Frequency independent offset cancellation scheme in touch receiver channel

• US 9,430,105 B2
• Filed: 02/28/2014
• Issued: 08/30/2016
• Est. Priority Date: 02/07/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Yao, Weijun, Syed, Taif A., Li, Yingxuan, Al-Dahle, Ahmad
• Primary Examiner(s): Watko, Julie Anne
• Application Number:
  US14/194,363
• Publication Number:
  US 20150227232A1
• Time in Patent Office: 914 Days
• Field of Search: 345/174
• US Class Current: 1/1
• CPC Class Codes: G06F 2203/04101 2.5D-digitiser, i.e. digitiser detecting the X/Y position of the input means, finger or stylus, also when it does not touch, but is proximate to the digitiser's interaction surface and also measures the distance of the input means within a short range in the Z direction, possibly with a separate measurement setup
• CPC Class Codes: G06F 2203/04112 Electrode mesh in capacitive digitiser: electrode for touch sensing is formed of a mesh of very fine, normally metallic, interconnected lines that are almost invisible to see. This provides a quite large but transparent electrode surface, without need for ITO or similar transparent conductive material
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• 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
• 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
• CPC Class Codes: G06F 3/047 using sets of wires, e.g. crossed wires

Abstract

A self-capacitance touch sensor panel including a plurality of touch electrodes and one or more sense circuits coupled to the touch electrodes. The touch sensor panel also includes at least one offset cancellation circuit coupled to at least one of the touch electrodes and configured to generate an offset cancellation signal to cancel an offset signal at the at least one touch electrode. In some examples, the offset cancellation signal can be an offset cancellation current to cancel an offset current. In some examples, the offset cancellation circuit comprises a variable resistor, and a magnitude of the offset cancellation current is based on a resistance of the variable resistor. In some examples, each touch electrode is coupled to an offset cancellation circuit. In other examples, a single offset cancellation circuit is shared by a plurality of touch electrodes.

Claims

1. A self-capacitance touch sensor panel, the touch sensor panel comprising:

a plurality of touch electrodes;

one or more sense circuits, the one or more sense circuits coupled to the plurality of touch electrodes; and

at least one offset cancellation circuit, the at least one offset cancellation circuit coupled to at least one touch electrode of the plurality of touch electrodes and configured to generate an offset cancellation current to cancel an offset current caused by a parasitic capacitance of the touch sensor panel at the at least one touch electrode, wherein the offset cancellation circuit includes a variable resistor coupled to the at least one touch electrode, and wherein the variable resistor is configured to be tuned until the offset cancellation current generated by the offset cancellation circuit is substantially equal in magnitude to the current caused by the parasitic capacitance.

2. The touch sensor panel of claim 1, further comprising:

a processor configured to set the resistance of the variable resistor such that the offset cancellation current substantially cancels out the offset current of the at least one touch electrode.

3. The touch sensor panel of claim 1, further comprising a stimulation source coupled to the offset cancellation circuit.

4. The touch sensor panel of claim 3, wherein the stimulation source is further coupled to the sense circuit of the at least one touch electrode.

5. The touch sensor panel of claim 3, wherein the stimulation source comprises a voltage source.

6. The touch sensor panel of claim 1, further comprising a plurality of offset cancellation circuits, each of the plurality of touch electrodes being coupled to a respective one of the plurality of offset cancellation circuits.

7. The touch sensor panel of claim 1, wherein the offset cancellation circuit is coupled to each of the plurality of touch electrodes and is configured to generate the offset cancellation signal used to cancel offset signals of each of the respective touch electrodes.

8. The touch sensor panel of claim 7, further comprising a stimulation source coupled to the offset cancellation circuit and one or more sense circuits of the plurality of touch electrodes.

9. The touch sensor panel of claim 7, further comprising a plurality of variable resistors, each variable resistor coupled to the offset cancellation circuit and a respective one of the plurality of touch electrodes and used to generate a respective one of a plurality of offset cancellation currents to cancel offset currents of each of the respective touch electrodes.

10. A method comprising:

tuning a variable resistor to generate an offset cancellation current using an offset cancellation circuit coupled to at least one touch electrode of a plurality of touch electrodes of a touch sensor panel, the offset cancellation current being for cancelling an offset current caused by a parasitic capacitance at the at least one touch electrode, and wherein the variable resistor is tuned until the offset cancellation current generated by the offset cancellation circuit is substantially equal in magnitude to the current caused by the parasitic capacitance.

11. The method of claim 10, wherein the touch sensor panel further comprises a stimulation source coupled to the offset cancellation circuit.

12. The method of claim 11, wherein the stimulation source is further coupled to a sense circuit of the at least one touch electrode.

13. The method of claim 11, wherein the stimulation source comprises a voltage source.

14. The method of claim 10, further comprising generating a plurality of offset cancellation signals using a plurality of offset cancellation circuits coupled to respective ones of the plurality of touch electrodes, the offset cancellation signals being for cancelling offset signals at the plurality of touch electrodes.

15. The method of claim 10, wherein:

the offset cancellation circuit is coupled to each of the plurality of touch electrodes, and

generating comprises generating the offset cancellation signal used to cancel offset signals of each of the respective touch electrodes.

16. The method of claim 15, wherein the touch sensor panel further comprises a stimulation source coupled to the offset cancellation circuit and one or more sense circuits of the plurality of touch electrodes.

17. The method of claim 16, wherein

the touch sensor panel further comprises a plurality of variable resistors, each variable resistor coupled to the offset cancellation circuit and a respective one of the plurality of touch electrodes, and

generating comprises generating a plurality of offset cancellation currents using the plurality of variable resistors to cancel respective offset currents at each of the touch electrodes.