KR20100014119A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: A liquid crystal display is provided to improve the picture quality by maintaining integrated intensity of illumination for each color constantly. CONSTITUTION: A liquid crystal display comprises a liquid crystal display unit(25), a plurality of fluorescent lamps(LR, LG, LB), and a plurality of lighting circuits(30R, 30G, 30B). The fluorescent lamps have phosphor layers illuminating in red, green and blue. The fluorescent lamps are turned on by the high frequency voltage during the on-period. The fluorescent lamps are turned off by the high frequency voltage applied to the fluorescent lamps during the off-period. The lighting circuit controls brightness of fluorescent lamps by changing a period ratio of the on-period and the off-period. The lighting circuit establishes the emission timing of fluorescent lamps differently. The fluorescent lamps illuminate in different color from each other as the lighting circuit applies the high frequency voltage sequentially.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and in particular, a red, green, and blue fluorescent lamp having a phosphor film that emits light in each color of red, green, and blue functions as a backlight of a liquid crystal display device, thereby making it possible to image a liquid crystal display device. It relates to a liquid crystal display device that displays.

In the colorization of the liquid crystal display device, a method of spatially mixing color of light passing through the color filter by providing a color filter of three primary colors of red, green, and blue on each pixel using a white backlight is common. However, since the light transmitted by each color by the color filter is limited to the wavelength corresponding to each color, the visible light portion has a transmittance of about 1/3 each of red, green, and blue. In addition, since it is divided into each color by the color filter, the amount of light becomes about 1/3 at this stage. The light emitted from the backlight has become one factor that causes a decrease in the utilization efficiency of the light at the stage of the color filter.

On the other hand, as a colorization method in which a color filter is unnecessary, a field sequential colorization method is known. The field sequential color liquid crystal display device is comprised from a liquid crystal display element and the backlight which can switch three primary colors of red, green, and blue, respectively. Each image frame is composed of three color fields of red, green, and blue, and by sequentially lighting a backlight having three color light sources of red, green, and blue for each color field, color display is obtained by color mixing by time division.

The field sequential color liquid crystal display device is connected to a low cost because a color filter is unnecessary. In addition, the field sequential color liquid crystal display device is composed of one segment per pixel, which is advantageous for high resolution. In addition, when the continuous color conversion exceeds the limit of the temporal resolution of the human eye, it uses the principle of mixed color, which is inherently excellent in color reproducibility.

In the conventional field sequential color liquid crystal display device, one frame is composed of three color field configurations of red, green, and blue, and in this color field period, image information is written to the liquid crystal display element, and in synchronization with the writing, It is necessary to control to emit a backlight light source of each color. However, the conventional field sequential color liquid crystal display has a problem that image quality is not good.

In the field sequential color liquid crystal display, when one frame is a three-color field configuration of red, green, and blue, it is necessary to switch three primary colors 30 frames per second in an NTSC signal in order not to feel flicker. It is necessary to switch one field displaying one color to about 1/90 seconds or less. In the field sequential color liquid crystal display device, it is necessary to control image light to be written in the liquid crystal display element within the screen display period of each color, and to control the fluorescent lamp of each color to emit light in synchronization with the writing. .

[Patent Document 1: Japanese Patent Application Laid-Open No. 11-237608]

However, when the red, green, and blue fluorescent lamps having phosphors emitting red, green, and blue light are used as backlights of field sequential color liquid crystal displays, the longer ones have an afterglow time of about 10 milliseconds. As a result, afterglow light emission of the previous color field remains until the next color field, which causes deterioration in image quality.

7 is a graph showing the afterglow characteristics of phosphors emitting red, green, and blue light, the horizontal axis representing afterglow time (milliseconds), and the vertical axis representing light quantity L (%). The afterglow time on the horizontal axis is a tenth afterglow time.

