A low-noise readout circuit for MEMS vibratory gyroscope

This paper presents a gain-programmable low-noise switched-capacitor circuit for readout of a bulk micromachined gyroscope with a resonance frequency of 3-4 kHz and signal bandwidth of 100 Hz. A charge transfer method is adopted which enables the common node of the sensing and driving structure in gyroscope to a stable biasing voltage, so that the driving force influence of the voltage fluctuation on the common node in the traditional readout method is eliminated. An offset cancellation scheme is used in the readout circuit to suppress the opamp´s offset and two programmable capacitor arrays are also implemented on-chip to compensate the initial capacitance offset from the MEMS gyroscope. In order to simulate the transient response of the circuit to the vibrating gyroscope, a simplified model is proposed which uses a time-varying voltage to generate a time-varying capacitor. The chip measures 2times2.5 mm² in a standard 0.35 mum CMOS process. Simulation results show that the readout circuit can resolve input capacitance variations of 95 aF in 100 Hz bandwidth with 83.4 dB dynamic range from a single 5 V supply.