Image analysis – Applications – Personnel identification
Reexamination Certificate
1997-05-16
2001-07-10
Tran, Phuoc (Department: 2721)
Image analysis
Applications
Personnel identification
C382S126000
Reexamination Certificate
active
06259804
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of personal identification and verification, and, more particularly, to the field of fingerprint sensing and processing.
BACKGROUND OF THE INVENTION
Fingerprint sensing and matching is a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes.
A typical electronic fingerprint sensor is based upon illuminating the finger surface using visible light, infrared light, or ultrasonic radiation. The reflected energy is captured with some form of camera, for example, and the resulting image is framed, digitized and stored as a static digital image. For example, U.S. Pat. No. 4,210,899 to Swonger et al. discloses an optical scanning fingerprint reader cooperating with a central processing station for a secure access application, such as admitting a person to a location or providing access to a computer terminal. U.S. Pat. No. 4,525,859 to Bowles similarly discloses a video camera for capturing a fingerprint image and uses the minutiae of the fingerprints, that is, the branches and endings of the fingerprint ridges, to determine a match with a database of reference fingerprints.
Unfortunately, optical sensing may be affected by stained fingers or an optical sensor may be deceived by presentation of a photograph or printed image of a fingerprint rather than a true live fingerprint. In addition, optical schemes may require relatively large spacings between the finger contact surface and associated imaging components. Moreover, such sensors typically require precise alignment and complex scanning of optical beams. Accordingly, optical sensors may thus be bulky and be susceptible to shock, vibration and surface contamination. Accordingly, an optical fingerprint sensor may be unreliable in service in addition to being bulky and relatively expensive due to optics and moving parts.
U.S. Pat. No. 4,353,056 to Tsikos discloses another approach to sensing a live fingerprint. In particular, the patent discloses an array of extremely small capacitors located in a plane parallel to the sensing surface of the device. When a finger touches the sensing surface and deforms the surface, a voltage distribution in a series connection of the capacitors may change. The voltages on each of the capacitors is determined by multiplexor techniques. Unfortunately, the resilient materials required for the sensor may suffer from long term reliability problems. In addition, multiplexing techniques for driving and scanning each of the individual capacitors may be relatively slow and cumbersome. Moreover, noise and stray capacitances may adversely affect the plurality of relatively small and closely spaced capacitors.
U.S. Pat. No. 5,325,442 to Knapp discloses a fingerprint sensor including a plurality of sensing electrodes. Active addressing of the sensing electrodes is made possible by the provision of a switching device associated with each sensing electrode. A capacitor is effectively formed by each sensing electrode in combination with the respective overlying portion of the finger surface which, in turn, is at ground potential. The sensor may be fabricated using semiconductor wafer and integrated circuit technology. The dielectric material upon which the finger is placed may be provided by silicon nitride or a polyimide which may be provided as a continuous layer over an array of sensing electrodes. Further conductors may be provided on the surface of the dielectric material remote from the sensing electrodes and extending over regions between the sensing electrodes, for example, as lines or in grid form, which conductors are grounded in order to improve the electrical contact to the finger surface.
Unfortunately, driving the array of closely spaced sensing electrodes as disclosed in the Knapp et al. patent may be difficult since adjacent electrodes may affect one another. Another difficulty with such a sensor may be its ability to distinguish ridges and valleys of a fingerprint when the conductivity of the skin and any contaminants may vary widely from person-to-person and even over a single fingerprint. Yet another difficulty with such a sensor, as with many optical sensors, is that different portions of the fingerprint may require relatively complicated post image collection processing to provide for usable signal levels and contrast to thereby permit accurate determination of the ridges and valleys of the fingerprint. For example, U.S. Pat. No. 4,811,414 to Fishbine et al. discloses methods for noise averaging, illumination equalizing, directional filtering, curvature correcting, and scale correcting for an optically generated fingerprint image. Unfortunately, the various processing steps are complex and require considerable computational power in a downstream processor. Signal processing of other fingerprint circuits may also be relatively complicated and therefore expensive and/or slow.
Greater advances in fingerprint sensing and matching for identification and verification are desirable for many applications. Unfortunately, current sensors and their associated circuitry may be too bulky, expensive and unreliable for a great many applications which would otherwise benefit from fingerprint identification and verification technology. In addition, fingerprint images generated by conventional sensors may vary considerably from individual-to-individual and for different sensing conditions. In addition, process variations in manufacturing may cause sensors to vary considerably from one to another. Accordingly, consistent results may be very difficult when using a conventional fingerprint sensor.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the present invention to provide a fingerprint sensor and related methods so that the fingerprint sensor may accommodate variations in image signal intensities, such as between different fingers, for different sensing conditions, or based on manufacturing process variations, for example.
This and other objects, features and advantages in accordance with the present invention are provided by a fingerprint sensor including an array of fingerprint sensing elements; analog-to-digital (A/D) conversion means having a controllable range; scanning means to perform sequential A/D conversions of predetermined ones of the array of fingerprint sensing elements; and range determining and setting means for controlling the range of the A/D conversion means based upon prior A/D conversions to thereby provide enhanced conversion resolution. The conversion resolution is enhanced despite variations in sensed fingers, conditions, or despite process variations resulting from manufacturing.
In one embodiment, the A/D conversion means preferably comprises a plurality or bank of A/D converters for simultaneously converting analog signals from a corresponding plurality of fingerprint sensing elements. By enabling dynamic exploitation of the full resolution range of the A/D converters, the accuracy of the sensing can be significantly improved.
The A/D conversion means may comprise at least one reference voltage input for permitting setting of the range. Accordingly, the range determining and setting means may comprise a processor, and at least one digital-to-analog converter connected between the processor and the at least one reference voltage input. In particular, the A/D converters may typically include a first reference voltage input and a second reference voltage input for setting corresponding first and second range points thereby defining the range. Alternately, or in addition thereto, the A/D conversion means may include at least one amplifier having a controllab
Cornett John
Gebauer Dave
Kilgore Brian
Setlak Dale R.
Williams Daryl
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Authentic Inc.
Tran Phuoc
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