An ASIC-based capacitance meter: principle, realization and experiments

An application specific integrated circuit (ASIC) dedicated to capacitance measurement is presented. After introducing the key features of capacitance meters and the necessity to obtain compatibility with most industrial transducers, and dealing with design issues related to achievement of accuracy, we present the circuit description. The designed circuit is based on a second-order switched-capacitor sigma-delta modulator and includes voltage output, frequency output and pulse width modulation (PWM) output. The capacitance to measure is part of the first integrator. Calibration and temperature compensation are integrated in the ASIC. We then present the ASIC architecture (CMOS 0.8 μm) which occupies 3.7 mm² and give experimental results demonstrating the accuracy of the circuit. We conclude by giving the test measurements for the different parts of the circuits.