Two-dimensional touch panel
A capacitive touch panel is provided capable of detecting multiple simultaneous touches. The touch panel delivers sets of capacitance signal values to a processor which computes the coordinates of single or multiple touch locations on the touch panel. The processing of each set is performed by (i) identifying the sensing element having the largest capacitance signal value; (ii) defining a region around that sensing element; and (iii) repeating the process iteratively, wherein each subsequent identifying step excludes signals that lie in previously defined regions. A multi-touch sensor is thus provided in which the signal processing is based on successive definition of regions or sub-blocks in the touch: panel. The touch location in each region can be determined more accurately by then applying interpolation between the adjacent signal values. This allows for position resolution at a finer scale than that defined by the touch panel's electrode patterning.
1. A two-dimensional touch-sensitive capacitive position sensor comprising:
a touch panel having a plurality of sensing elements distributed over its entire area;
a capacitance measurement circuit connected to the sensing elements and operable repeatedly to acquire sets of capacitance signal values, each set being made up of a capacitance signal value from each of the sensing elements; and
a processor connected to receive the sets of capacitance signal values and operable to sequentially process each set by performing operations comprising:
(a) identifying a sensing element that has a capacitance signal value that exceeds a threshold and that has a largest capacitance signal value from within the plurality of sensing elements distributed over the entire area of the touch panel that exceeds all other capacitance values for the plurality of sensing elements distributed over the entire area of the touch pad, including comparing the capacitance value of each of the plurality of sensing elements that exceeds the threshold with the capacitance value of at least one of the other of the plurality of sensing elements;
(b) defining a region within the entire area of the touch panel comprising the identified sensing element having the largest capacitance signal value and each sensing element that is immediately adjacent the identified sensing element whether or not each sensing element that is immediately adjacent the identified sensing element has a capacitance value that exceeds the threshold, the defining including determining which of the plurality of sensing elements are immediately adjacent the identified sensing element;
(c) selecting, from the defined region a particular sensing element within the defined region to be associated with a touch of the touch panel;
(d) excluding from future consideration as a sensing element having a largest capacitance signal value any sensing element within the defined region;
(e) identifying another sensing element that has a capacitance signal value that exceeds the threshold and that has a largest capacitance value from the plurality of sensing elements that exceeds all other capacitance values for the plurality of sensing elements distributed over the entire area of the touch pad, excluding any excluded sensing elements, including comparing the capacitance value of each of the plurality of sensing elements, excluding any excluded sensing elements, with at least one of the other of the plurality of sensing elements, excluding any excluded sensing elements;
(f) defining another region within the entire area of the touch panel comprising the another identified sensing element having a largest capacitance signal value and each sensing element that is immediately adjacent the another identified sensing element whether or not each sensing element that is immediately adjacent the identified sensing element has a capacitance value that exceeds the threshold, the defining another region including determining which of the plurality of sensing elements are immediately adjacent the another identified sensing element;
(g) selecting, from the another defined region a particular sensing element within the another defined region to be associated with another touch of the touch panel;
(h) excluding from future consideration as a sensing element having a largest capacitance signal value any sensing element within the another defined region; and
(i) repeating steps (e), (f), (g), and (h) until all of the plurality of sensing elements that have a capacitance signal value that exceeds the threshold are identified as having a largest capacitance signal value or are excluded from future consideration for having a largest capacitance signal value.
2. The sensor of claim 1 , wherein the particular sensing element that is selected to be associated with the touch comprises the sensing element having the largest capacitance signal value.
3. The sensor of claim 1 , wherein the particular sensing element that is selected to be associated with the touch comprises a sensing element that is at a topmost position on the touch panel among sensing elements that have a capacitance signal value above a threshold value.
4. The sensor of claim 3 , wherein a touch location in the region is taken to be at the particular sensing element that is selected to be associated with the touch.
5. The sensor of claim 1 , wherein a touch location in the region is determined by applying interpolation between the capacitance signal values of at least some of the sensing elements in the region.
6. The sensor of claim 5 , wherein the interpolation is limited to the particular sensing element that is selected to be associated with the touch and any neighboring sensor elements.
