Noise correction for stylus applications on tablets and other touch devices

• US 10,067,575 B2
• Filed: 11/30/2012
• Issued: 09/04/2018
• Est. Priority Date: 11/30/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Agarwal, Manu, Shahparnia, Shahrooz, Grunthaner, Martin Paul
• Primary Examiner(s): Pappas, Claire X
• Assistant Examiner(s): CASAREZ, BENJAMIN X.
• Application Number:
  US13/691,637
• Publication Number:
  US 20140152582A1
• Time in Patent Office: 2,104 Days
• Field of Search: None
• CPC Class Codes: G06F 3/033 Pointing devices displaced or positioned by the user , e.g. mice, trackballs, pens or joysticks; Accessories therefor digitisers characterised by the transducing means G06F3/041
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0442 using active external devices, e.g. active pens, for transmitting changes in electrical potential to be received by the digitiser
• 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 touch sensitive device can be capable of detecting signals generated by a stylus and correcting the detected stylus signals for effects due to noise present on the device. In one example, signals are taken from one or more electrodes that are a pre-determined distance away from an electrode in which a stylus signal is detected. The pre-determined distance can be empirically determined such that a noise estimate can be generated such that the electrodes have a higher probability of containing only noise that is highly correlated to the noise present on a detected stylus signal. The generated noise estimate is then subtracted from a detected stylus signal to reduce the effect of noise on the stylus signal.

Claims

1. A stylus detection apparatus for detecting contacts from an active stylus, the apparatus comprising:

a touch sensor panel comprising a plurality of electrodes configured to receive one or more signals generated by the active stylus, each respective electrode of the touch sensor panel is assigned, prior to receiving the one or more signals generated by the active stylus, a plurality of respective corresponding electrodes from which to generate a respective noise estimate for the respective electrode, wherein the plurality of respective corresponding electrodes are at fixed distances from the respective electrode and are separated from the respective electrode by at least one other electrode; and

a processor including one or more analog front end circuits, the processor capable of;

measuring a first signal from a first respective electrode coupled to a first input of the one or more analog front end circuits, the first signal including the one or more signals generated by the active stylus;

measuring, simultaneously with measuring the first signal, a second signal from a first respective corresponding electrode of the plurality of respective corresponding electrodes assigned to the first respective electrode coupled to a second input of the one or more analog front end circuits and a third signal from a second respective corresponding electrode of the plurality of respective corresponding electrodes assigned to the first respective electrode coupled to a third input of the one or more analog front end circuits;

generating a first respective noise estimate corresponding to the first respective electrode based on signals measured simultaneously with the first signal from the plurality of respective corresponding electrodes assigned to the first respective electrode, wherein the first respective noise estimate includes a weighted average of two or more of the simultaneously measured signals including the second and third signals; and

adjusting the first signal measured from the first respective electrode by subtracting the first respective noise estimate.

2. The apparatus of claim 1, wherein the first respective corresponding electrode and second respective corresponding electrode are adjacent electrodes.

3. The apparatus of claim 1, wherein the first respective corresponding electrode and second respective corresponding electrode are on opposite sides of the first respective electrode for the first respective electrode located in the center of the touch sensor panel.

4. The apparatus of claim 1, wherein the first respective corresponding electrode and second respective corresponding electrode are on a same side of the first respective electrode for the first respective electrode located within a predetermined distance from an edge of the touch sensor panel.

5. The apparatus of claim 1, wherein the fixed distances of the plurality of respective corresponding electrodes are based at least in part on a physical dimension of the stylus.

6. The apparatus of claim 5, wherein the physical dimension is a width of the stylus tip.

7. The apparatus of claim 1, wherein the fixed distances of the plurality of respective corresponding electrodes are based in part on a noise correlation between noise received at the plurality of respective corresponding electrodes and noise received by the first respective electrode.

8. The apparatus of claim 1, further comprising one or more analog-to-digital circuits coupled to the output of the one or more analog front end circuits.

9. The apparatus of claim 1, wherein the two or more of the simultaneously measured signals are equally weighted in the weighted average.

10. The apparatus of claim 1, wherein the plurality of respective corresponding electrodes consists of two respective corresponding electrodes.

11. The apparatus of claim 1, wherein the plurality of respective corresponding electrodes consists of three respective corresponding electrodes.

12. The apparatus of claim 1, wherein the first respective noise estimate corresponding to the first respective electrode is not generated based on the first signal.

