US Patent 7854170 Capacitance sensing circuit for membrane pressure sensor

A capacitance sensing circuit for a membrane pressure sensor is provided. The sensing circuit has a controller, two switches in signal communication with the controller, a charge amplifier and a charge injector. The charge amplifier is connected to the switches via a sensor capacitor Cs and a reference capacitor Cr. The sensor and reference capacitors are arranged in parallel with one another and a parasitic capacitance Cp to ground. The charge injector and amplifier are arranged in parallel connection between the capacitors and the controller. The controller is configured to determine a charge imbalance indicative of a pressure difference between membranes of the pressure sensor.