Swiped aperture capacitive fingerprint sensing systems and methods
View Patent ↗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.
1. Finger sensing apparatus comprising:
two or more finger detectors spaced apart along an expected direction of movement of a finger, each of said finger detectors including at least one drive plate and at least one pickup plate, wherein said finger detectors are dimensioned and spaced to sense a bulk of a finger rather than fingerprint features and wherein an end of a finger passing over each of said finger detectors produces a change in capacitance between respective drive plates and pickup plates;
an excitation circuit for energizing the drive plates of said finger detectors with drive signals;
a detection circuit for detecting the drive signals capacitively coupled from the drive plate to the pickup plate of each of said finger detectors to provide sensor signals; and
a processing circuit for determining a time delay between said sensor signals from said finger detectors, wherein said time delay between said sensor signals is representative of a speed of the finger.
2. Finger sensing apparatus as defined in claim 1 , wherein the drive plate and the pickup plate of each of said finger detectors are disposed generally laterally with respect to the expected direction of movement of the-finger.
3. Finger sensing apparatus as defined in claim 1 , wherein the pickup plates of said finger detectors are commonly connected.
4. Finger sensing apparatus as defined in claim 1 , wherein each of said finger detectors includes first and second pickup plates disposed on opposite sides of the drive plate to form a differential sensor.
5. Finger sensing apparatus as defined in claim 4 , wherein the drive plates of said finger detectors are commonly connected.
6. Finger sensing apparatus as defined in claim 1 , wherein the drive plates and the pickup plates of said finger detectors are curved to substantially match the curve of a typical finger end.
7. Finger sensing apparatus as defined in claim 1 , further comprising a substrate, wherein said drive plates and said pickup plates comprise conductive traces on said substrate.
8. Finger sensing apparatus as defined in claim 1 , further comprising a flexible substrate, wherein said drive plates and said pickup plates comprise conductive traces on said flexible substrate.
9. Finger sensing apparatus as defined in claim 7 , wherein said substrate comprises a printed circuit board.
10. Finger sensing apparatus as defined in claim 1 , wherein said drive signals comprise signal bursts.
11. Finger sensing apparatus as defined in claim 10 , wherein said signal bursts comprise bursts of a clock signal.
12. Finger sensing apparatus as defined in claim 10 , wherein said detection circuit comprises a synchronous detector.
13. Finger sensing apparatus as defined in claim 1 , wherein the drive plate and the pickup plate of each of said finger detectors are substantially coplanar.
14. Finger sensing apparatus as defined in claim 1 , wherein the drive signals are applied to said finger detectors sequentially.
15. A fingerprint sensing system comprising:
an image sensor comprising an array of sensors for sensing ridge peaks and ridge valleys of a fingerprint; and
a finger sensor comprising two or more finger detectors spaced apart along an expected direction of movement of a finger, each of said finger detectors including at least one drive plate and at least one pickup plate, wherein said finger detectors are dimensioned and spaced to sense a bulk of a finger rather than fingerprint features and wherein an end of a finger passing over each of said finger detectors produces a change in capacitance between respective drive plates and pickup plates;
an excitation circuit for energizing the drive plates of said finger detectors with drive signals;
a detection circuit for detecting the drive signals capacitively coupled from the drive plate to the pickup plate of each of said finger detectors to provide sensor signals; and
a processing circuit for determining a time delay between said sensor signals from said finger detectors, wherein said time delay between said sensor signals is representative of a speed of the finger.
16. A fingerprint sensing system as defined in claim 15 , wherein the image sensor and the finger sensor are fabricated as conductive traces on a substrate.