A High-Accuracy Capacitance-to-Voltage Converter for Capacitive Sensors

In this paper, a high-accuracy switched-capacitor f (SC) capacitance-to-voltage (C/V) converter is presented. The proposed circuit can greatly reduce the influences of the channel charge injection and clock feedthrough from analog switches, and the finite gain of the op-amp using three kinds of voltages. Performances of the proposed circuit are simulated by HSPICE using 0.18 mu m CMOS process parameters. Simulated results have demonstrated that the gain error is 0.00016 % and the maximum nonlinear error is 0.00029 % of the full scale. The conversion accuracy of 0.01 % or better can be achieved even when low-gain amplifier such as single-stage differential amplifier is used. A prototype chip was fabricated in 0.18 mu m CMOS process. The principles of operation of the prototype chip was confirmed by measurement results. The gain and maximum nonlinear errors are 2.34 % and 0.41 % of the full scale, respectively.