Swiped aperture capacitive fingerprint sensing systems and methods

• US 20040081339A1
• Filed: 10/20/2003
• Published: 04/29/2004
• Est. Priority Date: 12/05/2000
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Validity Sensors Incorporated (Synaptics Incorporated)
• Inventors: Benkley, Fred G. III
• Granted Patent: US 7,146,024 B2
• Time in Patent Office: Days
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• 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 fingerprint sensing system includes an image sensor, a rate sensor and a sensor circuit. The image sensor includes a linear array of capacitive sensors for capacitive sensing of ridge peaks and ridge valleys of a fingerprint on a swiped finger. The rate sensor senses the speed of the finger as it is swiped across the image sensor. The sensor circuit supplies image drive signals to the image sensor and detects image signals in response to the drive signals. The sensor circuit supplies rate drive signals to the rate sensor and detects rate signals in response to the rate drive signals. The sensor circuit further coordinates the image signals and the rate signals to provide a fingerprint image. The image sensor may be configured as an image pickup plate and multiple image drive plates formed on a substrate, such as a flexible printed circuit board or other flexible substrate which may conform to the shape of the finger.

Claims

1. Rate sensing apparatus comprising:

two or more object detectors spaced apart along a direction of movement of an object, each of said object detectors including at least one rate drive plate and at least one rate pickup plate, wherein an end of an object passing over each of said object detectors produces a change in capacitance between respective rate drive plates and rate pickup plates.

2. Rate sensing apparatus as defined in claim 1, wherein the rate drive plate and the rate pickup plate of each of said object detectors are disposed generally laterally with respect to the direction of movement of the object.

3. Rate sensing apparatus as defined in claim 1, wherein the rate pickup plates of said sets of rate sensing plates are commonly connected.

4. Rate sensing apparatus as defined in claim 1, wherein each of said object detectors includes first and second rate pickup plates disposed on opposite sides of the rate drive plate to form a differential rate sensor.

5. Rate sensing apparatus as defined in claim 4, wherein the rate drive plates of said object detectors are commonly connected.

6. Rate sensing apparatus as defined in claim 1, wherein the rate drive plates and the rate pickup plates of said object detectors are dimensioned and spaced for detecting the speed of a moving finger.

7. Rate sensing apparatus as defined in claim 6, wherein the rate drive plates and the rate pickup plates of said object detectors are curved to substantially match the curve of a typical finger end.

8. Rate sensing apparatus as defined in claim 6, further comprising a substrate, wherein said rate drive plates and said rate pickup plates comprise conductive traces on said substrate.

9. Rate sensing apparatus as defined in claim 6, further comprising a flexible substrate, wherein said rate drive plates and said rate pickup plates comprise conductive traces on said flexible substrate.

10. Rate sensing apparatus as defined in claim 8, wherein said substrate comprises a printed circuit board.

11. Rate sensing apparatus as defined in claim 1, further comprising:

an excitation circuit for energizing the rate drive plates of said object detectors with drive signals, and

a detection circuit for detecting the drive signals capacitively coupled from the rate drive plate to the rate pickup plate of each of said object detectors to provide rate signals.

12. Rate sensing apparatus as defined in claim 11, wherein said drive signals comprise signal bursts.

13. Rate sensing apparatus as defined in claim 12, wherein said signal bursts comprise bursts of a clock signal.

14. Rate sensing apparatus as defined in claim 12, wherein said detection circuit comprises a synchronous detector.

15. Rate sensing apparatus as defined in claim 11, further comprising a processing circuit for determining a time delay between said rate signals from said object detectors, wherein said time delay between said rate signals is representative of a speed of the object.

16. Rate sensing apparatus as defined in claim 1, wherein the rate drive plate and the rate pickup plate of each of said object detectors are substantially coplanar.