Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-03
2004-02-03
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000
Reexamination Certificate
active
06686985
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a wiring pattern for a liquid crystal display in which unevenness is not noticeable, a liquid crystal display, and an electronic equipment using the liquid crystal display.
2. Description of Related Art
In general, a color liquid crystal display in an active matrix system includes a plurality of pixel electrodes, a device substrate on which these pixel electrodes are provided with nonlinear (switching) devices, an opposing substrate on which counter electrodes opposed to the pixel electrodes and color filters are formed, and liquid crystal filled between the two substrates. Each pixel corresponds to one of three primary colors, R (red), G (green), and B (blue).
With this arrangement, when a selection signal is applied to scanning lines, the switching devices enter a conducting state. When a data signal is applied to data lines in the conducting state, a predetermined charge is accumulated in liquid crystal layers including the pixel electrodes, the counter electrodes, and the liquid crystal between the pixel electrodes and the counter electrodes. When the switching devices enter an off state after the charge has been accumulated, the accumulated charge in the liquid crystal layers is maintained if the resistance of the liquid crystal layers is sufficiently high. Accordingly, when the switching devices are driven so as to control the amount of charge to be accumulated, alignment of the liquid crystal varies according to each pixel, thus displaying predetermined information. It is only necessary to accumulate charge in each liquid crystal layer for a partial period. Therefore, time-division multiplexing driving in which the pixels share the scanning lines and the data lines is made possible by selecting the scanning lines using time-sharing.
Concerning the nonlinear devices, they are broadly classified into a three-terminal nonlinear device, such as a thin-film transistor (TFT), and a two-terminal nonlinear device, such as a thin-film diode (TFD). The latter, that is the two-terminal nonlinear device, is advantageous in that short circuit failure does not occur in theory since there are no intersections in the wiring and that a film deposition process and a photolithography process are shortened. If the two-terminal nonlinear device is to be employed as the nonlinear device, the two-terminal nonlinear device can be connected to either one of the scanning line and the data line. Here, it is assumed that the two-terminal nonlinear device is connected to the data line.
In contrast, concerning arrangements of the color filters in the liquid crystal display, those shown in FIGS.
10
(
a
) to (
d
) are known. Of these arrangements, the arrangement shown in FIG.
10
(
a
) is referred to as an RGB stripe arrangement or a trio arrangement, and is suitable for a computer display for displaying characters and straight lines. In comparison with the arrangements shown in FIGS.
10
(
b
) to (
d
), the effective resolution of the arrangement shown in FIG.
10
(
a
) is not so high.
The next arrangement shown in FIG.
10
(
b
) is referred to as an RGGB mosaic arrangement. Since this arrangement has a greater number of G pixels having a high visibility factor, it is generally said that this arrangement has high resolution. However, the arrangement is not necessarily evaluated highly by subjective evaluation experiments. Furthermore, the RGGB mosaic arrangement has a fewer number of B and R pixels. Thus, this arrangement has a drawback in that roughness of an image is noticeable when the viewing distance is short.
The arrangement shown in FIG.
10
(
c
) is referred to as an RGB mosaic arrangement. In this arrangement, a difference in display quality occurs between a rightward-rising diagonal and a leftward-rising diagonal. This generates diagonal noise in an overall image, and, in particular, the noise is noticeable when the number of pixels of a screen is small.
The arrangement shown in FIG.
10
(
d
) is referred to as an RGB delta arrangement, and has a horizontal resolution that is 1.5 times that of the mosaic arrangement. It is said that the RGB delta arrangement is disadvantageous in displaying the contour of an image. Generally, however, the RGB delta arrangement is evaluated highly by subjective evaluation experiments. It is thus suitable for achieving a high definition color liquid crystal display. Hereinafter, drawbacks involved in employing the RGB delta arrangement are discussed.
When the color filters are arranged in the RBG delta arrangement, a wiring pattern of connecting lines (one of the data lines and the scanning lines, and hereinafter simply referred to as lines) to be connected to the pixel electrodes that will be the base of these pixels is discussed below. Concerning the wiring pattern, there is a system in which two of the three RGB colors share a single line, as shown in FIGS.
11
(
a
) and (
b
). Specifically, line
1
(
1
′) is shared by R and G, line
2
(
2
′) is shared by G and B, and line
3
(
3
′) is shared by B and R. This system has a drawback in that unevenness occurs when displaying solid patterns of C (cyan), M (magenta), and Y (yellow) that are in a complementary-color relation with the RGB colors, that is, when displaying a relatively large area in a single color.
SUMMARY OF THE INVENTION
Regarding the principle of this development of unevenness, the case of displaying cyan is discussed. In this case, a liquid crystal display in a normally white mode displays white (off) in a no-applied-voltage state. When displaying cyan, the R pixels must be black (on) and the G and B pixels must be white. Thus, it is only necessary to write to the R pixels. Because the G pixels on even rows are connected to line
1
(
1
′), potentials of these G pixels tend towards potentials when writing to the R pixels. In contrast, the G pixels on odd rows are connected to line
2
(
2
′), and potentials of these G pixels are substantially independent of the potentials when writing to the R pixels. Similarly, because the B pixels on odd rows are connected to line
3
(
3
′), potentials of these B pixels tend towards the potentials when writing to the R pixels. In contrast, the B pixels on even rows are connected to line
2
(
2
′), and potentials of these B pixels are substantially independent of the potentials when writing to the R pixels.
As a result, an effective voltage value applied to the G pixels on the even rows and an effective voltage value applied to the G pixels on the odd rows are different from each other. In addition, an effective voltage value applied to the B pixels on the odd rows and an effective voltage value applied to the B pixels on the even rows are different from each other. Accordingly, a difference in gray level occurs every other row. The same drawback occurs when displaying magenta and yellow, and a difference in gray level occurs between odd rows and even rows.
In other words, the difference in gray level becomes uneven in the column direction. Specifically, the B and G pixels which are influenced by writing to the R pixels are alternately shifted by half a pitch of the pixels, and are connected in the column direction. In contrast, the B and G pixels which are not influenced by writing to the R pixels are alternately shifted by half a pitch in a similar manner, and are connected in the column direction. This generates a difference in gray level between the cyan in the column direction of the former pixels and the cyan in the column direction of the latter pixels. Hence, unevenness in the column direction is caused.
In order to prevent such unevenness from occurring, it is necessary to obtain a wiring pattern in which potentials when writing to pixels of a certain color do not influence the potentials of pixels of other colors. To this end, as shown in
FIG. 12
, it is possible to propose a system in which a single line is shared by only a single color. Specifically, line
4
is shared by G, line
5
is shared by B, and line
6
is s
Matsuo Mutsumi
Tanaka Chihiro
Tsuyuki Tadashi
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