A capacitance meter based on an oversampling sigma-delta modulator and its application to capacitive sensor interface

A precision capacitance meter has been developed based on a switched-capacitor sigma delta analog-to-digital converter (ADC). It consists on a second order sigma delta architecture in which the capacitance to be measured takes part of the first integrator. A voltage reference is converted through the sigma delta ADC depending on the capacitance value. The whole operation is insensitive to stray capacitance and amplifier offset. For accurate requirements, calibration as well as temperature compensation have been integrated in the final chip