Group scanning circuit and method for a capacitive touch sensor
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.
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.