Correction of Parasitic Capacitance Effect in Touch Sensor Panels

• US 20100073301A1
• Filed: 09/19/2008
• Published: 03/25/2010
• Est. Priority Date: 09/19/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: O'Connor, Sean, Yousefpor, Marduke, Westerman, Wayne
• Granted Patent: US 8,692,776 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/04186 Touch location disambiguation
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• 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

Abstract

Embodiments of the invention relate to correction of erroneous touch data on a touch sensor panel. Erroneous touch data may occur when a user is touching locations on the touch sensor panel but fails to be in good contact with another part of the device including the touch sensor panel. These erroneous readings may be statistically compensated for. A capacitance value that combines various external capacitances that may cause erroneous results can be calculated. Then, if necessary, received touch data can be modified to take into account the external capacitance. Accordingly, improved accuracy is provided for determining touch event(s) on a touch sensor panel.

Claims

1. A method for compensating for negative pixel effects on a touch sensor panel of a device, including:

measuring a plurality of pixel touch values;

calculating a ground capacitance associated with the device and an object in contact with the touch sensor panel, said calculating being performed without the use of any electronic elements in the device that are primarily used for detecting the ground capacitance or for providing stimulation signals for detection of the ground capacitance; and

calculating a plurality of corrected pixel touch values for respective pixels of the touch sensor panel based on the ground capacitance and measured pixel touch values.

2. The method of claim 1, wherein calculating the ground capacitance includes periodically calculating the ground capacitance during normal sensing operation of the touch sensor panel.

3. The method of claim 1, wherein calculating the plurality of corrected pixel touch values includes solving a generalized Sylvester equation.

4. The method of claim 3, wherein the solving of the generalized Sylvester equation includes solving the equation by iteration.

5. The method of claim 1, wherein the calculating of the ground capacitance includes:

providing an initial value for the ground capacitance;

calculating the plurality of corrected pixel touch values based on the initial value;

checking the accuracy of the calculation;

if the accuracy check is unsatisfactory, performing multiple iterations of choosing a new value for the ground capacitance and re-calculating the plurality of corrected pixel touch values and checking the accuracy of the re-calculation for the new value until the accuracy check is satisfactory; and

if the accuracy check is satisfactory, providing the last chosen value for the ground capacitance as the calculated ground capacitance value.

6. The method of claim 5, wherein the initial ground capacitance value is predefined at the device.

7. The method of claim 5, wherein the accuracy checking includes calculating an error value associated with the ground capacitance value being used during a particular iteration of the accuracy checking and comparing the error value to a predefined error threshold.

8. The method of claim 7, wherein the error value is based on negative values of the plurality of corrected pixel touch values.

9. The method of claim 7, further including providing a graph of the correlation of ground capacitance values and expected error values, wherein the new values for the ground capacitance are obtained based on the graph.

10. The method of claim 9, wherein the new values for the ground capacitance are obtained based on curve fitting ground capacitance values that have been tried in previous iterations of re-calculating the plurality of corrected pixel touch values and checking the accuracy of the re-calculation and their respective error rates to the graph.

11. A method for compensating for negative pixel effects on a touch sensor panel of a device, including:

measuring a plurality of pixel touch values;

providing a ground capacitance associated with the device and an object in contact with the touch sensor panel; and

calculating a plurality of corrected pixel touch values for respective pixels of the touch sensor panel based on the provided ground capacitance and measured pixel touch values;

examining the plurality of measured pixel touch values for patterns that are known to result from errors due to negative pixel effects; and

using the corrected pixel touch values to determine touch events only if patterns known to result in errors are found.

12. The method of claim 11, wherein the ground capacitance is predefined at the device and is obtained based on experimentation.

13. The method of claim 11, wherein calculating the plurality of corrected pixel touch values includes solving a generalized Sylvester equation.

14. The method of claim 13, wherein the solving of the generalized Sylvester equation includes solving the equation by iteration.

15. The method of claim 11, wherein the examining further includes:

performing segmentation on the measured pixel touch values to obtain a plurality of touch patches; and

checking the touch patches for any suspicious patterns that may be the result of negative pixels.

16. The method of claim 15, wherein the examining further includes:

if the checking of the touch patches results in suspicious patterns, determining one or more suspicious areas associated with the suspicious patterns;

using a subset of the measured pixel touch values and a subset of the corrected pixel touch values, both subsets being associated with the suspicious areas, to determine whether errors due to negative pixel effects have occurred.

17. The method of claim 16, wherein using the corrected pixel touch values to determine touch input includes:

upon determination that errors due to negative pixel effects have occurred, correcting one or more objects of the plurality of touch patches, said one or more objects being in or in proximity to the suspicious areas, resulting in one or more corrected touch patches; and

using the corrected touch patches to determine touch patches.

18. The method of claim 17, wherein the corrected pixel touch values are not used in pixel weighted measurements, other than their use to determine whether errors have occurred.

19. A device including a touch sensor panel, a processor and a memory, the memory including instructions configured to cause the processor to perform a method for compensating for negative pixel effects on the touch sensor panel, the method including:

measuring a plurality of pixel touch values;

calculating a ground capacitance associated with the device and an object in contact with the touch sensor panel, said calculating being performed without the use of any electronic elements in the device that are primarily used for detecting the ground capacitance or for providing stimulation signals for detection of the ground capacitance; and

calculating a plurality of corrected pixel touch values for respective pixels of the touch sensor panel based on the ground capacitance and measured pixel touch values.

