Finger position sensing methods and apparatus

• US 20050244038A1
• Filed: 04/15/2005
• Published: 11/03/2005
• Est. Priority Date: 04/16/2004
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Validity Sensors Incorporated (Synaptics Incorporated)
• Inventors: Benkley, Fred G. III
• Granted Patent: US 7,463,756 B2
• Time in Patent Office: Days
• US Class Current: 382/126
• CPC Class Codes: G06V 40/1335 Combining adjacent partial images (e.g. slices) to create a composite input or reference pattern; Tracking a sweeping finger movement

Abstract

A finger position sensing apparatus, typically used in a fingerprint sensing system, includes a position pickup plate disposed generally orthogonally with respect to an expected direction of movement of a finger and a plurality of position drive plates having different spacings from the position pickup plate to define plurality of position sensor gaps between respective position drive plates and the position pickup plate. The position drive plates are dimensioned and spaced from the position pickup plate to sense the bulk of a finger rather than fingerprint features.

Claims

1. Finger position sensing apparatus comprising:

a position pickup plate disposed generally orthogonally with respect to an expected direction of movement of a finger; and

a plurality of position drive plates having different spacings from said position pickup plate to define a plurality of position sensor gaps between respective finger drive plates and said position pickup plate, wherein the position drive plates are dimensioned and spaced from the position pickup plate to sense a bulk of a finger rather than fingerprint features.

2. Finger position sensing apparatus as defined in claim 1, wherein the position drive plates are disposed generally orthogonally with respect to the expected direction of movement of the finger.

3. Finger position sensing apparatus as defined in claim 1, further comprising conductive elements disposed between adjacent ones of said position drive plates and connected to a reference potential.

4. Finger position sensing apparatus as defined in claim 1, wherein said position drive plates increase in width with increasing distance from said position pickup plate.

5. Finger position sensing apparatus as defined in claim 1, further comprising a substrate, wherein said position pickup plate and said plurality of position drive plates comprise conductive traces on said substrate.

6. Finger position sensing apparatus as defined in claim 5, wherein said substrate comprises a flexible substrate.

7. Finger position sensing apparatus as defined in claim 1, further comprising:

an excitation circuit for sequentially energizing said position drive plates with drive signals, and

a detection circuit for detecting the drive signals coupled from said position drive plates to said position pickup plate to provide position signals.

8. Finger position sensing apparatus as defined in claim 7, wherein said drive signals comprise sequential signal bursts supplied to respective ones of said position drive plates.

9. Finger position sensing apparatus as defined in claim 8, wherein said excitation circuit includes circuitry to couple non-energized position drive plates to a reference potential.

10. Finger position sensing apparatus as defined in claim 1, wherein a center-to-center spacing between adjacent ones of said position drive plates is greater than about 0.025 inch.

11. A fingerprint sensing system comprising:

an image sensor to sense ridge peaks and ridge valleys of a fingerprint on a moving finger;

a finger position sensor to sense a position of the finger as it moves across said image sensor, said finger position sensor comprising a position pickup plate disposed generally orthogonally with respect an expected direction of movement of the finger and a plurality of position drive plates having different spacings from said position pickup plate to define a plurality of position sensor gaps between respective position drive plates and said position pickup plate; and

a sensor circuit for excitation of said image sensor with image drive signals and for detection of image signals generated by said image sensor in response to said image drive signals, and for sequentially energizing said position drive plates with position drive signals and for detection of position signals generated by said position sensor in response to said position drive signals, wherein the image signals and the position signals represent a fingerprint image.

12. A fingerprint sensing system as defined in claim 11, wherein the position drive plates are disposed generally orthogonally with respect to the expected direction of movement of the finger.

13. A fingerprint sensing system as defined in claim 11, further comprising conductive elements disposed between adjacent ones of the position drive plates and connected to a reference potential.

14. A fingerprint sensing system as defined in claim 11, wherein said position drive plates increase in width with increasing distance from said position pickup plate.

15. A fingerprint sensing system as defined in claim 11, further comprising a substrate, wherein said position pickup plate and said plurality of position drive plates comprise conductive traces on said substrate.

16. A fingerprint sensing system as defined in claim 11, wherein said position drive signals comprise sequential signal bursts supplied to respective ones of said position drive plates.

17. A fingerprint sensing system as defined in claim 16, wherein said sensor circuit includes circuitry to couple non-energized position drive plates to a reference potential.

18. A method for finger position sensing comprising:

providing a position sensor including a position pickup plate disposed generally orthogonally with respect to an expected direction of movement of a finger and a plurality of position drive plates having different spacings from said position pickup plate to define a plurality of position sensor gaps between respective position drive plates and said position pickup plate;

sequentially energizing the position drive plates with position drive signals;

detecting the position drive signals coupled from respective position drive plates to the position pickup plate to provide position signals; and

analyzing the position signals to determine the position of the finger on the position sensor.

19. A method as defined in claim 18, wherein analyzing includes calculating additional biometric information from the conduction mode signature to improve anti spoofing capabilities.