A μg resolution microacelerometer system with a second-order Σ-Δ readout circuitry

Abstract

This paper reports a 2nd order electromechanical sigma-delta accelerometer system. Accelerometer is fabricated using dissolved wafer process, and has a structural thickness of 15 mum. A large proof mass is used to decrease the mechanical noise of the accelerometer and 306 fingers per side are used to increase the sensitivity and operation range of the accelerometer. In order to obtain a high resolution, low noise accelerometer system, a fully differential, closed loop, oversampled sigma-delta capacitive readout circuit is designed and implemented. The chip includes a switched-capacitor charge integrator and a comparator, and can be used in either open-loop or closed-loop mode. The readout circuit has more than 115 dB dynamic range and can resolve less than 3 aF/radicHz. A digital filtration and decimation circuitry is also implemented to signal process the output bit stream of the readout circuit. The Sigma-Delta second order closed loop readout circuit consumes 16 mW power from a 5 V supply and the complete accelerometer system has a 0.3% non-linearity in plusmn1 g range 86 mug bias drift 74 mug/radicHz of noise level and maximum operation range of plusmn18.5 g.