As shown in the figure, the afterglow time of each phosphor emitting light in each color is different from each other. In the afterglow time, the blue light emitting phosphor (BaMgAl ₁₀ O ₁₇ : Eu) is the shortest (about 0.1 milliseconds in one tenth of the afterglow time), and then the red light emitting phosphor (Y ₂ 0 ₃ : Eu) is short. (About 1 millisecond in 1/10 afterglow time) and green light-emitting phosphor (LaPO ₄ : Tb or LaPO ₄ : Ce, Tb) are the longest (10-20 milliseconds in 1/10 afterglow time).

FIG. 8 is a schematic diagram of displaying red, green, and blue in a field sequential color liquid crystal display using red, green, and blue fluorescent lamps having phosphors emitting red, green, and blue light as backlights; FIG. .

First, in Fig. 8A, the red fluorescent lamp is turned off after a predetermined time is turned on, and light is transmitted to the liquid crystal in the region a for 1/90 seconds from the onset of the red fluorescent lamp. The liquid crystal in the region does not transmit light. As a result, in the area a, red is displayed. Next, in Fig. 8B, after about 1/90 seconds from the start of the lighting of the red fluorescent lamp, the green fluorescent lamp is turned off after lighting for a predetermined time, and in area b for 1/90 seconds from the start of the lighting of the green fluorescent lamp. In addition to transmitting light to the liquid crystal, light is not transmitted to the liquid crystal in a region other than the region b. As a result, in area b, green is displayed. Next, in Fig. 8 (c), after about 1/90 seconds from the start of lighting of the green fluorescent lamp, the blue fluorescent lamp is turned off after lighting for a predetermined time, and in area c for 1/90 seconds from the start of lighting of the blue fluorescent lamp. In addition to transmitting light to the liquid crystal, the liquid crystal in a region other than the region c is not transmitted. As a result, in area c, green will be displayed. However, in fact, since there is a green afterglow, a part of green overlaps with blue, and blue with a water color is displayed in the region c. As a result of the afterimage effect, the human eye is displayed with red, green, and watery blue at the same time as shown in Fig. 8D.

As described above, the conventional field sequential color liquid crystal display device has a problem that image quality deteriorates since afterglow of a backlight light source having a green light emitting phosphor remains until the next color field. In particular, since green has high visibility, it is easy to catch the viewer's eyes, and the image quality is greatly reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color liquid crystal display device having high image quality by using a liquid crystal display element having a simple structure that does not have a color filter as a component, which has been made to solve the above problems.

MEANS TO SOLVE THE PROBLEM This invention employ | adopts the following means in order to solve said subject.

The first means includes a red, green, and blue fluorescent lamp having a liquid crystal display unit, a phosphor film emitting red, green and blue colors, and an on-period in which the fluorescent lamp is turned on by applying a high frequency voltage to the fluorescent lamp; And a lighting circuit for stopping the application of the high frequency voltage to the fluorescent lamps and alternately repeating the off periods for turning off the fluorescent lamps, changing the time ratio between the on and off periods, and controlling the brightness of the respective fluorescent lamps. The red, green, and blue fluorescent lamps are lighted by sequentially applying high frequency voltage to shift the timing of the red, green, and blue fluorescent lamps, and to emit each color individually. And a blue fluorescent lamp functioning as a backlight of the liquid crystal display to display an image on the liquid crystal display. The on-period is changed for each of the red, green, and blue fluorescent lamps.

The second means is a liquid crystal display device wherein, in the first means, the on-period is set shorter as the fluorescent lamp which emits a color having a long afterglow time among the red, green, and blue fluorescent lamps.

In the first means or the second means, the third means sets the applied voltage value of the on-period higher as the fluorescent lamp which emits a long afterglow color among the red, green, and blue fluorescent lamps. It is a liquid crystal display device.

According to the present invention, a color liquid crystal display device having high image quality can be provided by using a liquid crystal display element having a simple structure that does not have a color filter as a component.

An embodiment of the present invention will be described with reference to FIGS. 1 to 7.

1 is a perspective view showing the overall configuration of a liquid crystal display device according to the present invention.

