Resistive finger detection for fingerprint sensor

• US 6,665,428 B1
• Filed: 08/28/2000
• Issued: 12/16/2003
• Est. Priority Date: 08/28/2000
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Gozzini, Giovanni
• Primary Examiner(s): Ahmed, Samir
• Assistant Examiner(s): Bali, Vikkram
• Application Number:
  US09/649,808
• Time in Patent Office: 1,205 Days
• Field of Search: 382/115, 382/116, 382/124, 382/125, 382/126, 324/681, 324/662, 324/672, 340/5.82, 340/5.83, 340/5.53
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: G06V 40/40 Spoof detection, e.g. liveness detection

Abstract

Within a capacitive fingerprint detection device, finger detection is provided by a plurality of resistive grids overlying the fingerprint sensor electrodes to measure the resistance of the finger placed on the sensor surface. A finger placed on the sensor surface connects the resistive rids and allows the skin resistivity to be measured. The measured resistance is compared to a reference resistance or range of resistances to determine whether the measured resistance matches the expected bio-characteristics of living skin tissue. The finger detection thus provides anti-spoofing protection for the fingerprint detection device.

Claims

1. A method of finger detection, comprising:

measuring a resistance between at least two isolated resistive grids on a sensing surface of a capacitive fingerprint detection device when connected by an object placed on the sensing surface of the fingerprint detection device, wherein the capacitive fingerprint detection device includes a plurality of capacitive sensor electrodes below the resistive grids for detecting fingerprint features;

comparing the measured resistance to a resistance range corresponding to living skin tissue to determine whether a finger has been placed on the surface of the fingerprint detection device.

2. The method of claim 1, further comprising:

responsive to determining that the measured resistance falls within the resistance range corresponding to living skin tissue, indicating that a finger has been placed on the surface of the fingerprint detection device.

3. The method of claim 2, wherein the step of measuring a resistance between at least two isolated resistive grids on a sensing surface of a capacitive fingerprint detection device when connected by an object placed on the sensing surface of the fingerprint detection device further comprises:

measuring a resistance between two resistive grids connected by the object.

4. The method of claim 3, further comprising:

measuring a resistance between two resistive grids electrically connected by a finger; and

responsive to determining that the measured resistance between the two resistive grids falls within the resistance range corresponding to living skin tissue, indicating that the object on the surface of the fingerprint detection device is the finger.

5. The method of claim 3, further comprising:

measuring a resistance between two resistive grids electrically connected by an object other than a finger; and

responsive to determining that the measured resistance between the two resistive grids falls outside the resistance range corresponding to living skin tissue, indicating that the object on the surface of the fingerprint detection device is not a finger.

6. The method of claim 2, further comprising:

comparing the measured resistance to a threshold resistance;

responsive to determining that the measured resistance is greater than the threshold resistance, indicating that a finger has been placed on the surface of the fingerprint detection device; and

responsive to determining that the measured resistance is not greater than the threshold resistance, indicating that an object other than a finger has been placed on the surface of the fingerprint detection device.

7. Anti-spoofing protection for a fingerprint detection device, comprising:

a plurality of resistive grids overlying capacitive sensor electrodes employed within the fingerprint detection device to detect fingerprint features on a sensing surface of the fingerprint detection device;

resistance measurement means measuring a resistance between two of the resistive grids when an object on the sensing surface electrically connects the two resistive grids; and

comparator means comparing the measured resistance to resistive bio-characteristics of living skin tissue to determine whether the object on the sensing surface of the fingerprint detection device is a finger.

8. The anti-spoofing protection of claim 7, wherein the plurality of resistive grids further comprises:

the two resistive grids.

9. The anti-spoofing protection of claim 7, wherein the plurality of resistive grids further comprises:

two resistive grids having interlocking regions adapted to be overlapped and electrically connected by an object on the sensing surface.

10. The anti-spoofing protection of claim 7, wherein the comparator means further comprises:

means for indicating whether the object on the sensing surface of the fingerprint detection device is a finger.

11. The anti-spoofing protection of claim 7, wherein the comparator means indicates that the object on the sensing surface of the fingerprint detection device is a finger if the measured resistance falls within a predefined range of resistances.

12. The anti-spoofing protection of claim 7, wherein the comparator means indicates that the object on the sensing surface of the fingerprint detection device is not a finger if the measured resistance falls outside a predefined range of resistances.

13. The anti-spoofing protection of claim 7, wherein the comparator means compares the measured resistance to a threshold resistance.

14. A fingerprint detection device, comprising:

capacitive sensor electrodes employed to detect fingerprint features;

a plurality of resistive grids on a sensing surface of the fingerprint detection device and overlying the capacitive sensor electrodes;

resistance measurement means measuring a resistance between two of the resistive grids when an object on the sensing surface electrically connects the two resistive grids; and

comparator means comparing the measured resistance to resistive bio-characteristics of living skin tissue to determine whether the object on the sensing surface of the fingerprint detection device is a finger.

15. The fingerprint detection device of claim 14, wherein the plurality of resistive grids further comprises:

the two resistive grids.

16. The fingerprint detection device of claim 14, wherein the plurality of resistive grids further comprises:

two resistive grids having interlocking regions adapted to be overlapped and electrically connected by an object on the sensing surface.

17. The fingerprint detection device of claim 14, wherein the comparator means further comprises:

means for indicating whether the object on the sensing surface of the fingerprint detection device is a finger.

18. The fingerprint detection device of claim 14, wherein the comparator means indicates that the object on the sensing surface of the fingerprint detection device is a finger if the measured resistance falls within a predefined range of resistances.

19. The fingerprint detection device of claim 14, wherein the comparator means indicates that the object on the sensing surface of the fingerprint detection device is not a finger if the measured resistance falls outside a predefined range of resistances.

20. The fingerprint detection device of claim 14, wherein the comparator means compares the measured resistance to a threshold resistance.