Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2001-10-16
2003-07-08
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C349S143000, C349S035000
Reexamination Certificate
active
06590411
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-62314, filed on Oct. 23, 2000 in Korea, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a method for measuring an image-sticking defect or residual image and for ascertaining whether the image-sticking defect or residual image exists or not.
2. Description of the Related Art
Until now, the cathode-ray tube (CRT) has been generally used for display systems. However, flat panel displays are increasingly beginning to be used because of their small depth dimensions, desirably low weight, and low power consumption requirements. Presently, thin film transistor-liquid crystal displays (TFT-LCDs) are being developed with high resolution and small depth dimensions.
Generally, liquid crystal display (LCD) devices make use of optical anisotropy and polarization properties of liquid crystal molecules to control alignment orientation. The alignment direction of the liquid crystal molecules can be controlled by application of an electric field. Accordingly, when the electric field is applied to liquid crystal molecules, the alignment of the liquid crystal molecules changes. Since refraction of incident light is determined by the alignment of the liquid crystal molecules, display of image data can be controlled by changing the applied electric field.
Of the different types of known LCDs, active matrix LCDs (AM-LCDs), which have thin film transistors and pixel electrodes arranged in a matrix form, are of particular interest because of their high resolution and superiority in displaying moving images. Because of their light weight, thin profile, and low power consumption characteristics, LCD devices have wide application in office automation (OA) equipment and video units. A typical liquid crystal display (LCD) panel may include an upper substrate, a lower substrate and a liquid crystal layer interposed therebetween. The upper substrate, commonly referred to as a color filter substrate, may include a common electrode and color filters. The lower substrate, commonly referred to as an array substrate, may include switching elements, such as thin film transistors (TFTs), and pixel electrodes.
FIG. 1
is a cross-sectional view of a pixel of a conventional LCD panel in an active matrix LCD. As shown, the LCD panel
20
includes upper and lower substrates
5
and
15
and a liquid crystal (LC) layer
10
interposed therebetween. The lower substrate
15
includes a thin film transistor (TFT) “K” as a switching element that transmits a voltage to the pixel electrode
14
to change the orientation of the LC molecules. The pixel electrode
14
disposed on a transparent substrate
1
applies an electric field across the LC layer
10
in response to signals applied to the TFT “K.” A first alignment layer
6
may be disposed over the TFT “K” and pixel electrode
14
adjacent to the LC layer
10
. Moreover, the lower substrate
15
may include a storage capacitor
16
that maintains the voltage on the pixel electrode
14
for a period of time.
The upper substrate
5
may include a color filter
2
for producing a specific color and a common electrode
4
disposed over the color filter
2
. The common electrode
4
serves as an electrode for producing the electric field across the LC layer (in combination with the pixel electrode
14
). The common electrode
4
may be arranged over a pixel portion “P,” i.e., a display area. The second alignment layer
7
may be disposed on the common electrode
4
. Further, to prevent light leakage of the LC layer
10
, a pair of substrates
5
and
15
may be sealed by a sealant
12
.
Although
FIG. 1
only shows one TFT “K,” the lower substrate
15
usually includes a plurality of TFTs as well as a plurality of pixel electrodes each of which electrically contact each of the plurality of TFTs. In the above-described LCD panel
20
, the lower substrate
15
and the upper substrate
5
are respectively formed through different manufacturing processes, and then attached to each other. As previously described, the liquid crystal display devices make use of the optical anisotropy and polarization properties of the liquid crystal molecules. Since the liquid crystal molecules are thin and long, and the electric field is applied to the liquid crystal layer, the alignment direction of the liquid crystal molecules can be changed and controlled by the applied electric field. Accordingly, incident light is modulated to display images.
FIG. 2
is a circuit diagram of a conventional active matrix liquid crystal display panel.
In
FIG. 2
, the active matrix liquid crystal display panel comprises a number of horizontal gate bus lines
32
, and a number of vertical data bus lines
42
intersecting the gate bus lines
32
, thereby forming a matrix of orthogonal bus lines
32
and
42
. One pixel is formed at each intersection of gate and data bus lines
32
and
42
. Moreover, a thin film transistor “K” is formed at each intersection of the gate and data bus lines
32
and
42
that includes a source electrode “S” connected to a corresponding data bus line
42
, a gate electrode “G” connected to a corresponding gate bus line
32
, and a drain electrode “D” connected to a storage capacitor “C
st
” and a corresponding individual or pixel electrode of liquid crystal cell “C
lc
.” A pixel voltage “V
p
” is applied to the pixel electrode of the liquid crystal cell “C
lc
” from the data lines
42
through the TFT “K.” A common voltage “V
com
” is applied to a common electrode that is connected to both the liquid crystal cell “C
lc
” and the storage capacitor “C
st
.” In the conventional liquid crystal display panel, the liquid crystal cell “C
lc
” and the storage capacitor “C
st
” are connected in parallel. A scanning line driving circuit
30
successively supplies a gate pulse voltage to the gate bus lines
32
with a horizontal scanning period. On the other hand, a signal line driving circuit
40
supplies a pixel signal voltage to the data bus lines
42
in each horizontal scanning period.
The array substrate of the active matrix liquid crystal display panel integrally comprises (m×n)-number of pixel electrodes
14
(of
FIG. 1
) arranged in a matrix, an m-number of gate bus lines G
1
to G
m
arranged along the rows of the pixel electrodes, an n-number of data bus lines D
1
to D
n
arranged along the columns of the pixel electrodes. Furthermore, an (m×n)-number of thin film transistors “K” are arranged as switching elements in the vicinity of cross points between the gate bus lines G
1
to G
m
and the data bus lines D
1
to D
n
corresponding to the (m×n)-number of the pixel electrodes. The scanning line driving circuit
30
drives these gate bus lines G
1
to G
m
, and a signal line driving circuit
40
drives the data bus lines D
1
to D
n
.
Therefore, the scanning line driving circuit
30
successively supplies the gate bus lines
32
with a signal that drives all the gate bus lines G
1
, G
2
, . . . G
m
to turn on all the TFTs “K” arranged in the direction of the column selected by these gate bus lines. The signal line driving circuit
40
also supplies to the data bus lines
42
a signal that drives all the data bus lines D
1
, D
2
, . . . D
n
to apply a predetermined potential through the data bus lines to all the TFTs “K” that have been turned on. When the gate pulse voltage is applied to the gate bus line G
1
, all the TFTs “K” connected to the gate bus line G
1
are turned on. At this time, the turned-on TFTs “K” electrically connect the data bus lines to the liquid crystal cell “C
lc
” and storage capacitor “C
st
” that are electrically connected to the gate bus line G
1
. As a result, the pixel signal voltage supplied from the signal line driving circuit
40
is applied to the determined liquid crystal cell “C
lc
” and storage capacitor “C
st
.” Specifically, the liquid crystal molecules are aligned and oriented by the pixel signal voltage applied t
Cuneo Kamand
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
Nguyen Trung Q.
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