All Digital Phase Detection and Tracking Method to Subdivide the Grating Moiré Fringe Signal

In order to improve the subdivision precision and speed of grating moiré fringe and meet the nanometer measurement requirement of grating displacement, the paper studies a new phase detection method that is the core technology of the classical phase-locked subdivision method and phase detection subdivision method. First, the output signal of grating sensor modulates the phase of the high frequency carrier wave signal,  then, the  new type system carries out real-time phase detection and tracking between the modulated carrier wave signal and carrier wave signal in every period, which assures the real-time feature and precision of phase detection. It can also discriminate the displacement direction according to the period relation of modulated carrier wave signal and carrier wave signal. All digital circuits are realized in FPGA. The method can improve the discrimination precision and remove the influence of carrier wave signal quality. Experiments prove that the system owns high anti-jamming ability, high tracking speed and high metrical precision.