Electronic fingerprint sensor with differential noise cancellation
First Claim
1. Image sensing apparatus comprising:
- an image pickup plate disposed generally orthogonally with respect to an expected direction of movement of an object;
a plurality of image drive plates in spaced relation to said image pickup plate to define a plurality of sensor gaps between respective image drive plates and said image pickup plate; and
a reference plate disposed substantially parallel to the image pickup plate, wherein the reference plate is spaced from the image pickup plate to permit common mode noise and coupling to be cancelled and is spaced from the image drive plates to permit a differential image signal to develop between the image pickup plate and the reference plate.
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Accused Products
Abstract
Image sensing apparatus includes an image pickup plate disposed generally orthogonally with respect to an expected direction of movement of an object, such as a finger, multiple image drive plates in spaced relation to the image pickup plate to define sensor gaps between respective image drive plates and the image pickup plate, and a reference plate disposed substantially parallel to the image pickup plate. The reference plate is spaced from the image pickup plate to permit common mode noise and coupling to be cancelled and is spaced from the image drive plates to permit a differential image signal to develop between the image pickup plate and the reference plate. A differential amplifier coupled to the image pickup plate and the reference plate provides noise cancellation. The apparatus may further include a comb plate spaced from the reference plate and coupled to a reference potential, such as ground.
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Citations
21 Claims
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1. Image sensing apparatus comprising:
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an image pickup plate disposed generally orthogonally with respect to an expected direction of movement of an object; a plurality of image drive plates in spaced relation to said image pickup plate to define a plurality of sensor gaps between respective image drive plates and said image pickup plate; and a reference plate disposed substantially parallel to the image pickup plate, wherein the reference plate is spaced from the image pickup plate to permit common mode noise and coupling to be cancelled and is spaced from the image drive plates to permit a differential image signal to develop between the image pickup plate and the reference plate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A fingerprint sensing system comprising:
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an image sensor including an array of sensors for sensing ridge peaks and ridge valleys of a fingerprint on a moving finger, said image sensor comprising; an image pickup plate disposed generally orthogonally with respect to an expected direction of movement of the finger; a plurality of image drive plates in spaced relation to said image pickup plate to define a plurality of sensor gaps between respective image drive plates and said image pickup plate; and a reference plate disposed substantially parallel to the image pickup plate, wherein the reference plate is spaced from the image pickup plate to permit common mode noise and coupling to be cancelled and is spaced from the image drive plates to permit a differential image signal to develop between the image pickup plate and the reference plate; a finger sensor for sensing a speed of the finger as it moves across the image sensor; and a sensor circuit for excitation of the image sensor with image drive signals and for detection of image signals between the image pickup plate and the reference plate in response to the image drive signals, for excitation of said finger sensor with finger drive signals and for detection of finger signals in response to said finger drive signals, and for coordinating said image signals and said finger signals to provide a fingerprint image. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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Specification