D. Fang and H. Xie (USA)
Integrated accelerometer, low power, preamplifier, capacitive interface circuits, chopper stabilization, MEMS
This paper presents a low-noise CMOS capacitive sensing amplifier with power consumption as low as 1mW for monolithic CMOS-MEMS inertial sensors. Low-power operation is achieved by using an open-loop, two-stage amplifier topology with fully differential input/output and chopper stabilization. High chopping frequency (up to 2 MHz) and capacitance matching with optimal transistor sizing are used to maximize signal-to-noise ratio. Offsets due to the sensor and circuits are reduced by ac offset calibration and dc offset cancellation. A pseudo-resistor MOS-Bipolar device is used to establish a stable dc bias at the sensing electrodes with very low noise. All the electronics, except the capacitor for the low-pass filter following the demodulation, are integrated on the same chip with MEMS inertial sensors. A prototype accelerometer integrated with this circuit has been fabricated using the TSMC 0.35-m CMOS process with 3.3-V power supply. Experimental results show that this interface circuit achieves a gain of 40 dB over the chopper frequency range of 50 kHz to 1 MHz, with an equivalent input offset of about 1 mV. The sensor offset is attenuated by the interface circuit by more than 26 dB.
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