20. The device of claim 19, wherein calculating the ground capacitance includes periodically calculating the ground capacitance during normal sensing operation of the touch sensor panel.

21. The device of claim 19, wherein calculating the plurality of corrected pixel touch values includes solving a generalized Sylvester equation.

22. The device of claim 21, wherein the solving of the generalized Sylvester equation includes solving the equation by iteration.

23. The device of claim 19, wherein the calculating of the ground capacitance includes:

providing an initial value for the ground capacitance;

calculating the plurality of corrected pixel touch values based on the initial value;

checking the accuracy of the calculation;

if the accuracy check is unsatisfactory, performing multiple iterations of choosing a new value for the ground capacitance and re-calculating the plurality of corrected pixel touch values and checking the accuracy of the re-calculation for the new value until the accuracy check is satisfactory; and

if the accuracy check is satisfactory, providing the last chosen value for the ground capacitance as the calculated ground capacitance value.

24. The device of claim 23, wherein the initial ground capacitance value is predefined at the device.

25. The device of claim 23, wherein the checking includes calculating an error value associated with the ground capacitance value being used during a particular iteration of the checking and comparing the error value to a predefined error threshold.

26. A portable music player including a touch sensor panel, a processor and a memory, the memory including instructions configured to cause the processor to perform a method for compensating for negative pixel effects on the touch sensor panel, the method including:

measuring a plurality of measured pixel touch values;

calculating a ground capacitance associated with the device and an object in contact with the touch sensor panel, said calculating being performed without the use of any electronic elements in the device that are primarily used for detecting the ground capacitance or for providing stimulation signals for detection of the ground capacitance; and

calculating a plurality of corrected pixel touch values for respective pixels of the touch sensor panel based on the ground capacitance and measured pixel touch values.

27. A mobile telephone including a touch sensor panel, a processor and a memory, the memory including instructions configured to cause the processor to perform a method for compensating for negative pixel effects on the touch sensor panel, the method including:

measuring a plurality of measured pixel touch values;

calculating a ground capacitance associated with the device and an object in contact with the touch sensor panel, said calculating being performed without the use of any electronic elements in the device that are primarily used for detecting the ground capacitance or for providing stimulation signals for detection of the ground capacitance; and

calculating a plurality of corrected pixel touch values for respective pixels of the touch sensor panel based on the ground capacitance and measured pixel touch values.

28. A device including a touch sensor panel, a processor and a memory, the memory including instructions configured to cause the processor to perform a method for compensating for negative pixel effects on the touch sensor panel, the method including:

measuring a plurality of pixel touch values;

providing a ground capacitance associated with the device and an object in contact with the touch sensor panel; and

calculating a plurality of corrected pixel touch values for respective pixels of the touch sensor panel based on the provided ground capacitance and measured pixel touch values;

examining the plurality of measured pixel touch values for patterns that are known to result from errors due to negative pixel effects; and

using the corrected pixel touch values to determine touch events only if patterns known to result in errors are found.

29. The device of claim 28, wherein the examining further includes:

performing segmentation on the measured pixel touch values to obtain a plurality of touch patches; and

checking the touch patches for any patterns that may be the result of negative pixels.

30. The device of claim 29, wherein the examining further includes:

if the checking of the touch patches results in suspicious patterns, determining one or more suspicious areas associated with the suspicious patterns;

using a subset of the measured pixel touch values and a subset of the corrected pixel touch values, both subsets being associated with the suspicious areas, to determine whether errors due to negative pixel effects have occurred.

31. The device of claim 30, wherein using the corrected pixel touch values to determine touch input includes:

upon determination that errors due to negative pixel effects have occurred, correcting one or more objects of the plurality of touch patches, said one or more objects being in or in proximity to the suspicious areas, resulting in one or more corrected touch patches; and

using the corrected touch patches to determine touch events.

32. The device of claim 31, wherein the corrected pixel touch values are not used in pixel weighted measurements, other than their use to determine whether errors have occurred.

33. A computer readable medium comprising a plurality of computer executable instructions, the instructions being configured to cause a processor to perform a method for compensating for negative pixel effects on a touch sensor panel of a device, the method including:

measuring a plurality of measured pixel touch values;

calculating a ground capacitance associated with the device and an object in contact with the touch sensor panel, said calculating being performed without the use of any electronic elements in the device that are primarily used for detecting the ground capacitance or for providing stimulation signals for detection of the ground capacitance; and

calculating a plurality of corrected pixel touch values for respective pixels of the touch sensor panel based on the ground capacitance and measured pixel touch values.

34. A computer readable medium comprising a plurality of computer executable instructions, the instructions being configured to cause a processor to perform a method for compensating for negative pixel effects on a touch sensor panel of a device, the method including:

measuring a plurality of pixel touch values;

providing a ground capacitance associated with the device and an object in contact with the touch sensor panel; and

calculating a plurality of corrected pixel touch values for respective pixels of the touch sensor panel based on the provided ground capacitance and measured pixel touch values;

examining the plurality of measured pixel touch values for patterns that are known to result from errors due to negative pixel effects; and

using the corrected pixel touch values to determine touch events only if patterns known to result in errors are found.