Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-02-09
2001-06-26
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S042000, C349S149000
Reexamination Certificate
active
06252643
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (or “LCD”) device which provides a structure that allows for detection of the distortion of the common voltage resulting from a delay time in application of the common voltage. More specifically, the present invention relates to a liquid crystal display device including a common line which eliminates the need for a common drive circuit and which is arranged to allow for detection of an amount of distortion of the common voltage so that such distortion can be corrected.
2. Description of the Related Art
As seen in
FIG. 1
, conventional LCDs include two transparent panels, i.e., an upper panel
11
and a lower panel
10
, and a liquid crystal material
15
injected between the upper panel
11
and the lower panel
10
. The lower panel
10
includes a plurality of scan lines
24
and a plurality of data lines
23
. The scan lines
24
and data lines
23
are arranged in a matrix form wherein the scan lines
24
and the data lines
23
intersect each other. At each intersecting point between the scan lines
24
and the data lines
23
, a thin film transistor
21
(or “TFT”) and a pixel electrode
20
are provided. The TFT
21
comprises a gate electrode
25
, a source electrode
27
and a drain electrode
29
. Each gate electrode
25
is connected to one of the scan lines
24
and each source electrode
27
is connected to one of the data lines
23
. Each drain electrode
29
is connected to a respective pixel electrode
20
. Although not shown in
FIG. 1
, one end of each scan line
24
is connected to an output of a scan driving IC and one end of each data line
23
is connected to an output of a data driving IC. Additionally, the lower panel
10
can comprise a portion of a common line carrying a common signal applied from an outer device.
As shown in
FIG. 1
, the upper panel
11
comprises a common electrode
14
and a color filter
13
. There are three kinds of the color filters
13
, a red filter (R), a green filter (G) and a blue filter (B). Each of the color filters
13
is disposed at a position corresponding to the position of the pixel electrode
20
in the lower panel
10
. The common electrode
14
is formed on the color filter
13
. Generally, the common electrode
14
is made with one body covering one of the major surfaces of the upper panel
11
. Alternatively, the common electrode
14
comprises many bodies which are formed as strips arranged along with the scan lines
24
or the data lines
23
.
A molecule array direction of the liquid crystal material
15
injected between the upper panel
10
and the lower panel
11
is changed by the voltage difference between the pixel electrodes
20
and the common electrode
14
. When a scan voltage is applied to the scan lines
24
, the TFT
21
is turned on by the voltage applied to the gate electrode
25
. At that time, a data voltage applied to the data line
23
is sent to the drain electrode
29
from the source electrode
27
of the TFT
21
so that the data voltage is applied to the pixel electrode
20
which is connected to the drain electrode
29
. Consequently, a voltage difference is generated between the pixel electrode
20
and the common electrode
14
. As a result of the change of the molecule array direction of the liquid crystal material, the LCD functions as a display device.
FIGS. 2
a
and
2
b
show the conventional structure of the common electrode
14
in a liquid crystal display device. Referring to the
FIGS. 2
a
and
2
b
, the common pads
59
a
and
59
b
of the scan driver IC
55
and the data driver IC
56
apply a common voltage for the lower panel
10
to the common electrode
14
formed in the upper panel
11
. A silver dot
40
(or Ag dot) is disposed in each of the four corners of the lower panel
10
in contact with the common electrode
14
and and to the scan driver IC common pad
59
a
and the data driver IC common pad
59
b
, so that the common voltage is applied to the common electrode
14
through the Ag dots
40
.
In the LCD according to the above-mentioned structure, the wave form of the common voltage which is detected at the portion of the common electrode
14
located near the Ag dot is different from the wave form of the common voltage which is detected at the portion of the common electrode
14
located spaced from the Ag dot. The difference in wave form is caused by a signal delay which occurs because the common voltage signal is delayed by the resistivity of the common electrode
14
. Therefore, it has been necessary to provide a third drive IC
57
for controlling the common electrode
14
.
In order to solve this problem without using a third drive circuit, U.S. Pat. No. 5,311,342 describes a structure, as shown in
FIG. 3
, in which an expanded common line
30
is formed continuously along two adjacent side portions of the matrix display portion of the LCD. The expanded common line
30
surrounds the matrix display portion by extending continuously from the scan pad part located at the lower left corner of the matrix portion in
FIG. 3
to the data pad part located at the upper right corner of the matrix portion in
FIG. 3
so that the scan pad part and the data pad part are connected each other. The common line
30
disposed in the lower panel
10
and the common electrode
14
, shown as a dashed-line square in FIG.
3
and disposed in the upper panel
11
, are connected to each other through the Ag dot
40
. Additionally, a conductive line
50
which is separately formed with the common line is connected to the common electrode
14
in order to reduce the time delay of the common voltage.
However, the structure described in U.S. Pat. No. 5,311,342 experiences problems caused by the expanded common line
30
which is continuously formed to extend from the scan driver IC common pad
59
a
located at the lower left corner of the matrix portion in
FIG. 3
to the data driver IC common pad
59
b
located at the upper right corner of the matrix portion of FIG.
3
. Because of the common line
30
extending continuously between the data pad part and scan pad part, it is not possible to detect the exact amount of the delay time of the common voltage at the center of the display area. So, it is not possible to calculate the amount of the drop down voltage of the common voltage resulting from the time delay. Because such calculation of the drop down voltage is not possible, there is no way to compensate and correct for the drop down voltage. These problems result in flicker being generated in the image displayed by the device shown in FIG.
3
and also prevent uniformity of contrast and brightness in images displayed in the device of FIG.
3
.
SUMMARY OF THE INVENTION
The preferred embodiments of the present invention overcome the problems described above by providing an LCD which is adapted to allow for detection of the time delay or the distortion amount of the common voltage while eliminating the need for a third drive circuit which functions as a common drive circuit in the prior art.
The preferred embodiments of the present invention also provide an LCD which is arranged for allowing for calculation of an amount of distortion of the common voltage resulting from the time delay of the common voltage signal in the common line and common electrode and also facilitates compensation for such distortion of the common voltage applied to the common line.
According to one preferred embodiment of the present invention, a liquid crystal display substrate includes a first substrate having a plurality of pixel electrodes arranged in a matrix; a plurality of row pads and common electrode pads arranged on one side of two adjacent sides of said first substrate; a plurality of column pads and common electrode pads arranged on the other side of the two adjacent sides of said first substrate; a second substrate arranged to be opposite to said first substrate and to interpose a liquid crystal with said first substrate and having a common electrode for performing liquid crystal dis
Graham & James LLP
LG LCD Inc.
Parker Kenneth
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