Heterodyne dual-frequency laser interference displacement measurement has been widely applied in the measurement in precision mechanical systems. A signal modulation circuit with four-phase quadrant-square wave output was proposed to improve the sensitivity of displacement detection in the differential dual-frequency laser interference displacement measurement system. A front-end photoelectric conversion circuit, mixing circuit, waveform conversion circuit and fourway quadrantal square wave shaping circuit are designed and manufactured. Heterodyne dual-frequency laser interference displacement testing platform was built in the laboratory and the circuit test was finished. The detection speed of the system reach 3m/s, the measurement frequency range is 3.3-10MHz, and the accuracy reach 0.5ppm. The theoretical resolution of the system is a quarter of the laser vacuum wavelength, which is about 0.158 μm.
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