JPH09244057A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make possible a full color display and a high definition monochrome display and to reduce power consumption by controlling a color of an ECB system liquid crystal panel and a monochrome/color display changeover and controlling an optical shutter mechanism. SOLUTION: This device is constituted so that the ECB system liquid crystal panel 3 instead of a layer like color filter is exclusively used for color display on the upper or lower side of the driving liquid crystal panel 5 having the optical shutter mechanism such as a TFT, etc., and the monochrome/color display changeover is made possible by controlling the ECB system liquid crystal panel 3. Thus, the display becomes possible at the resolution three times of the time when color is displayed at a monochrome time. Moreover, the power consumption is reduced by improving a panel transmissivity to three times or above compared with the case when the layer like color filter is used, and by reducing luminance of a back light 1 to 1/3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device for displaying color and monochrome.

[0002]

2. Description of the Related Art Among flat-panel displays that are comparable in image quality to CRTs, T is currently the most promising.
FT (Thin Film Transistor) -LCD. It is expected that the market will be further expanded by application to consumer products such as personal computers, word processors, office automation equipment, LCD TVs, and home appliances.

FIG. 1 shows a normally white mode TN (Twisted Nematic) type LCD which is most often used at present.
1 will be described. In the TN type LCD, two alignment films 101 and 102 whose alignment directions are shifted relative to each other by 90 ° are attached to upper and lower glass substrates 103 and 104.
A TN liquid crystal 105 of about 5 μm is sandwiched between 1,102. The liquid crystal molecules in contact with the alignment films 101 and 102 are aligned along the alignment direction of the alignment films 101 and 102, and the liquid crystal molecules around them are aligned along the liquid crystal molecules on the surfaces of the alignment films 101 and 102. This allows two alignment films
Between 101 and 102, the liquid crystal molecules are oriented so as to be twisted by 90 ° as shown in FIG. 11 (a). Further, two polarizing plates 106 and 107 whose polarization axes are aligned in the alignment direction are attached to the surfaces of the two substrates 103 and 104 on the side where the liquid crystal is not sandwiched.

When light enters a liquid crystal panel having such a structure, the light passing through the upper polarizing plate 106 becomes linearly polarized light and enters the liquid crystal 105. As a result, light can also pass through the lower polarizing plate 107 because the light passes along the liquid crystal twisted by 90 ° and twisted by 90 °. At this time, the display is in the "bright" state. On the contrary,
When a voltage is applied between the respective electrodes (not shown) of the upper and lower glass substrates 103 and 104 as shown in FIG. 11 (b), the liquid crystal molecules are erected and twisted. However, on the surface of the alignment films 101 and 102, the alignment control force on the surface is stronger,
It remains along the orientation direction of 2. Since such a liquid crystal is isotropic, the linearly polarized light incident on the liquid crystal layer 105 does not rotate in the polarization direction. In this case, the display is in the "dark" state. If the voltage is not applied again after this, the display returns to the "bright" state due to the regulating force of the alignment films 101 and 102.

It is already known that the normally white mode and the normally black mode can be selected as shown in FIG. 12 by changing the directions of the two deflection plates 106 and 107. In this way LCD is CR
T (Cathode-Ray-Tube) and PDP (Plasma Display Panel)
It is not a display element that emits light itself, but is a device that displays by acting as a shutter for whether or not liquid crystal transmits incident light.

The twist angle of liquid crystal molecules continuously changes depending on the balance between the applied voltage and the alignment regulating force of the alignment film. Therefore, as shown in Fig. 3, the transmissivity changes continuously with the voltage, and it is possible to display a fine halftone.
Furthermore, color display is possible by attaching a color filter to the panel having the structure shown in FIG. The three color filters of red (R), green (G), and blue (B), which are the three primary colors of light, are used to form red, edge, and blue picture elements, respectively.
Three pixels make one pixel. Eight colors can be displayed by a combination of the lightness and darkness of the three R, G, and B picture elements, and multicolor display is possible by adding gradation to each picture element.

