CORRECTION OF PARASITIC CAPACITANCE EFFECT IN TOUCH SENSOR PANELS

• US 20100060608A1
• Filed: 09/10/2008
• Published: 03/11/2010
• Est. Priority Date: 09/10/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: YOUSEFPOR, Marduke
• Granted Patent: US 8,810,542 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• 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

Compensation of pixels included in a touch sensor panel that generate erroneous readings (so called “negative pixels”) due to a poor grounding condition of the object touching the touch sensor panel is disclosed herein. To compensate for the erroneous readings, sense lines of the touch sensor panel can include reverse driving circuits to facilitate calculation of an object-to-ground capacitance. If the calculated object-to-ground capacitance indicates the presence of a poor grounding condition, then the object-to-ground capacitance and detected pixel touch output values are used to estimate new pixel touch output values that are used instead of the detected pixel touch output values to determine touch event(s).

Claims

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

determining an object-to-ground capacitance associated with an object in contact with the touch sensor panel; and

calculating an actual pixel touch output value for each pixel of the touch sensor panel based on the object-to-ground capacitance and measured pixel touch output values when the object-to-ground capacitance is at or below a predetermined threshold.

2. The method of claim 1, wherein determining the object-to-ground capacitance comprises periodically determining the object-to-ground capacitance during normal sensing operation of the touch sensor panel.

3. The method of claim 1, further comprising calculating a successive actual pixel touch output value for each pixel of the touch sensor panel based on the object-to-ground capacitance and the actual pixel touch output value for each pixel.

4. The method of claim 3, wherein the successive actual pixel touch output value for each pixel is more accurate than the actual pixel touch output value for each pixel.

5. The method of claim 1, wherein the touch sensor panel is incorporated within a computing system.

6. An apparatus for compensating for negative pixel effects on a touch sensor panel, comprising:

a first stimulation signal source coupled to each of a plurality of drive lines having a first orientation on the touch sensor panel, the first stimulation signal sources configured for being activated to generate first measured pixel touch output values;

a sense amplifier coupled to each of a plurality of sense lines having a second orientation different from the first orientation on the touch sensor panel, the sense amplifier including a second stimulation signal source coupled to an input of the sense amplifier, the second stimulation signal sources configured for being activated to generate second measured pixel touch output values; and

a panel processor configured for calculating actual pixel touch output values from iterative use of the first measured pixel touch output values and an object-to-ground capacitance.

7. The apparatus of claim 6, wherein the first stimulation signal sources are configured for being simultaneously activated to generate the first measured pixel touch output values.

8. The apparatus of claim 6, wherein the second stimulation signal sources are configured for being simultaneously activated to generate the second measured pixel touch output values.

9. The apparatus of claim 6, wherein the panel processor is configured for calculating the object-to-ground capacitance associated with an object in contact with the touch sensor panel based on the first measured pixel touch output values, second measured pixel touch output values, an average mutual capacitance, and a feedback capacitance associated with the sense amplifiers.

10. The apparatus of claim 9, wherein the panel processor is configured to calculate the object-to-ground capacitance periodically during normal operation of the touch sensor panel.

11. The apparatus of claim 6, wherein the second stimulation signal sources provide a reverse stimulation signal to the sense lines.

12. The apparatus of claim 6, wherein the touch sensor panel is incorporated in a computing system.

13. A system for compensating for negative pixel effects on a touch sensor panel, comprising:

a touch sensor panel having a plurality of drive lines and a plurality of sense lines;

a panel subsystem coupled to the touch sensor panel, the panel subsystem including

driver logic coupled to the drive lines of the touch sensor panel, the driver logic configured for generating first stimulation signals, and

sense channels coupled to the sense lines of the touch sensor panel, each sense channel including a sense amplifier having a second stimulation signal source coupled to an input of the sense amplifier, the sense channels configured for generating first measured pixel touch output values in response to the first stimulation signals from the driver logic and generating second measured pixel touch output values in response to second stimulation signals from the second stimulation signal sources; and

a panel processor coupled to the panel subsystem and configured for calculating an object-to-ground capacitance associated with an object in contact with the touch sensor panel.

14. The system of claim 13, wherein the driver logic is configured to simultaneously provide the first stimulation signals to the plurality of drive lines.

15. The system of claim 13, wherein the panel processor is configured for calculating a first precursor value to the object-to-ground capacitance based on the first stimulation signals, first measured pixel touch output values, and a feedback capacitance associated with the sense amplifiers.

16. The system of claim 13, wherein second stimulation signal source are configured to simultaneously provide the second stimulation signals to the plurality of sense lines.

