NEGATIVE PIXEL COMPENSATION

• US 20090160787A1
• Filed: 12/21/2007
• Published: 06/25/2009
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hotelling, Steve Porter, Westerman, Wayne Carl
• Granted Patent: US 9,075,483 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/04186 Touch location disambiguation
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

Compensation of pixels that generate erroneous readings (so-called “negative pixels”), produced when multiple touch events are generated by the same poorly grounded object on a touch sensor panel is disclosed. To minimize negative pixels, a thicker cover material and/or a lower dielectric constant can be used. Alternatively, narrower drive and sense lines can be employed. To compensate for negative pixels, a predicted negative pixel value can be computed as an indicator of pixels that are likely to be distorted. The negative pixel value for any particular pixel can be computing by summing up the touch output values for pixels in the drive line of that pixel, summing up the touch output values for pixels in the sense line of that pixel, and then multiplying these two sums. The predicted negative pixel value is added to the measured touch output value for the pixel to compensate for artificially negative readings.

Claims

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

computing a predicted negative pixel value for pixels on the touch sensor panel; and

compensating the pixels by adding a scaled first function of the predicted negative pixel values to raw pixel touch output values.

2. The method of claim 1, further comprising computing the negative pixel value for a particular pixel by:

summing a second function of the touch output values for pixels in a drive line of the particular pixel to generate a first sum;

summing the second function of the touch output values for pixels in a sense line of the particular pixel to generate a second sum; and

multiplying the first sum and the second sum to generate the negative pixel value.

3. The method of claim 1, further comprising normalizing the negative pixel values by dividing the negative pixel values by a product of a total number of drive lines and a total number of sense lines in the touch sensor panel.

4. The method of claim 2, wherein the second function is linear for low touch output values and reduces to zero for high touch output values.

5. The method of claim 2, further comprising:

summing the second function of the touch output values only for those pixels in the drive line of the particular pixel having a touch output value above a predetermined threshold; and

summing the second function of the touch output values only for those pixels in the sense line of the particular pixel having a touch output value above the predetermined threshold.

6. The method of claim 1, further comprising compensating a particular pixel by adding a scaled function of the predicted negative pixel value for that pixel to a raw pixel touch output value for that pixel only if the raw pixel touch output value is greater than or equal to a predetermined threshold.

7. The method of claim 1, further comprising compensating for a negative pixel effect caused by two or more simultaneous touch events from a poorly grounded object.

8. The method of claim 1, further comprising compensating pixels only after determining that a poorly grounded user is likely present.

9. The method of claim 7, further comprising determining that a poorly grounded user is likely present by computing a ratio of pixels with positive touch output values to pixels with negative touch output values.

10. The method of claim 1, wherein the first function is linear for low touch output values and flattens for high touch output values.

11. An apparatus for compensating for a negative pixel effect, comprising:

a processor programmed for

computing a predicted negative pixel value for pixels on the touch sensor panel, and

compensating the pixels by adding a scaled first function of the predicted negative pixel values to raw pixel touch output values.

12. The apparatus of claim 11, the processor further programmed for computing the negative pixel value for a particular pixel by:

summing a second function of the touch output values for pixels in a drive line of the particular pixel to generate a first sum;

summing the second function of the touch output values for pixels in a sense line of the particular pixel to generate a second sum; and

multiplying the first sum and the second sum to generate the negative pixel value.

13. The apparatus of claim 11, the processor further programmed for normalizing the negative pixel values by dividing the negative pixel values by a product of a total number of drive lines and a total number of sense lines in the touch sensor panel.

14. The apparatus of claim 11, wherein the second function is linear for low touch output values and reduces to zero for high touch output values.

15. The apparatus of claim 12, the processor further programmed for:

summing the second function of the touch output values only for those pixels in the drive line of the particular pixel having a touch output value above a predetermined threshold; and

summing the second function of the touch output values only for those pixels in the sense line of the particular pixel having a touch output value above the predetermined threshold.

16. The apparatus of claim 11, the processor further programmed for compensating a particular pixel by adding a scaled function of the predicted negative pixel value for that pixel to a raw pixel touch output value for that pixel only if the raw pixel touch output value is greater than or equal to a predetermined threshold.

17. The apparatus of claim 11, the processor further programmed for compensating for a negative pixel effect caused by two or more simultaneous touch events from a poorly grounded object.

18. The apparatus of claim 11, the processor further programmed for compensating pixels only after determining that a poorly grounded user is likely present.

19. The apparatus of claim 17, the processor further programmed for determining that a poorly grounded user is likely present by computing a ratio of pixels with positive touch output values to pixels with negative touch output values.

20. The apparatus of claim 11, wherein the first function is linear for low touch output values and flattens for high touch output values.

21. A computing system comprising the apparatus of claim 11.

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

computing a predicted negative pixel value for pixels on the touch sensor panel; and

compensating the pixels by adding a scaled first function of the predicted negative pixel values to raw pixel touch output values.

23. The computer-readable medium of claim 22, the program code further for computing the negative pixel value for a particular pixel by:

summing a second function of the touch output values for pixels in a drive line of the particular pixel to generate a first sum;

summing the second function of the touch output values for pixels in a sense line of the particular pixel to generate a second sum; and

multiplying the first sum and the second sum to generate the negative pixel value.

24. The computer-readable medium of claim 22, the program code further for normalizing the negative pixel values by dividing the negative pixel values by a product of a total number of drive lines and a total number of sense lines in the touch sensor panel.

25. The computer-readable medium of claim 22, the program code further for compensating a particular pixel by adding a scaled function of the predicted negative pixel value for that pixel to a raw pixel touch output value for that pixel only if the raw pixel touch output value is greater than or equal to a predetermined threshold.

26. A mobile telephone including an apparatus for compensating for a negative pixel effect, the apparatus comprising:

a processor programmed for

computing a predicted negative pixel value for pixels on the touch sensor panel, and

compensating the pixels by adding a scaled first function of the predicted negative pixel values to raw pixel touch output values.

27. A digital audio player including an apparatus for compensating for a negative pixel effect, the apparatus comprising:

a processor programmed for

computing a predicted negative pixel value for pixels on the touch sensor panel, and

compensating the pixels by adding a scaled first function of the predicted negative pixel values to raw pixel touch output values.