JPS60107022A - Color liquid-crystal display device - Google Patents

Abstract

PURPOSE:To display an image of high display quality with good color balance by arranging picture lements of red, green, and blue in a color filter as much as 1:2:1 proportion and obtaining white as the composite color when all picture elements are turned on. CONSTITUTION:Picture elements of green having a large coefficient of lightness are twice as many as those of red and blue to decrease relatively the ratio of picture elements which are seen dark. A basic repetition unit of 2X2 picture elements is employed to reduce the anisotropy of spatial resolution, so that no Moire fringe appears in a specific direcion. Picture elements of blue are not arranged successively, so no dark fringe pattern is formed. The lateral period is set to two picture elements to use one line memory each for an upper and a lower part and only one color switch circuit is only necessary before each line memory, thereby simplifying a driving circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a color liquid crystal display device, and particularly to a color liquid crystal display device for displaying images with good color balance and high display quality.

<Prior art> Regarding a color image display device using a liquid crystal, Japanese Patent Laid-Open No. 49
-57726 and No. 49-74438, etc., the former uses an x-y matrix type display device using striped color filters of three primary colors, and the latter uses a matrix type display device in which a switching element is provided for each picture element. A display device is disclosed.

However, in these examples, only striped or mosaic color filters of the three primary colors are used, but there is no particular mention of the hue, density, arrangement state, etc. of the three primary colors.

Regarding the hues of the three primary colors, JP-A-54-14119 indicates that the three primary colors must be selected so that the composite color of two of the three colors is complementary to the other color. This condition is equivalent to the condition that an achromatic color is obtained when three colors are combined. Regarding the density of the three primary colors, see JP-A-54-
No. 122996, blue, red, green (hereinafter B, R, respectively)
It has been shown that the transmittance of a color filter is decreased in the order of 1G (abbreviated as 1G). Also, JP-A-54-12299
No. 7 states that the area of the picture elements is made smaller in the order of B, R, and G. The purpose of these two cases is to equalize the bright state luminous flux of each B, R, and G picture element. However, when three primary colors with equal luminous flux are mixed, the mixed color is white (achromatic color)
It does not turn into a bluish color.

<Object of the Invention> The present inventors conducted research based on colorimetry, and as a result of selecting three primary colors according to the following criteria, a favorable conclusion was obtained.

(1) The area of the triangle obtained by plotting the chromaticity coordinates of each of the three primary colors on a chromaticity diagram and connecting them should be as wide as possible.

(2) The center of gravity of the chromaticity coordinates of the three primary colors (weighted average if the areas of each picture element are not equal) is close to the white point.

(3) The brightness (stimulus value Y) should be as large as possible.

(4) The chromaticity coordinates of the three primary colors are close to the chromaticity coordinates of the standard phosphor for color televisions.

Based on the above conclusion, it is an object of the present invention to provide a color liquid crystal display device with good color balance and high display quality.

<Description of Structure and Effects> First, a color liquid crystal display device according to the present invention will be described. A liquid crystal display device to which the present invention is applied has at least the following elements.

(1) A liquid crystal display panel 0 that has a large number of picture elements whose light transmittance or reflectance changes in response to applied voltage. A colored body.

(3) A light source for illumination provided in front or behind the liquid crystal display panel.

The light output from the illumination light source in (3) above is incident on the colored body in (2), and only the required wavelength range is transmitted (
1) enters the liquid crystal display panel. A color video signal corresponding to the color of the colored body is applied to each picture element of the liquid crystal display panel, and the amount of light passing through the liquid crystal display panel changes depending on the month of the month. If such a liquid crystal display device is observed from a certain distance, the three primary colors will not be seen separately but will appear as additive colors, so any color image can be displayed using the same principle as a color television. Next, the liquid crystal display panel (1) above is used to change the intensity of light passing through it in accordance with an image signal. There are various operating modes of liquid crystals, such as TN (twisted nematic), GH (guest host), DSM (dynamic scattering), phase transition, and birefringence, and the present invention can be applied to any of the modes. are possible, but TN and GH give particularly favorable results. GH uses a black pigment and is used as a so-called black shutter. The details of the operation mode of the liquid crystal are described in, for example, "Fundamentals and Applications of Liquid Crystal Electronics" edited by Sasaki, Ohmsha (1979).

An xy matrix method is normally used to drive and control each picture element. This is subdivided into the following three methods.