As shown in the figure, in this liquid crystal display device, red, green, and blue fluorescent lamps having respective phosphor films that emit red, green, and blue monochromatic colors are used as backlights of the liquid crystal display elements. Each fluorescent lamp is a red fluorescent lamp LR-1, LR-2, LR-3, a green fluorescent lamp LG-1, LG-2, LG-3, and a blue fluorescent lamp LB-1, LB-2, LB-3 Each of three, and fluorescent lamps of each color are arranged side by side with the same spacing in the order of red, green and blue in the direction parallel to the ground. As the red, green, and blue fluorescent lamps, for example, external electrode type rare gas fluorescent lamps or cold cathode lamps are used.

In this liquid crystal display device, for example, a diffusion reflecting sheet 21 such as foamed PET is disposed on the rear surface of the metallic body case 20 in which one direction is opened, and the diffusion plate 22 and the diffusion sheet are disposed. (23), the lens sheet 24 and the liquid crystal display element 25 overlap in this order with respect to the light irradiation direction of the main body case 20, and are arrange | positioned so that the opening of the main body case 20 may be blocked. As the materials constituting the diffusion plate 22, the diffusion sheet 23, the lens sheet 24, and the liquid crystal display element 25, those conventionally used suitably are used.

2 is a block diagram showing a circuit configuration of a liquid crystal display device according to the present invention.

Red fluorescent lamps LR-1, LR-2, LR-3, green fluorescent lamps LG-1, LG-2, LG-3, and blue fluorescent lamps LB-1, LB-2, LB-3, lighting circuit 30R By 30G and 30B, the timing lights up one color at a time corresponding to 1/3 frame sequentially. An image signal of each color is sampled by a sampling circuit (not shown) and stored in the field memories 32R, 32G, and 32B corresponding to each of R, G, and B. The image signals accumulated in the field memories 32R, 32G, and 32B are controlled by the timing controller 31 to be sent to the data driver 33 one by one. The scanning driver 34 sequentially selects the scanning lines one by one, and writes image signals from the data driver 33 to the pixels in synchronization with the selection pulse. Writing of the image signals of the respective colors is performed by the timing controller 31 by the fluorescent lamps LR (LR-1, LR-2, LR-3), LG (LG-1, LG-2, LG-3), and LB. (LB-1, LB-2, and LB-3) are controlled in synchronization with the switching of the lighting, and the red, green, and blue phases displayed in each 1/3 frame are mixed in time with time difference, and afterimages By effect, full-frame display of one frame is performed.

3 is a view for explaining a lighting control method of each color fluorescent lamp in the liquid crystal display device of the present invention, and timings of turning on / off the red, green, and blue fluorescent lamps, and red, green, and blue fluorescent lamps. The relationship between the light output of the lamp is shown.

In FIG. 3, the red, green, and blue fluorescent lamp lighting signals shown in FIGS. 3A to 3C are repetitive signals having t1 to t3 as one cycle, and an on-period for turning on by applying a high frequency voltage to the fluorescent lamp. And the off period for turning off the fluorescent lamp without applying a high frequency voltage to the fluorescent lamp. The period of t1 to t2 is an on period, and the period of t2 to t3 is an off period. FR, FG, and FB in Fig. 3E each show a time per field in which the liquid crystal display element 25 displays the red phase, the green phase, and the blue phase, respectively. The time per field of each color corresponds to 1/3 frame (1/90 second).

As shown in Fig. 3, the on-period of each fluorescent lamp is shortened in the order of green, red, and blue, which is for the following reason.

As shown in Fig. 7, the afterglow time has the longest light quantity Lg of the phosphor film emitting green light at 10 milliseconds, and then the light amount Lr of the phosphor film emitting red light is 1 millisecond, and blue The amount of light Lb by the phosphor film which emits light is shortest at 0.1 milliseconds. Therefore, since the afterglow time corresponds to a different phosphor for each of the phosphors emitting light in each color, as shown in FIG. 3, the on-period of the green fluorescent lamp having the phosphor film that emits the green light having the longest afterglow time is shortest, and then, The on-period of the red fluorescent lamp having the phosphor film emitting red light having a long afterglow time is set to a middle length in three colors, and the on-period of the blue fluorescent lamp having the phosphor film emitting blue light with the shortest afterglow time is longest.

