Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-12-28
2004-02-17
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S094000, C345S095000, C345S096000
Reexamination Certificate
active
06693618
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2001-40737, filed on Jul. 9, 2001 in Korea, 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 a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of driving the liquid crystal display device.
2. Discussion of the Related Art
Liquid crystal display devices have been gaining in popularity in the display field because of their low power consumption and superior portability. Generally, the liquid crystal display device comprises a lower substrate, also referred to as an array substrate, an upper substrate, also referred to as a color filter substrate, and interposed liquid crystal between the upper substrate and the lower substrate. The lower substrate includes a thin film transistor. The upper substrate includes a color filter. Liquid crystal display devices use optical anisotropy and polarization properties of liquid crystals to display images. Presently, active matrix LCD (AM LCD) devices are one of the most popular means for displaying images because of their high resolution and superiority in displaying moving images. Accordingly, for purposes of discussion, all liquid crystal display devices hereinafter described refer to active matrix LCD (AM LCD) devices.
FIG. 1
illustrates a schematic view of a liquid crystal panel used in a conventional liquid crystal display device. As shown in
FIG. 1
, a liquid crystal panel
2
includes an upper substrate
4
having a common electrode (not shown), and a lower substrate
6
having a pixel electrode (not shown). A liquid crystal layer
8
is interposed between the upper substrate
4
and the lower substrate
6
. A gate integrated circuit
10
and a data integrated circuit
12
, used for applying a gate signal and a data signal, respectively, are positioned on the left and upper portion of the liquid crystal panel
2
, respectively. A plurality of scanning lines g
i
, where “i” is a positive integer and
1
≦i≦n, are provided to receive a gate signal and a plurality of signal lines d
j
, where “j” is a positive integer and
1
≦j≦m, are provided to receive a data signal on the lower substrate
6
. The scanning lines and the signal lines cross each other to define a pixel region. A plurality of thin film transistors are formed at the crossing of the scanning lines and the signal lines. A liquid crystal capacitor C
LC
and a storage capacitor C
ST
are connected in parallel to the thin film transistor.
A conventional driving method of the abovementioned liquid crystal display device will now be described with reference to
FIGS. 2A-2C
,
3
A,
3
B, and
4
. Generally, the duration of time that the gate signal is applied to the scanning line such that the scanning line is in an “on-state” is called a selection time. Conventional driving methods apply a higher voltage to the gate, which is connected to the scanning line, than a voltage applied to the signal line to reduce a resistance of a channel between a source electrode and a drain electrode during the selection time. Accordingly, the voltage applied to the signal line, also becomes applied to the liquid crystal layer through the pixel electrode. Conventional driving methods further apply lower voltage to the gate than a voltage applied to the signal line to electrically sever the source electrode and the drain electrode during a non-selection time. Accordingly, the electric charge accumulated in the liquid crystal layer during the selection time is maintained. By causing each scanning, line, from the first to the last, to undergo a selection time and a non-selection time, a frame of an image is made.
Referring to
FIG. 2A
, a timing chart illustrates a gate pulse applying method for each frame of a liquid crystal display device according to the related art. As shown in the
FIG. 2A
, all scanning lines of one frame are selected by applying an on-off gate pulse sequentially from the first scanning line g
1
to the i
th
scanning line g
1
. For example, a first gate pulse
14
a
of a first frame and a second gate pulse
14
b
of a second frame are sequentially applied only once to pixels of the corresponding scanning line. After the first scanning line g
1
undergoes the on-off of the gate pulse
14
, the first scanning line g
1
should maintain an alignment of the liquid crystal for one frame period until the gate pulse
14
is applied to the i
th
scanning line g
i
. This driving method is referred to as a hold type driving method.
Referring to
FIG. 2B
, another timing chart illustrates a method of processing image information for each frame in the hold type driving method. As shown in
FIG. 2B
, the hold type driving method maintains uniform image information for one frame. This processing method is possible only when a response speed of the liquid crystal equal to a speed of processing image information. However, twisted nematic (TN) liquid crystal, which is typically used in conventional liquid crystal display devices, has a response speed of 20 msec. The response speed of the liquid crystal within the liquid crystal display device, driven according to the hold type driving method, cannot catch up with the image information processing speed because a response speed of the liquid crystal suitable for motion picture must be at least under 5 msec. Accordingly, deterioration of displayed images occurs and results in a blurred motion of an image because the image information of the previous frame also remains in the next frame. Referring to
FIG. 2B
, the difference in height of the image information region for each frame indicates a gray level difference.
Referring to
FIG. 2C
, a chart illustrates a screen processing method of a hold type liquid crystal display device according to related art. As shown in
FIG. 2C
, at an arbitrary time, only image information on the selected scanning line
17
is refreshed. The selected scanning line
17
receives the image information of a new frame and, if the response speed of the liquid crystal cannot catch up with the image information processing speed, the image of the previous frame remains in the corresponding pixels of the selected scanning line
17
and thereby blurred motion results. Additionally, a data signal voltage, applied through the data integrated circuit, has a voltage different from a pixel voltage, applied to the pixel, due to resistance between lines in the course of arriving at the pixel or a parasitic capacitance in a portion of the thin film transistor. This voltage difference causes an image information difference between desired image information and actual image information. This image information difference brings about blurred motion in terms of visual perception.
Referring to
FIG. 3A
, a timing chart illustrates light emission profiles of a conventional cathode cay tube (CRT) display device.
FIG. 3B
illustrates a timing chart for a lighting operation curve of a conventional liquid crystal display device. In
FIG. 3A
, the light emission profile is individually formed for each frame by placing a black image section “I”, which makes a light intensity to become zero in a frame. As shown in
FIG. 3B
, because the liquid crystal display device uses a hold type driving method, and maintains fixed image form each frame, a continuous lighting operation curve is formed. An error region “II” between the lighting operation curve and the data signal voltage brings about more blurred motion of an image as the frame is repeated. To overcome the above problem, a light emission profile according to two steps for each pixel is needed.
Referring to
FIG. 4
, a timing chart illustrates a related art method of processing image information for each frame in a liquid crystal display device using an impulsive type driving method. In the impulsive driving method, a certain portion of each frame is allocated a black image section “III” to prevent the image information of the previous fr
Park Ku-Hyun
Son Hyeon-Ho
Chang Kent
LG. Philips LCD Co., Ltd
McKenna Long & Aldridge LLP
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