A digital converter that directly translates variations in the capacitances of a differential-type capacitive sensor to a proportional digital value is described in this paper. A conventional dual-slope, analog-to-digital converter is suitably modified to obtain direct capacitance-to-digital conversion (CDC). Analysis of the proposed technique indicates that the effects of nonidealities and variations in circuit parameters on the performance of the CDC is either in the form of a gain error and/or an offset, both of which can be easily compensated. Simulation studies and experimental results obtained from a prototype built and tested prove the efficacy of the proposed scheme.
Dr. Madhu Mohan N., Shet, A. R., Kedarnath, S., and Kumar, V. J., “Digital Converter for Differential Capacitive Sensors”, IEEE Transactions on Instrumentation and Measurement, vol. 57, pp. 2576-2581, 2008.