Abstract: A capacitive measuring system includes capacitive sensors and an evaluation circuit having a multiplexer, a synchronous rectifier, a sinusoidal signal generator, and a reference voltage divider. The capacitive sensors are acted on by a mono-frequency voltage signal generated by the sinusoidal signal generator, output signals of the capacitive sensors are transmitted in alternation to the synchronous rectifier via the multiplexer, and signal amplification of output signals of the synchronous rectifier are calibrated as a function of an activatable reference impedance. The synchronous rectifier is formed by a MOS semiconductor switch. A source-drain section of the MOS semiconductor switch forms a shunt that is controlled by the mono-frequency voltage signal. A channel of the multiplexer is provided for transmitting a calibration signal, generated by the reference voltage divider, to the synchronous rectifier alternately with the output signals of the capacitive sensors.

Abstract: A capacitive measuring system includes capacitive sensors and an evaluation circuit having a multiplexer, a synchronous rectifier, a sinusoidal signal generator, and a reference voltage divider. The capacitive sensors are acted on by a mono-frequency voltage signal generated by the sinusoidal signal generator, output signals of the capacitive sensors are transmitted in alternation to the synchronous rectifier via the multiplexer, and signal amplification of output signals of the synchronous rectifier are calibrated as a function of an activatable reference impedance. The synchronous rectifier is formed by a MOS semiconductor switch. A source-drain section of the MOS semiconductor switch forms a shunt that is controlled by the mono-frequency voltage signal. A channel of the multiplexer is provided for transmitting a calibration signal, generated by the reference voltage divider, to the synchronous rectifier alternately with the output signals of the capacitive sensors.