For full-color display, at least R, G, and B filters are provided in one pixel, and each R, G, and B picture element has a T switching element.
It is common to form FT. The number of TFTs of a full-color liquid crystal display panel is 640 × 3 if, for example, in the case of a 640 × 480-dot medium-definition VGA panel, one transistor is used for each of R, G, and B in one pixel.
It is necessary to manufacture as many as × 480 = 921600 transistors on the display surface. If one pixel can display an arbitrary color, the number of transistors is ⅓, which is 307200.
It is very easy to manufacture because it requires only one piece. Moreover, in other words, it is possible to display the definition three times higher with the same manufacturing difficulty.

ECB (Electrically Contro) is a method for enabling multicolor display without using color filters.
lled Birefringence) method. This method utilizes the fact that the peak of the amount of light transmitted through the liquid crystal cell has wavelength dependence due to the birefringence effect of the liquid crystal. ECB method LC
In D, as shown in FIG. 13, when the light polarized in the θ direction is incident on the liquid crystal layer, it is divided into light oscillating in the directions of “n⊥” and “n //”.

In the birefringent material 112, each light travels at a different phase velocity and is recombined. For this reason, birefringent substances
The polarization state after passing through 112 is different from that before passing through the birefringent substance 112. Since the phase difference between the “n⊥” direction and the “n //” direction changes depending on the wavelength λ, the polarization state after transmission differs depending on the wavelength, that is, the transmittance differs depending on the wavelength, and coloring occurs. For example, the phase difference of light of wavelength λ is 2 m
When it is π, it becomes the original linearly polarized light, and the phase difference is π + 2.
In the case of mπ, the linearly polarized light is rotated by 2θ as shown in FIG.

If a cell in which a nematic liquid crystal having a dielectric anisotropy is arranged in a specific direction as the birefringent material 112 is sandwiched between the paranicol polarizers 110 and 111, the wavelength λ
The light turns on at 2 mπ and turns off at π + 2 mπ. When θ is 45 °, the contrast between the ON state and the OFF state becomes maximum. Also, when a change in voltage is observed on the liquid crystal panel, the effective retardation of the liquid crystal 112 changes as shown in FIG. 14, and the wavelength to be transmitted changes, so that the color changes.

In such an ECB system, it is generally difficult to display a full-color image, and multi-color display of about 8 colors is limited. In addition, the code | symbol d in FIG. 14 has shown the thickness of liquid crystal.

[0012]

By the way, since the technique of color multicoloring is in the limelight because it is gorgeous and conspicuous, there are not so many applications where color display is actually required. Especially for business use, it is overwhelmingly more common to run word processing software or spreadsheet software than to handle full-color image data.

In this case, the number of characters that can be displayed is more important than the number of colors that can be displayed. In addition, it is preferable that the battery drive time is as long as one minute for a business man who always carries a personal computer and performs business. That is, the required color display differs between the hobby use and the business use. However, in the case of displaying a monochrome image such as word processing software in a full-color liquid crystal display panel having the R, G, and B filters as described above, it is necessary to drive three transistors simultaneously in one pixel. Therefore, in the monochrome mode, it is not possible to obtain a character display and a line drawing with higher definition. Therefore, the current situation is that Kanji with a large number of strokes are apt to be crushed. Moreover, since the light transmission characteristics of the color filter are fixed, even if monochrome display is performed, power consumption is not reduced.

The present invention has been made in view of the above problems, and provides a liquid crystal display device capable of full-color display and high-definition monochrome display while reducing power consumption. With the goal.

[0015]

[Means for Solving the Problems]

(Procedure) As described above with reference to FIGS. 1 to 3, the above-mentioned problems are caused by a color-developing ECB liquid crystal panel 3 having a plurality of picture element regions, an ECB liquid crystal panel 3 facing the ECB liquid crystal panel 3, and a light source. The liquid crystal panel 5 for driving having the shutter mechanisms 5b, 5c, 5x, 5y and the color control of the ECB type liquid crystal panel 3 and the control of monochrome / color display switching are performed, and the optical shutter of the liquid crystal panel 5 for driving is also controlled. Mechanism 5
and a control circuit 7 for controlling b, 5c, 5x, and 5y.

