# Patent

## Title
Boundary resolution improvement for a capacitive touch panel

## Abstract

A capacitive touch panel has a plurality of traces including a boundary trace, and a virtual trace is defined outward of the boundary trace and assigned with a virtual coordinate and a virtual capacitance for interpolation to position a touch point around the boundary of the capacitive touch panel, thereby eliminating the non-addressable region of the capacitive touch panel.

## Background
FIELD OF THE INVENTION
The present invention is related generally to a capacitive touch panel and, more particularly, to a positioning method for a capacitive touch panel.
BACKGROUND OF THE INVENTION
As shown in FIG. 1, a capacitive touch panel 10 has a plurality of traces 14, 16, 18, 20 and 22 in X-direction, which are assigned with the coordinates X1, X2, X3, X4 and X5 respectively, from the boundary 12 to the right. Each coordinate Xm represents where the center of the corresponding trace is in the X-direction, and the coordinate Xm may be a relative coordinate or an absolute coordinate in the X-direction. When the capacitive touch panel 10 is touched, the capacitances of the touched traces are changed. By sensing the traces 14, 16, 18, 20 and 22 for the capacitances thereon, the measured capacitances Cm, typically converted by an analog-to-digital converter (not shown in FIG. 1) into digital values, are used together with the coordinate Xm for interpolation to position the touch point at the coordinate




  
    
      
        
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where n is the number of the traces. However, this method is good only for positioning the touch points within the range 24. If the usable area of the capacitive touch panel 10 is extended to the boundary 12 for hardware-related reasons, due to the coordinates Xm of the traces 14, 16, 18, 20 and 22 all defined in correspondence to their respective centers, any touch points around the boundary 12 and beyond (i.e., to the left of) the center X1 of the boundary trace 14 cannot be positioned precisely by the above interpolation algorithm and thus a non-addressable region 26 is present. All capacitive touch panels have such non-addressable regions at their boundaries that are useless for user's touch operation.

SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for boundary resolution improvement of a capacitive touch panel.
According to the present invention, a virtual trace outward of the boundary trace of a capacitive touch panel is defined and assigned with a virtual coordinate and a virtual capacitance for interpolation to position a touch point around the boundary, thereby eliminating the non-addressable region of the capacitive touch panel.



BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic diagram showing conventional positioning methods for a capacitive touch panel using interpolation algorithm;
FIG. 2 is a schematic diagram showing a positioning method for a capacitive touch panel according to the present invention; and
FIG. 3 is a flowchart of a positioning method for a capacitive touch panel.



DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, as shown in FIG. 2, for a capacitive touch panel 10 having a plurality of traces 14, 16, 18, 20 and 22 in X-direction, a virtual trace 28 is defined outward of the boundary trace 14 and assigned with a virtual coordinate X0 in the X-direction. The term “virtual” indicates the trace 28 not physical or hardware as are the traces 14, 16, 18, 20 and 22. When the capacitive touch panel 10 is touched, the capacitances of the touched physical traces are changed, and the measured capacitances Cm from the physical traces 14, 16, 18, 20 and 22 are converted by an analog-to-digital converter (not shown in FIG. 2) into digital values. For interpolation to calculate the coordinate X of the touch point, a virtual measured capacitance C0 is assigned to the virtual trace 28. For example, in this embodiment, the virtual measured capacitance C0 is preset at zero. In order to determine the coordinate X of the touch point, the mean coordinates of each two adjacent ones of the physical and virtual traces 14, 16, 18, 20, 22 and 28 are calculated by the equation X′m=(Xm−Xm+1)/2, as indicated by the coordinates X0′, X1′, X2′, X3′ and X4′ shown in FIG. 2, the averages of the measured capacitances of each two adjacent ones of the physical and virtual traces 14, 16, 18, 20, 22 and 28 are calculated by the equation C′m=(Cm+Cm+1)/2, as indicated by the measured capacitances C0′, C1′, C2′, C3′ and C4′ shown in FIG. 2, and then the mean coordinates and the averages measured capacitances are used for interpolation to calculate the coordinate




  
    
      
        
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where n is the number of the physical traces. With this method, any touch points within the region 30 can be positioned, thereby eliminating the addressable region 26 shown in FIG. 1.

FIG. 3 is a flowchart of the above positioning method, in which step S1 senses the physical traces 14, 16, 18, 20 and 22 for the capacitances C1, C2, C3, C4 and C5 thereon, step S2 defines the virtual trace 28 outward of the boundary trace 14 and assigns the virtual coordinate X0 and the virtual measured capacitance C0′ thereto, where the virtual measured capacitance can be set zero, non-zero constant, or variable with the measured capacitances C1, C2, C3, C4 and C5, step S3 calculates the average measured capacitances C0′, C1′, C2′, C3′ and C4′ and the mean coordinates X0′, X1′, X2′, X3′ and X4′ from each two adjacent ones of the physical and virtual traces 14, 16, 18, 20, 22 and 28, and step S4 interpolates with the average measured capacitances C0′, C1′, C2′, C3′ and C4′ and the mean coordinates X0′, X1′, X2′, X3′ and X4′ to calculate the X-coordinate of the touch point.
The method according to the present invention can be used in conjunction with any conventional positioning methods in the way that when the measured capacitance of the boundary trace 14 is non zero or is the maximum of the measured capacitances of all the physical traces, the above interpolation algorithm of the present invention is executed to calculate the coordinate of the touch point.
While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.

## Claims

1. A method for boundary resolution improvement of a capacitive touch panel having a plurality of physical traces in a direction, including a boundary trace, each of said plurality of physical traces being assigned with a respective coordinate in said direction, the method comprising the steps of:
sensing each of said plurality of physical traces for a measured capacitance therefrom;
defining a virtual trace outward of said boundary trace and assigning a virtual coordinate in said direction and a virtual measured capacitance thereto;
calculating a plurality of average measured capacitances by calculating an average value of capacitances from each two adjacent ones of said plurality of physical traces and said virtual trace using said measured capacitances and said virtual measured capacitance; and
calculating a plurality of mean coordinates by calculating a mean value of coordinates of each two adjacent ones of said plurality of physical traces and said virtual trace using said respective coordinates and said virtual coordinate; and
interpolating with said plurality of average measured capacitances and said plurality of mean coordinates to calculate a coordinate in said direction for a touch point.

2. The method of claim 1, wherein said virtual measured capacitance is zero.

3. The method of claim 1, wherein said virtual measured capacitance is a non-zero constant.

4. The method of claim 1, wherein said virtual measured capacitance is a variable related to said measured capacitances of said plurality of physical traces.