17. The system of claim 13, wherein the panel processor is configured for calculating a second precursor value to the object-to-ground capacitance based on the second stimulation signals, second measured pixel touch output values, and a feedback capacitance associated with the sense amplifiers.

18. The system of claim 17, wherein the second precursor value is further based on a panel lumped parasitic capacitance for the sense lines.

19. The system of claim 18, wherein the panel processor is configured for calculating the panel lumped parasitic capacitance for the sense lines during calibration of the touch sensor panel.

20. The system of claim 18, wherein the panel processor is configured for calculating the panel lumped parasitic capacitance for the sense lines based on the first stimulation signals, first measured pixel touch output values, second simulation signals, second measured pixel touch output values, and the feedback capacitance.

21. The system of claim 13, wherein the panel processor is configured for calculating actual pixel touch output values from iterative use of the first measured pixel touch output values and the object-to-ground capacitance.

22. A computer-readable medium comprising program code for compensating for negative pixel effects on a touch sensor panel, the program code for causing performance of a method comprising:

periodically determine existence of a poor grounding condition associated with an object in contact with the touch sensor panel; and

if the poor grounding condition exists, iteratively calculate actual reduction in charge coupling associated with the object in contact with the touch sensor panel for each pixel using detected reduction in charge coupling for each pixel from sense amplifiers coupled to sense lines and a ground capacitance indicative of the poor grounding condition.

23. The computer-readable medium of claim 22, the program code further for providing an actual pixel touch output value for each pixel based on the calculated actual reduction in charge coupling for each pixel and a mutual capacitance associated with each pixel prior to the object being in contact with the touch sensor panel.

24. The computer-readable medium of claim 22, the program code further for providing that after first iteration of calculated actual reduction in charge coupling for each pixel, the immediately previous calculated actual reduction in charge coupling and the ground capacitance are used to calculate subsequent iterations of the actual reduction in charge coupling for each pixel.

25. The computer-readable medium of claim 22, the program code further for determining convergence of the calculated actual reduction in charge coupling to an immediately preceding calculated actual reduction in charge coupling.

26. The computer-readable medium of claim 22, wherein the touch sensor panel and the computer-readable medium are incorporated in a computing system.

27. A mobile telephone including a touch sensor panel and configured to provide negative pixel compensation to the touch sensor panel, comprising:

a first stimulation signal source coupled to each of a plurality of drive lines having a first orientation on the touch sensor panel, the first stimulation signal sources configured for being activated to generate first measured pixel touch output values;

a sense amplifier coupled to each of a plurality of sense lines having a second orientation different from the first orientation on the touch sensor panel, the sense amplifier including a second stimulation signal source coupled to an input of the sense amplifier, the second stimulation signal sources configured for being activated to generate second measured pixel touch output values; and

a panel processor configured for calculating actual pixel touch output values from iterative use of the first measured pixel touch output values and an object-to-ground capacitance.

28. A media player including a touch sensor panel and configured to provide negative pixel compensation to a touch sensor panel, comprising:

the touch sensor panel having a plurality of drive lines and a plurality of sense lines;

a panel subsystem coupled to the touch sensor panel, the panel subsystem including

driver logic coupled to the drive lines of the touch sensor panel, the driver logic configured for generating first stimulation signals, and

sense channels coupled to the sense lines of the touch sensor panel, each sense channel including a sense amplifier having a second stimulation signal source coupled to an input of the sense amplifier, the sense channels configured for generating first measured pixel touch output values in response to the first stimulation signals from the driver logic and generating second measured pixel touch output values in response to second stimulation signals from the second stimulation signal sources; and

a panel processor coupled to the panel subsystem and configured for calculating an object-to-ground capacitance associated with an object in contact with the touch sensor panel.

29. A computing system including a touch sensor panel and configured to provide negative pixel compensation to the touch sensor panel, comprising:

a first stimulation signal source coupled to each of a plurality of drive lines having a first orientation on the touch sensor panel, the first stimulation signal sources configured for being activated to generate first measured pixel touch output values;

a sense amplifier coupled to each of a plurality of sense lines having a second orientation different from the first orientation on the touch sensor panel, the sense amplifier including a second stimulation signal source coupled to an input of the sense amplifier, the second stimulation signal sources configured for being activated to generate second measured pixel touch output values; and

a panel processor configured for calculating actual pixel touch output values from iterative use of the first measured pixel touch output values and an object-to-ground capacitance.

30. The computing system of claim 29, wherein the touch sensor panel comprises at least one of a trackpad, a touch screen, and a touch input surface device.