Development Of Digital Phase Locked Loop In Laser Ranging System

High precision laser ranging is one of the basic functions of surveying and mapping instruments,its ranging accuracy is up to millimeter level,therefore,it becomes a key technology to improve the precision of the surveying and mapping instrument,the PLL is a main unit in distance measuring system,its accuracy directly affects the measurement accuracy,so the development of high precision PLL principle with simple structure and low cost is very important.This paper is based on the analysis of the current domestic and foreign phase locked loop technology,using a combination of advanced FPGA technology and conventional charge pump technology,high precision phase discrimination principle based on FPGA internal carry delay chain,putting forward and developed system of digital PLL with subpicosecond precision.The main work of this paper includes: analysising the sub picosecond and high high precision digital phase discrimination principle of based on FPGA internal carry chain.In the hardware,designing the FPGA module circuit,the programming interface circuit,the two order passive filter circuit,charge pump circuit and PWM power circuit etc,completing the drawing of circuit schematic and PCB,a high precision digital phase lock circuit is produced in the end.In the software,using Verilog HDL hardware description language in Quartus II development environment to complete the digital phase detection and frequency divider software design based on FPGA,and complete the module programming and commissioning work;Adjusting the layout of FPGA bottom delay unit through the Quartus II software development tools chip planner,avoiding large delay error,when the reference signal passes through the time delay path,The phase detection accuracy and speed of digital phase locked loop are guaranteed.Finally,combining with ranging system to set up the experimental device,and using the model of Agilent54642 A to observe the two pulse waveform of phase locked,and applied the high precision digital phase lock circuit developed in this paper to the pulse ranging system,the test results show that:Phase locked accuracy can satisfy the requirement of high precision pulsed laser ranging.