Micro capacitance measuring circuit based on peak detection for MEMS device

For the measurement of weak signal in MEMS device, a micro capacitance measuring circuit was proposed. The circuit has simple principle and structure, which is based on peak detection method and only measures capacitance variation. Moreover, it can be used not only for differential detection, but also when there is only one sensing capacitor. First, capacitances were modulated by sine carrier wave and differential circuits. Then, sine signal with amplitude proportional to capacitance variation was got by subtraction circuit. Last, modulated signal was demodulated to DC output with peak detection method. Calibration was done with micro adjustable capacitors and a high precision LCR tester. Results indicate that the linearity of the circuit is good, the sensitivity is 3.631 V/pF, and the accuracy reaches 0.2%. Experiment was carried out with the comb actuator with vibration frequency of 2.85 kHz on a MEMS gyroscope. The frequency of output signal is (2.85±0.02) kHZ with relative error no more than 0.7%, which indicates that the micro capacitance measuring circuit is applicable for capacitive MEMS device.