(1) A liquid crystal cell is constructed by attaching a large number of striped electrodes arranged in parallel and orthogonally to each of two simple matrix substrates. A row selection signal is sequentially applied to the row electrodes (electrodes extending in the horizontal direction), and the row electrodes are time-divisionally driven. An image signal is applied to the column electrodes (electrodes extending in the vertical direction) in synchronization with the row selection signal. The intersections of row and column electrodes form picture elements;
The liquid crystal at that location is driven to display in the various modes described above in response to the effective value of the potential difference between the row electrode and column electrode.

Since the liquid crystal is of an effective value response type, the number of scanning lines cannot be increased too much in terms of crosstalk and dynamic range. In order to overcome these limitations, the following two methods can be used.

(2) Addition of non-linear element Varistor to each pixel, old M (metal/1nsul
ator/meta! ) is added to suppress crosstalk.

(3) Addition of a switching transistor A switching transistor is provided on one substrate corresponding to each picture element, and the structure is similar to that of a dynamic RAM, and the liquid crystal of each picture element is driven by the voltage stored in the memory capacitor. In some cases, the liquid crystal itself can also serve as a memory capacitor. If the on/off ratio of the switching transistor is large, a large number of picture elements can be driven.

As a switching transistor, a thin film transistor or a MOS-FET (
(field-effect transistor) is used.

As the colored body, a color filter is usually provided on the outer or inner surface of the liquid crystal substrate, but it is also possible to use a color polarizing plate. The colored body may be provided on the light source side of the liquid crystal layer, or may be provided on the opposite side. In a color display panel, only about 1/3 of the white light incident on each picture element is used, and the rest is absorbed by the colored body. Furthermore, in the case of a liquid crystal operation mode using a polarizing plate, the amount of light is further reduced to less than half, so in a simple reflective display mode without illumination means, it becomes dark. Therefore, as illumination means, a light source such as an incandescent lamp, a fluorescent lamp, an EL panel, or a light guide for collecting ambient light and guiding it to the back surface of the liquid crystal display panel is used. Generally, when considering application to portable equipment, the luminous efficiency of the light source becomes an important factor because power supply capacity is severely constrained. Furthermore, the spectrum of the light source is important in determining the reproducible color range.

Next, an overview of the colorimetric method will be described. For more information, see Color Science/
・Ndopu Yuri (Colorful Society of Japan Line 1980, University of Tokyo Press) 1 Basics of Color Engineering (Ikeda Koretsu 1980 Asakura Shoten) and JIS Z8701/Z8728 0 Any color light spectrum P (λ) is Stimulus value x when given
, y, and z are given by the following equations.

X=JP(λ)x(λ)dλ, Y=/P(λ)y(λ)dλ, Z=/P(λ)z(λ)dλ, X(λ),y(λ),2( The values of λ) are listed in the above reference as a numerical table. The stimulus values x, y, and z are obtained by linearly transforming the stimulus values R, G, and B corresponding to the three primary colors of light, green, and blue for practical reasons, and in the case of transmissive lighting, P(λ)− L(λ)·T(λ). Here, L(^) is the spectrum of the light source, T(
λ) is the spectral transmittance of the liquid crystal panel.

Y, /'/o corresponds to brightness. However, YO is the stimulus value Y of the light source itself, and is given by the following equation.

Yo=/L(λ)y(λ)dλ X, Y, and Z are normalized to become X+Y+Z:I as shown in the following equation.

x=X/(X+Y+ Z), y=Y/(X+Y+
Z), z=Z/(X+Y+Z) These are called chromaticity coordinates, and usually X and y are plotted on the xy plane. This is called a chromaticity diagram. Chromaticity coordinates contain information regarding hue and saturation. FIG. 1 shows a standard phosphor chromaticity coordinate diagram for monochromatic light and color television (NTSC system).

The curve with a chevron-shaped loop in the figure is the locus of monochromatic light,
The lower side of this curve is the trajectory when monochromatic light of 780 nm and 380 nm is mixed. The area surrounded by these is the range of colors that can actually exist. When two arbitrary colors are mixed, the chromaticity coordinates of the mixed color become internal division points of the chromaticity coordinates of the original two colors. Therefore, the range in which the chromaticity coordinates of a color obtained by mixing arbitrary three colors exists is inside the triangle obtained by connecting the chromaticity coordinates of the original three colors. R, G, and B in the diagram are NTS
These are the standard phosphor chromaticity coordinates for C-scheme color televisions, and the interior of the triangle formed by connecting these coordinates is the range of colors that can be reproduced on color televisions. In the figure, W is the chromaticity coordinate of the standard illumination light C, which corresponds to an achromatic color (white).

