Design Of High-speed Demodulation System For Interferometer Signal Based On FPGA

Optical interferometers can achieve high precision,high resolution,and large range in the precision instrument and machine tool manufacturing,are widely used in precision engineering fields and dimensional metrology applications,especially in CNC lathe measuring,nano-measurement,and sophisticated manufacturing.Interference signal processing is the core component of the interferometry system and an effective means to improve the measurement accuracy and resolution.This paper introduces a high-speed signal processing system design of homodyne interferometer based on FPGA.According to the Heydemann correction algorithm,the design develops a high-speed and real-time error compensation system of the quadrature interfering signal in measuring process based on FPGA.The design overcomes the shortcomings of off-line processing.The contents include:1.Introduction of the importance of a laser interferometer in precision engineering fields and dimensional metrology applications.Summary the main interferometer models in recent years and their working principles.On this basis,this paper proposes the scheme of the interference signal processing — demodulate the interference signals with FPGA because of its high speed and resource-rich features,use digital signal processing circuits and analog circuits to minimize the complexity of the uncertainties and errors.2.Analysis of the effect of the offsets,amplitude and the phase lag in the signal on the measurement results,established a corresponding mathematical model to quantify the interference signal error.3.Designed the hardware circuit of the signal processing system: Photoelectric conversion circuit,AD conversion circuit and FPGA signal processing circuit.They provide FPGA hardware architecture of the compensation algorithm.The function of each part of the circuit has been debugged,including the test of the high-speed AD acquisition driving module in FPGA.4.Design of error compensation algorithm.Based on the foregoing research,the paper then introduces the principle of Heydemann correction algorithm,and analyzes its applications.Finally,a new error compensation algorithm is proposed.The improved algorithm can realize real-time correction in the use of FPGA,and was verified in the FPGA simulation module that this algorithm can achieve real-time and high-speed compensation compared with traditional off-line correction.