Capacitive sensor coupling correction

• US 8,300,019 B2
• Filed: 07/15/2008
• Issued: 10/30/2012
• Est. Priority Date: 07/15/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Elias, John G., Hotelling, Steve Porter
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): CRAWLEY, KEITH L
• Application Number:
  US12/173,730
• Publication Number:
  US 20100013800A1
• Time in Patent Office: 1,568 Days
• Field of Search: None
• US Class Current: 345/173
• 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 with at least one drive signal, the drive structure comprises one of a plurality of drive lines on the touch sensor panel, each drive line comprising a plurality of drive line conductive elements, the drive line conductive elements being coupled together by a plurality of connecting traces, the connecting traces extend parallel to a plurality of sense lines and disposed between the plurality of sense lines and the plurality of drive line conductive elements;

detecting at least one sense signal at one or more of the plurality of sense lines on the touch sensor panel, each sense line comprising at least one sense line conductive element, the plurality of sense lines being disposed transverse to the plurality of drive lines;

correcting the magnitude of the at least one sense 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 detected sense signals to provide at least one corrected sense signal; and

determining a touch position based on the at least one drive signal and the at least one corrected sense signal; and

wherein the set of previously sensed signals is determined by;

positioning a conductive element upon the touch sensor panel;

stimulating a plurality of drive structures; and

sensing a signal for each drive structure stimulated.

2. The method of claim 1, wherein said positioning a conductive element upon the touch sensor panel comprises completely covering the touch sensor panel with the conductive element.

3. The method of claim 1, wherein the conductive element comprises a conductive rubber sheet.

4. The method of claim 1, wherein the conductive element comprises an electrically active cover.

5. The method of claim 1, wherein the set of correctional coefficients is based at least in part upon an expected signal.

6. The method of claim 5, 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.

7. The method of claim 6, wherein the expected signal is set to be equal to a first signal from the set of previously sensed signals.

8. The method of claim 7, 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.

9. The method of claim 5, 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.

10. The method of claim 9, wherein the expected signal is determined from a function adapted to fit at least two signals from the set of previously sensed signals.

11. The method of claim 10, 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.

12. The method of claim 10, wherein the function comprises a polynomial function.

13. The method of claim 12, wherein the function comprises a polynomial function of an order smaller than the number of said at least two signals.

26. The method of claim 1, wherein:

one or more metal traces are disposed in a border area of the touch sensor panel and are coupled to the plurality of drive lines,

whereby the one or more metal traces exhibit parasitic capacitive coupling to one or more of the plurality of sense lines.

27. The method of claim 26, wherein:

the plurality of drive line conductive elements form a matrix on the touch sensor panel, and

a first set of drive line conductive elements in a first direction comprise the plurality of drive lines, and a second set of drive line conductive elements in a second direction comprise columns of drive line conductive elements disposed between adjacent sense lines.

14. A touch sensor apparatus having a touch sensor panel, the apparatus adapted to normalize the effects of parasitic coupling in the touch sensor panel, the apparatus comprising:

a drive structure comprises one of a plurality of drive lines on the touch sensor panel, each drive line comprising a plurality of drive line conductive elements, the drive line conductive elements being coupled together by a plurality of connecting traces, the connecting traces extend parallel to a plurality of sense lines and disposed between the plurality of sense lines and the plurality of drive line conductive elements

one or more of the plurality of sense lines on the touch sensor panel, each sense line comprising at least one sense line conductive element, the plurality of sense lines being disposed transverse to the plurality of drive lines;

a first module adapted to stimulate a set of drive lines of the plurality of drive lines;

a second module adapted to sense at least one sense signal on at least one of the plurality of sense lines for each drive line stimulated; and

a third module adapted to correct the magnitude of the at least one sense 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; and

wherein the set of sensed signals is determined after positioning a conductive element proximate to a sensing portion of the touch sensor panel.

15. The apparatus of claim 14, wherein the set of correctional coefficients is adapted to correct for changes to parasitic capacitive coupling associated with one or more of the plurality of connecting traces.

16. The apparatus of claim 15, wherein the expected signal is set to be equal to a first sensed signal.

17. The apparatus of claim 16, wherein the first sensed signal is obtained from a shorter connecting trace than any other connecting trace in a group of conductive elements extending parallel to the sense lines.

18. The apparatus of claim 14, 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 connecting traces.

19. The apparatus of claim 18, wherein the expected signal is determined by interpolating a plurality of sensed signals from the set of sensed signals.

20. The apparatus of claim 18, wherein the expected signal is derived from a function adapted to fit a plurality of sensed signals from the set of sensed signals.

