Method for multiple touch position estimation

1. A method, comprising:

scanning, by a processing device, a touch sensor array to generate a grid of cells corresponding to the touch sensor array, wherein each cell in the grid of cells represents a measured capacitance on a sensor element in the touch sensor array;

upsampling the grid of cells corresponding to the touch sensor array to generate an upsampled grid of cells comprising additional cells that is denser than the grid of cells corresponding to the touch sensor array, wherein each additional cell is located between at least two original cells, wherein each additional cell in the upsampled grid of cells represents an interpolated capacitance value based on the measured capacitance of the at least two original cells;

detecting a plurality of local maximum cells of the upsampled grid of cells; and

estimating a plurality of touch positions on the touch sensor array by calculating a corresponding plurality of centroids using cells adjacent to the detected local maximum cells.

2. The method of claim 1 , wherein detecting a local maximum cell of the plurality of local maximum cells comprises:

determining whether a signal of a current sensor element is above a presence threshold;

comparing the signal of the current sensor element, when the signal of the current sensor element is above the presence threshold, with signals of all adjacent sensor elements to the current sensor element; and

storing row and column numbers of the current sensor element as coordinates of the local maximum cell.

3. The method of claim 2 , wherein the detecting the local maximum cell comprises using one of a Hill Climbing technique or a Gradient Descent technique.

4. The method of claim 2 , wherein the signal represents a sensor element capacitance.

5. The method of claim 2 , further comprising jitter filtering a result of the calculation of the centroid.

6. The method of claim 2 , wherein prior to detecting the local maximum cell, the method further comprises filtering raw data generated from the scanning.

7. The method of claim 6 , wherein after filtering, the method further comprises establishing a baseline for the signal of a current sensor element using the filtered raw data.

8. The method of claim 7 , wherein establishing a baseline comprises using a baseline calculation algorithm having an infinite impulse response (IIR) low pass filter (LPF).

9. The method of claim 1 , wherein the upsampled grid of cells is generated using bicubic splines.

10. An apparatus, comprising:

processing logic configured to scan a touch sensor array to generate a grid of cells corresponding to the touch sensor array, wherein each cell in the grid of cells represents a measured capacitance on a sensor element in the touch sensor array, upsample the grid of cells corresponding to the touch sensor array to generate an upsampled grid of cells comprising additional cells that is denser than the grid of cells corresponding to the touch sensor array, wherein each additional cell is located between at least two original cells, wherein each additional cell in the upsampled grid of cells represents an interpolated capacitance value based on the measured capacitance of the at least two original cells, and detect a plurality of local maximum cells of the upsampled grid of cells, wherein the processing logic is further configured to estimate a plurality of touch positions on the touch sensor array by calculating a corresponding plurality of centroids using cells adjacent to the detected local maximum cells.

11. The apparatus of claim 10 , wherein in detecting a local maximum cell of the plurality of local maximum cells, the processing logic is configured to:

determine whether a signal of a current sensor element is above a presence threshold,

compare the signal of the current sensor element, when the signal of the current sensor element is above the presence threshold, with signals of adjacent sensor elements to the current sensor element, and

store row and column numbers of the current sensor element as coordinates of the local maximum cell.

12. The apparatus of claim 10 , wherein the signal represents a sensor element capacitance.

13. The apparatus of claim 12 , wherein the processing logic is further configured to jitter filter a result of the calculation of the centroid.

14. The apparatus of claim 10 , further comprising the touch sensor array operatively coupled with the processing logic.

15. The apparatus of claim 14 , wherein the processing logic resides within a processing device coupled between the touch sensor array and a host.

16. The apparatus of claim 14 , wherein the processing logic resides within a host.

17. The apparatus of claim 10 , wherein the upsampled grid of cells is generated using bicubic splines.

18. An apparatus, comprising:

means for scanning a touch sensor array to generate a grid of cells corresponding to the touch sensor array, wherein each cell in the grid of cells represents a measured capacitance on a sensor element in the touch sensor array;

means for upsampling the grid of cells corresponding to the touch sensor array to generate an upsampled grid of cells comprising additional cells that is denser than the grid of cells corresponding to the touch sensor array, wherein each additional cell is located between at least two original cells, wherein each additional cell in the upsampled grid of cells represents an interpolated capacitance value based on the measured capacitance of the at least two original cells;

means for detecting a plurality of local maxima cells of the upsampled grid of cells; and

means for estimating a plurality of touch positions on the touch sensor array by calculating a corresponding plurality of centroids using cells adjacent to the detected local maximum cells.

19. The apparatus of claim 18 , wherein the means for detecting a plurality of local maximum cells comprises:

means for determining whether a signal of a current sensor element is above a presence threshold;

means for comparing the signal of the current sensor element, when the signal of the current sensor element is above the presence threshold, with signals of adjacent sensor elements to the current sensor element; and

means for storing row and column numbers of the current sensor element as coordinates of a local maximum cell.

20. The apparatus of claim 19 , further comprising the touch sensor array operatively coupled with the means for scanning.