Patent ID: 8041083

Claim:
A fingerprint sensing circuit for sensing a fingerprint of a user, comprising: a signal source, for providing a reference signal; an electrode, coupled to a reference level; at least a sensing unit, coupled to an output node, for generating at least a sensed value according to the electrode and the fingerprint of the user; a resistor, coupled between the signal source and the output node; a detecting circuit, coupled to the output node; wherein the resistor, the sensing unit, and the electrode constitute a filter circuit, at least a first signal is generated at the output node according to the reference signal and the sensed value, and the detecting circuit detects the first signal to generate a corresponded detected result which indicates the fingerprint of the user: and a comparator coupled to the detecting circuit, for comparing the detected result with a reference value to generate a corresponding indication signal; wherein a cut-off frequency of the filter circuit is moved towards a frequency of the reference signal by adjusting the resistance of the resistor until the detected result is equal to the reference value.