GROUP SCANNING CIRCUIT AND METHOD FOR A CAPACITIVE TOUCH SENSOR

• US 20100200310A1
• Filed: 02/05/2010
• Published: 08/12/2010
• Est. Priority Date: 02/11/2009
• Status: Active Grant

• Current Assignee: Elan Microelectronics Corporation
• Original Assignee: Elan Microelectronics Corporation
• Inventors: LIN, CHUN-YU, YEH, I-HAU
• Granted Patent: US 8,988,362 B2
• Time in Patent Office: Days
• US Class Current: 178/18.30
• CPC Class Codes: G06F 3/041661 using detection at multiple resolutions, e.g. coarse and fine scanning; using detection within a limited area, e.g. object tracking window
• 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

Abstract

For object detection, a two-step group scan to the traces of a capacitive touch sensor is performed, thereby dramatically shortening the overall scanning time and reducing noise effect. After all the traces are scanned by the pre-scan step to find out the trace of a touch point, the trace of the touch point and traces adjacent thereto are scanned by the re-scan step for more accurate positioning of the touch point.

Claims

1. A circuit for a capacitive touch sensor, comprising:

a plurality of channels;

a multiplexer connected to the plurality of channels, for selecting a group of traces from a plurality of traces to connect to the plurality of channels; and

a front-end circuit connected to the plurality of channels, for simultaneously detecting the group of traces to extract analog-to-digital conversion values therefrom.

2. The circuit of claim 1, wherein the front-end circuit finds out a target trace having a maximum analog-to-digital conversion value from the plurality of traces after all of the plurality of traces are scanned.

3. The circuit of claim 2, wherein the multiplexer selects a second group of traces with the target trace as a center and traces adjacent to the target trace to connect to the plurality of channels for a re-scan after all of the plurality of traces are scanned.

4. The circuit of claim 3, further comprising a noise equalizer connected to the front-end circuit, for performing noise equalization to the analog-to-digital conversion values of the second group of traces after the re-scan.

5. A method for a capacitive touch sensor, comprising:

(a) group scanning a plurality of traces, each time simultaneously scanning a group of traces;

(b) selecting a target trace from the plurality of traces after all of the plurality of traces are scanned; and

(c) re-scanning a second group of traces including the target trace for more accurate positioning of a touch point.

6. The method of claim 5, further comprising noise equalization to ADC values of all of the second group of traces after the step c.

7. The method of claim 5, wherein the step b comprises selecting the trace having a most significant capacitance variation as the target trace.

8. The method of claim 5, wherein the step b comprises selecting the trace having a maximum analog-to-digital conversion value as the target trace.

9. The method of claim 5, wherein the step c comprises selecting the target trace as a center and traces adjacent to the target trace as the second group of traces.