An interface circuit for high-accuracy signal processing of differential-capacitance transducers

For high-accuracy signal processing of differential-capacitance transducers, an interface circuit is developed. The architecture is based on the idea that the ratio of one of the transducer capacitances to its total capacitance represents the offset binary equivalent of the physical quantity under measurement. An op amp-based capacitance-to-voltage converter is commonly used for capacitance detection and an analog-to-digital converter is used for the ratiometric operation. A circuit analysis shows that the interface can detect the capacitance change as small as 0.01% of the total capacitance. Experimental results are also given to confirm the analysis.