Capacitive Sensing Array Modulation

• US 20140218339A1
• Filed: 04/11/2014
• Published: 08/07/2014
• Est. Priority Date: 04/13/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hotelling, Steven P., Bussat, Jean-Marie, Lyon, Benjamin B.
• Granted Patent: US 9,880,675 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

A capacitive fingerprint sensor that may be formed of an array of sensing elements. Each capacitive sensing element of the array may register a voltage that varies with the capacitance of a capacitive coupling. A finger may capacitively couple to the individual capacitive sensing elements of the sensor, such that the sensor may sense a capacitance between each capacitive sensing element and the flesh of the fingerprint. The capacitance signal may be detected by sensing the change in voltage on the capacitive sensing element as the relative voltage between the finger and the sensing chip is changed. Alternately, the capacitance signal may be detected by sensing the change in charge received by the capacitive sensing elements as the relative voltage between the finger and the sensing chip is changed.

Claims

1. An electronic device, comprising:

a fingerprint sensor comprising a sensor pad and a drive ring adjacent to the sensor pad; and

a modulating circuit operably connected to the sensor pad and the drive ring, wherein the modulating circuit is adapted to control a modulated signal received by the sensor pad while maintaining a drive signal received by the drive ring substantially at a constant signal level.

2. The electronic device as in claim 1, wherein one signal level of the modulated signal comprises a low signal level.

3. The electronic device as in claim 1, wherein one signal level of the modulated signal comprises a high signal level.

4. The electronic device as in claim 3, further comprising an inductive boost circuit operably connected to the sensor pad and the modulating circuit and adapted to boost the input signal to the high signal level.

5. The electronic device as in claim 3, wherein the high signal level is greater than a power supply signal level.

6. The electronic device as in claim 1, further comprising a housing surrounding the sensor pad and the drive ring, wherein the sensor pad is disposed below a button operably connected to the housing.

7. The electronic device as in claim 1, further comprising a housing surrounding a display surface, the sensor pad and the drive ring, wherein the sensor pad is disposed below the display surface.

8. The electronic device as in claim 1, wherein the modulating circuit is included in the fingerprint sensor.

9. The electronic device as in claim 8, wherein the sensor pad and the drive ring are disposed below a dielectric material.

10. The electronic device as in claim 8, wherein the fingerprint sensor comprises a capacitive fingerprint sensor.

11. A fingerprint sensing system, comprising:

a sensor pad;

a drive ring adjacent to the sensor pad; and

a modulating circuit operably connected to the sensor pad and the drive ring, wherein the modulating circuit is adapted to control a modulated signal received by the sensor pad while maintaining a drive signal received by the drive ring substantially at a constant signal level.

12. The fingerprint sensing system as in claim 11, wherein one signal level of the modulated signal comprises a low signal level.

13. The fingerprint sensing system as in claim 11, wherein one signal level of the modulated signal comprises a high signal level that is greater than a power supply signal level.

14. The fingerprint sensing system as in claim 13, further comprising an inductive boost circuit electrically connected to the sensor pad and the modulating circuit and adapted to provide the high signal level.

15. The fingerprint sensing system as in claim 11, further comprising a housing surrounding the fingerprint sensing system, wherein the sensor pad and the drive ring are disposed below a button operably connected to the housing.

16. The fingerprint sensing system as in claim 11, further comprising a housing surrounding a display surface and the fingerprint sensing system, wherein the sensor pad and drive ring are disposed below the display surface.

17. A method for operating a fingerprint sensor that includes a sensor pad comprising a plurality of sensing elements and a drive ring adjacent to the sensor pad, the method comprising:

obtaining a first signal from at least one sensing element when an input signal to the sensor pad is in a first state and an input signal to the drive ring is in a low state;

obtaining a second signal from the at least one sensing element when the input signal to the sensor pad is in a different second state and the input signal to the drive ring is substantially maintained at the low state; and

constructing an image of at least a portion of a fingerprint based at least partially on the first and second signals.

18. The method as in claim 17, wherein obtaining a first signal from at least one sensing element when an input signal to the sensor pad is in a first state and an input signal to the drive ring is in a low state comprises obtaining a first signal from at least one sensing element when an input signal to the sensor pad is at a low voltage level and an input signal to the drive ring is at a system ground voltage level.

19. The method as in claim 18, wherein obtaining a second signal from the at least one sensing element when the input signal to the sensor pad is in a different second state and the input signal to the drive ring is substantially maintained at the low state comprises obtaining a second signal from the at least one sensing element when the input signal to the sensor pad is at a high voltage level exceeding a power supply voltage level and the input signal to the drive ring is substantially maintained at the system ground voltage level.

20. The method as in claim 19, further comprising boosting the input signal to the high voltage level using an inductive boost circuit prior to obtaining the second signal from the at least one sensing element.