Research And Development Of FPGA-based Digital Phase Comparison Technology

Absolute distance measurement technology is of great significance in the field of measurement.Laser interferometric ranging has many advantages,such as high range,high sensitivity,high precision and strong anti-interference ability,so it has been widely used in many fields.In the signal processing of absolute distance interferometric ranging system,the frequency of reference signal and measurement signal is the same but the phase is different.The fraction of interference fringes of synthetic wavelength can be obtained by measuring the phase difference of two sinusoidal signals,and then the measured distance can be obtained.Therefore,the phase difference measurement technique of two sinusoidal signals with the same frequency is one of the key techniques in absolute distance interferometry.Based on the technical requirements of double frequency Nd:YAG solid-state laser super-heterodyne absolute distance interferometry,a digital phase comparison technology based on FPGA is studied.The main'research contents include the following aspects:First,the basic principle of phase comparison and the common digital phase comparison method are introduced.The advantages and disadvantages of the digital phase comparison method are analyzed.Combining with the signal characteristics of the laser ranging system,the high frequency pulse phase comparison method is selected.The research scheme of digital phase comparison system based on FPGA is designed.Secondly,The FPGA-based digital phase comparison hardware system is designed,which mainly includes signal preprocessing circuits,dual-channel A/D sampling,FPGA peripherals,system power supply,etc.The signal preprocessing circuits include the in-phase amplifying circuit,the band-pass filter circuit and the shaping circuit,and the preprocessing module circuit is simulated and analyzed;In the dual AID module,the AD9226 chip is selected according to the sampling requirements.In the FPGA peripheral module,the crystal oscillator circuit,download interface and man-machine interaction module of FPGA are introduced.In the system power supply module,the FPGA power supply circuit is introduced.Thirdly,the FPGA-based digital phase comparison software system is designed,the design idea of digital phase comparison is introduced in detail,the square wave module,phase difference and cycle counting state machine,algorithm module and display module based on Verilog language are designed.The programs are writtened,compiled and run in the Quartus ?software.The feasibility of software design is verified by Modelsim software simulation.Fourthly,the FPGA-based digital phase comparison test platform is established,and the characteristics of A/D sampling,measuring range and measuring precision are studied experimentally.In conclusion,a FPGA-based digital phase comparison system has been designed and developed in this thesis,the measurement range of phase comparison system is 0°?360°.When the frequency of signal is lower than 100kHz,its phase comparison precision is better,which lays an important foundation for the research and application of phase comparison technology in the future.