Importance

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Abstract

A fingerprint sensor includes an array of impedance sensing elements for generating signals related to an object positioned adjacent thereto, and a spoof reducing circuit for determining whether or not an impedance of the object positioned adjacent the array of impedance sensing elements corresponds to a live finger to thereby reduce spoofing of the fingerprint sensor by an object other than a live finger. A spoofing may be indicated and/or used to block further processing. In one embodiment, the spoof reducing circuit may detect a complex impedance having a phase angle in a range of about 10 to 60 degrees corresponding to a live finger. Alternately, the spoof reducing circuit may detect an impedance having a phase angle of about 0 degrees or 90 degrees corresponding to some objects other than a live finger. The fingerprint sensor may preferably include a drive circuit for driving the array of impedance sensing elements, and a synchronous demodulator for synchronously demodulating signals from the array of impedance sensing elements. Accordingly, in one particularly advantageous embodiment of the invention, the spoof reducing circuit may operate the synchronous demodulator at least one predetermined phase rotation angle. More preferably, the spoof reducing circuit may cooperate with the synchronous demodulator for synchronously demodulating signals at first and second phase angles and generating an amplitude ratio thereof, and may also compare the amplitude ratio to a predetermined threshold.

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First Claim