13. A method of correcting a detected stylus signal for effects of noise in a touch sensor panel comprising a plurality of electrodes configured to receive one or more signals generated by an active stylus, each respective electrode of the touch sensor panel is assigned, prior to receiving the one or more signals generated by the active stylus, a plurality of respective corresponding electrodes from which to generate a respective noise estimate for the respective electrode, wherein the plurality of respective corresponding electrodes are at fixed distances from the respective electrode and are separated from the respective electrode by at least one other electrode, the method comprising:

measuring a first signal from a first respective electrode coupled to a first input of one or more analog front end circuits, the first signal including one or more signals generated by the active stylus;

measuring, simultaneously with measuring the first signal, a second signal from a first respective corresponding electrode of the plurality of respective corresponding electrodes assigned to the first respective electrode coupled to a second input of the one or more analog front end circuits and a third signal from a second respective corresponding electrode of the plurality of respective corresponding electrodes assigned to the first respective electrode coupled to a third input of the one or more analog front end circuits;

generating a first respective noise estimate corresponding to the first respective electrode based on signals measured simultaneously with the first signal from the plurality of respective corresponding electrodes assigned to the first respective electrode, wherein the first respective noise estimate includes a weighted average of two or more of the simultaneously measured signals including the second and third signals; and

adjusting the first signal measured from the first respective electrode by subtracting the first respective noise estimate.

14. The method of claim 13, wherein the first respective corresponding electrode and second respective corresponding electrode are adjacent electrodes.

15. The method of claim 13, wherein the first respective corresponding electrode and second respective corresponding electrode are on opposite sides of the first respective electrode for the first respective electrode located in the center of the touch sensor panel.

16. The method of claim 13, wherein the first respective corresponding electrode and second respective corresponding electrode are on a same side of the first respective electrode for the first respective electrode located within a predetermined distance from an edge of the touch sensor panel.

17. The method of claim 13, wherein the fixed distances of the plurality of respective corresponding electrodes are based at least in part on a physical dimension of the stylus.

18. The method of claim 17, wherein the physical dimension is a width of the stylus tip.

19. The method of claim 13, wherein the fixed distances of the plurality of respective corresponding electrodes are based in part on a noise correlation between noise received at the plurality of respective corresponding electrodes and noise received by the first respective electrode.

20. The method of claim 13, wherein the two or more of the simultaneously measured signals are equally weighted in the weighted average.

21. A non-transitory computer readable storage medium having stored thereon a set of instructions for detecting a stylus signal and correcting the stylus signal for effects caused by noise in a touch sensor panel, the touch sensor panel comprising a plurality of electrodes configured to receive one or more signals generated by an active stylus, each respective electrode of the touch sensor panel is assigned, prior to receiving the one or more signals generated by the active stylus, a plurality of respective corresponding electrodes from which to generate a respective noise estimate for the respective electrode, wherein the plurality of respective corresponding electrodes are at fixed distances from the respective electrode and are separated from the respective electrode by at least one other electrode, that when executed by a processor causes the processor to:

measure a first signal from a first respective electrode coupled to a first input of one or more analog front end circuits, the first signal including one or more signals generated by the active stylus;

measure, simultaneously with measuring the first signal, a second signal from a first respective corresponding electrode of the plurality of respective corresponding electrodes assigned to the first respective electrode coupled to a second input of the one or more analog front end circuits and a third signal from a second respective corresponding electrode of the plurality of respective corresponding electrodes assigned to the first respective electrode coupled to a third input of the one or more analog front end circuits;

generate a first respective noise estimate corresponding to the first respective electrode based on signals measured simultaneously with the first signal from the plurality of respective corresponding electrodes assigned to the first respective electrode, wherein the first respective noise estimate includes a weighted average of two or more of the simultaneously measured signals including the second and third signals; and

adjust the first signal measured from the first respective electrode by subtracting the first respective noise estimate.

22. The non-transitory computer readable storage medium of claim 21, wherein the first respective corresponding electrode and second respective corresponding electrode are adjacent electrodes.

23. The non-transitory computer readable storage medium of claim 21, wherein the first respective corresponding electrode and second respective corresponding electrode are on opposite sides of the first respective electrode for the first respective electrode located in the center of the touch sensor panel.

24. The non-transitory computer readable storage medium of claim 21, wherein the first respective corresponding electrode and second respective corresponding electrode are on a same side of the first respective electrode for the first respective electrode located within a predetermined distance from an edge of the touch sensor panel.

25. The non-transitory computer readable storage medium of claim 21, wherein the fixed distances of the plurality of respective corresponding electrodes are based at least in part on a physical dimension of the stylus.

26. The non-transitory computer readable storage medium of claim 25, wherein the physical dimension is a width of the stylus tip.

27. The non-transitory computer readable storage medium of claim 21, wherein the fixed distances of the plurality of respective corresponding electrodes are based in part on a noise correlation between noise received at the plurality of respective corresponding electrodes and noise received by the first respective electrode.

28. The non-transitory computer readable storage medium of claim 21, wherein the two or more of the simultaneously measured signals are equally weighted in the weighted average.