The closer the chromaticity coordinate is to W, the lower the saturation, and the farther the chromaticity coordinate is from W, the higher the saturation.

Hereinafter, the conditions for selecting the three primary colors mentioned above will be explained.

(1) The area of the triangle formed by plotting the chromaticity coordinates of each picture element of the three primary colors in the bright state on a chromaticity diagram and connecting them should be as large as possible.

As already mentioned, the interior of the triangle is the color reproduction range, so it is desirable that the triangle be as large as possible. That is, it is better for the colors to have high saturation and to be far apart from each other.

(2) The mixed color when all picture elements are in a bright state is close to white.

In the case of a CRT (cathode ray tube), even if there is some difference in the luminous efficiency of the phosphors of each color, it is easy to adjust the drive conditions to achieve white balance. However, in cases where the brightness of the light source is limited as in the application example of the present invention, it is desirable that all the picture elements be in a bright state and that when they are mixed, the color becomes white. If the color does not become white, it is necessary to limit the transmittance of the bright state of the picture element corresponding to the color that is too strong.
This results in a part of the light from the light source being wasted. In addition, since the applied voltage lamp light transmittance characteristics of a liquid crystal display panel are generally not linear, when displaying halftones, if the dynamic range of the signal voltage corresponding to each color does not match, it is difficult to display colors of the same hue. However, if the brightness changes, the hue may also change.

In addition, the stimulus values are Xa, Ya, Za and xb, yb, respectively.
.

The chromaticity coordinates of a color obtained by mixing two colors zb with a weight of A:B are given by the following equation.

In the present invention, the number of green picture elements is twice that of red and blue, so the weight of green is doubled. Therefore, if you use three primary color filters and white light wrinkles with similar densities, the green will become too strong, so in order to maintain white balance, you should either make the green filter darker or change the spectral distribution of the light source so that the green part must be weakened. When using a three-wavelength fluorescent lamp as a light source, white balance can be achieved by reducing the proportion of phosphors that emit green and increasing the proportion of phosphors that emit red and blue. This method makes the utilization of the light source's luminous flux higher than when using a white light source and making the green filter darker.

(3) It should be as bright as possible.

As already mentioned, if there are restrictions on the brightness of the light source, it is preferable to make it as bright as possible. If the chromaticity coordinates x and y are the same, it is better that the stimulus value Y corresponding to brightness is larger. However, since this condition is contradictory to (1), it is necessary to optimize it so that both conditions are satisfied. The narrower the transmission band of a colored body, the closer the transmitted light becomes to monochromatic light and the saturation increases, but the color decreases and becomes darker.

(4) The chromaticity coordinates of the three primary colors are close to the chromaticity coordinates of the standard phosphor for color televisions.

It is most preferable to match the two, but if this is not possible, it is desirable to form similar triangles centered on the white point. In this case, an image with good color balance can be reproduced without performing any special processing on the color video signal. however,
The quality can be further improved by performing T correction according to the voltage-transmittance characteristics of the liquid crystal display panel as necessary.

The above is the configuration of the color display device for image display and the basic design elements of the colored body. Next, the mosaic pattern of the present invention will be explained.

Conventionally, the colored bodies have been arranged in vertical, horizontal or diagonal stripes as shown in FIG.

However, these patterns had the following drawbacks.

(1) The brightness of the blue picture element is lower than the brightness of the red and green picture elements, so it appears dark, and a striped pattern is visible in the direction in which the blue picture elements are continuous. This is because the brightness coefficient of blue is very small. According to CIEI931, the ratio of brightness coefficients (ratio of brightness to stimulus value) of red, green, and blue is determined as follows.

tr: tg: tb = I: 4.5907
: 0.060+As can be seen from this equation, the brightness of blue that gives the same stimulus value is just over 1% of the brightness of green.

(2) Since the spatial resolution in the direction perpendicular to the stripes is poor, moiré fringes are likely to occur when an image having a high spatial frequency in that direction is reproduced.

The uninvented solution solves the above-mentioned drawbacks, and the third
The figures show various examples of colored body arrays. Figure 3(a) below
List the characteristics of the colored object arrays shown in (b), (c), and (d).

(1) The number of green pixels, which have a large brightness coefficient, is doubled as compared to red and blue pixels, and the proportion of blue pixels that appear dark is made relatively small.

