Linear analysis of closed loop capacitive accelerometer due to distance mismatch between plates

MEMS sensors often suffer from distance mismatch that the proof mass does not lie in the right middle of the two fixed plates. The mathematical formulae presented in this paper show that this asymmetry of MEMS sensor does not influence the linearity of accelerometer as a whole, and only introduces an offset. This is true not only for continuous time closed loop, but also for time divided architecture. For this kind of asymmetric sensors, Matlab/Simulink models are established. Simulation results confirm theoretical formulae. To testify this theory, a readout circuit of time divided architecture is designed and fabricated using 0.35μm HV CMOS process. Test results show that the nonlinearity of the tested accelerometer with the asymmetric sensor is within 0.3%.