Capacitance measurement circuit with digital output

摘要

A capacitance measurement circuit detects a change in capacitance between a variable capacitor and a fixed reference capacitor in a bridge network and provides feedback current to null-balance the bridge. An error signal is amplified at high gain by a differential integrator having an output that is converted to a high-frequency stream of digital pulses of constant amplitude and width. The pulse stream is integrated to provide a voltage to control feedback current used to balance the bridge. The average pulse density per unit time, or the frequency of the digital pulses, is linearly proportional to a change in capacitance of said variable capacitor to high accuracy over a wide dynamic range.