Negative pixel compensation

• US 8,570,301 B2
• Filed: 09/30/2011
• Issued: 10/29/2013
• 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:
  US13/251,049
• Publication Number:
  US 20120081335A1
• Time in Patent Office: 760 Days
• Field of Search: 345/173, 345/174
• 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 to compensate for a negative pixel effect in touch signal outputs due to poor grounding of an object touching the device is disclosed. 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. 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. The grounding signal can be applied to the touch signal to compensate for the negative pixel effect.

Claims

1. A circuit comprising:

compensation circuitry couplable to a plurality of drive lines in a touch sensor panel, wherein the drive lines are capable of being switched between being coupled to the compensation circuitry and being coupled to a stimulation circuit of the touch sensor panel, the compensation circuitry being capable of;

receiving a capacitance signal transmitted by at least one of the drive lines; and

compensating a touch signal by computing a compensation factor from the capacitance signal and applying the compensation factor to captured touch data.

2. The circuit of claim 1, wherein the compensation circuitry can couple at least one drive line of the plurality of drive lines to ground.

3. The circuit of claim 1, wherein the compensation circuitry is further for measuring a touch of the object at the circuit by switching at least a third of the drive lines to couple to ground.

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

5. The circuit of claim 1, wherein the compensation circuitry is capable of switching at least one drive line to act as an auxiliary sense line.

6. 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 lines being configured to receive a first capacitance between an object proximate to the circuit and ground wherein the first lines also include switching circuitry capable of switching each of the first lines into a configuration to drive the circuit with a stimulation signal, and switching each of the first lines into a configuration to receive the first capacitance;

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 by calculating a compensation factor based on a grounding condition of the object and adjusting the second capacitance using the compensation factor.

7. The circuit of claim 6, 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.

8. The circuit of claim 6, 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.

9. The circuit of claim 6, 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.

10. A method comprising:

switching one or more drive lines of a touch sensitive device to be coupled to a stimulation circuit and switching one or more drive lines of the touch sensitive device to be coupled to a compensation circuit, wherein each drive line can be selectively switched between being coupled to a stimulation circuit and being coupled to a compensation circuit;

transmitting a stimulation signal to at least one drive line that has been coupled to a stimulation circuit of the touch sensitive device having multiple drive and sense lines;

receiving a capacitance signal from the at least one drive line that has been coupled to a compensation circuit and sensing a grounding condition of an object touching a touch sensitive device with at least one other drive line; and

compensating sense signals detected on one or more of the sense lines based on the sensed grounding condition by calculating a ratio between a signal indicative of the sensed grounding condition and an estimate based on at least one sense signal.

11. The method of claim 10, further comprising configuring at least a third drive line to couple to ground.

12. The method of claim 10, wherein compensating the sense signals comprises determining a compensation factor based on the calculated ratio.

13. The method of claim 12, 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.

14. A touch sensitive device comprising:

a touch sensor panel configured to sense an object proximate thereto;

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, by receiving a capacitance signal on at least one of the plurality of drive lines transmitted by at least another one of the plurality of drive lines, wherein the plurality of drive lines can be switchably configured to receive a capacitance signal and to transmit a capacitance signal; and

a processor configured to compensate touch measurements by calculating a compensation factor based on the measured touch by the object and the measured grounding of the object.

15. The device of claim 14, 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.

16. The device of claim 14, 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.

17. The device of claim 14, wherein the scan sequence comprises a first scan to measure the touch and a second scan to measure the grounding.