ELIMINATION OF ENVIRONMENTAL INTERFERENCE TO A CAPACITIVE TOUCH PAD BY A DUMMY TRACE

• US 20120256875A1
• Filed: 04/03/2012
• Published: 10/11/2012
• Est. Priority Date: 04/08/2011
• Status: Active Grant

• Current Assignee: Elan Microelectronics Corporation
• Original Assignee: Elan Microelectronics Corporation
• Inventors: HO, Han-Chang, LIN, Cheng-Hui, HUANG, Kuo-Ming, WANG, Kuo-Tai
• Granted Patent: US 8,823,680 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 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer

Abstract

A capacitive touch pad includes a sensor layer for sensing a touch of an object and a dummy trace below the sensor layer. The dummy trace is sensed to obtain a sensed value while the dummy trace is shielded by the sensor layer from interference of the object such that the sensed value reflects only environmental variation. Therefore, environmental variation can be identified depending on the sensed value, and the sensor layer can be calibrated properly.

Claims

1. A capacitive touch pad, comprising:

a sensor layer operative to sense a touch of an object; and

a dummy trace below the sensor layer;

wherein the dummy trace is sensed to obtain a sensed value while the dummy trace is shielded by the sensor layer from interference of the object such that the sensed value reflects only environmental variation.

2. The capacitive touch pad of claim 1, further comprising a shielding layer below the dummy trace.

3. The capacitive touch pad of claim 2, wherein the dummy trace is at a same voltage potential as the shielding layer while the sensor layer is sensed.

4. The capacitive touch pad of claim 2, further comprising a component layer below the shielding layer.

5. The capacitive touch pad of claim 1, further comprising a shielding layer in a same layer as the dummy trace, but not electrically connected to the dummy trace.

6. The capacitive touch pad of claim 5, wherein the dummy trace is at a same voltage potential as the shielding layer while the sensor layer is sensed.

7. The capacitive touch pad of claim 5, further comprising a component layer below the shielding layer.

8. A method for eliminating environmental interference to a capacitive touch pad having a sensor layer for sensing a touch of an object and a dummy trace below the sensor layer, the method comprising steps of:

sensing the dummy trace to obtain a sensed value while the dummy trace is shielded by the sensor layer from interference of the object such that the sensed value reflects only environmental variation;

comparing a difference between the sensed value and a base value with a threshold value; and

calibrating the sensor layer if the difference is greater than the threshold value.

9. The method of claim 8, further comprising a step of averaging a plurality of previous sensed values of the dummy trace as the base value.

10. The method of claim 8, further comprising a step of setting the base value at the sensed value after calibrating the sensor layer.

11. The method of claim 8, further comprising a step of setting different threshold values for different environmental changes.