Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-08-28
2002-12-31
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S662000, C324S672000, C324S688000
Reexamination Certificate
active
06501284
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fingerprint detection and recognition and in particular to finger detection within integrated circuit devices employed for fingerprint-based identification and security mechanisms.
2. Description of the Related Art
Fingerprint detection and recognition has become a widely implemented identification and security (verification) measure for a variety of applications, including credit card usage, governmental licensing and registration, and premises access control. Integrated circuit fingerprint sensors used in such detection usually contain a two-dimensional array of sensing electrodes at a pitch substantially smaller than the size of the lines on the skin surface of a fingertip, allowing an image of the fingerprint pattern to be acquired for processing, analysis and comparison.
The structure of a typical electronic fingerprint sensor is depicted in FIG.
4
. Fingerprint sensor
402
includes a planar array of sensing electrodes
404
conductively coupled to detection and image capture circuitry (not shown). Sensing electrodes
404
may be covered by a protective layer
406
against which the skin surface
408
of the fingertip is placed. Ridges
410
and valleys
412
formed by the lines on the fingertip skin surface
408
are then detected utilizing sensing electrodes
404
.
Fingerprint detection is most commonly achieved at least partially through capacitive coupling with the finger. In such embodiments, skin surface
408
and sensing electrodes
404
each form a capacitor having a capacitance proportional to the distance between a respective sensing electrode
404
and the overlying skin surface
408
. Thus, for example, the capacitance measured by sensor
402
at a point near the top of a fingerprint ridge
410
by a sensing electrode separated from skin surface
408
by a distance d
x,y
(where x and y denote the position of the respective sensing electrode within the two-dimensional sensor array) will differ from the capacitance measured through another sensing electrode at a point near the bottom of a fingerprint valley
412
, where the intervening distance d
x,y+2
is greater. In this manner an electronic image of the fingerprint may be captured for further processing.
Fingerprint detection normally involves a relative or comparative process, in which a characteristic such as capacitance) at one sensing electrode within the array is processed relative to similar measurements by the other sensing electrodes. As a result, the fingerprint sensor is subject to attack by “spoofing,” or presentation of the appropriate fingerprint pattern by an unauthorized individual. For example, the simplest spoofing technique might involve use of a finger severed from an authorized individual for that purpose.
It would be desirable, therefore, to protect against unauthorized uses of fingerprint patterns being employed in order to circumvent fingerprint-based identification and security mechanisms.
SUMMARY OF THE INVENTION
Within a capacitive fingerprint detection device, finger detection is provided by a capacitive grid overlying the fingerprint sensor electrodes to measure the absolute capacitance of the finger placed on the sensor surface. The capacitive measurement is converted to a representative frequency, which is then compared to a reference frequency or frequency range to determine whether the measured capacitance matches the expected bio-characteristics of living skin tissue. The finger detection thus provides anti-spoofing protection for the fingerprint detection device.
REFERENCES:
patent: 4209740 (1980-06-01), Marthe et al.
patent: 4935207 (1990-06-01), Stanbro et al.
patent: 5673041 (1997-09-01), Chatigny et al.
patent: 6016355 (2000-01-01), Dickinson et al.
patent: 6114862 (2000-09-01), Tartagni et al.
Deb Anjan K.
Jorgenson Lisa K.
Le N.
Munck William A.
STMicroelectronics Inc.
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