In the above liquid crystal display device, as shown in FIG. 5, a compensation panel 8 for retardation correction is superposed on the ECB type liquid crystal panel 3. A liquid crystal panel or a twisted phase film is used as the compensation panel 8. In the above liquid crystal display device, as illustrated in FIG. 10, a plurality of pixel electrodes are formed on the driving liquid crystal panel 5, and the pixel electrodes are provided in two in one region surrounded by the gate bus 5x and the drain bus 5y. It is characterized in that one pixel electrode 5h, 5j is present.

(Operation) Next, the operation of the present invention will be described. According to the present invention, an ECB type liquid crystal panel is dedicated to color display below or above a driving liquid crystal panel having an optical shutter mechanism such as a TFT, instead of a layered color filter, and an ECB type liquid crystal panel is provided. It is possible to switch between monochrome and color display by controlling the color of.

Therefore, in monochrome, it is possible to display at a resolution three times as high as that in color display, and moreover, the panel transmittance is improved three times or more as compared with the case where a layered color filter is used, and the backlight is Lowering the brightness to 1/3 enables low power consumption operation. Naturally, color display and monochrome display are possible even with the conventional method, but since the transmission characteristics of the color filter are fixed, the display density and panel transmittance cannot be changed.

By using two pixel electrodes in the area surrounded by the gate bus and the drain bus, the resolution in color display can be doubled to 1 to 2 times, and in monochrome, 1 to 6 times. .

[0020]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing a liquid crystal display device according to a first embodiment of the present invention. In FIG. 1, on the backlight 1, a first deflector 2, a color-developing ECB liquid crystal panel 3, a second deflector 4, a drive liquid crystal panel 5, and a third deflector 6 are laminated in this order. There is. And
The control circuit 7 turns on and off the backlight 1, adjusts the brightness thereof, drives the ECB liquid crystal panel 3 for coloring, or drives the liquid crystal panel 5 for driving.

The ECB liquid crystal panel 3 for color development has a first and second transparent electrodes 3 having a simple matrix structure as shown in FIG.
a, 3b. That is, a plurality of stripe-shaped first transparent electrodes 3a are formed in parallel on the first transparent substrate 3c, and stripe-shaped second transparent electrodes 3b extending in a direction orthogonal to the first transparent electrodes 3a. Are formed in parallel on the second transparent substrate 3d, the intersection of the first transparent electrode 3a and the second transparent electrode 3b is a pixel region, and in the pixel region, depending on the voltage birefringence. Red (R),
Either green (G) or blue (B) light is transmitted. First transparent electrode 3a and second transparent electrode 3b
An alignment film (not shown) is formed on each of the
The alignment direction of these alignment films is determined by the twist angle of the liquid crystal 3e sealed between the first transparent substrate 3c and the second transparent substrate 3d.

As shown in FIG. 3, the driving liquid crystal panel 5 which plays the role of a light shutter is an active matrix drive in which a plurality of TFTs 5b are arranged in a matrix on a first transparent substrate 5a, and each of them is an active matrix drive. The pixel electrode 5c is connected to the TFT 5b. Further, a counter transparent electrode 5e facing the pixel electrode 5c is arranged on the second substrate 5d. Alignment films (not shown) are formed on the respective surfaces of the pixel electrode 5c and the counter electrode 5e, and the alignment directions of these alignment films are orthogonal to each other. Further, a TN liquid crystal 5f is provided between the first transparent substrate 5a and the second transparent substrate 5d.
Is enclosed. Each of the pixel electrodes 5c is arranged so as to match any one of the red (R), green (G), and blue (B) picture element regions of the ECB system coloring panel, and the three R, G, and B pixel regions are arranged. One pixel region is formed by the three pixel electrodes 5c corresponding to the picture elements.

In FIG. 3, 5x indicates a gate bus line and 5y indicates a drain bus line. The deflection axis of each of the first deflector 2 and the second deflector 4 is E for color development.
It is determined by the twist angle of the liquid crystal in the CB liquid crystal panel 3. The deflection axis of the third deflector plate 6 is parallel to the deflector axis of the second deflector plate 4 so that the liquid crystal display device is normally white and advantageous for color development of highly transmissive white. Has become. When using normally black, set to crossed nicols.

