A Robust Switched-Capacitor CDC

TLDR: In this paper, a capacitance-to-digital converter (CDC) is proposed to possess negligible sensitivity to non-ideal circuit parameters, such as leakage resistance and stray capacitance of the sensor.

Abstract: A capacitance-to-digital converter (CDC) designed to possess negligible sensitivity to non-ideal circuit parameters is presented in this paper. The scheme is based on switched capacitor integrating technique and the conversion process is such that the final output is fundamentally insensitive to leakage resistance and stray capacitance of the sensor, offset voltage and bias current of the opamp, delay, offset voltage, and bias current of the comparator, leakage current, delay, and charge injection of the switches employed, and so on. Such a characteristic is highly useful for precision measurement. The proposed CDC achieves it without any special compensating circuits, unlike some of the existing CDCs that partially meet the above feature. The performance of the CDC has been experimentally evaluated. Results show high insensitivity to the non-ideal circuit parameters. In addition, the worst case non-linearity error of the prototype CDC was found to be less than 0.1%, when tested for a range of 10 to 400 pF.