Micro-capacitance Measurement Based on Phase-Sensitive Detection

To improve the accuracy of measurement and response speed, a phase-sensitive detection (PSD) theory based micro-capacitance detect circuit is designed. In the front of circuit, the DDS chip generate a sinusoidal signal to excite the capacitor under test, the measured signal and reference signal enter into phase-sensitive detector after the capacitance/voltage convertion. After lock-in amplify and phase-sensitive detection, the output high frequency signals are filtered by low-pass filter. With the high resolution character of DDS, the PSD can contract bandwidth into 0.001Hz. SNR can be reached 36dB. The accuracy of measurement can be improved to 99.94%.