Negative pixel compensation

• US 8,482,544 B2
• Filed: 07/10/2009
• Issued: 07/09/2013
• Est. Priority Date: 07/10/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Land, Brian Richards, Yousefpor, Marduke, Hotelling, Steven Porter
• Primary Examiner(s): Mengistu, Amare
• Assistant Examiner(s): ZUBAJLO, JENNIFER L
• Application Number:
  US12/500,870
• Publication Number:
  US 20110006832A1
• Time in Patent Office: 1,460 Days
• Field of Search: 345/173, 345/174, 178/18.01, 178/18.03, 178/18.06
• 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 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/044 by capacitive means
• 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

Negative pixel compensation in a touch sensitive device is disclosed. The device can compensate for a negative pixel effect in touch signal outputs due to poor grounding of an object touching the device. To do so, the device can switch to a configuration to measure the grounding condition of the touching object and use the measurement to compensate the touch output values from the device accordingly. In the switched configuration, a first set of lines of the device can be switched between a coupling to a stimulation signal input to drive the device, a coupling to a capacitance signal output to output a signal indicative of the object'"'"'s grounding condition, and a coupling to ground. A second set of lines of the device can be coupled to a touch signal output to output a signal indicative of the object'"'"'s touch at the device. In addition or alternatively, in the switched configuration, the first set of lines of the device can be switched to function as the second set of lines and vice versa. The grounding signal can be applied to the touch signal to compensate for the negative pixel effect.

Claims

1. A circuit comprising:

multiple first lines, each first line configured to be switchable;

multiple second lines configured to associate with the first lines;

switching circuitry coupled to at least the first lines and configured to operate the circuit in a configuration for measuring a grounding condition of an object proximate to the circuit by switching at least one of the first lines to transmit a stimulation signal and at least another of the first lines to sense a capacitance signal indicative of the grounding condition of the object; and

a processing unit configured to compensate a touch signal based on a compensation factor, wherein the compensation factor is a function of the measured grounding condition and a mutual capacitance of the first lines that transmit a stimulation signal to a plurality of sense lines.

2. The circuit of claim 1, wherein the configuration includes the switching circuitry coupling the remaining first lines to ground.

3. The circuit of claim 1, wherein the configuration includes the switching circuitry coupled to the second lines, the switching circuitry switching the second lines to function as the first lines and the first lines to function as the second lines.

4. The circuit of claim 1, wherein the configuration includes the switching circuitry coupled to the second lines, the switching circuitry coupling the second lines to ground.

5. The circuit of claim 1, wherein the switching circuitry is configured to switch the first lines between multiple couplings, the multiple couplings including at least one of a coupling to stimulation signal input circuitry, a coupling to capacitive signal output circuitry, or a coupling to ground.

6. The circuit of claim 1, wherein the switching circuitry is coupled to the second lines and configured to switch the second lines between multiple couplings, the multiple couplings including at least one of a coupling to touch sensing circuitry or a coupling to ground.

7. The circuit of claim 1, wherein the configuration is further for measuring a touch of the object at the circuit by switching at least a third of the first lines to couple to ground and by at least one of the second lines transmitting a touch signal indicative of the touch of the object at the circuit.

8. The circuit of claim 1, wherein the first lines comprise drive lines and the second lines comprise sense lines.

9. The circuit of claim 1 incorporated into at least one of a mobile telephone, a digital media player, or a personal computer.

10. A circuit comprising:

multiple first lines, at least one of the first lines being configured to drive the circuit with a stimulation signal and at least one other first line being configured to sense a first capacitance between an object proximate to the circuit and ground;

multiple second lines associated with to the first lines to form pixels and configured to sense a second capacitance at the pixels indicative of a touch by the object; and

a processor programmable for compensating the second capacitance with the first capacitance based on a grounding condition of the object;

wherein a compensation factor is a function of the measured grounding condition and a mutual capacitance of the multiple first lines that transmit a stimulation signal to a plurality of sense lines.

11. The circuit of claim 10, wherein the first lines are numbered, the first line configured to drive the circuit has a first number, and the first lines configured to sense the first capacitance are even numbered first lines lower than the first number and odd numbered first lines higher than the first number.

