A capacitive pressure sensor interface using oversampling Δ-Σ demodulation techniques

An interface for a capacitive pressure sensor which accommodates digital encoding and linearization functions has been developed. The front-end is a switched-capacitor bridge which converts the sensor capacitance into a proportional voltage. This voltage is applied to a pulse-width modulator to be compared with a model signal generated by a digital waveform synthesizer (DWS). This model-based signal processing provides the digital equivalent of the pressure being measured. For high-yield, monolithic implementation of the interface, oversampling Δ-Σ demodulation techniques are used for the DWS. In addition to the digital functions, offset and scale adjustment, and cross-parameter compensation are also possible with this architecture. A prototype interface is described to demonstrate these capabilities