A high-order closed-loop ΣΔ interface for micro-machined accelerometer sensor

Abstract

This paper presents a closed-loop interface for micro-machined accelerometer sensor based on a force-feedback sigma-delta loop. A high-order closed-loop accelerometer interface circuit is investigated, and a time-shared multiplexing electrostatic feedback technique is used to eliminate feedthrough between feedback signals and pick-up charge signals. A low noise capacitance detection circuit is proposed with correlated-double-sampling technique to eliminate the 1/f noise and offset of operational amplifier. The interface is fabricated in a standard 0.5 μm CMOS process and the active circuit area is about 13 mm2. The chip consumes 20 mW from a 5 V supply with a sampling clock of 250 kHz. The average noise floor of the digital accelerometer is about ?115 dBV/Hz1/2 over a 1.5 kHz bandwidth. Corresponding to a sensitivity of 302 mV/g, the measured resolution of the accelerometer system is about 6 μg/Hz1/2. The nonlinearity is 0.085 %. The figure of merit shows that the proposed sigma-delta interface achieves a good performance.