A Low-Noise Closed-Loop Interface for High-G Capacitive Micro-Accelerometer

A switched capacitor interface is presented in this paper for a +/- 50g capacitive micro-accelerometer. In order to suppress the flicker noise of the frontend, a switched capacitor proportional-integral controller combined with a charge sensitive amplifier using correlated double sampling is proposed. The controller has a simple structure with minimized number of switches and cancels the offset of both the charge sensitive amplifier and itself. A delay buffer following the controller is used to generate a z(-1/2) delay and drive the middle plate of the sensing element. The interface is implemented in a 0.35 mu m 3.3V/15V CMOS process and the area of the chip is 11.75 mm(2). The fabricated prototype circuit operates under 15 V and 3.3 V supply at a sampling clock of 100 kHz. Meanwhile, a sensitivity of 99.7 mV/g is achieved with the bias instability of 200 mu g. The dynamic range of the accelerometer is 106.16 dB over a signal bandwidth of 200 Hz.