Self capacitance implementation method

• US 9,377,907 B2
• Filed: 09/21/2012
• Issued: 06/28/2016
• Est. Priority Date: 09/21/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Shahparnia, Shahrooz
• Primary Examiner(s): Sitta, Grant
• Assistant Examiner(s): BOGALE, AMEN W
• Application Number:
  US13/624,718
• Publication Number:
  US 20140085246A1
• Time in Patent Office: 1,376 Days
• Field of Search: 345/173, 345/174, 331/177.R, 331/179
• US Class Current: 1/1
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• 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

Abstract

A circuit for detecting a touch or proximity event on a touch input device is provided. The circuit is able to mitigate the effects that parasitic capacitance has on a self-capacitance touch sensor panel by injecting a signal into the sensing circuitry. The signal is adjusted until it calibrates the circuitry for the effects that parasitic capacitance imparts on the detection of touch or proximity events on a touch sensor panel.

Claims

1. A system for detecting changes in self-capacitance indicative of a touch or proximity event on or near a touch electrode, the system comprising:

a first circuit configured to receive a first stimulation signal and supply a first output signal in response to the first stimulation signal;

a touch electrode configured to experience a change in self-capacitance in response to the touch or proximity event;

a second circuit configured to receive both a signal indicative of the change in self-capacitance from the touch electrode and a second stimulation signal, and supply a second output signal in response to the signal indicative of the change in self-capacitance from the touch electrode and the second stimulation signal; and

a processor capable of adjusting the second stimulation signal when no touch or proximity event is detected on the touch electrode such that the first output signal and the second output signal are substantially identical.

2. The system of claim 1, wherein the processor is further capable of measuring a difference between the first output signal and the second output signal created by the touch or proximity event occurring on the touch electrode.

3. The system of claim 1, wherein the second stimulation signal is a voltage and wherein the processor is capable of adjusting the voltage of the second stimulation signal when no touch or proximity event is detected on the touch electrode, such that the first output signal and the second output signal are substantially identical, and then maintaining the adjusted voltage of second stimulation signal during touch or proximity event detection.

4. The system of claim 1, wherein the second stimulation signal is a current and wherein the processor is capable of adjusting the current of the second stimulation signal when no touch or proximity event is detected on the touch electrode, such that the first output signal and the second output signal are substantially identical, and then maintaining the adjusted current of second stimulation signal during touch or proximity event detection.

5. A touch sensor panel that includes a plurality of touch electrodes, each touch electrode of the plurality of touch electrodes incorporating the system of claim 1.

6. The system of claim 1, wherein the processor determines that no touch or proximity event is detected on the touch electrode based on a difference between the first output signal and the second output signal, the difference detected by the processor, and adjusts the second stimulation signal in response to the determination.

7. The system of claim 1, wherein the first circuit comprises a first amplifier configured to receive the first stimulation signal and supply the first output signal and the second circuit comprises a second amplifier configured to receive the signal indicative of the change in self-capacitance and the second stimulation signal and supply the second output signal.

8. The system of claim 1, wherein the first stimulation signal is a first type of signal, and the second stimulation signal is a second type of signal, different from the first type of signal.

9. The system of claim 8, wherein the first stimulation signal is a voltage signal and the second stimulation signal is a current signal.

10. A method for detecting a touch or proximity event on a touch electrode, the method comprising:

stimulating a touch electrode such that a self-capacitance of the touch electrode changes in response to the touch or proximity event occurring on or near the touch electrode;

receiving a first stimulation signal at a first circuit, and generating a first output signal from the first circuit in response to the first stimulation signal;

receiving a second stimulation signal and a signal indicative of the self-capacitance of the touch electrode at a second circuit, and generating a second output from the second circuit in response to the second stimulation signal and the signal indicative of the self-capacitance of the touch electrode; and

adjusting the second stimulation signal when no touch or proximity event is occurring on the touch electrode such that the first output signal and the second output signal are substantially identical.

11. The method of claim 10, wherein the method further comprises measuring a difference between the first output signal and the second output signals created by the touch or proximity event occurring on the touch electrode.

12. The method of claim 10, wherein the second stimulation signal is a voltage and wherein adjusting the second stimulation signal when no touch or proximity event is occurring on the touch electrode includes adjusting the voltage of the second stimulation signal.

13. The method of claim 10, wherein the second stimulation signal is a current and wherein adjusting the second stimulation signal when no touch or proximity event is occurring on the panel includes adjusting the current of the second stimulation signal.

14. The method of claim 10, wherein adjusting the second stimulation signal is in response to a determination that no touch or proximity event is detected on the touch electrode based on a difference between the first output signal and the second output signal.

15. The method of claim 10, wherein the first circuit comprises a first amplifier configured to receive the first stimulation signal and supply the first output signal and the second circuit comprises a second amplifier configured to receive the signal indicative of the change in self-capacitance and the second stimulation signal and supply the second output signal.

16. The method of claim 10, wherein the first stimulation signal isa first type of signal, and the second stimulation signal is a second type of signal, different from the first type of signal.

17. The method of claim 16, wherein the first stimulation signal is a voltage signal and the second stimulation signal is a current signal.

18. A non-transitory computer readable storage medium having stored thereon a set of instructions for detecting a change in self-capacitance of a touch electrode in a touch sensor panel that when executed by a processor causes the processor to:

stimulate a touch electrode such that a self-capacitance of the touch electrode changes in response to a touch or proximity event occurring on or near the touch electrode;

receive a first stimulation signal at a first circuit, and generate a first output signal from the first circuit in response to the first stimulation signal;

receive a second stimulation signal and a signal indicative of the self-capacitance of the touch electrode at a second circuit, and generate a second output from the second circuit in response to the second stimulation signal and the signal indicative of the self-capacitance of the touch electrode; and

adjust the second stimulation signal when no touch or proximity event is occurring on or near the touch electrode such that the first output signal and the second output signal are substantially identical.

19. The non-transitory computer readable storage medium of claim 18, that further causes the processor to measure a difference between the first output signal and the second output signal created by the touch or proximity event occurring on the touch electrode.

20. The non-transitory computer readable storage medium of claim 18, wherein the second stimulation signal is a voltage and wherein the processor further adjusts the voltage of the second stimulation signal when no touch or proximity event is occurring on the touch electrode.

21. The non-transitory computer readable storage medium of claim 18, wherein the second stimulation signal is a current and wherein the processor further adjusts the current of the second stimulation signal when no touch or proximity event is occurring on or near the touch electrode.

22. The non-transitory computer readable storage medium of claim 18, wherein the processor determines that no touch or proximity event is detected on the touch electrode based on a difference between the first output signal and the second output signal, the difference detected by the processor, and adjusts the second stimulation signal in response to the determination.

23. The non-transitory computer readable storage medium of claim 18, wherein the first circuit comprises a first amplifier configured to receive the first stimulation signal and supply the first output signal and the second circuit comprises a second amplifier configured to receive the signal indicative of the change in self-capacitance and the second stimulation signal and supply the second output signal.

24. The non-transitory computer readable storage medium of claim 18, wherein the first stimulation signal is a first type of signal and the second stimulation signal is a second type of signal, different from the first type of signal.

25. The non-transitory computer readable storage medium of claim 24, wherein the first stimulation signal is a voltage signal and the second stimulation signal is a current signal.