A circuit and method are given, which realizes a stable yet sensitive differential
capacitance measuring device with good RF-suppression and with very acceptable
noise features for use in capacitive sensor evaluation systems. By evaluating the
difference of capacitor values only—with the help of a switched capacitor
front-end—large spreads of transducer capacitor values are tolerable. Furthermore
a mode of operation can be set up, where no essential galvanic connection between
sensor input and the active read-out input at any given time is existing. The solution
found exhibits a highly symmetrical construction. Using the intrinsic advantages
of that solution the circuit of the invention is manufactured as an integrated
circuit with standard CMOS technology at low cost.