Analysis of parasitic feed-through capacitance effect in closed-loop drive circuit design for capacitive micro-gyroscope

Abstract

The drive axis of a capacitive micro-gyroscope sensor forms an `electrical-mechanical' resonator with closed-loop drive circuits when the gyro is in full operation. The parasitic feed-through capacitance, which exists between the driving and sensing electrodes of the sensor, induces two main negative effects: preventing the expected `electrical-mechanical' oscillation and introducing an undesired high frequency `electrical' oscillation. In this paper, mathematical expression of the critical parasitic feed-through capacitance allowing the occurrence of `electrical-mechanical' oscillation is derived for the first time. Based on the derived expression, a conclusion that increasing the polarization voltage on the sensor mass be the only electrical way to increase the critical value of parasitic feed-through capacitance is revealed. Then with an implemented silicon chip for the drive circuit, the reason of occurring electrical oscillation is analyzed, and an effective solution to avoid the electrical oscillation referred as increasing the polarization voltage is proposed. Experiments on a capacitive micro-gyroscope prototype show that when the polarization voltage is increased from 10 to 18 V, the closed-loop drive circuit eliminates possibility of the electrical oscillation effectively. As a result, the proposed electrical oscillation solution has been verified.