Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2000-10-20
2002-11-12
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S061000, C349S106000
Reexamination Certificate
active
06480247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a liquid crystal display that realizes full color without using color filters in sub-pixels by sequentially providing different colors of light to the display.
2. Description of the Related Art
Generally, liquid crystal displays (LCD's) tend toward wider and wider application by virtue of their characteristics such as low weight, thin form factor, and low power consumption. Accordingly, LCD's have been used for office automation equipment, video/audio equipment, etc. The LCD controls an amount of transmitted light in response to data signals applied to a number of control switches arranged in a matrix, to display a desired picture on the screen.
Referring to
FIG. 1
, the conventional LCD includes a back light unit
10
for generating and uniformly supplying a light beam to the liquid crystal panel
50
. The liquid crystal panel
50
includes a lower polarizer
22
arranged at the upper portion of back light unit
10
to change a polarization characteristic of the light beam. A lower substrate
24
is arranged on the lower polarizer
22
, and thin film transistors (TFT's)
38
for applying a signal controlling a transmitted amount of the light beam are arranged in a matrix configuration. A liquid crystal layer
28
is provided at the upper portion of the lower substrate
24
, and a common electrode layer
30
is provided on the liquid crystal layer
28
. Color filter layers
36
are provided at the upper portion of the common electrode layer
30
. An upper substrate
32
is provided on the color filter layers
36
, and an upper polarizer
34
is arranged on the upper substrate
32
to convert a polarization characteristic of the light beam.
The back light unit
10
consists of a light source (not shown) for generating a light beam, a light guide (not shown) for uniformly guiding the light beam from the light source into a liquid crystal panel, and a reflector (not shown) arranged at the lower portion of the light guide to reflect a light beam from the bottom or side surfaces of the light guide toward the liquid crystal panel
50
. By such a configuration, a light beam from the back light unit
10
progresses uniformly toward the liquid crystal panel
50
. An exemplary energy distribution spectrum of a white light beam generated from the back light unit
10
is illustrated in FIG.
2
.
The white light beam going from the back light unit
10
into the liquid crystal panel
50
is polarized by the lower polarizer
22
. When the polarized light beam passes through a liquid crystal
28
controlled by the TFT
38
, the polarization state of the polarized light beam is changed. More specifically, if the TFT
38
is turned on, then an image signal is applied via the TFT
38
to a pixel electrode
26
. At this time, the liquid crystal
28
has a different orientation state in response to a potential between the pixel electrode
26
and the common electrode
30
. A light beam changed in a polarization state by virtue of the liquid crystal layer
28
passes through the color filter layer
36
, which transmits only wavelengths of light (i.e., colors) corresponding to each color filter element.
An exemplary spectrum of a light beam transmitted by the color filters is illustrated in FIG.
3
. As shown in
FIG. 4
, one pixel
42
has sub-pixels
40
corresponding to red (R), green (G) and blue (B) colors. In other words, the three sub-pixels
40
make up a single pixel
42
. As described above, a light beam transformed into a desired color by the color filter layer
36
passes through the upper substrate
32
, and thereafter goes into the upper polarizer
34
to display a picture corresponding to an image signal.
The conventional color-filter LCD has a high manufacturing cost because the color filter material is expensive. Also, the conventional color-filter LCD has a problem that a resolution of a displayed image is deteriorated, since one pixel consists of three sub-pixels. Also, a production yield is lower, since a process of configuring the sub-pixels and a process of forming the color filter layers are additionally required. In order to solve these problems, a color-filterless LCD employing a sequential lighting system as shown in
FIG. 5
has been suggested. As used herein, the term “color-filterless” refers to a display that realizes full color without using color filters in sub-pixels of a liquid crystal panel, e.g., as shown in FIG.
4
.
Referring to
FIG. 5
, the conventional color-filterless LCD includes three primary color light sources
12
R,
12
G and
12
B turned on sequentially to generate sequential light beams corresponding to R, G and B colors. An optical medium
13
uniformly distributes the sequential light beams from the light sources. The liquid crystal panel
50
is not provided with any color filters. In order to implement a color image from such a structure, the back light unit
10
is provided with the three primary light sources
12
R,
12
G and
12
B. In this case, a reflector (not shown) is arranged under the optical medium
13
and the three primary color light sources
12
R,
12
G and
12
B. A diffusing sheet
66
and the like are arranged on the optical medium.
A method of driving the color-filterless LCD employing a sequential lighting system will be described below in conjunction with FIG.
6
. As shown in
FIG. 6
, in order to display an image
6
in color, an R light beam is transmitted by a portion of the liquid crystal panel
50
corresponding to an R color of the entire image. In turn, a G light beam is transmitted by a portion corresponding to a G color of the entire image. Finally, a B light beam is transmitted by a portion corresponding to a B color of the entire image.
In order to realize a full color image, the three primary color light sources are sequentially turned on color-by-color, and the pixels of the liquid crystal panel
50
are controlled to have a transmissivity corresponding to a color brightness of the turned-on light source. When any one of the three color light sources
12
R,
12
G, and
12
B has been turned on, other color light sources are turned off or have a minimum brightness. When such sequential turned-on times are controlled to have a very short time interval, an observer does not sense a turning on and off of the displayed image, but views a full color image. Since the color-filterless LCD shown in
FIG. 5
does not use any color filters, a manufacturing cost of the liquid crystal panel can be reduced. Also, because it permits an expression of a picture corresponding to an image signal using only single pixels without any sub-pixels, the LCD's resolution, brightness and aperture ratio can be improved.
The conventional color-filterless LCD may be configured by a back light directly under the liquid crystal panel
50
as shown in
FIG. 5
, and the back light includes a light guide
14
under the liquid crystal panel
50
and lamps to the side of the light guide
14
as shown in
FIGS. 7A and 7B
. However, since the conventional color-filterless LCD has to turn on the three primary color independent light sources during a short period, the number of light sources as well as a size of the light source driver is increased. Thus, the conventional color-filterless LCD has problems of a complex driving system and a short life. Also, the back light under the liquid crystal panel
50
has a disadvantage in that it has large thickness and high power consumption. On the other hand, the back light to the side of liquid crystal panel
50
can achieve a thin form factor, low weight and low power consumption, but has a difficulty in arranging the three primary color light sources efficiently as shown in FIG.
7
B. As a result, a novel strategy for overcoming the above-mentioned problems has been required.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to overcome one or more disadvantages of the conventional displays noted above.
In order to achieve these and
Birch & Stewart Kolasch & Birch, LLP
Dudek James A.
LG Philips LCD Co., Ltd.
LandOfFree
Color-filterless liquid crystal display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Color-filterless liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color-filterless liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2978870