(2) Since the basic repeating unit is 2 picture elements x 2 picture elements, the anisotropy of spatial resolution is small. Therefore, moiré fringes do not tend to appear in a specific direction.

(3) Since blue picture elements are not connected, dark striped patterns do not occur.

Figures 3(c) and 3(d) show two sets of 2 picture elements x 2 picture elements as repeating units, but it is also within the scope of the present invention to perform symmetry operations such as rotation and reflection on these. This is consistent with the following.

Furthermore, such an arrangement brings about the following advantages in terms of the structure of the drive circuit.

Since the electrode pitch of the display panel to which the present invention is applied is short, the signal electrodes of the panel are often drawn out alternately from top to bottom. In this case, in the pattern of the present invention exemplified by light, the period in the horizontal direction is two picture elements, so if we look at just one row, the picture elements drawn upward and the picture elements drawn downward are the same color. Focusing on this point simplifies the configuration of the drive circuit. FIG. 4 shows a conventional example, and FIG. 5 shows an example of the configuration of a drive circuit suitable for the present invention. In the conventional example, upper and lower line memories are provided for each of the three primary colors, and the signals stored there are selected by color switching circuits provided in each column electrode. On the other hand, in the example shown in FIG. 5, there is only one line memory at the top and one at the top, and there is only one color switching circuit in front of each line memory, so the circuit configuration of the drive circuit becomes very simple.

<Example> A color liquid crystal display panel with the pattern shown in FIG. 3 was prototyped and display experiments were conducted. The characteristics of the color filter used are as follows.

Red: Transmission range 600-640 nm, absorption range 560 nm or less Edge: Transmission range 530-560 nm, absorption range 600 nm or more and below 500 nm Blue: Transmission range 420-500 nm, absorption range 530 nm or more Since a three-wavelength fluorescent lamp was used as a light source, , the optical properties outside the above band had little effect on the results. As shown in Figure 4, most of the radiant energy of a three-wavelength fluorescent lamp is around 611 nm, around 543 nm, and around 400 to 50 nm.
It is concentrated around 0 nm. Since the composite color of these must be white, the value to be taken for the ratio of the radiant energies of each band can be determined as follows.

For simplicity, the light in each band is 610nm, 540nm, 46nm.
Approximate with monochromatic light of 0 nm, and each filter is ideal (transmittance is 100% in the transmission range and 0% in the absorption range)
Assume that

The magnitude of the radiant energy emitted by each phosphor is RlG,
When B is used, RlG and B must be determined so that the chromaticity coordinates of the color that is combined with 1, 2: I is x = 0.310.0, 1116 (white under C light source). .

However, s = (1,0Q26+0.5θ8Q+O,QQQ
8)・R+2+0.2904+o, 954Q+0.02
08)・G+(0,2908+0.0600+1.66
92)・B Solving this, R:G:B=35:21:4
It becomes 4.

The spectrum of the fluorescent lamp shown in FIG. 6 is obtained by mixing phosphors to satisfy this relationship. .

The display panel manufactured in this manner has a wide color reproduction range and provides good images with good color balance. Furthermore, striped patterns caused by a series of blue picture elements do not occur, and a fine-grained image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a chromaticity coordinate diagram of a standard phosphor for monochromatic light and N, TSC color televisions. FIG. 2 is an arrangement pattern diagram of a conventional coloring means.Q FIG. 3 is an arrangement pattern diagram of a colored body showing an embodiment of the present invention. FIG. 4 is a drive circuit diagram corresponding to the conventional pattern. FIG. 5 is a drive circuit diagram corresponding to the pattern of FIG. 3. FIG. 6 is an explanatory diagram illustrating the spectrum of a fluorescent lamp used in the present invention. Tochroma circuit 2...Line memory 3...Color switching circuit 4...Line selection circuit Agent Patent attorney Yoshihiko Fukushi (and 2 others) Figure 1 Figure 2

Claims (1)

[Claims] l. In a color liquid crystal display device for image display in which picture elements of three colors consisting of red, green, and blue are arranged periodically, red, green, The ratio of the number of each blue picture element is I:2:
] A color liquid crystal display device characterized in that the spectrum of the light source and the density of the coloring means are controlled and set so that the composite color when all picture elements are brought into a bright state is white. 2.More than 70% of the radiant energy in the visible range is 42
0~500nm, 580~560nm, 600~6
It is concentrated in the 40 nm band, and the radiant energy in each band has a ratio of 9-intensity of 35:21:44 (each ±10
) A color liquid crystal display device according to claim 1.