CAPACITIVE SENSING DEVICE

摘要

A capacitive sensing device comprises an antenna electrode for emitting an alternating electric field in response to an alternating voltage caused in the antenna electrode and a control and evaluation circuit that comprises a transimpedance amplifier configured to maintain the alternating voltage equal to an alternating reference voltage on a reference voltage node by injecting a current into the antenna electrode and to measure the current. The control and evaluation circuit comprises a microcontroller and a multiplexer configured and arranged to switch the antenna electrode alternately to a current input of the transimpedance amplifier and to the alternating reference voltage node. The microcontroller is configured to control the multiplexer. The multiplexer and the transimpedance amplifier and a low-pass filter operatively connected to the transimpedance amplifier form together a synchronous rectifier arrangement. The current input node of the transimpedance amplifier is AC- coupled to the reference voltage node by a protection capacitor.