Digitizer

Details Digitizer Digitizer

2000-07-19

2003-12-30

Saras, Steven (Department: 2675)

Computer graphics processing and selective visual display system

Display peripheral interface input device

Touch panel

C345S174000, C349S012000, C178S018030, C178S018040

Reexamination Certificate

active

06670949

ABSTRACT:

CROSS REFERENCE
This application claims the benefit of Korean Patent Application No. 1999-29057, filed on Jul. 19, 1999, under 35 U.S.C. §119, the entirety of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digitizer, and more particularly, to a digitizer for use in a liquid crystal display (LCD) device.
2. Discussion of the Related Art
A digitizer is one of a class of devices that responds to location information input by a finger or a stylus on a touch panel to generate paired analog coordinate signals corresponding to the location on a touch panel to which the finger or stylus has been applied. In a digitizer, the generated analog coordinate signals are digitized and conveyed to a display device for use in a.notebook computer. Digitizers have also been used generally in computer graphics, computer aided design (CAD), and computer aided manufacturing systems.
FIG. 1
shows a resistive touch panel
10
of a conventional digitizer disclosed in U.S. Pat. No. 4,853,493, having a resistive layer represented at grid “Rg”, a plurality of linear resistors R
LXN
and R
LYN
, chain resistors R
CHX
and R
CHY
, and corner resistors R
CXN
and R
CYN
. Corner resistors R
CX1
and R
CY1
are coupled or connected with terminal V
1
; corner resistors R
CX2
and R
CY2
are coupled or connected with terminal V
2
; comer resistor R
CX3
and R
CY3
are coupled or connected with terminal V
3
; and comer resistors R
CX4
and R
CY4
are coupled or connected with terminal V
4
. The terminals V
1
, V
2
, V
3
and V
4
are coupled or connected to a digitizer drive circuit (not shown).
To derive signals representing analog coordinate pairs corresponding to the position of the stylus or the finger in the conventional digitizer of
FIG. 1
, a reference potential is alternately applied to every two adjacent terminals, moving in a clockwise or counterclockwise direction using predetermined switching techniques. The reference potential is derived from a voltage source (not shown). For example, in case of a clockwise direction, when an a.c. reference voltage of 5 volts is applied to the terminals V
1
and V
2
, the terminals V
3
and V
4
are retained in a ‘ground’ condition. Further, when an a.c. reference voltage of 5 volts is applied to the terminals V
2
and V
4
, the terminals V
1
and V
3
are retained in a ‘ground’ condition. Electrical signals from the digitizer drive circuit are applied to the chain resistors R
CHX
and R
CHY
through the corner resistors R
CX
and R
CY
and then applied to the grid resistor Rg through a plurality of the linear resistors R
LXN
and R
LYN
. The resistance of the linear resistors R
LXN
and R
LYN
differs according to their locations so as to form equipotential lines perpendicular to the applied signals. In other words, in order to form the equipotential lines, the linear resistors R
LXN
and R
LYN
become shorter in length or wider in width as they get further from the corner resistors R
CXN
and R
CYN
, respectively. This is because the voltage drop between the terminal and the grid resistor Rg becomes greater as the linear resistors R
LXN
and R
LYN
get farther from the corner resistors R
CXN
and R
CYN
.
However, as shown in
FIG. 2
, the potential distribution is not uniform, and the potential distribution becomes more uniform closer to the central portion of the grid resistor Rg. This is because the arrangement of the linear resistors R
LXN
and R
LYN
is not as dense as the arrangement of the grid resistor Rg. Therefore, there are connection portions and non-connection portions between the borders of the grid resistor Rg and the linear resistors R
LXN
and R
LYN
, resulting in a potential difference between the confection portions and the non-connection portions. Therefore, portions “B” of the grid resistor Rg, in which a significant potential difference occurs, cannot serve as an active region “C” for sensing a location of a stylus or a finger. Thus, the non-active area, which is unusable for sensing, is relatively large.
FIG. 3
shows a touch panel
12
of a digitizer disclosed in U.S. Pat. No. 4,755,634. As shown in
FIG. 3
, a resistive touch panel
12
includes a plurality of parallel resistive elements R
STR
in the form of a strip, whose ends are interconnected with two chain resistor elements R
CH
through linear resistor elements R
Ln
. The linear resistors R
Ln
differ in resistance so that the same potential is applied to each strip resistor R
STR
. The chain resistor elements R
CH
are connected to the terminals V
1
, V
2
, V
3
and V
4
through input resistor electrodes R
IN1
, R
IN2
R
IN3
and R
IN4
, respectively. The terminals V
1
, V
2
, V
3
and V
4
are connected to the digitizer drive circuit (not shown).
To derive signals representing coordinate pairs corresponding to the position of a stylus or a finger using the touch panel of
FIG. 3
, four electrical signals are simultaneously applied to the terminals V
1
, V
2
, V
3
and V
4
from the digitizer drive circuit (not shown). To detect precise x-y coordinate values, it is preferred that the parallel resistive elements R
STR
have equipotential lines at the same locations along the y-axis of each parallel resistive element R
STR
, regardless of the difference in the signals respectively applied to the terminals V
1
, V
2
, V
3
and V
4
.
However, as shown in
FIG. 4
, the resistive touch panel
12
does not show such desired equipotential distributions when different electrical signals are applied to the terminals V
1
, V
2
, V
3
and V
4
. For example, different potentials at each terminal can result when the wires that connect each terminal with the digitizer drive circuit differ in resistance, so that the electrical signals applied at each of the terminals differ. Thus, the actual potential distribution throughout the panel is not uniform and differs from the designed potential distribution. This non-uniform potential distribution results from the resistor structure of the resistive touch panel
12
. Because the parallel resistor elements R
CH
of the resistive touch panel
12
are arranged only in the direction of the x-axis, the potential distribution of the parallel resistor elements R
CH
shown in
FIG. 4
is inferior to that of the grid having an x-y coordinate arrangement. That is, the potential lines are skewed, and therefore, the digitizer cannot produce or detect precise location information indicative of the location of a stylus or a finger.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a digitizer that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a digitizer having an improved potential distribution.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof, as well as the appended drawings.
To achieve the above object, and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a touch panel for sensing a point of contact on a display. The present invention also provides an apparatus for locating a selected touch point.
One embodiment of the present invention provides an apparatus for locating a selected touch point physically touched by a human finger or a stylus and producing an electrical signal corresponding thereto. The apparatus of this embodiment includes an insulating substrate and a resistor touch pattern supported on the insulating substrate. The resistive touch pattern includes a plurality of strip resistors that are parallel to a center line. The center line is defined by the plurality of strip resistors. Each of the strip resistors has two ends. The re

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