Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-09-20
2004-12-28
Decady, Albert (Department: 2133)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S055000, C345S077000, C345S079000
Reexamination Certificate
active
06836265
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-40985, filed on Sep. 22, 1999, 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 method of driving a liquid crystal display panel, and more particularly to a method of driving a liquid crystal display panel that is adaptive for providing the entire panel with a uniform brightness.
2. Discussion of the Related Art
Generally, in a liquid crystal display panel, a liquid crystal layer controls a transmissivity of a light generated from a backlight in accordance with a voltage level of a data signal applied to the liquid crystal layer to display a picture. Such a liquid crystal display panel has a structure in which pixels provided with a liquid crystal layer and pixel electrodes and a reference electrode for applying a driving voltage to the liquid crystal layer and a reference electrode are arranged in a matrix type.
FIG. 1
is a schematic view of a liquid crystal display and a driving apparatus therefor. In
FIG. 1
, each pixel
22
is provided at each of intersections between m data lines D
1
to Dm and n gate lines G
1
to Gn within the liquid crystal panel
20
. The pixels
22
arranged along each gate line form scanning lines and are connected, via the gate lines G
1
to Gn, to a gate driver
24
. Also, the pixels
22
are connected, via the data lines D
1
to Dm, to the data driver
26
. An equivalent circuit of the pixel
22
as a unit picture element is illustrated within an exploded view within the “circle” of FIG.
1
. Herein, a liquid crystal layer driven by a voltage difference between the pixel electrode and the reference electrode within a single pixel
22
is equivalent to a liquid crystal capacitor Clc. The pixel electrode is connected to a drain electrode of a thin film transistor (TFT) as a switching device, whereas the reference electrode is connected to a common voltage source Vcom. A gate electrode and a source electrode of the TFT are connected to a gate line and a data line, respectively.
The gate driver
24
sequentially applies a gate driving voltage to each gate line G
1
to Gn to drive each scanning line of the panel sequentially. If a voltage is applied, via the gate lines G
1
to Gn, to the gate electrodes of the TFT, then a channel is formed between the source electrode and the drain electrode of the TFT. At this time, a data voltage applied from the data driver
24
, via the data lines D
1
to Dn, to the source electrode of the TFT is applied to the drain electrode of the TFT. A difference voltage between a voltage applied to the drain electrode and a common voltage source Vcom is charged in the liquid crystal capacitor Clc to drive a liquid crystal layer of each pixel
22
. Then, the liquid crystal layer controls a transmissivity of a light generated from the backlight in accordance with a difference voltage between the common voltage source Vcom and the data voltage.
In a general color display panel, a mixed ratio of colors three red (R), green (G) and blue (B), is controlled to realize various colors. In the liquid crystal display panel, red (R), green (G) and blue (B) color filers are mounted at each pixel
22
for transmitting a white light, or a color filer is replaced by three backlight lamps for generating red (R), green (G) and blue (B) lights. A driving method of a liquid crystal display panel without color filters is different from that of a liquid crystal display panel with color filters. In a liquid crystal display panel including three color backlight lamps instead of color filters, one frame making a picture is trisected to apply red (R), green (G) and blue (B) color data to the panel sequentially during each frame interval.
FIG. 2
is a timing chart showing an operation process made during one frame interval in a liquid crystal display panel with no conventional color filter. Referring to
FIG. 2
, in the case of the liquid crystal display panel with no color filter, a data voltage for each of the red (R), green (G) and blue (B) colors applied from the data driver
26
is time-divided during one frame interval to be sequentially charged in the pixels
22
of the panel
20
. A backlight lamp having the corresponding color is turned on from a certain time when a data voltage for one color is being charged sequentially for one scanning line within the panel
20
, until a time when a data voltage for another color begins to be charged in each ⅓ frame interval.
Herein, to turn on the backlight lamp having the corresponding color before a charge of a data voltage for any one color has been completed aims at lengthening a lamp turn-on time sufficiently to improve the brightness of a picture. If the backlight lamp is turned on before a data voltage for any one color was charged in all of the pixels
22
within the panel
20
as mentioned above, however, there exists a problem in that color purity of a picture displayed on the lower part of the panel
20
is deteriorated. As described earlier, during a time interval when a data voltage is charged in the panel
20
, the gate driver
24
drives each gate line G
1
to Gn in sequence from the first gate line G
1
to the n gate line Gn. In other words, a scanning direction of the panel
20
is set to a direction going from the upper end of the panel to lower end thereof. In the pixels within the scanning line to which a gate voltage is applied, a conductive channel is provided between the source electrode and the drain electrode of the TFT to charge a data voltage applied, via the data driver
24
, from the data lines D
1
to Dm. Accordingly, if the backlight lamp is turned on before the scanning lines provided at the lower part of the panel
20
have been charged, then color purity of a picture displayed on the pixels at the lower part of the panel
20
is deteriorated because they is in a state of maintaining a data voltage for the preceding color. In order to solve this problem, the liquid crystal display panel with no color filter takes advantages of a scheme of simultaneously resetting all the pixels
22
within the panel
20
before applying a data voltage for any one color, to erase the entire previous data having been charged into each pixel
22
as shown in FIG.
2
. If such a scheme is used, then, even though the backlight lamp having the corresponding color is turned on before charging of a data voltage for any one color has been completed, the pixels in which charging of the data voltage for the color has not been made go into a state of erasing the data for the preceding color, so that it is possible to prevent a problem of the color purity deterioration caused by residual data.
In a driving method including the step of sequentially charging a data voltage and the step of simultaneously resetting the pixels
22
, however, a brightness non-uniformity phenomenon, differentiating the brightness of a picture displayed on the upper part of the panel
20
from the brightness of a picture displayed on the lower part thereof, is generated. Such a problem will be described in conjunction with FIG.
3
and FIG.
4
. In the conventional panel driving method, each gate line G
1
to Gn provided within the panel
20
is driven in sequence from the first gate line G
1
positioned at the top of the panel, to the nth gate line Gn positioned at the bottom thereof. As shown in
FIG. 3
, the scanning direction of the panel
20
is always constant for each frame interval. As mentioned above, when all the pixels
22
are simultaneously reset prior to charging the next data, a data sustaining interval until a pixel
22
is to be reset becomes different in accordance with whether the pixel
22
is located at any part of the panel. In other words, since all the pixels
22
are not charged simultaneously, the data-sustaining intervals of the pixels
22
become different for each scanning line at the reset time. For instance, data sustaining intervals between A pixels positioned at the first scanning line
Choi Yong Hoon
Lee Hyun Chang
Alphonse Fritz
De'cady Albert
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
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