Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-11-27
2004-09-07
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S098000, C345S099000
Reexamination Certificate
active
06788280
ABSTRACT:
This application claims the benefit of Korean Application No. P2001-54127 filed on Sep. 4, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a method and apparatus for driving a liquid crystal display. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for enhancing a picture quality.
2. Discussion of the Related Art
Generally, a liquid crystal display (LCD) controls a light transmittance of each liquid crystal cell in accordance with a video signal, thereby displaying a picture. An active matrix LCD including a switching device for each liquid crystal cell is suitable for displaying a dynamic image. The active matrix LCD uses a thin film transistor (TFT) as a switching device.
The LCD has a disadvantage in that it has a slow response time due to inherent characteristics of a liquid crystal, such as a viscosity and an elasticity, etc. Such characteristics can be explained by using the following equations (1) and (2):
&tgr;
r
∝&ggr;d
2
/&Dgr;&egr;|V
a
2
−V
F
2
| (1)
where &tgr;
r
represents a rising time when a voltage is applied to a liquid crystal, V
a
is an applied voltage, V
F
represents a Freederick transition voltage at which liquid crystal molecules begin to perform an inclined motion, d is a cell gap of the liquid crystal cells, and &ggr; represents a rotational viscosity of the liquid crystal molecules.
&tgr;
f
=&ggr;d
2
/K (2)
where &tgr;
f
represents a falling time at which a liquid crystal is returned into the initial position by an elastic restoring force after a voltage applied to the liquid crystal was turned off, and K is an elastic constant.
A twisted nematic (TN) mode liquid crystal has a different response time due to physical characteristics of the liquid crystal and a cell gap, etc. Typically, the TN mode liquid crystal has a rising time of 20 to 80 ms and a falling time of 20 to 30 ms. Since such a liquid crystal has a response time longer than one frame interval (i.e., 16.67 ms in the case of NTSC system) of a moving picture, a voltage charged in the liquid crystal cell is progressed into the next frame prior to arriving at a target voltage. Thus, due to a motion-blurring phenomenon a screen is blurred out at the moving picture.
Referring to
FIG. 1
, the conventional LCD cannot express desired color and brightness. Upon implementation of a moving picture, a display brightness BL fails to arrive at a target brightness corresponding to a change of the video data VD from one level to another level due to its slow response time. Accordingly, a motion-blurring phenomenon appears from the moving picture and a display quality is deteriorated in the LCD due to a reduction in a contrast ratio.
In order to overcome such a slow response time of the LCD, U.S. Pat. No. 5,495,265 and PCT International Publication No. WO99/05567 have suggested to modulate data in accordance with a difference in the data by using a look-up table (hereinafter referred to as high-speed driving method). This high-speed driving method allows data to be modulated by a principle as shown in FIG.
2
.
Referring to
FIG. 2
, a conventional high-speed driving method modulates input data VD and applies the modulated data MVD to the liquid crystal cell, thereby obtaining a desired brightness MBL. This high-speed driving method increases |V
a
2
−V
F
2
| from the above equation (1) on the basis of a difference in the data so that a desired brightness can be obtained in response to a brightness value of the input data within one frame interval, thereby rapidly reducing a response time of the liquid crystal. Accordingly, the LCD employing such a high-speed driving method compensates for a slow response time of the liquid crystal by modulating a data value in order to alleviate a motion-blurring phenomenon in a moving picture, thereby displaying a picture at desired color and brightness.
In other words, the high-speed driving method detects a variation in most significant bit data through a comparison of most significant bit data MSB of a current frame Fn with most significant bit data MSB of the previous frame Fn−1. If the variation in the most significant bit data MSB is detected, a modulated data corresponding to the variation is selected from a look-up table so that the most significant bit data MSB is modulated as shown in FIG.
3
. The high-speed driving method modulates only a part of the most significant bits among the input data for reducing a memory capacity. For example, the high-speed driving method can be implemented as shown in FIG.
4
.
Referring to
FIG. 4
, a conventional high-speed driving apparatus includes a frame memory
43
connected to a most significant bit output bus line
42
and a look-up table
44
connected to the most significant bit output bus line
42
and an output terminal of the frame memory
43
.
The frame memory
43
stores most significant bit data MSB during one frame period and supplies the stored data to the look-up table
44
. Herein, the most significant bit data MSB are high-order 4 bits among 8 bits of the source data RGB.
The look-up table
44
makes a mapping of the most significant bit data of the current frame Fn inputted from the most significant bit output bus line
42
and the most significant bit data of the previous frame Fn−1 inputted from the frame memory
43
into a modulation data table such as Table 1 to select modulated most significant bit data Mdata. Such modulated most significant bit data Mdata are added to an non-modulated least significant bit data LSB from a least significant bit output bus line
41
before outputting to a liquid crystal display.
TABLE 1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
0
2
3
4
5
6
7
9
10
12
13
14
15
15
15
15
1
0
1
3
4
5
6
7
8
10
12
13
14
15
15
15
15
2
0
0
2
4
5
6
7
8
10
12
13
14
15
15
15
15
3
0
0
1
3
5
6
7
8
10
11
13
14
15
15
15
15
4
0
0
1
3
4
6
7
8
9
11
12
13
14
15
15
15
5
0
0
1
2
3
5
7
8
9
11
12
13
14
15
15
15
6
0
0
1
2
3
4
6
8
9
10
12
13
14
15
15
15
7
0
0
1
2
3
4
5
7
9
10
11
13
14
15
15
15
8
0
0
1
2
3
4
5
6
8
10
11
12
14
15
15
15
9
0
0
1
2
3
4
5
6
7
9
11
12
13
14
15
15
10
0
0
1
2
3
4
5
6
7
8
10
12
13
14
15
15
11
0
0
1
2
3
4
5
6
7
8
9
11
13
14
15
15
12
0
0
1
2
3
4
5
6
7
8
9
10
12
14
15
15
13
0
0
1
2
3
3
4
5
6
7
8
10
11
13
15
15
14
0
0
1
2
3
3
4
5
6
7
8
9
11
12
14
15
15
0
0
0
1
2
3
3
4
5
6
7
8
9
11
13
15
In the above Table 1, a left column is for a data voltage VDn−1 of the previous frame Fn−1 while an uppermost row is for a voltage VDn of the current frame Fn.
Such a conventional high-speed driving method enhances a dynamic contrast ratio in comparison with a conventional normal driving method that does not modulate the source data. However, the conventional high-speed driving method gradually enhances brightness so that a desired brightness level is achieved at the end of one frame period. Due to this, in the conventional high-speed driving method, the dynamic contrast ratio cannot be reached at a desired level. Furthermore, a color represented by combining red, green, and blue is distorted when those colors are reproduced.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method and apparatus for driving a liquid crystal display that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
Another object of the present invention is to provide a method and apparatus for driving a liquid crystal display that is adaptive for enhancing a picture quality.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended
LG.Philips LCD Co. , Ltd.
Morgan & Lewis & Bockius, LLP
Wu Xiao
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