CMU MEMS Laboratory Publication Abstract


in IEEE Journal of Solid-State Circuits, Volume 39, Issue 21, pp. 722-730, May 2004.
A Low-Noise Low-Offset Capacitive Sensing Amplifier for a 50-μg/ÖHz Monolithic CMOS MEMS Accelerometer
J. Wu, G. Fedder and R. Carley
This paper describes a CMOS capacitive sensing amplifier for a monolithic MEMS accelerometer fabricated by post-CMOS surface micromachining. Thos chopper stabilized amplifier employs capacitance matching with optimal transistor sizing to minimize sensor noise floor. Offsets due to sensor and circuit are reduced by ac offset calibration and dc offset cancellation based on a differential difference amplifier (DDA). Low-duty-cycle periodic reset is used to establish robust dc bias at the sensing electrodes with a low noise. This work shows that continuous-time voltage sensing can achieve lower noise than switched-capacitor charge integration for sensing ultra-small capacitance changes, A prototype accelerometer integrated with this circuit achieves 50-μg/ÖHz acceleration noise floor and a 0.02-aF/ÖHz capacitance noise floor while chopped at 1 MHz.
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