A Low-Power Highly Sensitive Capacitive Accelerometer IC Using Auto-Zero Time-Multiplexed Differential Technique

This paper presents a low-power highly sensitive switched-capacitor (SC) readout integrated circuit (IC) for a capacitive accelerometer. Fabricated using bulk micromachining technique, the mechanical sensor with a cantilever structure achieves a high sensitivity and low noise feature. An autozero time-multiplexed differential capacitance-to-voltage converter (AZTMD-CVC) is proposed in the SC readout interface. The CVC is based on a simple single-ended topology to yield a time-multiplexed differential output. As such, dc offset, 1/f noise, thermal drift, and component mismatch errors are significantly reduced in form of common mode errors through the time-multiplexed differential operation. In addition, the thermal noise of the AZTMD-CVC is analyzed and optimized with power so as to achieve good noise-power efficiency. The application specified IC chip is fabricated using 0.35-μm CMOS technology and draws a total current of 240 μA at a ±2.5 V supply. The accelerometer system's sensitivity is 1.95 V/g. The measured system noise floor is only 1.16 μg/√Hz at 250 Hz and the output noise-power product figure of merit (FOM) is 0.28 (μg/√Hz) x mA.