Touch sensor panel using dummy ground conductors

• US 8,614,690 B2
• Filed: 09/26/2008
• Issued: 12/24/2013
• Est. Priority Date: 09/26/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Grunthaner, Martin Paul, Hotelling, Steve Porter
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Lubit, Ryan A
• Application Number:
  US12/239,622
• Publication Number:
  US 20100079402A1
• Time in Patent Office: 1,915 Days
• Field of Search: 345173-178, 178 1801- 2004, 324658-690
• US Class Current: 345/174
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

Methods and apparatus for correcting electrical noise coupling from a liquid crystal module to a plurality of sense elements disposed within a touch sensor panel, and for reducing errors in touch detection algorithms. Erroneous signal values detected by the sense elements may be corrected by utilizing a set of reference elements for detecting noise common to both the sense elements and the reference elements, and a correction module for effectively subtracting out the noise from the sensed values. Errors in touch detection algorithms may be reduced by providing a more uniform spacing between successive sense elements. In some embodiments, one or more dummy ground elements may be inserted between adjacent sense elements in order to reduce signal interference.

Claims

1. A touch sensor panel adapted to compensate for received electromagnetic noise, the touch sensor panel comprising:

a plurality of drive elements;

a plurality of sense elements disposed adjacent and corresponding to the plurality of drive elements and adapted to capacitively couple to the plurality of drive elements and detect touch events;

a plurality of reference elements, each reference element being in proximity to at least one sense element, the reference elements adapted for capacitively coupling electromagnetic noise and providing reference output signals;

a plurality of dummy ground conductors adapted to provide substantially uniform spacing between sense elements across the touch sensor panel, each reference element being positioned between two dummy ground conductors; and

at least one correction module adapted to correct for noise in the detected touch events based at least in part upon the reference output signals.

2. The touch sensor panel of claim 1, wherein each reference element is dedicated to one or more sense elements.

3. The touch sensor panel of claim 2, wherein each reference element comprises an area that is a fraction of an area of the sense element.

4. The touch sensor panel of claim 1 further comprising at least one scaling module connected to at least one respective reference element, and wherein the at least one scaling module is adapted to scale an output from the respective reference element.

5. The touch sensor panel of claim 4, wherein at least some of the plurality of sense elements are arranged in sense columns having reference elements and the at least one scaling module is adapted to scale an output of the at least one sense column.

6. The touch sensor panel of claim 1, wherein each reference element is situated between adjacent sense elements.

7. The touch sensor panel of claim 1, wherein each reference element is commonly routed.

8. The touch sensor panel of claim 1, wherein each reference element comprises an area that is a fraction of an area of the sense element.

9. The touch sensor panel of claim 1 further comprising a set of scaling modules, wherein each scaling module of the set is connected to at least one respective reference element, and wherein each scaling module is adapted to scale an output from the respective reference element.

10. The touch sensor panel of claim 9, wherein at least some of the scaling modules are adapted to scale the output from the respective reference element based at least in part upon a size of a sense element relative to a size of a reference element.

11. The touch sensor panel of claim 1, wherein the touch sensor panel has the plurality of touch sensing elements disposed in either a plurality of rows or a plurality of columns wherein each of the plurality of rows or the plurality of columns of the touch sensing elements traverses the touch sensor panel for measuring touch along the ones of the plurality of rows or the plurality of columns.

12. The touch sensor panel of claim 1, wherein the electromagnetic noise comprises common mode noise generated by a liquid crystal display module.

13. The touch sensor panel of claim 1, wherein the drive elements and the sense elements together form drive-sense elements having centers of touch sensitivity that are evenly spaced.

14. A method of compensating for common mode noise in a touch sensor panel comprising a plurality of sense elements, the method comprising:

providing a plurality of drive elements;

providing a plurality of sense elements disposed adjacent and corresponding to the plurality of drive elements;

providing a plurality of reference elements in a touch sensor panel, the reference elements adapted for sensing the common mode noise;

providing a plurality of dummy ground conductors adapted to provide substantially uniform spacing between sense elements across the touch sensor panel, each reference element being positioned between two dummy ground conductors;

detecting a set of signals from the plurality of sense elements;

detecting a set of signals from the plurality of reference elements; and

correcting the set of signals from the plurality of sense elements based at least in part on the detected set of signals from the plurality of reference elements.

15. The method of claim 14, wherein the number of reference elements provided is smaller than the number of sense elements disposed within the touch sensor panel.

16. The method of claim 14, wherein correcting the set of signals from the plurality of sense elements based on the detected set of signals from the plurality of reference elements comprises reducing the value of the sensed touch signal by a correction value.

17. The method of claim 14, wherein each of the reference elements is positioned such that the amount of capacitive coupling between a reference element and an associated drive element is smaller than the amount of capacitive coupling between an associated sense element and the associated drive element.

18. The method of claim 14, wherein at least some of the plurality of sense elements are arranged in sense columns having reference elements and the at least one scaling module is adapted to scale an output of the at least one sense column.

19. The method of claim 18, wherein the plurality of sense elements are disposed in either a plurality of rows or a plurality of columns wherein each of the plurality of rows or the plurality of columns of the sense elements traverses the touch sensor panel for measuring touch along the ones of the plurality of rows or the plurality of columns.

20. The method of claim 14, wherein the drive elements and the sense elements together form drive-sense elements having centers of touch sensitivity that are evenly spaced using one or more dummy ground conductors between adjacent sense elements.

21. An electronic device including a touch sensor panel adapted to compensate for received electromagnetic noise, the touch sensor panel comprising:

a plurality of drive elements;

a plurality of sense elements in proximity to one or more of the plurality of drive elements and adapted to capacitively couple to one or more of the drive elements and detect touch events;

a plurality of reference elements, each reference element being in proximity to at least one sense element, the reference elements adapted for capacitively coupling electromagnetic noise and providing reference output signals;

a plurality of dummy ground conductors adapted to provide substantially uniform spacing between sense elements across the touch sensor panel, each reference element being positioned between two dummy ground conductors; and

at least one correction module adapted to correct for noise in the detected touch events based at least in part upon the reference output signals.

22. The electronic device of claim 21, wherein the touch sensor panel is incorporated into a mobile telephone or a digital media player.

23. A personal computer comprising:

a panel subsystem comprising;

sense channels;

driver logic; and

a touch sensor panel;

wherein the touch sensor panel comprises;

a plurality of drive elements;

a plurality of sense elements in proximity to one or more of the plurality of drive elements and adapted to capacitively couple to one or more of the drive elements and detect touch events;

a plurality of reference elements, each reference element being in proximity to at least one sense element, the reference elements adapted for capacitively coupling electromagnetic noise and providing reference output signals;

a plurality of dummy ground conductors adapted to provide substantially uniform spacing between sense elements across the touch sensor panel, each reference element being positioned between two dummy ground conductors; and

at least one correction module adapted to correct for noise in the detected touch events based at least in part upon the reference output signals; and

the sense channels adapted to receive outputs from the plurality of sense elements and the driver logic adapted to provide drive signals to the plurality of drive elements.