Capacitive sensing in displacement type pointing devices

• US 20080018596A1
• Filed: 07/18/2006
• Published: 01/24/2008
• Est. Priority Date: 07/18/2006
• Status: Active Grant

• Current Assignee: PixArt Imaging Incorporated
• Original Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Inventors: Harley, Jonah, Wilson, Robert E.
• Granted Patent: US 7,889,176 B2
• Time in Patent Office: Days
• US Class Current: 345/157
• CPC Class Codes: G06F 3/0354 with detection of 2D relative movements between the device, or an operating part thereof, and a plane or surface, e.g. 2D mice, trackballs, pens or pucks
• CPC Class Codes: G06F 3/0448 Details of the electrode shape, e.g. for enhancing the detection of touches, for generating specific electric field shapes, for enhancing display quality

Abstract

Systems and methods of capacitive sensing in displacement type point devices are described. In one aspect, a pointing device includes a sense electrode structure and a displaceable member. The sense electrode structure includes an arrangement of peripheral sense electrodes in a peripheral region surrounding a central sense electrode. The displaceable member is movable in an operational zone over the sense electrode structure. The displaceable member includes a target electrode facing the sense electrodes and overlapping at least a respective portion of the central sense electrode in each position of the displaceable member in the operational zone.

Claims

1. A pointing device, comprising:

a sense electrode structure comprising an arrangement of peripheral sense electrodes in a peripheral region surrounding a central sense electrode; and

a displaceable member movable in an operational zone over the sense electrode structure and comprising a target electrode facing the sense electrodes and overlapping at least a respective portion of the central sense electrode in each position of the displaceable member in the operational zone.

2. The pointing device of claim 1, wherein the target electrode completely overlaps the central sense electrode in each position of the displaceable member in the operational zone.

3. The pointing device of claim 1, wherein the sense electrodes extend across a sense region that completely overlaps the target electrode in each position of the displaceable member in the operational zone.

4. The pointing device of claim 1, wherein the target electrode comprises a peripheral target electrode structure surrounding a central target electrode structure comprising a displaceable electrode that is movable towards and away from the sense electrode structure substantially independently of the surrounding peripheral target electrode structure.

5. The pointing device of claim 4, wherein the central sense electrode completely overlaps the displaceable electrode in each position of the displaceable member in the operational zone.

6. The pointing device of claim 4, wherein the central target electrode structure comprises a resilient restoring mechanism connecting the displaceable electrode to the peripheral target electrode structure, the restoring mechanism being operable to urge the displaceable electrode towards an equilibrium position in response to application of an external force to the displaceable electrode.

7. The pointing device of claim 1, further comprising a dielectric spacer between the target electrode and the sense electrode structure.

8. The pointing device of claim 7, wherein the dielectric spacer comprises discrete dielectric films attached to respective spaced apart surface areas of the target electrode facing the sense electrode structure, the dielectric films being free to slide over surfaces of the sense electrode structure.

9. The pointing device of claim 8, wherein respective ones of the discrete dielectric films are attached to peripheral surface areas of the target electrode and at least one central surface area of the target electrode.

10. The pointing device of claim 1, wherein the target electrode is resilient and conforms to surface areas of the sense electrode structure in response to a force applied to the displaceable member and urging the target electrode adjacent the sense electrode structure.

11. The pointing device of claim 10, wherein the target electrode comprises a central target electrode structure surrounded by a peripheral target electrode structure comprising discrete segments that are individually conformable to the surface areas of the sense electrode structure.

12. The pointing device of claim 11, wherein in an undeformed state each of the segments of the peripheral target electrode structure is angled towards the sense electrode structure.

13. The pointing device of claim 1, further comprising a measurement circuit coupled to the sense electrodes and operable to generate measurement values indicative of degrees of overlap between the target electrode and respective ones of the sense electrodes.

14. The pointing device of claim 13, wherein in a given measurement cycle the measurement circuit is operable to generate a respective measurement value for each of the peripheral sense electrodes by applying a respective input signal across the corresponding peripheral sense electrode and the central sense electrode, each of the measurement values being indicative of a respective degree of overlap between the target electrode and the corresponding peripheral sense electrode.

15. The pointing device of claim 14, further comprising a processing system operable to produce display control signals from the measurement values.

16. The pointing device of claim 15, wherein the processing system is operable to determine a difference value between (i) measurement values generated in the given measurement cycle for peripheral sense electrodes having positions defined solely on one side of a coordinate axis defined in relation to the operational zone and (ii) measurement values generated in the given measurement cycle for peripheral sense electrodes having positions defined solely on an opposite side of the coordinate axis, and determine a respective displacement value by normalizing the difference value with respect to a sum of all the measurement values generated in the given measurement cycle.

17. The pointing device of claim 15, wherein:

the target electrode comprises a peripheral target electrode structure surrounding a central target electrode structure comprising a displaceable electrode that is movable towards and away from the sense electrode structure substantially independently of the surrounding target electrode structure; and

the processing system is operable to detect movement of the displaceable electrode towards the central sense electrode based on a sum of all the measurement values generated in the given measurement cycle.

18. The pointing device of claim 17, wherein the processing system is operable to generate a touch state signal indicating that the displaceable member has been contacted by an external force in response to a determination that the sum of all the measurement values generated in the given measurement cycle exceeds a first threshold.

19. The pointing device of claim 18, wherein the processing system is operable to generate a select state signal indicating that the displaceable member has been depressed to make a selection in response to a determination that the sum of all the measurement values generated in the given measurement cycle exceeds a second threshold greater than the first threshold.

20. The pointing device of claim 15, wherein:

the target electrode is generally convex in an undeformed equilibrium state and is generally planar in a biased state in which the target electrode is urged adjacent the sense electrode structure by an applied force; and

the processing system is operable to generate a touch state signal indicating that the displaceable member has been contacted by an external force from the measurement values generated by the measurement circuit during movement of the target electrode from the equilibrium state to the biased state.

21. The pointing device of claim 20, wherein the target electrode comprises a peripheral target electrode structure surrounding a central target electrode structure comprising a displaceable electrode that is movable towards and away from the sense electrode structure substantially independently of the surrounding peripheral target electrode structure, and the processing system is operable to generate a select state signal indicating that the displaceable member has been depressed to make a selection from the measurement values generated by the measurement circuit during movement of the central target electrode structure toward the sense electrode structure after the peripheral target electrode structure has been urged adjacent the sense electrode structure.

22. A pointing device, comprising:

a sense electrode structure means comprising an arrangement of peripheral sense electrode means in a peripheral region surrounding a central sense electrode means; and

displaceable member means for moving in an operational zone over the sense electrode structure and comprising target electrode means facing the sense electrode means and overlapping at least a respective portion of the central sense electrode means in each position of the displaceable member means in the operational zone.