US Patent 7516669 Capacitance sensing circuit for a pressure sensor

The invention provides for a capacitance sensing circuit for a pressure sensor. The pressure sensor includes a sensor membrane and a compensation membrane. The circuit includes a controller arranged in signal communication with a charge amplifier, a charge injector and two switches. The charge amplifier is connected to the switches via a sensor capacitor in parallel with a reference capacitor in parallel with a parasitic capacitance to ground. The charge injector and charge amplifier are arranged in parallel connection between the capacitors and the controller. The controller operates the circuit to determine a charge imbalance indicative of a pressure difference between the sensor and compensation membranes.