Oversampling Successive Approximation Technique for MEMS Differential Capacitive Sensor

This paper proposed an oversampling successive approximation (OSSA) technique to build switched-capacitor capacitance-to-voltage convertor (SC-CVC) for readout circuit of MEMS differential capacitive sensor. The readout circuit employing the OSSA technique has significantly improved resistance to common-mode parasitic capacitance of the input terminal of the readout circuit. In the OSSA readout circuit, there are five main non-ideal characteristics: holding error, recovery degradation, increment degradation, rise-edge degradation, and charge injection which reduce the accuracy and the settling time of the circuit. These problems are explained in detail and their solutions are given in this paper. The OSSA readout circuit is fabricated in a commercial 0.18-μm BCD process. To show the improvement evidently, a reported traditional readout circuit is also reproduced and fabricated using the same process. Compared with the traditional readout circuit, the proposed readout circuit reduces the effect of common-mode parasitic capacitance on the accuracy of SC-CVC by more than 23.8 dB, power dissipation by 69.3%, and die area by 50%.