As described above, in the liquid crystal display of the present invention, since the time per field of each color is 1/90 seconds or less, the on periods of the red, green, and blue fluorescent lamps are 8 milliseconds and 1 millisecond, respectively. , 9 milliseconds. The on periods of the fluorescent lamps LR, LG, and LB of each color are controlled in a predetermined period by controlling the on / off periods of the lighting signals of each color input from the timing controller 31 to the lighting circuits 30R, 30G, and 30B. do.

As described above, according to the liquid crystal display of the present invention, by setting the on-period of the green fluorescent lamp with a long afterglow time short, as shown in FIGS. 3D and 3E, the next blue field of the green field is shown. Since the afterglow of the green field is attenuated to a considerable extent, the deterioration of image quality can be prevented.

In particular, in the liquid crystal display device of the present invention, one field of red, green, and blue shown in Fig. 3E during the on periods of the red, green, and blue fluorescent lamps shown in Figs. 3A to 3C. When the ratio with respect to sugar time is set to tr, tg, and tb, when using said fluorescent substance, it is preferable that tr, tg, and tb are set so that the following relational expression may satisfy | fill. Since the on-period of each color fluorescent lamp is set in this way, the influence which the afterglow of each color fluorescent lamp has on the following color field can be made as small as possible.

(Relationship)

tr ： tg ： tb = 4-8 ： 0.5-2 ： 5-9

4 is a view for explaining the lighting control of each color fluorescent lamp of the liquid crystal display device of the prior art shown in contrast with the liquid crystal display device of the present invention, and the lighting / lighting out of the red, green, and blue fluorescent lamps. The relationship between timing and light output of red, green, and blue fluorescent lamps is shown.

As shown in the figure, in the liquid crystal display of the prior art, as shown in Figs. 4A to 4C, the respective ON periods in the red, green, and blue fluorescent lamps are set equally. . That is, in the conventional liquid crystal display device, it has not been examined to control what the afterglow time of each color fluorescent lamp is different. Therefore, as shown in FIG.4 (d), the influence by the afterglow of a green fluorescent lamp with long afterglow time extends to the blue screen display time following each green screen display time, and the afterglow of a green fluorescent lamp and a blue fluorescent lamp The light emission of the superposition | emission superimposed on each other and connected with the fall of image quality.

FIG. 5 is a diagram for explaining a lighting control method different from the lighting control method of each of the fluorescent lamps shown in FIG. 3; FIG. 5 shows timings for turning on / off the red, green, and blue fluorescent lamps, and red, green, and blue fluorescent lamps. The relationship between the light output of the lamp is shown.

In this lighting control method, as in the case of the lighting control method shown in Fig. 3, using the three types of the above composition as the phosphor, the long / short timing of the lighting / lighting timing is also determined by the afterglow time, and each fluorescent lamp Is also shortened in order of green, red, and blue. What is different from the lighting control method shown in FIG. 3 is that the voltage value of the high frequency voltage applied to the red, green, and blue fluorescent lamps differs for each color.

As shown in Fig. 5, the on periods of the red, green, and blue fluorescent lamps are set short in the order of green, red, and blue, and the applied voltages of the red, green, and blue fluorescent lamps are green, It is set high in order of red and blue. The on periods of the red, green, and blue fluorescent lamps are adjusted in the same manner as the lighting control method shown in FIG. 3. The voltage value applied to the red, green, and blue fluorescent lamps can be adjusted to the desired value, for example, by increasing or decreasing the number of turns of the secondary windings of the boost transformers of the lighting circuits 30R, 30G, and 30B, or by lowering the input voltage. have.

Thus, the fluorescent lamp which emits a color with a long afterglow time can shorten the on-period and set the applied voltage high, thereby making it possible to make the integrated intensity of light emission of each color constant. Therefore, compared with the lighting control method shown in FIG. 3, image quality can be improved further.

FIG. 6: is a perspective view which shows the whole structure of the liquid crystal display device provided with the side edge type backlight which differs in the arrangement | positioning of the fluorescent lamp and the liquid crystal display device shown in FIG.

As shown in the figure, the liquid crystal display device has a main body case 20 in which one direction is opened, a diffuse reflection sheet 21 disposed on the rear surface of the main body case 20, and red fluorescent light that functions as a backlight light source. Diffusion plate 22, diffuser sheet 23, lens sheet 24 having lamps LR-1, LR-2, green fluorescent lamps LG-1, LG-2, and blue fluorescent lamps LB-1, LB-2 ) And the liquid crystal display element 25 are superposed so that the opening of the main body case 20 may be blocked in this order in the light emission direction. Each of the red, green, and blue fluorescent lamps is arranged side by side in parallel with each other on one end side and the other end side of the main body case 20. The red, green, and blue fluorescent lamps disposed on one end side of the main body case 20 include red, green, and blue fluorescent lamps disposed on the other end side of the main body case 20 with the liquid crystal display element 25 interposed therebetween. Oppose the lamp. The lighting control method of each color fluorescent lamp can be applied like the lighting control method shown in FIG. 3 and FIG. In this case, it is also possible to use a light guide plate on the entire surface of the diffuse reflection sheet 21 and to instead omit the diffuser plate 22. The fluorescent lamp can be used, for example, as an external electrode type rare gas fluorescent lamp or a cold cathode fluorescent lamp.

1 is a perspective view showing the overall configuration of a liquid crystal display device according to the present invention.

2 is a block diagram showing a circuit configuration of a liquid crystal display device according to the present invention.

It is a figure for demonstrating the lighting control method of each color fluorescent lamp in the liquid crystal display device of this invention.

4 is a diagram for explaining lighting control of each color fluorescent lamp of the liquid crystal display of the prior art.

FIG. 5 is a diagram for explaining a lighting control method different from the lighting control method of each color fluorescent lamp shown in FIG. 3.

FIG. 6 is a perspective view showing the overall configuration of a liquid crystal display device having a side edge type backlight having a different arrangement of the liquid crystal display device shown in FIG. 1 and a fluorescent lamp. FIG.

7 is a graph showing the afterglow characteristics of phosphors emitting red, green, and blue light.

FIG. 8 is a schematic diagram of a case of displaying red, green, and blue colors using a red, green, and blue fluorescent lamp having phosphors emitting red, green, and blue colors as a backlight in a field sequential color liquid crystal display device. FIG.

[Description of Symbols for Main Parts of Drawing]

20 Body Case 21 Diffuse Reflective Sheet

22 diffuser 23 diffuser sheet

24 Lens Sheet 25 Liquid Crystal Display Element

30R, 30G, 30B lighting circuit 31 timing controller

32R, 32G, 32B Field Memory 33 Data Drivers

34 scanning driver

LR, LR-1, LR-2, LR-3 red fluorescent lamps

LG, LG-1, LG-2, LG-3 Green Fluorescent Lamps

LB, LB-1, LB-2, LB-3 Blue Fluorescent Lamps

Claims (3)

A red, green, and blue fluorescent lamp having a liquid crystal display unit, and a phosphor film emitting red, green, and blue colors, and an on-period for applying a high frequency voltage to the fluorescent lamp to light the fluorescent lamp; A lighting circuit for controlling the brightness of each fluorescent lamp by alternately repeating an off period for stopping the application of the high frequency voltage of the fluorescent lamp and turning off the fluorescent lamp; The red, green, and blue fluorescent lamps are lighted by sequentially applying high frequency voltage so as to shift the emission timing of the red, green, and blue fluorescent lamps, and to emit each color individually. A liquid crystal display device which displays an image on the liquid crystal display by functioning a blue fluorescent lamp as a backlight of the liquid crystal display. The on-period is changed for each of the red, green, and blue fluorescent lamps. The method according to claim 1, The on-line period is set shorter as a fluorescent lamp which emits a color with a long afterglow time among the red, green, and blue fluorescent lamps. The method according to claim 1 or 2, The red, green, and blue fluorescent lamps, wherein the fluorescent lamp for emitting a long afterglow time, the higher the applied voltage value of the on period, characterized in that the liquid crystal display device.

Images