Circuit and method for monitoring a capacitive signal source

摘要

A circuit for monitoring capacitive signal sources, and particularly detecting changes in capacitance of a variable capacitor, comprises the capacitive signal source (40) and a differential analogue to digital converter (42). A voltage source (44) provides a DC voltage (Vcm) to a first input terminal of the differential analogue to digital converter, and the capacitive signal source(40) is connected to the other terminal of the differential analogue to digital converter (42). A feedback path (46) low pass filters the output of the differential analogue to digital converter (42) to derive a DC offset value (Vcmfb) and couples the DC offset value to the other terminal of the differential analogue to digital converter (42).