Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-10-23
2002-11-19
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C345S087000, C349S152000
Reexamination Certificate
active
06483565
ABSTRACT:
BACKGROUND OF THE INVENTION
1. (a) Field of the Invention
The present invention relates to an in-plane switching mode LCD (liquid crystal display) device and, more particularly, to an improvement of such a LCD device for a uniform brightness and a higher image quality.
2. (b) Description of the Related Art
LCD panels used for LCD devices are generally categorized by the mode of the liquid crystal into a plurality of types including a TN-mode (twisted nematic mode) LCD panel wherein the LC layer is driven by a perpendicular electric field, and an in-plane switching mode LCD panel, wherein the LC layer is driven by a lateral electric field.
FIG. 1A
shows a TN-mode LCD panel in a sectional view, and
FIG. 1B
shows the TN-mode LCD panel in a perspective view for illustrating the viewing angle dependency thereof. In the TN-mode LCD panel of
FIG. 1A
, a perpendicular electric field “F” is generated in a LC layer
100
by a set of electrodes. The term “perpendicular” as used herein means that the electric field is perpendicular to the surfaces of front and rear panels
101
and
102
sandwiching therebetween the LC layer
100
. Each of the panels
101
and
102
mounts thereon an electrode layer for generating the perpendicular electric field.
More specifically, the front panel
101
mounts thereon a common electrode
103
at the interface between the LC layer
100
and the surface of the front panel
101
, whereas the rear panel
102
mounts thereon a pixel electrode
104
for each of pixels at the interface between the LC layer
100
and the surface of the rear panel
102
.
The common electrode
103
is common to all the pixels of the LCD panel and formed on the entire area of the front panel
101
. The pixel electrode
104
is separately disposed for each of the pixels whereby each pixel displays the own image based on the data supplied to the pixel electrode
104
. The common electrode
103
and the pixel electrodes
104
are made of transparent substance so that the user observes the image on the LCD panel by way of the light passing through these transparent electrodes
103
and
104
.
As shown in
FIG. 1B
, since the LC molecules
105
in the TN-mode LC layer stands upright with respect to the panels
101
and
102
based on the perpendicular electric field, the image on the LCD panel depends on the direction in which the user observes the LCD panel. That is, the LCD panel has a large viewing angle dependency. For example, the effective viewing angle providing an image having a contrast ratio above 10 is limited to around 30° with respect to a perpendicular of the panel as viewed from the upper position, around 20° from the lower position and around ±45° as viewed in the horizontal direction.
FIG. 2
shows an equivalent circuit diagram of the LCD panel shown in
FIG. 1A
, as viewed from the front thereof. A single pixel
106
includes an equivalent capacitor having a LC layer
100
acting as a capacitor insulator film, and a common electrode
103
and a pixel electrode
104
sandwiching therebetween the LC layer
100
, and a thin film MOSFET (TFT)
107
disposed for the pixel electrode
104
. The TFT
107
has a source connected to the pixel electrode
104
, a drain connected to a corresponding signal line D
1
disposed for each column of the pixels, and a gate connected to a scanning line disposed for a row of the pixels.
FIG. 3
shows a schematic overall front view of the LCD panel of
FIG. 2
, wherein a plurality of the pixels
106
shown in
FIG. 2
are arranged in a matrix on the screen of the LCD panel
108
. A plurality of scanning lines G
1
, G
2
, . . . are disposed for respective rows of the pixels
106
, whereas a plurality of data lines D, D
2
, . . . are disposed for respective columns of the pixels
106
. The terminals of the scanning lines G
1
, G
2
, . . . are connected to respective output terminals of a gate driver
109
disposed at the left side of the LCD panel
108
, whereas the terminals of the data lines D
1
, D
2
, . . . are connected to respective terminals of a data driver
110
disposed at the top of the LCD panel
108
. The terminal
103
T of the common electrode
103
is connected to a ground line.
The in-plane switching mode LCD panel is now replacing the conventional TN-mode LCD panel due to the smaller viewing angle dependency of the in-plane switching mode LCD panel.
FIGS. 4A and 4B
show the in-plane switching mode LCD panel, similarly to
FIGS. 1A and 1B
for the TN-mode LCD panel.
In
FIG. 4A
, the pixel electrodes
204
and the common electrodes
203
are disposed on the rear panel
204
, whereby a lateral electric field F
1
is formed between the pixel electrode
204
and the corresponding common electrode
203
in each pixel in a direction substantially parallel to the surfaces of both the panels
201
and
202
. Other configurations of the in-plane switching mode LCD panel are similar to those of the TN-mode LCD panel shown in
FIGS. 2 and 3
.
In
FIG. 4B
, the LC molecules
205
are rotated by the lateral electric field within a plane parallel to both the panels
201
and
203
. This configuration affords a smaller difference in the contrast ratio between different angles of the observation by the user. For example, the effective viewing angle of the in-plane switching mode LCD panel affording a contrast ratio of 10 or more is ±70 degrees from the top, bottom, left and right sides in observation.
In the in-plane switching mode LCD panel, the common electrodes, pixel electrodes, common electrode line, scanning lines and data lines are generally made of metallic films disposed on the single rear panel. This necessitates smaller widths or a smaller line pitch for these electrodes and lines for achieving a specific light transmittance ratio (or opening ratio) in each pixel area, compared to the conventional TN-mode LCD panel.
The smaller width raises line resistances to increase the voltage drop along the electrodes and the lines and thereby degrade the uniformity in the brightness among the pixels, especially in a large screen LCD panel. The smaller line pitch for the lines and electrodes increases cross-talks between the pixels. Thus, image quality of the in-plane switching mode LCD panel is degraded.
SUMMARY OF THE INVENTION
In view of the above problems in the conventional in-plane switching mode LCD device, it is an object of the present invention to provide an in-plane switching mode LCD panel having less cross-talks, a uniform brightness and a high image quality by reducing and substantially equalizing the voltage drop among the pixels.
The present invention provides an in-plane switching mode LCD panel including a LC layer, and first and second panels sandwiching therebetween the LC layer to define a plurality of pixels arranged in a matrix, the first panel including a plurality of data lines each disposed for a corresponding column of the pixels, a plurality of scanning lines each disposed for a corresponding row of the pixels, a common electrode line disposed for the plurality of pixels, each of the pixels including a pixel electrode, a common electrode connected to the common electrode line, and a TFT having a source connected to the pixel electrode, a drain connected to a corresponding one of the data lines and a gate connected to a corresponding one of the scanning lines, a common terminal connected to an end of the common electrode line, a plurality of data terminals each connected to an end of a corresponding one of the data lines, a plurality of first scanning terminals each connected to one of ends of a corresponding one of the scanning lines, and a plurality of second scanning terminals each connected to the other of ends of the corresponding one of the scanning lines.
In accordance with the in-plane switching mode LCD device of the present invention, the first and second scanning terminals connected to each scanning line reduces the signal delay caused by the parasitic capacitance and parasitic resistance of each the scanning line, whereby the scanning line may have a smaller width and thus a smaller li
Hidehira Masanobu
Kuroha Syouichi
Matsumoto Seiichi
Tamura Fuminori
McGinn & Gibb PLLC
NEC Corporation
Rude Timothy L
Ton Toan
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