Differential capacitance measuring circuit for pressure sensor

摘要

The circuit alternately switches two capacitors to an integrator with a differential amplifier. The input current of the amplifier is positive when the first capacitor is integrated and negative when the second capacitor is integrated. The differential amplifier holds the voltage of both capacitors equal. A control unit provides synchronous switching and measures and adds the charge and discharge times. The control unit also measures and adds the output voltage of the integrator and controls the last charge cycle so that the capacitor voltage is equal to the initial voltage. The relative or absolute differential capacitance is calculated from the sums and digitally output.