Switched capacitor single-slope capacitance to direct digital converter for differential capacitive sensors

Abstract

A novel, simple and accurate Single-Slope Capacitance-to-Digital Converter (SSCDC) suitable for differential capacitive sensors is presented in this paper. Differential capacitive sensors have two capacitors that vary in a push-pull manner with-respect-to the measurand. In many such sensors, the relationship between capacitance and measurand is non-linear. The proposed SSCDC accepts the sensor capacitances having non-linear characteristics, and provides a linear digital output directly proportional to the measurand (without employing a dedicated ADC) for the full range of input. It also provides a faster conversion rate when compared to its Dual-Slope CDC counterpart. Simulation studies and experimental results obtained from a prototype built and tested prove the efficacy of the proposed scheme. The worst case non-linearity was within 0.3%.