Capacitive fingerprint acquisition sensor

• US 6,016,355 A
• Filed: 12/15/1995
• Issued: 01/18/2000
• Est. Priority Date: 12/15/1995
• Status: Expired due to Term

• Current Assignee: Apple Inc., Veridicom International, Inc.
• Original Assignee: Veridicom, Inc. (Veridicom International, Inc.)
• Inventors: Tyson, John A., Dickinson, Alexander George, Ross, Paul C., Mendis, Sunetra, McPherson, Ross
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): Werner, Brian P.
• Application Number:
  US08/573,100
• Time in Patent Office: 1,495 Days
• Field of Search: 382/115, 382/116, 382/124, 382/125, 382/126, 382/127, 382/108, 356/71, 324/519, 324/678, 324/677, 73/862.4
• US Class Current: 382/124
• CPC Class Codes: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: G01B 7/34 for measuring roughness or irregularity of surfaces
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: G07C 9/37 using biometric data, e.g. fingerprints, iris scans or voice recognition

Abstract

An apparatus for detecting topographic variations on an object such as a finger includes an array of sensing elements disposed on a substrate which each have a parasitic capacitance. An insulating receiving surface is disposed over the array of sensing elements and is adapted to receive the object such that a sensing element and a portion of the object located thereabove creates a measurable change in capacitance with respect to the parasitic capacitance. An electronic circuit is coupled to the array of sensing elements for measuring the measurable change in capacitance.

Claims

1. A sensor for detecting topographic variations on an object, comprising:

an array of sensing elements disposed on a substrate and each having a parasitic capacitance;

an insulating receiving surface disposed over said array of sensing elements, said receiving surface being adapted to receive the object such that a sensing element and a portion of said object located there above creates a measurable change in capacitance with respect to said parasitic capacitance;

an electronic circuit coupled to said array of sensing elements for measuring relative magnitudes of said measurable change in capacitance of the sensing elements as the sensing elements are distributed over the array including, a voltage source for imparting a first potential on said sensing elements;

a current source for draining charge at a constant rate for a prescribed method of time from said respective sensing elements in said array after the first potential has been applied; and

a circuit for reading a second potential from each of said respective sensing elements in the array after the prescribed period of time, and outputing a signal indicating the relative capacitance caused by the object on each respective sensing element in the array based on the first and second potentials, the constant rate of discharge and the prescribed period of time.

2. The sensor of claim 1, wherein sensing elements are configured to detect topographic variations constituting a fingerprint on a finger.

3. The sensor of claim 2, wherein said sensing elements are spaced apart from each other by approximately 50 microns.

4. The sensor of claim 2, wherein said parasitic capacitance is approximately 180 fF.

5. The sensor of claim 2, wherein said array of sensing elements are of a type fabricated by CMOS technology.

6. The sensor of claim 1, wherein said array of sensing elements are of a type fabricated by CMOS technology.

7. In combination with a device that authenticates a user prior to use thereof, a sensor for detecting a fingerprint on a finger, said sensor comprising:

an array of sensing elements disposed on a substrate and each having a parasitic capacitance;

an insulating receiving surface disposed over said array of sensing elements, said receiving surface being adapted to receive the finger such that a sensing element and a portion of said finger located there above creates a measurable change in capacitance with respect to said parasitic capacitance;

an electronic circuit coupled to said array of sensing elements for measuring relative magnitudes of said measurable change in capacitance of the sensing elements as the sensing elements are distributed over the array to provide a signal representing said fingerprint including, a voltage source for imparting a first potential on said sensing elements;

a current source for draining charge at a constant rate for a prescribed period of time from said respective sensing elements in said array after the first potential has been applied; and

a circuit for reading a second potential from each of said respective sensing elements in the array after the prescribed period of time and outputting a signal indicating the relative capacitance caused by the finger on each respective sensing element in the array based on the first and second potentials, the constant rate of discharge, and the prescribed period of time;

a memory for storing a fingerprint of at least one authorized user;

a circuit for comparing said signal against said stored fingerprint.

8. The combination of claim 7, wherein said device is an authorization card, including circuitry for storing data representing fingerprints of authorized users.

9. A method for detecting topographic variations on an object, said method comprising the steps of:

receiving the object on an insulating surface disposed over an array of sensing elements each having a parasitic capacitance such that a sensing element and a portion of said object located there above creates a measurable change in capacitance with respect to said parasitic capacitance; and

generating a signal representing said topographic variations by measuring relative magnitudes of said measurable changes in capacitance of said sensing elements as the sensing elements are distributed over in the array, wherein generating the signal includes, charging to a first potential said array of sensing elements, applying a controlled amount of current to cause a constant rate of discharge for a prescribed time period to said respective sensing elements in the array after the first potential has been applied, measuring changes in potential of said respective sensing elements in the array with respect to said first potential afte the prescribed period of time, and thereafter outputting a signal indicating the relative capacitance caused by the object on each respective sensing element in the array based on the changes in potential, the constant rate of discharge, and said prescribed time period.

10. The method of claim 9, wherein the step of receiving the object comprises the step of receiving a finger and the step of generating a signal comprises the step of generating a signal representing a fingerprint on said finger.

11. A method for authenticating a user prior to use of a device, said method comprising the steps of:

receiving a finger of the user on an insulating surface disposed over an array of sensing elements located on said device, each of said sensing elements having a parasitic capacitance such that a sensing element and a portion of said finger located there above creates a measurable change in capacitance with respect to said parasitic capacitance;

generating a signal representing a fingerprint of said finger by measuring relative magnitudes of said measurable changes in capacitance of said sensing elements as the sensing elements are distributed over the array, wherein generating the signal includes, charging to a first potential said array of sensing elements, applying a controlled amount of current to cause a constant rate of discharge for a prescribed time period to said respective sensing elements in the array after the first potential has been applied, measuring changesin potential of said respective sensing elements in the array with respect to said first potential after the prescribed period of time, and thereafter outputting a signal indicating the relative capacitance caused by the object on each respective sensing element in the array based on the changes in potential, the constant rate of discharge, and said prescribed time period; and

comparing said signal against a stored fingerprint of at least one authorized user.

12. The method of claim 11, wherein said device is an authorization card, including a memory for storing data representing fingerprints of authorized users.

13. The method of claim 11, wherein said device is an automated teller machine.

14. The method of claim 11, wherein said device is a authorization device at a point of sale.

15. The method of claim 11, wherein said device is an authorization card, including:

a memory for storing data representing fingerprints of authorized users; and

circuitry for comparing data representing an acquired fingerprint against the fingerprints of authorized users.