Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-03-06
2004-12-07
Chow, Dennis-Doon (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S088000, C345S103000, C349S061000
Reexamination Certificate
active
06828954
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a liquid crystal display device of a color light source type for providing a full-color display by causing a back-light to emit three colored lights in a time-divided manner.
BACKGROUND ART
Along with the recent developments of so-called office automation (OA), OA apparatuses such as word processors and personal computers have been widely used. Further, as such OA apparatuses have become prevalent in portable-type OA apparatuses that can be used in offices as well as outdoors, there have been demands for small-size and light-weight apparatuses. Liquid crystal display devices have been widely used as one of the means to meet such demands. In particular, liquid crystal display devices not only achieve small size and light weight, but also include an indispensable technique in an attempt to achieve low power consumption in portable OA apparatuses that are driven by batteries.
By the way, the liquid crystal display devices are roughly classified into the reflection type and the transmission type. The reflection type liquid crystal display devices are constructed so that light rays incident on the front face of a liquid crystal panel are reflected by the rear face of the liquid crystal panel and an image is visualized by the reflected light, while the transmission type liquid crystal display devices are constructed so that an image is visualized by transmitted light from a light source (back-light) provided on the rear face of the liquid crystal panel. Although the reflection type liquid crystal display devices have poor visibility resulting from the reflected light amount varying depending on environmental conditions, they have been widely used as monochrome (such as black-and-white) display devices for portable calculators, watches, etc. because of their low costs, but they are not suitable for the display devices of personal computers, etc. providing a multi-color or full-color display. For this reason, in general, transmission type liquid crystal display devices are used as display devices of personal computers, etc. providing a multi-color or full-color display.
Meanwhile, currently-used color liquid crystal display devices are generally classified into the STN (Super Twisted Nematic) type and the TFT-TN (Thin Film Transistor-Twisted Nematic) type based on the liquid crystal materials to be used. The STN type liquid crystal display devices have comparatively low production costs, but they are not suitable for the display of a moving image because they are susceptible to crosstalk and comparatively slow in the response rate. In contrast, the TFT-TN type liquid crystal display devices have better display quality than the STN type, but they require a back-light with high intensity because the transmittance of the liquid crystal panel is only 4% or so at present. For this reason, in the TFT-TN type liquid crystal display devices, a lot of power is consumed by the back-light, and there would be a problem when used with a battery power source. The TFT-TN type liquid crystal display devices have also problems such as a low response rate, particularly in displaying half tones, a narrow viewing angle, and a difficult color balance adjustment.
Additionally, conventional transmission type liquid crystal display devices are generally of the color-filter type which uses a back-light of white light and is designed to provide a multi-color or full-color display by selectively transmitting white light through color filters of the three primary colors. However, in such a color-filter type, since a display pixel is formed by a certain area including adjacent three color filters as one unit, the resolution is lowered to virtually one-third.
In view of the above-mentioned problems, there has been proposed a color liquid crystal display device (Japanese Patent Application Laid-Open No. 7-281150, etc.) which uses a ferroelectric liquid crystal element or an anti-ferroelectric liquid crystal element having a high response speed with respect to an applied electric field as its liquid crystal element and causes the same pixel to emit lights of the three primary colors in a time-divided manner so as not to cause a substantial lowering of the resolution.
With this color liquid crystal display device, it is possible to provide a color display by combining a liquid crystal panel using a ferroelectric liquid crystal element or an anti-ferroelectric liquid crystal element capable of responding at a high speed of several hundreds to several &mgr; order with a back-light capable of emitting lights of red, green and blue colors in a time-divided manner and by synchronizing the switching of the liquid crystal element with the light emission of the back-light. In the case where a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal is used as the liquid crystal material, since the liquid crystal molecules are constantly maintained parallel to the substrate (glass substrate) regardless of the presence or absence of an applied voltage, a very wide viewing angle is obtained, and thus no problem arises in practical use. Moreover, in the case where a back-light constituted by red, green and blue light-emitting diodes (LEDs) is used, it is possible to adjust the color balance by controlling a current flowing through each LED.
FIG. 1
is a time chart showing one example of conventional display control in such a color liquid crystal display device, wherein FIG.
1
(
a
) indicates the light-emitting timing of the LEDs of the respective colors of the back-light and FIG.
1
(
b
) shows the scanning timing of the respective lines of the liquid crystal panel.
As shown in FIG.
1
(
a
), the LEDs of the back-light are caused to emit red, green and blue lights sequentially in this order every 5.6 ms, for example, and the pixels of the liquid crystal panel are switched on a line by line basis in synchronism with the light emission so as to provide a display. Besides, in the case where 60 frames are displayed in one second, one frame period is 16.6 ms, and this one frame period is further divided into three sub-frames, each having a period of 5.6 ms, so that in the case illustrated in FIG.
1
(
a
), for example, the red LED, the green LED and the blue LED emit light in the first sub-frame, the second sub-frame and the third sub-frame, respectively.
Meanwhile, as shown in FIG.
1
(
b
), with respect to the liquid crystal panel, data scanning is performed twice within each of the sub-frames of the respective red, green and blue colors. However, timing adjustments are performed so that the start timing (timing for the first line) of the first scanning (data-writing scanning) coincides with the start timing of each sub-frame and the end timing (timing for the final line) of the second scanning (data-erasing scanning) coincides with the end timing of each sub-frame.
During the data-writing scanning, a voltage corresponding to pixel data is supplied to each pixel of the liquid crystal panel so as to adjust the transmittance. It is thus possible to provide a full-color display. During the data-erasing scanning, a voltage which is the same as the voltage for the data-writing scanning but has opposite polarity is supplied to each pixel of the liquid crystal panel so as to erase the display of the pixels of the liquid crystal panel, thereby preventing application of a direct-current component to the liquid crystal.
By the way, in such a liquid crystal panel, the intensity of the transmitted light varies according to write/erasure scanning of the liquid crystal panel. In other words, it has been confirmed by experiments that, even when the same voltage is applied, there is a difference in the light transmittance between the scanning start area and the scanning end area because of a problem associated with the liquid crystal panel's own characteristics.
FIGS. 2 and 3
are illustrations for explaining such a phenomenon:
FIG. 2
shows the respective areas (areas
1
-
4
) given by virtually dividing the display area of the liquid crystal panel into four areas together with
Kiyota Yoshinori
Makino Tetsuya
Shiroto Hironori
Yoshihara Toshiaki
Chow Dennis-Doon
Greer Burns & Crain Ltd.
LandOfFree
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 Liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3331368