Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2001-11-02
2003-10-21
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S678000
Reexamination Certificate
active
06636053
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to semiconductor fingerprint detectors, and more particularly to improvements in capacitive elements used to sense the fingerprint pattern of a finger pressed against a sensing surface.
A capacitive distance sensor is disclosed in commonly-assigned U.S. Pat. No. 6,114,862 by Tartagni et al., the disclosure of which is hereby incorporated by reference. The Tartagni et al. patent discloses a fringing capacitive sensing technique in which two side-by-side capacitor plates are disposed just beneath a sensing surface at each of many cell locations in a two-dimensional array of sensor cells or “pixel” cells. The side-by-side capacitor plates of each pixel cell form part of a feedback circuit having an effective feedback capacitance that is modulated by the presence of live skin close to the sensing surface.
The technique disclosed in the Tartagni et al. patent is an active sensing technique in which transistor circuitry is employed at each pixel location to assist in the detection and output signal generation of the signal from each pixel cell. Passive capacitive sensor cells are also known in the art, as disclosed by example in U.S. Pat. No. 4,353,056.
SUMMARY OF THE INVENTION
The present invention provides an improved capacitive pixel for a fingerprint sensing device. Active sensing is used in a solid-state pixel structure that directly senses the electric field potential of a fingerprint of a user's finger pressed against a sensing surface. A floating capacitor plate is disposed beneath the sensing surface to define a sensing capacitor with the skin of the user's finger. The capacitance of the sensing capacitor varies with the proximity of the skin to the sensing surface so that fingerprint ridges produce a higher capacitance than fingerprint valleys. First and second coupling capacitor plates are disposed beneath the floating capacitor plate to define first and second coupling capacitors. The coupling capacitors are connected in series between a reference voltage source and an input to a charge integrator. When a reference voltage signal is applied to the pixel, the charge integrator generates an output signal that is a function of the capacitance of the sensing capacitor.
Accordingly, a compact pixel structure can be provided in an array of pixels to enable capturing of a high resolution fingerprint image. The structure gives a high signal-to-noise level response and is relatively insensitive to parasitic capacitive effects.
REFERENCES:
patent: 4353056 (1982-10-01), Tsikos
patent: 6114862 (2000-09-01), Tartagni et al.
patent: 6317508 (2001-11-01), Kramer et al.
patent: 6483931 (2002-11-01), Kalnitsky et al.
patent: 6512381 (2003-01-01), Kramer
patent: 6515488 (2003-02-01), Thomas
patent: 6525547 (2003-02-01), Hayes
patent: 6538456 (2003-03-01), Dickinson et al.
patent: 2003/0016849 (2003-01-01), Andrade
Benson Walter
Jorgenson Lisa K.
Le N.
STMicroelectronics Inc.
Thomas Peter J.
LandOfFree
Capacitive pixel for fingerprint sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Capacitive pixel for fingerprint sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Capacitive pixel for fingerprint sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3112012