A Detector Circuit Design for Amplitude Modulation Inductance Sensor Based on the Phase-Sensitive Detection

To solve the problem of inaccurate demodulation resulted from the system uncertain phase shift which exists in the demodulation process of the amplitude modulation (AM) for an inductance displacement sensor, and also to improve the deficiency induced by phase sensitive detection process which would bring in high-frequency noises and decrease the circuit signal to noise ratio, an improved phase sensitive detection process was proposed. The measuring circuit of amplitude modulation inductance displacement sensor was analyzed. One reason of the phase shift occurred in demodulation process was discussed. Meanwhile the principles of the phase sensitive detection and its bringing in the noises were analyzed. Then a symmetric phase-adjustable low pass filter structure was proposed. The AM inductance displacement sensor was prototyped using printed circuit boards and its performance indices were tested. Finally, the experiment results were analyzed. It shows that circuit measuring stability is better than 0.02 μm/30min, the maximum measured deviation is 0.09 μm within the range of -50 μm ~50 μm. The maximum amplitude deviation approximates 1% when the excitation signal frequency varies in the Center frequency range of ± 5%. Measuring results showed that the symmetric phase-adjustable low pass filter structure can effectively solve the inaccuracy caused by the system uncertainty phase shift and greatly reduce high-frequency noises brought in by the phase sensitive detection process. The proposed inductance sensor meets the requirements of the high precision measurement.