7. The sensor of claim 5 , wherein the interpolation includes all sensing elements in the region.
8. A method sequentially performing the following:
(a) identifying a sensing element having a capacitance signal value that exceeds a threshold and that has a largest capacitance signal value from within the plurality of sensing elements distributed over the entire area of the touch panel that exceeds all other capacitance values for the plurality of sensing elements distributed over the entire area of the touch pad, including comparing the capacitance value of each of the plurality of sensing elements that exceeds the threshold with the capacitance value of at least one of the other of the plurality of sensing elements;
(b) defining a region within the entire area of the touch panel comprising the identified sensing element having the largest capacitance signal value and each sensing element that is immediately adjacent the identified sensing element whether or not each sensing element that is immediately adjacent the identified sensing element has a capacitance value that exceeds the threshold, the defining including determining which of the plurality of sensing elements are immediately adjacent the identified sensing element;
(c) selecting, from the defined region a particular sensing element within the defined region to be associated with a touch of the touch panel;
(d) excluding from future consideration as a sensing element having a largest capacitance signal value any sensing element within the defined region;
(e) identifying another sensing element having a capacitive signal value that exceeds the threshold and that has a largest capacitance value from the plurality of sensing elements that exceeds all other capacitance values for the plurality of sensing elements distributed over the entire area of the touch pad, excluding any excluded sensing elements, including comparing the capacitance value of each of the plurality of sensing elements, excluding any excluded sensing elements, with at least one of the other of the plurality of sensing elements, excluding any excluded sensing elements;
(f) defining another region within the entire area of the touch panel comprising the another identified sensing element having a largest capacitance signal value and each sensing element that is immediately adjacent the another identified sensing element whether or not each sensing element that is immediately adjacent the identified sensing element has a capacitance value that exceeds the threshold, the defining another region including determining which of the plurality of sensing elements are immediately adjacent the another identified sensing element;
(g) selecting, from the another defined region a particular sensing element within the another defined region to be associated with another touch of the touch panel;
(h) excluding from future consideration as a sensing element having a largest capacitance signal value any sensing element within the another defined region; and
(i) repeating steps (e), (f), (g), and (h) until all of the plurality of sensing elements having a capacitance signal value that exceeds the threshold are identified as having a largest capacitance signal value or are excluded from future consideration for having a largest capacitance signal value.
9. The method of claim 8 , wherein the particular sensing element that is selected to be associated with the touch comprises the sensing element having the largest capacitance signal value.
10. The method of claim 9 , wherein a touch location in the region is taken to be at the particular sensing element that is selected to be associated with the touch.
11. The method claim 9 , wherein a touch location in the region is determined by applying interpolation between the capacitance signal values of at least some of the sensing elements in the region.
12. The method of claim 11 , wherein the interpolation is limited to the particular sensing element that is selected to be associated with the touch and any neighboring sensor elements.
13. The method of claim 11 , wherein the interpolation includes all sensing elements in the region.
14. The method of claim 8 , wherein the particular sensing element that is selected to be associated with the touch comprises a sensing element that is at a topmost position on the touch panel among sensing elements that have a capacitance signal value above a threshold value.
15. The method of claim 8 , further comprising subtracting a background signal value from raw signal values of the plurality of sensing elements before identifying the sensing element having the largest capacitance signal value.
16. An apparatus comprising:
a processor communicatively coupled to a capacitance measurement circuit, the capacitance measurement circuit operable to acquire a capacitance signal value from each of a plurality of sensing elements of a touch panel, the processor operable to sequentially perform operations comprising:
(a) identifying a sensing element having a capacitance signal value that exceeds a threshold and that has a largest capacitance signal value from within the plurality of sensing elements distributed over an entire area of the touch panel that exceeds all other capacitance values for the plurality of sensing elements distributed over the entire area of the touch pad, including comparing the capacitance value of each of the plurality of sensing elements that exceeds the threshold with the capacitance value of at least one of the other of the plurality of sensing elements;
(b) defining a region within the entire area of the touch panel comprising the identified sensing element having the largest capacitance signal value and each sensing element that is immediately adjacent the identified sensing element whether or not each sensing element that is immediately adjacent the identified sensing element has a capacitance value that exceeds the threshold, the defining including determining which of the plurality of sensing elements are immediately adjacent the identified sensing element;
(c) selecting, from the defined region a particular sensing element within the defined region to be associated with a touch of the touch panel;
(d) excluding from future consideration as a sensing element having a largest capacitance signal value any sensing element within the defined region;
(e) identifying another sensing element that has a capacitance signal value that exceeds the threshold and that has a largest capacitance value from the plurality of sensing elements that exceeds all other capacitance values for the plurality of sensing elements distributed over the entire area of the touch pad, excluding any excluded sensing elements, including comparing the capacitance value of each of the plurality of sensing elements, excluding any excluded sensing elements, with at least one of the other of the plurality of sensing elements, excluding any excluded sensing elements;
(f) defining another region within the entire area of the touch panel comprising the another identified sensing element having a largest capacitance signal value and each sensing element that is immediately adjacent the another identified sensing element whether or not each sensing element that is immediately adjacent the identified sensing element has a capacitance value that exceeds the threshold, the defining another region including determining which of the plurality of sensing elements are immediately adjacent the another identified sensing element;
(g) selecting, from the another defined region a particular sensing element within the another defined region to be associated with another touch of the touch panel;
(h) excluding from future consideration as a sensing element having a largest capacitance signal value any sensing element within the another defined region; and
(i) repeating steps (e), (f), (g), and (h) until all of the plurality of sensing elements having a capacitance signal value that exceeds the threshold are identified as having a largest capacitance signal value or are excluded from future consideration for having a largest capacitance signal value.