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Phase-shift correlation method for accurate phase difference estimation in range finder.

High-precision phase-difference measurement is a key technology for a phase-shift laser range finder. In order to improve the estimation accuracy of phase difference between two sinusoidal signals with identical frequency, the phase-shift correlation method is described. Theoretical analysis shows that the conventional cross-correlation method will bring notable deviations when the true phase difference is close to 0° or 180° in the presence of noise. For reducing the influence of noise, two step calculations--phase-shift autocorrelation and phase-shift cross correlation--are used in the phase-shift correlation method. The estimation bias is eliminated by phase-shift autocorrelation in which the autocorrelation is calculated between the 2π phase-shifted signal and the original signal, and the periodic errors are eliminated by phase-shift cross correlation in which the phase difference is estimated when the true phase difference is near 90° or 270°. The effect of frequency drift on the phase difference is also discussed. The experiment results show that the maximum error of the conventional method is about 0.15°, while the estimation error of our proposed method is much less than 0.01° under the same conditions.