A ΔΣ interface for MEMS accelerometers using electrostatic spring-constant modulation for cancellation of bondwire capacitance drift

Precision accelerometers are used in a variety of automotive applications, navigation systems, and low-level vibration-monitoring systems. Currently, these sensors are factory-calibrated to null their input offset. However, the residual offset drifts mainly due to thermal and mechanical stress and humidity. As a result, the offset accuracy of high-end MEMS accelerometers is specified on the order of ±100mg. With continuously increasing precision requirements, it is desirable to develop new techniques that address post-calibration drift. In this paper, we describe an accelerometer interface that continuously measures and cancels offset drift due to change in parasitic capacitance of the bondwires in a system-in-package-type MEMS accelerometer. The proposed technique reduces the bondwire offset of the measured prototypes by 41dB down to 6.24mg.