A low-noise readout circuit for bulk micro-machined capacitive gyroscope

Readout circuit is a key factor determining the performance of MEMS gyroscope system, being at the forefront of the signal loop. This paper presents a low-noise readout circuit for a bulk micromachined tuning fork gyroscope. Using the chopper technique, the circuit can improve the resolution and dynamic range by canceling 1/f noise and offset of the amplifier, and mismatch between reference voltages. Theory predicting the resolution of the readout circuit is given which is based on noise charge transfer method. In order to simulate the response of the circuit with the vibrating gyroscope, a simplified time-varying capacitor model is also proposed. The chip measures 2×2.5 mm2 in a standard 0.35 μm 2P4M CMOS process. Chip tests with the MEMS gyroscope prove the validity of the concepts proposed and show that the readout circuit achieves a resolution of 4 aF/√Hz with 94 dB dynamic range from a single 5 V supply.