21. The apparatus of claim 20, wherein the function comprises a second-order fit polynomial function.

22. The apparatus of claim 20, wherein the function comprises a third-order fit polynomial function.

23. A mobile phone comprising a touch sensor panel, the mobile phone adapted to normalize the effects of parasitic coupling, the mobile phone comprising:

a drive structure comprises one of a plurality of drive lines on the touch sensor panel, each drive line comprising a plurality of drive line conductive elements, the drive line conductive elements being coupled together by a plurality of connecting traces, the connecting traces extend parallel to a plurality of sense lines and disposed between the plurality of sense lines and the plurality of drive line conductive elements

one or more of the plurality of sense lines on the touch sensor panel, each sense line comprising at least one sense line conductive element, the plurality of sense lines being disposed transverse to the plurality of drive lines;

a first module adapted to stimulate a set of drive lines of the plurality of drive lines;

a second module adapted to sense at least one sense signal on at least one of the plurality of sense lines for each drive lines stimulated; and

a third module adapted to correct the magnitude of 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 signal; and

wherein the set of sensed signals is determined after positioning a conductive element proximate to a sensing portion of the touch sensor panel.

24. A digital media player comprising a touch sensor panel, the digital media player adapted to normalize the effects of parasitic coupling, the digital media player comprising:

a drive structure comprises one of a plurality of drive lines on the touch sensor panel, each drive line comprising a plurality of drive line conductive elements, the drive line conductive elements being coupled together by a plurality of connecting traces, the connecting traces extend parallel to a plurality of sense lines and disposed between the plurality of sense lines and the plurality of drive line conductive elements

one or more of the plurality of sense lines on the touch sensor panel, each sense line comprising at least one sense line conductive element, the plurality of sense lines being disposed transverse to the plurality of drive lines;

a first module adapted to stimulate a set of drive lines of the plurality of drive lines;

a second module adapted to sense at least one sense signal on at least one of the plurality of sense lines for each drive lines stimulated; and

a third module adapted to correct the magnitude of 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; and

wherein the set of sensed signals is determined after positioning a conductive element proximate to a sensing portion of the touch sensor panel.

25. A personal computer comprising a touch sensor panel, the personal computer adapted to normalize the effects of parasitic coupling, the personal computer comprising:

a drive structure comprises one of a plurality of drive lines on the touch sensor panel, each drive line comprising a plurality of drive line conductive elements, the drive line conductive elements being coupled together by a plurality of connecting traces, the connecting traces extend parallel to a plurality of sense lines and disposed between the plurality of sense lines and the plurality of drive line conductive elements

one or more of the plurality of sense lines on the touch sensor panel, each sense line comprising at least one sense line conductive element, the plurality of sense lines being disposed transverse to the plurality of drive lines;

a first module adapted to stimulate a set of drive lines of the plurality of drive lines;

a second module adapted to sense at least one sense signal on at least one of the plurality of sense lines for each drive structure stimulated; and

a third module adapted to correct the magnitude of the at least one sense 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; and

wherein the set of sensed signals is determined after positioning a conductive element proximate to a sensing portion of the touch sensor panel.

28. 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,

wherein the set of previously sensed signals is determined by a process comprising;

completely covering the touch sensor panel with a conductive element;

stimulating a plurality of drive structures; and

sensing a signal for each drive structure stimulated.

29. The method of claim 28, wherein the conductive element comprises a conductive rubber sheet.

30. The method of claim 28, wherein the conductive element comprises an electrically active cover.

31. The method of claim 28, wherein the set of correctional coefficients is based at least in part upon an expected signal.

32. The method of claim 31, 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.

33. The method of claim 32, wherein the expected signal is set to be equal to a first signal from the set of previously sensed signals.

34. The method of claim 33, 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.

35. The method of claim 31, 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.

36. The method of claim 35, wherein the expected signal is determined from a function adapted to fit at least two signals from the set of previously sensed signals.

37. The method of claim 36, 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.

38. The method of claim 36, wherein the function comprises a polynomial function.

39. The method of claim 38, wherein the function comprises a polynomial function of an order smaller than the number of said at least two signals.

40. 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

wherein the set of previously sensed signals is determined by a process comprising;

completely covering a conductive element upon the touch sensor panel;

stimulating a plurality of drive structures; and

sensing a signal for each drive structure stimulated.

41. 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;

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; and

the expected signal is set to be equal to a first sensed signal; and

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.

42. 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;

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;

the expected signal is derived from a function adapted to fit a plurality of sensed signals from the set of sensed signals; and

the function comprises a third-order fit polynomial function.