Capacitive fingerprint sensing device with sensing element demodulation circuit configuration

摘要

A capacitive fingerprint sensing system includes excitation signal providing circuitry and a plurality of sensing elements. Each sensing element includes a protective dielectric top layer, an electrically conductive sensing structure coupled to the excitation signal for providing a sensing signal indicative of a change of a charge carried by the sensing structure resulting from a change in potential difference between the finger and the sensing structure, and demodulation circuitry connected to the sensing circuitry for combining the sensing signal and a demodulation signal being timing-related to the excitation signal to provide a combined signal including a DC signal component indicating the change of the charge carried by the sensing structure. The fingerprint sensing system further includes readout circuitry connected to each of the sensing elements for providing a representation of the fingerprint pattern based on the DC signal component from each of the sensing elements.