Abstract: A fingerprint sensor includes an array of fingerprint sensing elements; analog-to-digital (A/D) converters having a controllable range; a scanner to perform sequential A/D conversions of predetermined ones of the array of fingerprint sensing elements; and a range determining and setting circuit for controlling the range of the A/D converters based upon prior A/D conversions to thereby provide enhanced conversion resolution. A plurality of A/D converters are preferably used for simultaneously converting analog signals from a corresponding plurality of fingerprint sensing elements. The A/D converters may include at least one reference voltage input for permitting setting of first and second points of the range. The range scale determining and setting circuit may generate a histogram based upon prior A/D conversions. In addition, the range scale determining and setting circuit may set a default range for initial ones of the fingerprint sensing elements.

Abstract: A fingerprint sensor includes an array of fingerprint sensing elements and associated active circuits and an impedance matrix filter connected to the active circuits for filtering the signals. The impedance matrix filter preferably comprises a plurality of impedance elements with a respective impedance element connectable between each the active circuit for each fingerprint sensing element and at least one other active circuit for an adjacent fingerprint sensing element. The impedance matrix filter may also include a plurality of switches with a respective switch connected in series with each impedance element. In one embodiment, the switches may be selectively operated to determine ridge flow directions of the fingerprint image. In addition, the ridge flow directions may be used to determined a core location of the fingerprint image. The switches may also be selectively operated to convert a gray scale fingerprint image to a binarized fingerprint image.

Abstract: A fingerprint sensor includes a plurality of semiconductor devices adjacent a substrate and defining active circuit portions, and having only three metal layers. More particularly, the sensor may include a first metal layer interconnecting predetermined ones of the plurality of semiconductor devices; a second metal layer defining a ground plane; and a third metal layer comprising an array of electric field sensing electrodes connected to active circuit portions for generating an output related to a sensed fingerprint. The fingerprint sensor may also include a package surrounding the substrate and having an opening aligned with the sensing electrodes. In addition, a first external electrode may be carried by the package for contact by a finger. The sensor may thus also include an excitation drive circuit connected between the ground plane and the first external electrode for generating electric fields between the electric field sensing electrodes and adjacent finger portions.