A liquid crystal display device having such a configuration was prototyped,
The characteristics were evaluated. The driving liquid crystal panel 5 has a generally known structure having no color filter, and has no special characteristic different from the conventional one. Further, the arrangement of the first and second deflecting plates 2 and 4 above and below the color-developing ECB liquid crystal panel 3 is as follows.
Parallel Nicols are used for the highly transparent white color. Further, the retardation R ₀ has a homogeneous alignment of 1500 nm, and the twist angle of the liquid crystal 3e is 180 degrees. The retardation of 1500 nm is 0 to 1500 to obtain red, green, blue and white under parallel Nicols.
This is because it requires a retardation change of nm.

Next, FIG. 4 shows a voltage change of the transmittance of the ECB liquid crystal panel 3 for color development. In FIG. 4, ECB for color development
When the applied voltage between the first and second transparent electrodes 3a and 3b of the liquid crystal panel 3 is increased, the retardation decreases due to the change in the refractive index of the liquid crystal 3e, and the color development according to the retardation is obtained. That is, when the applied voltage is 0V, green is red when the voltage is 2.4V, yellow when the voltage is 2.5V, blue when the voltage is 3.2V, and black when the voltage is 4.4V. However, in the case of 6V, a gray color was obtained, but a white display was not obtained.

As long as color display is performed only by the liquid crystal panel having this structure, it is not possible to display a highly transparent black-and-white display, so it is conceivable to use gray instead of white to obtain a gray-black display. Light transmittance is as low as a few percent. Therefore, it is necessary to use yellow for monochrome display in order to perform monochromatic display with high transmission. In this case, since the light transmittance is 20%, the light transmittance is almost double that in color display. Actually, as a result of performing display by combining the ECB liquid crystal panel 3 for color development with the liquid crystal panel 5 for driving, it was possible to obtain the same color display as the conventional system. Naturally, full color display is possible.

At the time of color display, in the ECB liquid crystal panel 3 for color development, the first transparent electrode 3a and the second transparent electrode 3 are provided.
A voltage is applied by the control circuit 7 so that the crossing region of b serves as a kind of filter that selectively transmits red (R), green (G), and blue (B) light. During color display, the voltage application is made constant in each intersection region of the first transparent electrode 3a and the second transparent electrode 3b so as not to change, and the R, G, B colors obtained thereby are obtained. The arrangement is in the form of stripes, mosaics, deltas, or squares, similar to the usual color filters.

During monochrome display, a voltage of about 2.5 V is applied between all the first transparent electrodes 3b and all the second transparent electrodes 3d, so that the maximum transmittance is obtained at all electrode intersections. Generate a yellow transmission filter of. In the liquid crystal display device having the above-mentioned structure, it is naturally possible to switch between the fineness between the color display and the monochrome display with gray or yellow.

As described above, in this embodiment, the ECB
Since the liquid crystal panel 3 plays the role of the color filter and the shutter of the pixel region plays the role of the general driving liquid crystal panel 5, the full-color display has the same definition as the conventional one. Moreover, the ECB liquid crystal panel 3 for color development
Since it suffices to play the role of a color filter and the display color is always constant, there is no need to consider the response speed in the liquid crystal tilt direction with respect to voltage changes, and a simple matrix drive with a simple and inexpensive structure is adopted. it can.

Further, in color display, three picture element electrodes corresponding to red, green, and blue form one pixel area, but in monochrome display, one picture element electrode forms one pixel area.
It is possible to achieve high transmittance display with a resolution three times higher than that of color display. Moreover, in monochrome display, the light transmittance of the panel is significantly improved, and the amount of light transmitted from one pixel is about three times or more that in the case of using a normal color filter even if simply considered. Accordingly, the control circuit 7 can reduce the brightness of the backlight 1 to about 1/3, and low power consumption operation can be performed. (Second Embodiment) As an improvement of the first embodiment, an E for color development is used.
The retardation of the CB display panel 3 when no voltage is applied,
A method of compensating by compensating for the compensation panels may be considered. The principle of the improvement is shown in FIG.

