Impact of Parasitics on the Settling Time of a Readout Circuit for High Performance MEMS Accelerometers

Abstract

This work analyses the impact of parasitic capacitances and resistances of MEMS sensors on the settling time of their readout circuit. The type of sensor considered is the capacitive sensing and the readout circuit is realised as a switched-capacitor circuit. The frontend is first represented as a low pass filter and then the simulations are performed on transistor level. The results are also verified analytically and with measurements. This work demonstrates that besides the overall capacitance and resistance of the frontend, also the parasitics of the MEMS accelerometer have an important impact on the settling. Furthermore, it is shown that the simplified model of the frontend and the MEMS are quite accurate regarding settling time evaluation enabling a faster verification.