Capacitive Sensor Coupling Correction

• US 20100013800A1
• Filed: 07/15/2008
• Published: 01/21/2010
• Est. Priority Date: 07/15/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: ELIAS, John G., Hotelling, Steve Porter
• Granted Patent: US 8,300,019 B2
• Time in Patent Office: Days
• US Class Current: 345/178
• CPC Class Codes: G06F 3/04164 Connections between sensors and controllers, e.g. routing lines between electrodes and connection pads
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe

Abstract

Methods and apparatus for normalizing the effects of the changes to the parasitic capacitive coupling that can occur in touch sensor panels so as to reduce or eliminate the appearance of erroneous touch events. In some embodiments, at some time prior to regular device use (e.g. during factory calibration), a conductive sheet is initially positioned so as to entirely cover a touch surface of a touch sensor panel. A set of sensed signals may be determined upon driving the drive lines and sensing the sense lines of the panel. Correctional coefficients may then be calculated based in part upon the difference between a sensed signal and an expected signal. The correctional coefficients may then be stored in the device and used to determine signal corrections for a set of measured signals during normal operation.

Claims

1. A method of normalizing the effects of parasitic coupling in a touch sensor panel, the method comprising:

stimulating a drive structure;

detecting a signal at a sense structure in response to stimulating the drive structure; and

correcting the signal by utilizing a set of correctional coefficients, wherein the set of correctional coefficients is based at least in part upon a set of previously sensed signals.

2. The method of claim 1, wherein the set of previously sensed signals is determined by a process comprising:

positioning a conductive element upon the touch sensor panel;

stimulating a plurality of drive structures; and

sensing a signal for each drive structure stimulated.

3. The method of claim 2, wherein said positioning a conductive element upon the touch sensor panel comprises completely covering the touch sensor panel with the conductive element.

4. The method of claim 2, wherein the conductive element comprises a conductive rubber sheet.

5. The method of claim 2, wherein the conductive element comprises an electrically active cover.

6. The method of claim 2, wherein the set of correctional coefficients is based at least in part upon an expected signal.

7. The method of claim 6, wherein the set of correctional coefficients is adapted to correct for changes to parasitic capacitive coupling associated with one or more connecting traces coupled to the plurality of drive structures.

8. The method of claim 7, wherein the expected signal is set to be equal to a first signal from the set of previously sensed signals.

9. The method of claim 8, wherein the first signal is obtained from a drive structure having a shorter connecting trace than any other drive structure of a first set of drive structures.

10. The method of claim 6, wherein the set of correctional coefficients is adapted to correct for changes to parasitic capacitive coupling associated with one or more metal traces coupled to the plurality of drive structures.

11. The method of claim 10, wherein the expected signal is determined from a function adapted to fit at least two signals from the set of previously sensed signals.

12. The method of claim 11, wherein said at least two signals comprise signals obtained from drive structures which do not generate parasitic coupling with said one or more metal traces.

13. The method of claim 11, wherein the function comprises a polynomial function.

14. The method of claim 13, wherein the function comprises a polynomial function of an order smaller than the number of said at least two signals.

15. An apparatus adapted to normalize the effects of parasitic coupling, the apparatus comprising:

a memory unit adapted to store data,

a first module adapted to stimulate a set of drive structures;

a second module adapted to sense a signal for each drive structure stimulated; and

a third module adapted to correct a signal by utilizing a set of correctional coefficients, wherein at least one correctional coefficient depends upon an expected signal and a set of sensed signals.

16. The apparatus of claim 15, wherein the set of sensed signals is determined after positioning a conductive element proximate to a sensing portion of the second module.

17. The apparatus of claim 15, wherein the set of correctional coefficients is adapted to correct for changes to parasitic capacitive coupling associated with one or more connecting traces coupled to the set of drive structures.

18. The apparatus of claim 17, wherein the expected signal is set to be equal to a first sensed signal.

19. The apparatus of claim 18, wherein the first sensed signal is obtained from a drive structure having a shorter connecting trace than any other drive structure of the set of drive structures.

20. The apparatus of claim 15, wherein the set of correctional coefficients is adapted to correct for changes to parasitic capacitive coupling associated with one or more metal traces coupled to the set of drive structures.

21. The apparatus of claim 20, wherein the expected signal is determined by interpolating a plurality of sensed signals from the set of sensed signals.

22. The apparatus of claim 20 wherein the expected signal is derived from a function adapted to fit a plurality of sensed signals from the set of sensed signals.

23. The apparatus of claim 22, wherein the function comprises a second-order fit polynomial function.

24. The apparatus of claim 22, wherein the function comprises a third-order fit polynomial function.

25. The apparatus of claim 15, the apparatus formed within a touch sensor panel.

26. The apparatus of claim 25, the touch sensor panel incorporated within a computing system.

27. A mobile phone comprising an apparatus adapted to normalize the effects of parasitic coupling, the apparatus comprising:

a memory unit adapted to store data;

a first module adapted to stimulate a set of drive structures;

a second module adapted to sense a signal for each drive structure stimulated; and

a third module adapted to correct a signal by utilizing a set of correctional coefficients, wherein at least one correctional coefficient depends upon an expected signal and a set of sensed signals.

28. A digital media player comprising an apparatus adapted to normalize the effects of parasitic coupling, the apparatus comprising:

a memory unit adapted to store data;

a first module adapted to stimulate a set of drive structures;

a second module adapted to sense a signal for each drive structure stimulated; and

a third module adapted to correct a signal by utilizing a set of correctional coefficients, wherein at least one correctional coefficient depends upon an expected signal and a set of sensed signals.

29. A personal computer comprising an apparatus adapted to normalize the effects of parasitic coupling, the apparatus comprising:

a memory unit adapted to store data;

a first module adapted to stimulate a set of drive structures;

a second module adapted to sense a signal for each drive structure stimulated; and

a third module adapted to correct a signal by utilizing a set of correctional coefficients, wherein at least one correctional coefficient depends upon an expected signal and a set of sensed signals.