined with self-triggered measurement method is selected to improve the accuracy.The laser transmitter uses a low-power,human-eye safe semiconductor laser,and a narrow pulse signal generator is designed as the driving circuit of the laser transmitter.In order to effectively reduce the influence of background light on the ranging accuracy of the system,a laser receiving unit which combines the sampling and holding circuit to realize the background light suppression effect is designed.A PIN type photodiode is used as a photodetector to design the current-voltage conversion circuit.According to the characteristics of low signal-to-noise ratio,the low noise amplifier circuit and the filter shaping circuit are designed.The first signal output from the narrow pulse signal generator is input into the time interval measurement unit as the start signal.In order to prevent the subsequent narrow pulse signal from repeatedly triggering the start of the measurement,a logic signal locking circuit is designed.The design of FPGA program is completed in Verilog HDL language on Quartus ?software,which mainly realizes the design of delay module,counting module and display module.This paper first introduces the performance parameters of the FPGA chip and the chip expansion circuit,then uses the high frequency clock latch method to complete the design of the delay module according to the design requirements.The display module is designed by seven-digit digital tube.The binary data information output by the counting module is bcd decoded and dynamically scanned.Finally,by comparing with the output signal of the traditional laser receiving unit,it is verified that the laser receiving unit in thesis can realize the background light suppression effect,make the echo signal clearer,and benefit the subsequent signal processing.Through the calibration experiment and the actual measurement experiment,the measurement results show that the system basically meets the design requirements,has the characteristics of high precision and strong anti-interference ability,and has a good application prospect.