Liquid crystal display device

Details Liquid crystal display device Liquid crystal display device

2002-07-11

2004-12-14

Mengistu, Amare (Department: 2673)

Computer graphics processing and selective visual display system

Plural physical display element control system

Display elements arranged in matrix

C345S102000

Reexamination Certificate

active

06831621

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color liquid crystal display device for presenting color display using a backlight which emits light of a plurality of colors.
2. Description of the Background Art
A transmissive liquid crystal display device is a device such that light emitted from a backlight disposed on the backside thereof is transmitted through a liquid crystal panel and is then used to recognize an image.
FIG. 25
shows an example of a sectional structure of a liquid crystal panel
100
for use in the transmissive liquid crystal display device. The liquid crystal panel
100
comprises polarizing filters
101
,
102
, an array substrate
103
, a glass substrate
104
with a color filter
106
placed on a surface thereof, the substrates
103
and
104
being disposed in opposed relation to each other between the polarizing filters
101
and
102
, and a liquid crystal layer
105
sealed in a space between the substrates
103
and
104
. Although not shown, pixel electrodes and active elements are disposed in a matrix on a surface of the array substrate
103
, and transparent electrodes opposed to the pixel electrodes are formed between the color filter
106
and the liquid crystal layer
105
. A backlight
107
which emits white light
108
is provided on the backside of such a liquid crystal panel
100
. The white light
108
is colored when passing through the color filter
106
of the liquid crystal panel
100
. As shown in
FIG. 26
, the color filter
106
has R (red), G (green) and B (blue) colored layers corresponding to each pixel and disposed in a matrix on the glass substrate
104
. Each of the colors for each pixel corresponds to one liquid crystal cell.
Also known is another transmissive liquid crystal display device which employs backlights
206
R,
206
G and
206
B for emitting light of three colors R, G and B, respectively, as shown in
FIG. 27. A
liquid crystal panel
200
shown in
FIG. 27
comprises polarizing filters
201
,
202
, an array substrate
203
and a glass substrate
204
which are disposed in opposed relation to each other between the polarizing filters
201
and
202
, and a liquid crystal layer
205
sealed in a space between the substrates
203
and
204
. The remaining structure of the liquid crystal panel
200
is substantially similar to the corresponding structure shown in
FIG. 25
except that the liquid crystal panel
200
comprises no color filter. The backlights
206
R,
206
G and
206
B disposed on the backside of such a liquid crystal panel
200
are controlled to turn on in a time-shared manner for each emitted color. As shown in
FIG. 28
, each pixel of the liquid crystal panel
200
corresponds to one liquid crystal cell. Thus, the liquid crystal panel
200
is required to have liquid crystal cells the number of which is one third the number of liquid crystal cells of the liquid crystal panel
100
of the color filter type shown in
FIG. 25
under the same specifications. The liquid crystal panel
200
has the advantage of greatly reducing light losses because of the non-use of the color filter, to require a smaller amount of backlight to achieve the same intensity of the transmitted light as that of the color filter type.
FIGS. 29 and 31
are schematic diagrams of background art transmissive liquid crystal display devices using a backlight for emitting light of three colors R, G and B. A liquid crystal display device
300
shown in
FIG. 29
is disclosed in Japanese Patent Application Laid-Open No. 2000-28984. In
FIG. 29
, the reference numeral
301
designates a liquid crystal panel using ferroelectric or antiferroelectric liquid crystal elements capable of high-speed response;
302
designates a backlight having a group of LEDs (Light-Emitting Diodes) for emitting light of each of the colors R, G and B;
305
designates a source driver for driving signal lines of the liquid crystal panel
301
; and
306
designates a gate driver for selectively driving scanning lines of the liquid crystal panel
301
. Light emitted from the backlight
302
is directed through a light guide plate (not shown) onto the backside of the liquid crystal panel
301
. Display data DD for display on the liquid crystal panel
301
is inputted to an image memory
303
from, for example, a personal computer. The image memory
303
temporarily stores therein the inputted display data DD, and then outputs data (referred to hereinafter as pixel data PD) for each pixel in synchronism with a synchronizing signal SYN provided from a control signal generating circuit
304
. The pixel data PD is transmitted to a first input terminal of a selector
310
and to an inverted data generating circuit
309
.
The control signal generating circuit
304
generates the synchronizing signal SYN to output the synchronizing signal SYN to the gate driver
306
, a reference voltage generating circuit
307
and a backlight control circuit
308
including a drive power supply. The gate driver
306
controls the on/off operation of the scanning lines of the liquid crystal panel
301
in synchronism with the synchronizing signal SYN. The reference voltage generating circuit
307
generates a reference voltage VR in synchronism with the synchronizing signal SYN to provide the reference voltage VR to the source driver
305
and the gate driver
306
. The backlight control circuit
308
provides a drive voltage synchronous with the synchronizing signal SYN to the backlight
302
to cause the LEDs constituting the backlight
302
to emit light.
FIG. 30A
is a timing chart showing the lighting timing of the backlight. The backlight
302
emits R light, G light and B light corresponding to an R subframe, a G subframe and a B subframe, respectively, in a time-shared manner during one frame display period ({fraction (1/60)} second).
FIG. 30B
is a timing chart showing a data write scanning signal and a data erase scanning signal in timed relation to the lighting of the LEDs of the three colors shown in FIG.
30
A.
The inverted data generating circuit
309
produces inverted data #PD which is an inverted version of the pixel data PD to output the inverted data #PD to a second input terminal of the selector
310
. The selector
310
selects one of the pixel data PD and the inverted data #PD in accordance with a control signal CS transmitted from the control signal generating circuit
304
to output the selected data to the source driver
305
. The source driver
305
provides a voltage signal corresponding to the pixel data PD or the inverted data #PD through the signal lines of the liquid crystal panel
301
to the pixel electrodes. When the voltage signal corresponding to the inverted data #PD is provided, an electric field equal in intensity to but opposite in polarity from an electric field applied during data write scanning is applied to the pixel electrodes of the liquid crystal panel
301
during data erase scanning shown in
FIG. 30B
to erase (or turn off) display of pixels.
One of the features of a display control method for the liquid crystal display device
300
lies in producing a difference in time interval of light emission from the backlight
302
between at least two of the colors R, G and B. Additionally, the time intervals of light emission from the backlight
302
are not constant for the respective colors, and a scanning signal is provided so as to correspond to a light emission sequence in which the light emission time intervals are adjusted depending on the light emission intensities of the LEDs of the respective colors. Thus providing variable control of at least one of the light emission time interval of and the light emission intensity of the LEDs of each color of the backlight
302
allows adjustment of chromaticity of a display color and a wide range of color balance adjustment.
A background art liquid crystal display device
311
shown in
FIG. 31
is disclosed in Japanese Patent Application Laid-Open No. 2000-147454. The liquid crystal display device
311
is substantially similar i

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