SENSING ELEMENT ARRANGEMENT FOR A FINGERPRINT SENSOR
First Claim
1. In a fingerprint sensor having a plurality of pixels for sensing a fingerprint of a user'"'"'s finger, each pixel having a sensing element coupled to an amplifier for generating an output corresponding to a fingerprint characteristic appearing at the pixel location, the sensing element comprising:
- a body of dielectric material;
a surface plate of conductive material retained by the dielectric body and having an upper surface defining a sensing surface for contact with the fingerprint-bearing skin of a user'"'"'s finger;
first and second coplanar electrodes embedded in the dielectric body at a first level below the surface plate; and
a third electrode embedded in the dielectric body at a second level below the surface plate, the third plate being connected by a conductor to the surface plate;
wherein a first sensor is formed by the third electrode and the first electrode, a second sensor is formed by the third electrode and the second electrode, and a fingerprint sensor is formed between the surface plate and the skin of the user'"'"'s finger thereover during a sensing operation.
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Abstract
For each pixel in an array of pixels in a fingerprint sensor, a fingerprint capacitor is defined by the fingerprint-bearing skin of a user'"'"'s finger proximate to the top exposed surface of a sensing plate of the pixel. First and second plates are embedded in dielectric material beneath the sensing plate, and define therewith first and second capacitors of a sensing element. The capacitance of the fingerprint capacitor is coupled by the sensing element to an amplifier. During a sensing operation, the amplifier generates a pixel output signal that is a function of the variable capacitance of the fingerprint capacitor, which varies according to the presence of a fingerprint ridge or valley appearing directly above the sensing plate when the user'"'"'s finger is in contact with the fingerprint sensor.
24 Citations
8 Claims
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1. In a fingerprint sensor having a plurality of pixels for sensing a fingerprint of a user'"'"'s finger, each pixel having a sensing element coupled to an amplifier for generating an output corresponding to a fingerprint characteristic appearing at the pixel location, the sensing element comprising:
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a body of dielectric material;
a surface plate of conductive material retained by the dielectric body and having an upper surface defining a sensing surface for contact with the fingerprint-bearing skin of a user'"'"'s finger;
first and second coplanar electrodes embedded in the dielectric body at a first level below the surface plate; and
a third electrode embedded in the dielectric body at a second level below the surface plate, the third plate being connected by a conductor to the surface plate;
wherein a first sensor is formed by the third electrode and the first electrode, a second sensor is formed by the third electrode and the second electrode, and a fingerprint sensor is formed between the surface plate and the skin of the user'"'"'s finger thereover during a sensing operation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification