JPH09325317A - Color liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high-resolution video on the color liquid-crystal display device which uses a liquid crystal panel and increase the utilization efficiency of light source light. SOLUTION: The liquid crystal panel 1 displays the video by varying the transmissivity of illumination light which is made incident from behind, pixel by pixel, according to a video signal. A back light 2 is composed of a surface light source which can be switched in light emission color electrically among red, green, and blue to make tri-colored illumination light incident on the liquid crystal panel 1 in order. A control system consisting of a signal processing circuit 3, an image memory 4, a liquid crystal panel driving circuit 5, a timing generator 6, a back light control circuit 7, etc., controls the operation of the back light 2 and liquid crystal panel 1. Namely, the illumination light is changed among the three colors in order by controlling the back light 2 within a period of one field or frame constituting one video picture, and the liquid crystal panel 1 is controlled to write a video signal of a corresponding color to a pixel in timing with the emission of color illumination light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device using an active matrix type liquid crystal panel as a display. More specifically, the present invention relates to a color liquid crystal display device that displays three color images of red, green, and blue at a high speed within a period of one field or one frame and displays a full-color image in a so-called frame sequential manner.

[0002]

2. Description of the Related Art In the case of displaying a color image on an active matrix type liquid crystal panel, it is common to provide a color filter for each pixel. This method will be briefly described with reference to FIG. The liquid crystal panel is a pair of glass substrates 7
1, 72 are arranged to face each other, and a liquid crystal layer 73 is provided in the gap.
It is configured to enclose. On the lower glass substrate 71, the signal lines 74 and the scanning lines 7 arranged in a matrix are formed.
5 and the thin film transistor 76 arranged at the intersection thereof
And a pixel electrode 77 are formed. Thin film transistor 7
6 are sequentially selected by the scanning line 75 and the signal line 7
The video signal supplied from No. 4 is written in the corresponding pixel electrode 77. On the other hand, a counter electrode 78 and a color filter 79 are formed on the inner surface of the upper glass substrate 72. The color filter 79 is an R corresponding to each pixel electrode 77.
It is divided into (red), G (green), and B (blue) segments. A desired full-color image display can be obtained by sandwiching an active matrix type liquid crystal panel having such a configuration between two polarizing plates 80 and 81 and allowing white light to enter from a backlight (not shown).

[0003]

When a color filter is used as in the above-mentioned conventional liquid crystal panel, the light absorption thereof reduces the utilization efficiency of white light incident from the backlight to 1 /.
There is a problem of falling below 3. Also, because each pixel electrode must be assigned to each color of red, green and blue,
Since one set of three pixel electrodes is the minimum unit of display as an RGB trio, there is a drawback that the resolution is lowered.

A so-called frame-sequential drive system has been devised to increase the resolution. In this system, red, green, and blue filters are sequentially switched in a field or in a frame on a white light backlight to obtain red illumination light, green illumination light, and blue illumination light. In synchronization with the switching of the filters, a red video signal, a green video signal and a blue video signal are sequentially supplied to the liquid crystal panel side. In such a field sequential driving method, the liquid crystal panel may be a black and white display type, and one pixel functions as a red pixel, a green pixel and a blue pixel in a time division manner. Therefore, a high resolution can be secured in the frame sequential driving method. However, since the filter facing the backlight of the white light source is used, the utilization efficiency of the light from the light source is reduced as in the case of the micro color filter method shown in FIG. Further, there is a drawback that a drive mechanism for switching the filters at high speed is required, which makes the device large in size.

[0005]

The following means have been taken in order to solve the above-mentioned problems of the prior art. That is, the color liquid crystal display device according to the present invention has a liquid crystal panel, a backlight, and a control circuit as a basic configuration. The liquid crystal panel displays the image by changing the transmittance of the illumination light incident from the back surface for each pixel according to the image signal. The backlight is a surface light source whose emission color can be electrically switched between three colors of red, green, and blue, and three colors of illumination light are sequentially incident on the back surface of the liquid crystal panel. The control circuit controls the backlight to sequentially change the illumination light among the three colors within a period of one field or one frame which constitutes one image, and controls the liquid crystal panel to control the emission timing of each color illumination light. The video signal of the corresponding color is written in the pixel while synchronizing. Preferably, the surface light source is a diode element array in which a red diode element, a green diode element and a blue diode element are two-dimensionally arranged. Alternatively, the surface light source may use an electroluminescence element array in which a red electroluminescence element, a green electroluminescence element and a blue electroluminescence element are two-dimensionally arranged.

According to the present invention, a transmissive and monochrome display type liquid crystal panel for displaying an image by transmitted light is used. As the backlight, a surface light source that can freely switch white light among three colors of red, green, and blue is used. The emission color of the backlight is changed at high speed to red, green, and blue within a period of one field or one frame forming one image. A video signal corresponding to each color is written on the liquid crystal panel within the emission time of each color. As a result, a full-color image can be obtained by utilizing the afterimage phenomenon of human eyes.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the basic configuration of a color liquid crystal display device according to the present invention. As shown in the figure, this color liquid crystal display device includes a liquid crystal panel 1, a backlight 2, and various control circuits. The liquid crystal panel 1 is a monochrome type active matrix type, and changes the transmittance of illumination light incident from the back side for each pixel according to a video signal to display a video. The backlight 2 is a surface light source whose emission can be electrically switched between the three colors of red, green, and blue, and three colors of illumination light are sequentially incident on the back surface of the liquid crystal panel 1. Further, as various control circuits, a signal processing circuit 3, an image memory 4, a liquid crystal panel drive circuit 5, a timing generator 6, a backlight control circuit 7 and the like are provided. These circuits form an integrated control circuit as a whole and control the operations of the liquid crystal panel 1 and the backlight 2. That is, the backlight 2 is controlled within a period of one field or one frame forming one image to sequentially change the illumination light among the three colors, and the liquid crystal panel 1 is controlled to emit light of each color. The video signal of the corresponding color is written in the pixel in synchronism with. Specifically, the signal processing circuit 3 separates a color video signal input from the outside for each color of red, green, and blue. The image memory 4 records the video signal of each color for one field or one frame. Further, the synchronization signal included in the input video signal such as the composite video signal is separated by the timing generator 6. The timing generator 6 is based on this separated sync signal,
Timing signals for controlling writing and reading to and from the image memory 4, timing signals for controlling the liquid crystal panel drive circuit 5, timing signals for switching the emission color of the backlight 2 via the backlight control circuit 7, and liquid crystal panel drive circuit 5 Control timing signals are output respectively. The backlight control circuit 7 controls the operation of the backlight 2 according to the timing signal output from the timing controller 6, and the emission colors are red, green, and blue at high speed in the order of one field or one frame of the input video signal. Switch. At this time, a video signal corresponding to the emission color of the backlight 2 is read out at high speed from the image memory 4 within the emission time of each color and written in the liquid crystal panel 1 via the liquid crystal panel drive circuit 5. With the above procedure, red, green, and blue images are sequentially displayed on the liquid crystal panel 1 within a period of one field or one frame, and are recognized as full-color images by the observer's eyes.

FIG. 2 schematically shows the operation of the color liquid crystal display device shown in FIG. As shown
The backlight 2 sequentially emits red light, green light, and blue light within one field or one frame. For example, when interlaced drive is adopted, the field frequency is 60 Hz. Therefore, the emission frequency of the backlight 2 is 3
It is double 180Hz. In the case of non-interlaced driving, the frame frequency is 30 Hz, for example. In this case, the emission frequencies of the three primary colors are tripled to 90 Hz. Whatever it is,
In the present invention, since a surface light source capable of electrically switching the emission colors among the three colors of red, green, and blue is used as the backlight, it is possible to sufficiently cope with it. On the other hand, the liquid crystal panel 1 sequentially displays a red image, a green image, and a blue image in synchronization with the above-described timings of red light emission, green light emission, and blue light emission. Since these three-color images are switched at high speed, they are perceived by the human eye as full-color images in which the three primary-color images are overlapped due to the afterimage phenomenon. In such a color display system in which each color image is rewritten in the frame sequential manner, the liquid crystal panel 1 may be a monochrome display type. Since one pixel is used in three colors in a time division manner,
The resolution will be higher. However, since the screen must be rewritten at a speed three times higher than the normal field frequency or frame frequency, a liquid crystal panel having a high-speed response is required. For example, by using a ferroelectric liquid crystal as the liquid crystal material, a liquid crystal panel having a high-speed response suitable for frame sequential driving can be obtained. Further, in the color liquid crystal display system according to the present invention, since no filter is used at all, the utilization efficiency of light from the light source is not impaired. Therefore, a bright and high-resolution image can be obtained. Furthermore, since the emission color of the surface light source is switched by electrical control without using a mechanical switching structure, the color liquid crystal display device is quiet and highly reliable without increasing in size.

FIG. 3 is a schematic sectional view showing a specific example of the structure of the surface light source adopted in the present invention. In this embodiment, the surface light source includes a red diode element 11, a green diode element 12, a blue diode element 13, and an alumina substrate 14.
It is a diode element array arranged two-dimensionally along the surface of the. Each diode element is a fine chip including a pn junction and is integrated as a hybrid structure on the alumina substrate 14. Reflective film 1 for diode element
It is stored in the recess surrounded by 5. The upper part thereof is covered with the diffusion plate 16 to make the surface distribution of the illumination light uniform. A black resin 17 is provided on the lower surface of the reflective film 15.
The n layer of the diode element is connected to the negative electrode 18, and the positive electrode 19 is patterned on the p layer. The red diode element 11, the green diode element 12, and the blue diode element 13 are sequentially turned on / off via these electrodes 18 and 19. The red diode element 11 is, for example, GaAs _0.6 P _0.4 , GaP, Al _0.35 Ga _0.65 A
It is known that s is used as a semiconductor material. Especially, the third aluminum gallium arsenide (AlGaAs)
In the red diode element using, it is possible to use aluminum, gallium, and arsenic having a wide energy band not only for the substrate but also for extracting light, and it is possible to eliminate extra absorption. Also, by using a wide band width on both sides of the light emitting layer, electrons and holes can be confined and intensive recombination can be performed in a narrow region. The red diode element made of aluminum, gallium, and arsenic has a high luminous efficiency of about 4% and is capable of emitting light of high brightness. Gallium phosphorus (GaP) is used as a semiconductor material for the green diode element 12. The same Group V nitrogen as phosphorus is added. Nitrogen has a higher electronegativity than phosphorus and captures electrons. This is called an isoelectronic trap because it is an electron capture by the same family. When the trapped electrons have their positions fixed and the position blur becomes small, the momentum blur increases based on the uncertainty principle, and even in the indirect transition type semiconductor, the emission efficiency close to that of the direct transition type is obtained. Human visibility is near green, and even if the amount of light emitted is the same as red, it looks brighter in green. Regarding the blue diode element 13, zinc sulfide (ZnS) or zinc selenide (Z) which is a II-IV group semiconductor material is used.
nSe), etc., which are direct transition types. recent years,
A group I lithium is added as an acceptor, and a result of obtaining oxygen p-type by adding oxygen by an ion implantation method is obtained, and blue light emission by a pn junction is obtained. further,
A blue diode device using silicon carbide (SiC), which is a group IV-IV compound, and gallium nitride (GaN), which is a group III-V compound, has been developed. Both have the advantage that pn junction is possible.

FIG. 4 is a schematic sectional view showing another embodiment of the surface light source. The surface light source of this example is an electroluminescence element array in which a red electroluminescence element, a green electroluminescence element, and a blue electroluminescence element are two-dimensionally arranged. Figure 1
Only the electroluminescent elements for the colors are schematically shown. This electroluminescent element is typical for realizing a surface light source, while an incandescent lamp is a point light source and a fluorescent lamp is a line light source. As shown in the figure, the electroluminescence element is a glass plate 31.
On top of which a transparent electrode 32, a phosphor 33, and a binder 34
The back electrode 35 made of aluminum or the like is stacked on the light emitting film formed by forming the mixture of the above. The outer surface of the glass plate 31 is a diffusion surface 36. A powder obtained by dispersing the powder of the phosphor 33 in a binder 34 made of synthetic resin or low melting point glass is applied for 20 to 10 by a coating method or a screen printing method.
A light emitting film having a thickness of 0 μm is formed. This electroluminescent device can emit light of about 1000 foot-transvers at an applied electric field of 10 ⁴ to 10 ⁵ V / cm, and an efficiency of 1 to 15 lumen / watt. Such an amount of light emission is sufficient as a back light source of a liquid crystal panel. Various emission colors can be obtained by selecting the phosphor 33. For example, blue luminescence can be obtained by using strontium sulfide (SrS) and cerium (Ce). Further, green light emission can be obtained by using calcium sulfide (CaS) and cerium (Ce), or calcium sulfide (CaS) and erbium (Er). In addition, calcium sulfide (CaS) and europium (Eu)
Red emission is possible by using.

Finally, with reference to FIG. 5, a concrete example of the configuration of the liquid crystal panel 1 shown in FIG. 1 will be described. This liquid crystal panel has a flat structure including a driving substrate 51, a counter substrate 52, and a liquid crystal substance 53 held between them. As the liquid crystal substance 53, a ferroelectric liquid crystal excellent in high speed response is used. A pixel array section 54 and a scanning circuit section are integrally formed on the drive substrate 51. The scanning circuit section is divided into a vertical scanning circuit 55 and a horizontal scanning circuit 56. A terminal portion 57 for external connection is formed on the upper end of the peripheral portion of the drive substrate 51. The terminal portion 57 is connected to the vertical scanning circuit 55 and the horizontal scanning circuit 56 via the wiring 58. On the other hand, a counter electrode (not shown) is entirely formed on the inner surface of the counter substrate 52. The pixel array section 54 has a row-shaped scanning line 5
9 and a signal line 60 in a row are formed. The scanning line 59 is connected to the vertical scanning circuit 55, and the signal line 60 is connected to the horizontal scanning circuit 56. A pixel electrode 61 and a thin film transistor 62 for driving the pixel electrode 61 are integrally formed at the intersection of both wirings. The vertical scanning circuit 55 operates according to the timing signal supplied from the timing generator 6 shown in FIG. 1, and selectively scans each pixel electrode 61 for each row. On the other hand, the horizontal scanning circuit 56 also includes the timing generator 6 shown in FIG.
It operates according to the timing signal supplied from the device, and sequentially writes the video signal to the selected pixel electrode.

[0012]

As described above, according to the present invention, 1
The illumination light is sequentially changed between the three colors within a period of one field or one frame which constitutes one image, and the video signal of the corresponding color is written to the pixels of the liquid crystal panel in synchronization with the emission timing of each color illumination light. I'm out. With such a configuration, it is possible to display a color image by using a monochrome type liquid crystal panel, and it is possible to improve the resolution. This time,
Since no color filter is used, light utilization efficiency is not impaired at all, and a bright image can be obtained. In addition, the backlight can change the emission color at high speed by electrical switching control, and because it does not use any mechanical switching structure, the color liquid crystal display device is quiet and has a highly reliable device structure without increasing in size. Is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a color liquid crystal display device according to the present invention.

FIG. 2 is a schematic diagram for explaining the operation of the color liquid crystal display device shown in FIG.

FIG. 3 is a schematic cross-sectional view showing an example of a surface light source that constitutes the backlight shown in FIG.

FIG. 4 is a schematic cross-sectional view showing another specific example of the surface light source that also constitutes the backlight.

5 is a perspective view showing a specific configuration example of the liquid crystal panel shown in FIG.

FIG. 6 is a schematic perspective view showing an example of a conventional color liquid crystal display device.

[Explanation of symbols]

1 ... Liquid crystal panel, 2 ... Backlight, 3 ... Signal processing circuit, 4 ... Image memory, 5 ... Liquid crystal panel drive circuit, 6 ... Timing generator, 7 ... Backlight control circuit

Claims (3)

[Claims] 1. A liquid crystal panel for displaying an image by changing the transmittance of illumination light incident from the back for each pixel according to an image signal, and a surface on which an emission color can be electrically switched between three colors of red, green and blue. A backlight that consists of a light source and sequentially enters three colors of illumination light on the back surface of the liquid crystal panel, and the backlight is controlled within a period of one field or one frame that constitutes one image, and the illumination light is sequentially switched between three colors. And a control circuit for controlling the liquid crystal panel and writing the video signal of the corresponding color into the pixel in synchronization with the emission timing of each color illumination light. 2. The color liquid crystal display device according to claim 1, wherein the surface light source is a diode element array in which a red diode element, a green diode element and a blue diode element are two-dimensionally arranged. 3. The color liquid crystal display device according to claim 1, wherein the surface light source is an electroluminescence element array in which a red electroluminescence element, a green electroluminescence element and a blue electroluminescence element are two-dimensionally arranged.