A micropower differential charge-balancing switched-capacitor front-end for capacitive microaccelerometers

In this paper, a micropower differential switched-capacitor front-end for capacitive microaccelerometers is presented. The front-end preserves charge balance in the sensor being read, thus avoiding distortion caused by nonlinear electrostatic forces. All signal paths except the one connected to the middle electrode of the sensor are differential, making integration on the same substrate with digital signal processing easier. Transfer function, -3 dB corner frequency and stability conditions are analysed. The effect of finite DC gain of the operational amplifiers is presented. The front-end achieves a 58dB maximum simulated SNR with 1.8 V operating voltage, when sampling four channels in a time-multiplexed fashion with 10 kHz sampling frequency for each channel. The worst case current consumption is 45 μA. A prototype chip was designed and fabricated in a 0.13 μm CMOS process.