Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-01-09
2003-07-01
Ngo, Julie (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S150000, C349S152000
Reexamination Certificate
active
06587176
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-10300, filed on Mar. 2, 2000, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to liquid crystal displays (LCD). More particularly it relates to an improvement in the LCD lines which drive the liquid crystal cells to display information.
2. Discussion of the Related Art
An LCD device comprises an LCD panel having upper and lower substrates that are spaced apart and opposed to each other and that have a liquid crystal layer there between. The upper substrate includes a color filter layer and a common electrode formed on the color filter layer. The lower substrate includes a switching element, such as a thin film transistor (TFT), and a pixel electrode.
The common electrode and the pixel electrode apply an electric field across the liquid crystal layer. The TFT serves to operate the pixel electrode using signals from an external drive circuit. The TFT includes a gate electrode, a source electrode, and a drain electrode. The gate electrode is connected to a gate line, the source electrode is connected to a data line, and the drain electrode is connected to the pixel electrode. The gate and source electrodes are connected to the external drive circuits through gate and data pads, respectively, formed at their terminals.
The external drive circuit comprises a gate drive circuit that drives the gate electrode and a data drive circuit that drives the source electrode. Techniques for connecting the drive circuit to the LCD panel include WB (wire bonding), COB (chip on board), TAB (tape automated bonding), and COG (chip on glass).
For a low resolution LCD it is easy to connect drive circuit leads on a PCB (printed circuit board) to the LCD panel since the number of leads is small. However, for a high resolution LCD, it is not so easy to connect drive circuits having a large number of leads to a PCB. For example, an LCD having a resolution of 600×800 (SVGA) has 600×800×3 pixels, which are all connected to drive circuits and thus requires an involved connecting process.
The TAB technique has been introduced to address the problem described above.
FIG. 1
shows a typical TAB technique. As shown in
FIG. 1
, a tape carrier
53
has a drive circuit
51
mounted thereon. The package in which the drive circuit is mounted on the tape carrier is referred to as a TCP (tape carrier package). In other words, a TCP
50
has the drive circuit
51
. The LCD panel
20
and the PCB
52
are connected to the drive circuit
51
through the tape carrier
53
. The TAB technique uses an inner lead bonding (ILB) process that connects the tape carrier to the chip using heat and pressure, and an encapsulation process that applies an epoxy-based resin on the chip. The TAB technique also includes an outer lead bonding (OLB) process that connects the outer leads to the pads on the PCB
52
and to the gate or data pads on the substrate, respectively.
Referring now to
FIG. 2
, gate drive circuits
100
G are placed along the left side of the LCD panel, and data drive circuits
100
D are placed across both the upper and lower sides of the LCD panel. Such a structure is referred to as a dual-bank structure. For an LCD having a resolution of 1600×1200×3 (UXGA), each of the typical data drive circuits
100
D has 384 channels that can control 384 data lines. The number of the data and gate lines is thus 1600×3 and 1200, respectively. Therefore, 14 drive circuits are required to control all of the 1600×3 data lines. In the conventional dual-bank structure, seven drive circuits are arranged across both the upper and lower sides of the LCD panel, respectively. The seven data drive circuits mounted on the lower portion are connected to 2400 data lines. The data drive circuits D
1
to D
6
are each connected to 384 data lines, but the outmost data drive circuit D
7
is connected to only 96 data lines. As shown in
FIG. 2
, the intervals between adjacent drive circuits are all “a” and the seven data drive circuits are symmetrically arranged with respect to the center line “C” of the LCD panel
20
. However, as explained in more detail below, when the intervals between the data drive circuits are all equal a resistance difference occurs in the wiring region (see FIG.
4
).
FIG. 3
is an enlarged view illustrating a portion F
1
of FIG.
2
. Each data line has a display line d-n located on a display region (d-
384
and d-
385
are shown), a leadout line L-n located on a wiring region (L-
384
and L-
385
are shown), and a terminal line T-n located on a pad region (T-
384
and T-
385
are shown). Each terminal line T-n connects to a corresponding data drive circuit. As shown in
FIG. 3
, the last data line d-
384
of a data drive circuit D
1
and the first data line d-
385
of a data drive circuit D
2
have almost the same wiring distance. That is, the readout line L-
384
and the leadout line L-
385
have almost the same length. However, this is not the case in portion F
2
, shown in
FIG. 4
, which is an enlarged view of portion F
2
of FIG.
2
.
In
FIG. 4
, the last leadout line L-
2304
connected to a data drive circuit D
6
and the first leadout line L-
2305
connected to a data drive circuit D
7
differ significantly in length, resulting in a resistance difference between the leadout line L-
2304
and L-
2305
. Such a resistance difference between adjacent leadout lines causes shadowing (uneven brightness) and distortions (such as deformations of liquid crystal drive waveforms and crosstalk).
FIG. 5
shows a simplified LCD panel having only 14 data lines, with each data drive circuit having only three channels. As shown, as a data drive circuit is positioned farther away from the first data drive circuit D
1
, the difference in length between the leadout lines of adjacent last and first data lines becomes greater. Namely, if all intervals between adjacent data drive circuits are equal, and if the data drive circuits are symmetrical about the center of the display, the lengths of the leadout lines of the last data lines become greater as a data drive circuit is positioned farther from the first data drive circuit D
1
. This causes a resistance difference between the readout lines of the adjacent last and first data lines. With regard to
FIG. 5
, the greatest difference in length between adjacent leadout lines occurs between the leadout line of the last data line connected to the data drive circuit D
4
, specifically data line d-
12
, and the leadout line of the first data line connected to data drive circuit D
5
, specifically d-
13
.
To alleviate display distortions due to resistance differences described above, one technique employs a method of adjusting the widths of the data lines to compensate for the RC (Resistance×Capacitance) delay. See U.S. Pat. No. 5,757,450. However, for a high resolution LCD device with a large number of data lines, it is rather difficult to accurately design and fabricate the data lines to compensate for the RC delay.
The problem described above results from the outermost data drive circuit having more channels than data lines. For example, the outermost data drive circuit D
5
of
FIG. 5
has three channels but connects to only two data lines. Such a problem could be addressed by employing data drive circuits in which all channels connect to a data line. For example, a liquid crystal display conceivably could use data drive circuits having 300 channels each to drive 4800 data lines. However,
16
data drive circuits would be required, leading to high production costs due to the additional data drive circuits and to their interconnections. Furthermore, data drive circuits with 300 channels would have to be designed and manufactured to replace those currently existing. Therefore, a display having reduced distortions caused by wiring resistance differences would be beneficial.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to
LG.Philips LCD Co. , Ltd.
McKenna, Long and Aldridge
Ngo Julie
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