Group scanning circuit and method for a capacitive touch sensor

• US 8,988,362 B2
• Filed: 02/05/2010
• Issued: 03/24/2015
• Est. Priority Date: 02/11/2009
• Status: Active Grant

• Current Assignee: Elan Microelectronics Corporation
• Original Assignee: Elan Microelectronics Corporation
• Inventors: Yeh, I-Hau, Lin, Chun-Yu
• Primary Examiner(s): Okebato, Sahlu
• Application Number:
  US12/700,866
• Publication Number:
  US 20100200310A1
• Time in Patent Office: 1,873 Days
• Field of Search: 345/173, 345/175, 178/18.06
• US Class Current: 345/173
• 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, wherein the capacitive touch sensor includes a plurality of traces, the circuit comprising:

n number channels;

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

a front-end circuit connected to the n number of channels, for simultaneously detecting the n number of adjacent traces to extract analog-to-digital conversion values therefrom,

wherein the front-end circuit selects a target trace having a maximum analog-to-digital conversion value corresponding to a touch point from the plurality of traces after all of the plurality of traces are scanned, and then p number of adjacent traces including the target trace, and

a noise equalizer connected to the front-end circuit, for performing noise equalization over the analog-to-digital conversion values of the p number of adjacent traces after the p number of adjacent traces are scanned;

wherein n and p are integers, and n≧

2, p≧

2; and

wherein p is less than a number of the plurality of traces.

2. The circuit of claim 1, wherein the multiplexer selects the p number of adjacent traces with the target trace as a center and traces adjacent to the target trace to connect to p number of the channels from the n number of channels for a scanning after all of the plurality of traces are scanned.

3. A method for a capacitive touch sensor, wherein the capacitive touch sensor includes a plurality of traces, comprising:

(a) selecting n number of adjacent traces from the plurality of traces to connect ton number of channels;

(b) scanning the n number of adjacent traces simultaneously;

(c) selecting 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, wherein the target trace corresponds to a touch point; and

(d) scanning p number of adjacent traces including the target trace for more accurate positioning of the touch point to extract ADC values of all of the p number of adjacent traces, and

(e) performing a noise equalization over the ADC values of all of the p number of adjacent traces after the step (d),

wherein n and p are integers, and n≧

2, p≧

2; and

wherein p is less than a number of the plurality of traces.

4. The method of claim 3, wherein the step (d) comprises selecting the target trace as a center and traces adjacent to the target trace as the p number of adjacent traces.

5. A method for a capacitive touch sensor;

wherein the capacitive touch sensor includes a plurality of traces, comprising;

executing a first scan by simultaneously scanning n number of adjacent traces from the plurality of traces to extract capacitance variations therefrom;

selecting at least one trace having a most significant capacitance variation corresponding to a touch point according to the capacitance variations;

executing a second scan to scan p number of adjacent traces including the at least one trace selected by the previous step to extract ADC values of all of the p number of adjacent traces, and

performing a noise equalization over the ADC values of all the p number ofadjacent traces after the step of executing the second scan,

wherein n and p are integers, and n≧

2, p≧

2; and

wherein p is less than a number of the plurality of traces.