CAPACITIVE SENSOR WITH ADDITIONAL ELECTRODE

• US 20100301879A1
• Filed: 08/20/2008
• Published: 12/02/2010
• Est. Priority Date: 08/26/2007
• Status: Active Grant

• Current Assignee: Neodrón Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Philipp, Harald
• Granted Patent: US 8,536,880 B2
• Time in Patent Office: Days
• US Class Current: 324/679
• CPC Class Codes: G06F 2203/0339 Touch strips, e.g. orthogonal touch strips to control cursor movement or scrolling; single touch strip to adjust parameter or to implement a row of soft keys
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• 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: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2017/9602 characterised by the type or shape of the sensing electrodes

Abstract

A capacitive touch sensor employing adjacent drive and sense electrodes, in which an additional sense electrode is provided as well as a conventional drive electrode and sense electrode. The drive and two sense electrodes are arranged on the bottom side of a dielectric panel, the top side providing a sensing surface to be touched by a user'"'"'s finger or a stylus. The additional sense electrode is positioned on the underside of the dielectric panel so that it is shielded from the drive electrode by the conventional sense electrode. The signal collected from the additional sense electrode is subtracted from the signal collected from the conventional sense electrode to cancel noise.

Claims

1. A capacitive touch sensor comprising:

a dielectric panel overlying a drive electrode, a first sense electrode and a second sense electrode, the electrodes being separated by coupling gaps, wherein the second sense electrode is positioned to be shielded from the drive electrode by the first sense electrode, so that in use the first sense electrode receives the majority of charge coupled from the drive electrode and the second sense electrode primarily registers noise.

2. The sensor of claim 1, further comprising a sensing circuit including first and second detector channels connected to the first and second sense electrodes to receive first and second signal samples respectively, and operable to output a final signal obtained by subtracting the second signal sample from the first signal sample, thereby to cancel noise.

3. The sensor of claim 2, wherein the second sample is subtracted from the first sample on a sample-by-sample basis.

4. The sensor of claim 2, wherein the second sample is subtracted from the first sample after summing a plurality of samples on each detector channel separately and performing the subtraction on the summed samples from each detector channel.

5. The sensor of claim 1 wherein the first sense electrode and at least one of the drive electrode and the second sense electrode each comprise at least two electrode elements, and the electrode elements are arranged interleaved on the dielectric panel in at least one repeat of the sequence:

drive electrode element, first sense electrode element, second sense electrode element, first sense electrode element, drive electrode element.

6. The sensor of claim 1 wherein the first sense electrode and at least one of the drive electrode and the second sense electrode each comprise at least two electrode elements, and the electrode elements are arranged interleaved on the dielectric panel in at least one repeat of the sequence:

second sense electrode element, first sense electrode element, drive electrode element, first sense electrode element, second sense electrode element.

7. A method of capacitive touch sensing comprising:

providing a capacitive touch sensor comprising a dielectric panel overlying a drive electrode, a first sense electrode and a second sense electrode, the electrodes being separated by coupling gaps, wherein the second sense electrode is positioned to be shielded from the drive electrode by the first sense electrode;

actuating the drive electrode to couple the majority of charge from the drive electrode to the first sense electrode;

sampling the first sense electrode to collect a first signal sample;

sampling the second sense electrode to collect a second signal sample;

subtracting the second signal sample from the first signal sample to obtain a final signal; and

outputting the final signal.

8. The method of claim 7, wherein said sampling steps are carried out simultaneously.

9. A capacitive touch sensor comprising:

a dielectric panel overlying a measurement electrode and a noise electrode separated by a gap, wherein the measurement electrode is located at an input area and the noise electrode is positioned adjacent thereto, so that in use the measurement electrode receives the majority of charge coupled from a pointing object and the noise electrode primarily registers noise.

10. The sensor of claim 9, wherein there are multiple measurement electrodes, and a noise electrode is distributed over an area common to a plurality of the measurement electrodes.

11. A method of capacitive touch sensing comprising:

providing a capacitive touch sensor comprising a dielectric panel overlying a measurement electrode and a noise electrode separated by a gap, wherein the measurement electrode is located at an input area and the noise electrode is positioned adjacent thereto;

sampling the measurement electrode to collect a first signal sample;

sampling the noise electrode to collect a second signal sample;

subtracting the second signal sample from the first signal sample to obtain a final signal; and

outputting the final signal.

12. The method of claim 11, wherein said sampling steps are carried out simultaneously.