12. The circuit of claim 10, wherein the first lines configured to sense the first capacitance are the first lines disposed on the circuit below the first line configured to drive the circuit.

13. The circuit of claim 10, wherein the first lines configured to sense the first capacitance are the first lines disposed on the circuit above the first line configured to drive the circuit.

14. A method comprising:

configuring at least one drive line of a touch sensitive device having multiple drive and sense lines to receive a stimulation signal;

configuring at least one other drive line to sense a grounding condition of an object touching the device; and

compensating sense signals detected on one or more sense lines based on the sensed grounding condition;

wherein a compensation factor is a function of the measured grounding condition and a mutual capacitance of the multiple first lines that transmit a stimulation signal to a plurality of sense lines.

15. The method of claim 14, comprising:

configuring at least a third drive line to couple to ground.

16. The method of claim 14, wherein compensating the sense signals comprises calculating a ratio between a signal indicative of the sensed grounding condition and an estimate based on at least one sense signal of the grounding condition.

17. The method of claim 16, wherein compensating the sense signals comprises determining a the compensation factor is based on the calculated ratio.

18. The method of claim 17, wherein compensating the sense signals comprises:

calculating a compensation touch value based on the compensation factor; and

subtracting the compensation touch value from the sense signals.

19. A touch sensor panel comprising:

multiple drive lines, at least one of the drive lines being switchably configured to receive a stimulation signal to drive the panel, a group of other drive lines being switchably configured to measure a proximate object capacitance generated by the driving of the stimulation signal, the measured capacitance indicative of a grounding condition of the object;

multiple sense lines configured to associate with the drive lines and transmit touch signals indicative of a touch by the object at the panel; and

switching circuitry coupled to the drive lines and configured to switch the drive lines; and

a processor configured to compensate the touch signals with the measured capacitance;

wherein the measured capacitance is used in determining a compensation factor that is a function of the measured capacitance and a mutual capacitance of the multiple drive lines that transmit a stimulation signal to the multiple sense lines.

20. The panel of claim 19, comprising multiple pixels formed by crossings of the drive lines and the sense lines, the pixels being configured to receive the touch by the object, the receiving touch comprising multiple simultaneous touches by the object, and the touch signals comprising touch information to be compensated for by the measured capacitance.

21. A touch sensitive device comprising:

a touch sensor panel configured to sense an object proximate thereto and switchable to have at least one drive line of the of the panel coupled to a stimulation signal supply to drive the panel, at least another of the drive lines of the panel coupled to a sensor to sense the object grounding, and at least one sensor line of the panel coupled to a sensor to sense the object touch concurrently with the object grounding;

scan logic couplable to the touch sensor panel and configured to perform a scan sequence on the panel to measure a touch by the object at the panel and to measure grounding of the object; and

a processor configured to compensate touch measurements according to grounding measurements;

wherein the grounding measurements are used in determining a compensation factor that is a function of the measured capacitance and a mutual capacitance of the multiple drive lines that transmit a stimulation signal to the multiple sense lines.

22. The device of claim 21, wherein the device measures the touch and the grounding concurrently, the touch sensor panel switching to a configuration comprising at least one drive line of the panel coupled to a stimulation signal supply to drive the panel, at least another of the drive lines of the panel coupled to a sensor to sense the object grounding, and at least one sense line of the panel coupled to a sensor to sense the object touch.

23. The device of claim 21, wherein the touch sensor panel switches between a first configuration to measure the touch and a second configuration to measure the grounding, the first configuration comprising at least one drive line of the panel coupled to a stimulation signal supply to drive the panel, at least another of the drive lines of the panel coupled to ground, and at least one sense line of the panel coupled to a sensor to sense the object touch, and the second configuration comprising at least one drive line of the panel coupled to the stimulation signal supply to drive the panel and at least another of the drive lines of the panel coupled to a sensor to sense the object grounding.

24. The device of claim 21, wherein the scan sequence comprises a first scan to measure the touch and a second scan to measure the grounding.