The compensation panel 8 shown in FIG. 5 (b) has a negative retardation and acts as -Ro with respect to the retardation Ro of the ECB liquid crystal panel 3 of FIG. 5 (a). There is an optically anisotropic film and a twist phase plate formed by uniaxially stretching. As a result, the long-sleeved direction of the closest liquid crystal molecules of the ECB liquid crystal panel 3 and the compensation panel 8 goes straight, and the twist directions become opposite to each other. In this configuration, the retardation Re of the ECB liquid crystal panel 3 when no voltage is applied is compensated and becomes zero, and the polarization state of the emitted light becomes the same linearly polarized light as the incident light. Therefore, it is bright when no voltage is applied (V = 0). Achromatic white can be obtained.

On the other hand, the retardation of the ECB liquid crystal panel 3 decreases as the voltage application increases, and the ECB liquid crystal panel 3 develops color according to the effective retardation Re = Ro-R (v). R (v)
Is the retardation of the ECB liquid crystal panel 3 when a voltage is applied, and changes depending on the magnitude of the applied voltage. But,
When the compensation panel 8 is not provided, white display is impossible even if the applied voltage is increased as shown in FIG. 5 (c).

By the way, as shown in FIG.
When the liquid crystal molecules 3e of the liquid crystal panel 3 stand up completely by applying a high voltage, the retardation of the compensation panel 8 is 1500 nm, so the transmitted light should emit green. However, in reality, as shown in FIG. 6, the ECB liquid crystal panel 3 does not become zero because the residual retardation Rrem due to anchoring cannot be erased, and does not develop green.

In order to eliminate such inconvenience, the problem is solved by increasing the retardation of the compensation panel 8 by Rrem as shown in FIG. 5 (d), for example. EC of this structure
The effective retardation of B liquid crystal panel 3 is R'o = 1800.
When the voltage is set to nm, the voltage characteristic becomes as shown in Fig. 7 and 5V
Within the range, a retardation change of 0 to 1500 nm is obtained.

Next, the transmittance (T) -applied voltage (V) characteristic is shown in FIG. 8 and the chromaticity change is shown in FIG. As can be seen from FIG. 9, the use of the compensation panel produces white, blue, red and green colors. Further, from FIG. 8, when the compensation panel 8 is used, the panel transmittance of the ECB liquid crystal panel 3 during white display is 35% or more, which is significantly higher than that during color development.
Moreover, it was found that the amount was about 10% when in color. Moreover, the voltage applied to the ECB liquid crystal panel 3 in the case of white display is 0.
V, which enables low power consumption during monochrome display.

This panel was driven in the same manner as in the first embodiment so as to overlap the drive panel. In the color display, the first embodiment is the same as it is, but in the monochrome display, a good monochrome display is obtained. Moreover, the total transmittance after overlapping was more than three times that in color display. A white display is obtained when the applied voltage is zero. As the compensation panel 8 described above, a liquid crystal panel having a retardation opposite to that of the ECB panel may be used, but there is a drawback that the weight and the manufacturing cost are increased because the panel structure has three layers. The display results showed good image quality, which was the same as when the optically anisotropic film was used. The retardation was matched with the above-mentioned conditions. (Third Embodiment) In the first and second embodiments, the definition can be increased to about three times during monochrome display. But,
It is only in the vertical or horizontal direction, and it is not possible to increase the definition in the horizontal and vertical directions. This is because the plane shape of one pixel electrode is rectangular, and the aspect ratio in monochrome display is different from that in normal color display.

As a measure against this, some improvement can be achieved by devising the pixel electrode 5c of the driving liquid crystal panel 5 as shown in FIG. That is, as shown in FIG. 10, two TFTs 5f and 5g and two pixel electrodes 5h, which are surrounded by the gate bus 5x and the drain bus 5y shown in FIG.
By providing 5j, the definition in monochrome display can be increased to 6 times that in color display. If the two pixels in the y direction are arranged in different colors, it is possible to increase the fineness in color.

