Techniques for fingerprint detection and user authentication

1. A method for operating a touch sensitive array to obtain information representative of a person's fingerprint comprising:

in a first mode, scanning touch sensitive elements of the array to at a first rate to provide outputs from the array sufficient to detect a position of the finger;

in a second mode, scanning touch sensitive elements of the array at a second rate higher than the first rate, the second rate sufficient to provide outputs from the array comprising a time-varying sequence of digital amplitude values that, over time, are representative of a ridge and valley detail of a rectangular portion of the fingerprint that passes adjacent the corresponding one of the touchscreen array elements as the person uses the touchscreen;

periodically switching between the first mode and the second mode; and

using the position of the finger detected in first mode to determine when to switch to the second mode;

wherein the array is a capacitive array comprising a set of parallel transmit electrodes located along a first axis in a first plane, and a set of parallel receive electrodes located along a second axis in a second plane, with the elements located adjacent where the transmit and receive electrodes cross.

2. The method of claim 1 additionally comprising:

in the first mode, determining a sequence of digital amplitude values representative of one or more gestures.

3. The method of claim 2 wherein the first rate is sufficient to detect simultaneous gestures from two or more fingers.

4. The method of claim 1 additionally comprising:

filtering outputs of the array provided in the first mode, to determine a likely subsequent position of the finger.

5. The method of claim 1 additionally comprising:

matching the time-varying sequence of digital amplitude values against one or more templates to authenticate the person.

6. The method of claim 1 wherein the templates each comprise two or more overlapping rectangular sub-templates, and the matching further comprises:

matching selected portions of the time-varying sequence of digital amplitude values against the sub-templates.

7. The method of claim 6 additionally comprising:

rotating at least one sub-template before the step of matching selected portions of the time-varying sequence of digital amplitude values.

8. A method for operating a touch sensitive array to obtain information representative of a person's fingerprint comprising:

in a first mode, scanning touch sensitive elements of the array to at a first rate to provide outputs from the array sufficient to detect a position of the finger;

in a second mode, scanning touch sensitive elements of the array at a second rate higher than the first rate, the second rate sufficient to provide outputs from the array comprising a time-varying sequence of digital amplitude values that, over time, are representative of a ridge and valley detail of a rectangular portion of the fingerprint that passes adjacent the corresponding one of the touchscreen array elements as the person uses the touchscreen;

periodically switching between the first mode and the second mode; and

using the position of the finger detected in first mode to determine when to switch to the second mode;

wherein a spacing between adjacent elements of the array is at least ten times greater than a ridge and valley spacing of the person's fingerprint.

9. The method of claim 8 additionally comprising:

in the first mode, determining a sequence of digital amplitude values representative of one or more gestures.

10. The method of claim 9 wherein the first rate is sufficient to detect simultaneous gestures from two or more fingers.

11. The method of claim 8 additionally comprising:

filtering outputs of the array provided in the first mode, to determine a likely subsequent position of the finger.

12. The method of claim 8 additionally comprising:

matching the time-varying sequence of digital amplitude values against one or more templates to authenticate the person.

13. The method of claim 8 wherein the templates each comprise two or more overlapping rectangular sub-templates, and the matching further comprises:

matching selected portions of the time-varying sequence of digital amplitude values against the sub-templates.

14. The method of claim 13 additionally comprising:

rotating at least one sub-template before the step of matching selected portions of the time-varying sequence of digital amplitude values.