Method and Device for Reducing Noise Interference in a Capacitive Touchscreen System

• US 20120105353A1
• Filed: 10/31/2010
• Published: 05/03/2012
• Est. Priority Date: 10/31/2010
• Status: Active Grant

• Current Assignee: PixArt Imaging Incorporated
• Original Assignee: Avago Technologies ECBU IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Brosnan, Michael John
• Granted Patent: US 8,836,666 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• 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

Abstract

Disclosed herein are various embodiments of means and methods for reducing noise interference in a capacitive touchscreen system. Second noise signals related to first noise signals generated by an external noise source are provided to a touchscreen controller, which determines fundamental and harmonic frequencies associated with the first noise signals. In response to determining the fundamental and harmonic frequencies associated with the first noise signals, the touchscreen controller may shift the frequency at which drive signals generated thereby are provided to a capacitive touchscreen. As a result, undesired interference between the first noise signals and the drive signals is minimized or avoided.

Claims

1. A method of reducing interference between a first noise signal, and drive and sense signals, in a capacitive touchscreen system comprising a capacitive touchscreen and a touchscreen controller operably connected to the touchscreen and configured to provide the drive signals thereto and to receive the sense signals therefrom, the capacitive touchscreen comprising drive electrodes configured to provide the drive signals and sense electrodes configured to receive the sense signals, mutual capacitances existing between the drive and sense electrodes at locations where the drive and sense electrodes intersect, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto, the method comprising:

receiving, in the touchscreen controller as an input thereto, a second noise signal related to the first noise signal, the second noise signal being generated by a device external to the capacitive touchscreen;

determining, in the touchscreen controller, an initial fundamental frequency and at least one initial harmonic frequency of the first noise signal;

adjusting, in the touchscreen controller, the frequency of the drive signal to an initial adjusted drive signal frequency that is between about 10% greater than the fundamental frequency and about 10% less than the harmonic frequency;

determining, in the touchscreen controller, an updated fundamental frequency and an updated at least one initial harmonic frequency of the first noise signal, and

adjusting, in the touchscreen controller, the initial adjusted frequency of the drive signal to an updated adjusted drive signal frequency that is between about 10% greater than the updated fundamental frequency and about 10% less than the updated harmonic frequency.

2. The method of claim 1, wherein the initial adjusted drive signal frequency is between about 20% greater than the fundamental frequency and about 20% less than the harmonic frequency.

3. The method of claim 1, wherein the initial adjusted drive signal frequency is between about 30% greater than the fundamental frequency and about 30% less than the harmonic frequency.

4. The method of claim 1, wherein the initial adjusted drive signal frequency is between about 40% greater than the fundamental frequency and about 40% less than the harmonic frequency.

5. The method of claim 1, wherein the initial adjusted drive signal frequency is between about 50% greater than the fundamental frequency and about 50% less than the harmonic frequency.

6. The method of claim 1, further comprising providing wherein the source of the external noise signal is one of a liquid crystal display and a switched-mode power supply.

7. The method of claim 1, further comprising providing the noise signal from the source of the external noise signal as a direct input to the touchscreen controller.

8. The method of claim 1, further comprising incorporating the capacitive touchscreen system into a mobile electronic device.

9. The method of claim 8, wherein the mobile electronic device is one of a computer, a notebook computer, a laptop computer, a personal data assistant (PDA), a mobile telephone, a smart phone, an electronic book reader, a radio, an MP3 player, and a portable music player.

10. A method of reducing interference between a first noise signal, and capacitive touchscreen drive and sense signals, in a capacitive touchscreen system comprising a capacitive touchscreen and a touchscreen controller operably connected to the touchscreen and configured to provide the drive signals thereto and to receive the sense signals therefrom, the capacitive touchscreen comprising drive electrodes configured to provide the drive signals and sense electrodes configured to receive the sense signals, mutual capacitances existing between the drive and sense electrodes at locations where the drive and sense electrodes intersect, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto, the method comprising:

receiving, in the touchscreen controller as an input thereto, a second noise signal related to the first noise signal, the second signal being generated by a device external to the capacitive touchscreen;

determining, in the touchscreen controller, an initial fundamental frequency f_{fundamental,noise} of the first noise signal;

adjusting, in the touchscreen controller, the frequency of the drive signal to an initial adjusted drive signal frequency that is about (n+k_noise)×

(f_{fundamental,noise} initial), where n is an integer;

determining, in the touchscreen controller, an updated fundamental frequency f_{fundamental,noise} updated and

adjusting, in the touchscreen controller, the initial adjusted frequency of the drive signal to an updated adjusted drive signal frequency that is about (n+k_noise)×

(f_{fundamental,noise} updated), where n is an integer.

11. The method of claim 10, wherein k_noise ranges between about 0.001 and about 0.999.

12. The method of claim 10, wherein k_noise ranges between about 0.01 and about 0.99.

13. The method of claim 10, wherein k_noise ranges between about 0.1 and about 0.9.

14. The method of claim 10, wherein k_noise ranges between about 0.5 and about 0.9.

15. The method of claim 10, wherein k_noise is selected from the group consisting of about ⅛

, about ¼

, about ⅓

, about ⅜

, about ½

, about ⅝

, about ⅔

, about ¾

, and about ⅞

.

16. The method of claim 10, wherein k_noise is selected from the group consisting of about 13/16, about 15/19, about 21/25, about 33/43, and about 49/57.

17. The method of claim 10, wherein k_noise comprises a first odd integer as a denominator thereof, and a second odd integer as a denominator thereof.

18. The method of claim 17, the first odd integer is greater than 11 and the second odd integer is greater than 13.

19. The method of claim 10, further comprising providing wherein the source of the external noise signal is one of a liquid crystal display and a switched-mode power supply.

20. The method of claim 10, further comprising providing the noise signal from the source of the external noise signal as a direct input to the touchscreen controller.

21. The method of claim 10, further comprising incorporating the capacitive touchscreen system into a mobile electronic device.

22. The method of claim 21, wherein the mobile electronic device is one of a computer, a notebook computer, a laptop computer, a personal data assistant (PDA), a mobile telephone, a smart phone, an electronic book reader, a radio, an MP3 player, and a portable music player.