Anisotropic Touch Screen Element

• US 20060207806A1
• Filed: 06/07/2006
• Published: 09/21/2006
• Est. Priority Date: 08/21/2003
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Philipp, Harald
• Granted Patent: US 7,825,905 B2
• Time in Patent Office: Days
• US Class Current: 178/18.50
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

A touch sensitive position sensor for detecting the position of an object in two dimensions is described. The position sensor has first and second resistive bus-bars spaced apart with an anisotropic conductive area between them. Electric currents induced in the anisotropic conductive area by touch or proximity flow preferentially towards the bus-bars to be sensed by detection circuitry. Because induced currents, for example those induced by drive circuitry, flow preferentially along one direction, pin-cushion distortions in position estimates are largely constrained to this single direction. Such one-dimensional distortions can be corrected for very simply by applying scalar correction factors, thereby avoiding the need for complicated vector correction.

Claims

1. A touch sensitive position sensor comprising:

a substrate defining a touch sensitive platform;

first and second resistive bus-bars arranged spaced apart on the substrate; and

an anisotropic conductive area having non-zero resistance arranged between the bus-bars such that currents induced in the anisotropic conductive area flow preferentially towards the bus-bars.

2. A touch sensitive position sensor according to claim 1, wherein the first resistive bus-bar extends between a first and a second electrode and the second resistive bus-bar extends between a third and a fourth electrode, the position sensor further comprising first, second, third and fourth drive channels associated with respective ones of the first, second, third and fourth electrodes, each drive channel being operable to generate an output signal dependent on the resistance between its electrode and the position of the object.

3. A touch sensitive position sensor according to claim 2, further comprising a fifth electrode coupled to the first resistive bus-bar at a location between the first and second electrodes, a sixth electrode coupled to the second resistive bus-bar at a location between the third and fourth electrodes, and fifth and sixth drive channels respectively associated with the fifth and sixth electrodes, wherein the fifth and six drive channels are operable to generate output signals dependent on the resistance between their respective electrode and the position of the object.

4. A touch sensitive position sensor according to claim 3, further comprising a processor operable to generate an estimate for the position of the object by comparing the output signals from the fifth and sixth drive channels and the output signals from a selected pair of the output signals from either the first and second drive signals or the third and fourth drive signals.

5. A touch sensitive position sensor according to claim 4, wherein the processor is configured to estimate the position of the object in a first direction running between the bus-bars from a ratiometric analysis of the sum of the signals associated with the fifth and sixth electrodes and the sum of the signals associated with the selected pair of the other output signals.

6. A touch sensitive position sensor according to claim 4, wherein the processor is configured to estimate the position of the object in a second direction running along the bus-bars from a ratiometric analysis of the sum of the signals associated with the fifth and the one of the selected pair of the other output signals associated with the first resistive bus bar, and the sum of the signals associated with the sixth and the one of the selected pair of the other output signals associated with the second resistive bus bar.

7. A touch sensitive position sensor according to claim 3 further comprising a seventh electrode coupled to the first resistive bus-bar at a location between the first and second electrodes, an eighth electrode coupled to the second resistive bus-bar at a location between the third and fourth electrodes, and seventh and eighth drive channels respectively associated with the seventh and eighth electrodes, wherein the seventh and eighth drive channels are operable to generate output signals dependent on the resistance between their respective electrode and the position of the object.

8. A touch sensitive position sensor according to claim 1, further comprising a further substrate defining a further touch sensitive platform adjacent the first-mentioned touch sensitive platform;

further first and second resistive bus-bars arranged spaced apart on the further substrate; and

a further anisotropic conductive area having non-zero resistance arranged between the further bus-bars such that currents induced in the further anisotropic conductive area flow preferentially towards the further bus-bars, wherein one of the first mentioned first and second resistive bus-bars and one of the further first and second resistive bus-bars are a shared bus-bar.

9. A touch sensitive position sensor according to claim 1, further comprising:

a third resistive bus-bar arranged on the substrate spaced apart from the second resistive bus-bar; and

a further anisotropic conductive area having non-zero resistance arranged between the second and third bus-bars such that currents induced in the further anisotropic conductive area flow preferentially towards the second and third bus-bars.

10. A touch sensitive position sensor according to claim 1, wherein the resistive bus bars are configured to have a path length between two locations which is greater than the straight line distance between the two locations.

11. A touch sensitive position sensor according to claim 10, wherein the resistive bus bars are configured in a zig-zag pattern.

12. A touch sensitive position sensor according to claim 10, wherein the resistive bus bars are configured to double-back on themselves multiple times.

13. A touch sensitive position sensor according to claim 1, wherein the anisotropic conducting area is formed from a plurality of resistive strips connecting between the bus bars, and wherein the resistive strips are configured to have a path length which is greater than the straight line distance between the bus bars.

14. A touch sensitive position sensor according to claim 13, wherein the strips are configured in a zig-zag pattern.

15. A touch sensitive position sensor according to claim 13, wherein the strips are configured to double-back on themselves multiple times.

16. A touch sensitive position sensor according to claim 13, wherein neighboring strips are configured to interleave with one another.

17. A touch sensitive position sensor according to claim 2, further comprising a guard electrode adjacent to the bus bars and/or the anisotropic conducting area.

18. A touch sensitive position sensor according to claim 17, wherein the guard electrode at least partially surrounds the bus bars and the anisotropic conducting area.

19. A touch sensitive position sensor according to claim 17, further comprising a guard drive channel associated with the guard electrode, the guard drive channel being operable to generate a guard electrode output signal indicative of a coupling between an object and the guard electrode.

20. A touch sensitive position sensor according to claim 19, further comprising a processor operable to compare the output signal from the guard electrode with the output signals from at least one of the other electrodes to compensate for changes in the output signal from the at least one of the other electrodes which are not associated with an object whose position is to be determined.

21. A touch sensitive position sensor according to claim 19, further comprising a processor operable to disregard output signals from the electrodes coupled to the resistive bus bars according to the output signal from the guard electrode.