Measuring and calibrating of the parasitic mismatch in MEMS accelerometer based on harmonic distortion self-test

Capacitive MEMS (micro-electromechanical systems) accelerometers have inherent parasitic capacitors, the existence of which will increase the system bias-instability and non-linearity. The parasitic mismatch induced signal is indistinguishable to the sensed signal and cannot be canceled by traditional offset cancellation technique. In this paper, a method to realize the on-line measuring and calibrating of this parasitic effect is proposed, which is based on the digital harmonic distortion self-test. The effect of different parasitic mismatch on the system output response is analyzed in detail. As will show, in self-test mode, the parasitic mismatch will induce distinctive even-order harmonics. An on-chip digital self-test circuit is built to excite and measure this characteristic. According to the measured results, the parasitic mismatch of the front-end interface can be effectively tuned out whereby preserved calibrating unit. The test result shows, using proposed technique, the parasitic mismatch could be reduced in two orders of magnitude.