As a matter of course, monochrome normal resolution display is also possible in all of the above embodiments. In this case, the aspect ratio does not change, but the advantage of high transmission remains. (Fourth Embodiment) In the above embodiment, a TFT drive system is used for a gradation display panel on a color development panel. However, it does not matter if another method is used for this.

For example, an STN panel may be used. However, the number of gradations was reduced compared to the TFT method, and full-color display was not possible, but gradation display of about 256 colors was possible.

[0040]

As described above, according to the present invention, color display is performed by an ECB type liquid crystal panel, and light blocking and light transmission of pixels are controlled by a normal monochrome liquid crystal panel. As a result, full-color display can maintain the same image quality as before, and can be changed to high definition and low power consumption during monochrome display.

By using two pixel electrodes in the area surrounded by the gate bus and the drain bus, the resolution in color display can be doubled to 1 to 2 times, and in monochrome, 1 to 6 times. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a schematic configuration of an ECB type liquid crystal panel used in the liquid crystal display device of the first embodiment of the present invention.

FIG. 3 is a perspective view showing a schematic configuration of a driving liquid crystal panel used in the liquid crystal display device of the first embodiment of the present invention.

FIG. 4 is a characteristic diagram showing applied voltage and light transmittance of an ECB type liquid crystal panel used in the liquid crystal display device of the first embodiment of the present invention.

FIG. 5 is a diagram showing light transmission states of an ECB type liquid crystal panel and a compensation panel used in the liquid crystal display device of the second embodiment of the present invention.

FIG. 6 is a characteristic diagram showing a relationship between applied voltage and retardation of an ECB type liquid crystal panel used in the liquid crystal display device of the second embodiment of the present invention.

FIG. 7 is a characteristic diagram showing a relationship between an applied voltage of an ECB type liquid crystal panel used in the liquid crystal display device of the second embodiment of the present invention and a retardation of an ECB type liquid crystal panel whose retardation is compensated by the compensation panel.

FIG. 8 is a characteristic diagram showing a relationship between applied voltage and light transmittance of an ECB type liquid crystal panel obtained by the liquid crystal display device according to the second embodiment of the present invention.

FIG. 9 is a characteristic diagram showing changes in chromaticity of an ECB type liquid crystal panel used in the liquid crystal display device of the second embodiment of the present invention.

FIG. 10 is a plan view showing a pixel electrode used in a liquid crystal display device according to a third embodiment of the present invention.

FIG. 11 is an exploded perspective view showing a general TN type liquid crystal display device and its operation.

FIG. 12 is a diagram showing voltage / light transmission characteristics in a normally white mode and a normally black mode of a general TN type liquid crystal display device.

FIG. 13 is an exploded perspective view showing the principle of a general ECB type liquid crystal display device.

FIG. 14 is a diagram showing the principle of color change depending on the birefringence of a general ECB type liquid crystal display device.

[Explanation of symbols]

 1 Backlight 2 1st deflection plate 3 ECB liquid crystal panel for color development 4 2nd deflection plate 5 Liquid crystal panel for driving 6 3rd deflection plate 7 Control circuit 8 Compensation panel

Claims (4)

[Claims] 1. An ECB type liquid crystal panel for color development having a plurality of picture element regions, a drive liquid crystal panel arranged facing the ECB liquid crystal panel and having an optical shutter mechanism, and a color of the ECB type liquid crystal panel. And a control circuit for controlling the optical shutter mechanism of the driving liquid crystal panel, as well as controlling the above-mentioned control and monochrome / color display switching. 2. The liquid crystal display device according to claim 1, wherein a compensation panel for retardation correction is superposed on the ECB type liquid crystal panel. 3. The liquid crystal display device according to claim 2, wherein a liquid crystal panel or a twisted phase film is used as the compensation panel. 4. A plurality of pixel electrodes are formed on the driving liquid crystal panel, and the pixel electrodes have two pixel electrodes in one region surrounded by a gate bus and a drain bus. 1. The liquid crystal display device according to 1.