Research Of DSP-based Real-time Demodulation Method Of One-frequency Laser Interferometer

With the development of precision machining technology, the measurment of nano-vibration and nano-displacement is studied widly. In most measurement methods, with the high accuracy, simple structure, adaption to most experimental environment and high dynamic range, the optical measurement is used widly. The output signal of interferometer is quadratue, so, the demodulation of quadarature signal is closely related to the precion of optical measurement. To relize the real-time demodulation, not only suitable demodulation method, conclude nonlinearity correction, ellipse fitting and so on, but also high-speed data acquisition system and high-speed data processing system, which can provide a efficient hardware platform for signal demodulation, are needed.A DSP-based real-time demodulation system of one-frequency laser interferometer is discussed. A multiple-trigger 8-channel high-speed data acquisition system is designed, which keep FPGA(Altera-EP3C25) as the main controller. To complishment the nonlinearity correction and look-up table, a high-speed data processing system is designed, which keep DSP(TI-TMS320C6713B300) as the core. Data transmission between two systems is finished by on-chip peripherals of DSP(HPI interface) and FIFO. Furthermore, according to the feature of hardware system, the realization of algorithm of demodulation is probed in this paper. The main contents concluded in the paper as follows:The contemporary development of real-time demodulation is introduced in the first chapter, besides, the contemporary development of high-speed data acquisition and method of real-time demodulation are disserted exhaustive, then, the specification of demodulation system is provided. In the second chapter, the feature of output signal of interferometer is discussed at first, and then, the algorithm of real-time demodulation is introduced. In the third chapter, the structure of hardware system is provided at first, and then, the circuit design of high-speed data acquisition system is analyzed, the results of timing stimulation are also presented. At next, the circuit design of high-speed data processing system is studied, transmission path of data in the system is also discussed. In the fourth chapter, algorithm is narrated, the optimization of algorithm is detailed analyzed, time-consuming analysis are presented. In the fifth chapter, results of stimulation and measurement, include experimental data acquisition and experimental data processing, are provided and analyzed. At last, full-paper summary and conclusion are given.