JPH10333590A - Backlight for color liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent color unsharp and to improve luminance by improving a fall characteristic of red and preventing overlapping with other colors from causing even when a duty ratio of a light emission pulse is made to a 1/3 extent of the maximum. SOLUTION: By making at least a red (R) light source 12 a rare gas discharge tube (neon tube) among the light sources 10, 11, 12, the fall characteristic of red is improved, and the overlapping with other colors is prevented even when the duty ratio of the light emission pulse is made to the 1/3 extent of the maximum. Thus, the color unsharp is prevented, and the luminance is improved. Further, since a control circuit 19 equalizing the temp. characteristic of the rare gas discharge tube to that of a cold cathode tube is provided, the backlight isn't affected by a temp. change, and excellent performance is obtained in a wide temp. range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a backlight for a color liquid crystal display.

[0002]

2. Description of the Related Art Recently, OA of personal computers and the like has been developed.
2. Description of the Related Art A color liquid crystal display device is used for a display of a home appliance such as a device or a television. As this type of color liquid crystal display device, a TFT type color liquid crystal display device is widely known. That is, the three primary colors (red (R), green (G),
A color filter corresponding to blue (B) color and a color liquid crystal cell equipped with a thin film transistor (TFT) are combined with a backlight of a white light source, and the liquid crystal corresponding to each color filter is opened by a drive circuit to transmit light. As a result, the structure is such that a mosaic color mixture can be obtained by a combination of red (R), green (G), and blue (B) colors.

Such a TFT type color liquid crystal display device can obtain a clear full color image, but requires a color filter and a thin film transistor for each pixel (liquid crystal cell). Processing is required, and there are also problems such as difficulty in color balance adjustment.

Therefore, a color filter-less color liquid crystal display device in which a monochrome liquid crystal cell that does not require a color filter or a thin film transistor is combined with a backlight of three primary colors has recently been proposed (for example, Japanese Patent Application Laid-Open No.
-281647). That is, the light sources of the three primary colors are sequentially pulse-emitted, and the liquid crystal is opened at the same timing as the emitted light, so that an afterimage by a combination of red (R), green (G), and blue (B) colors is obtained. Mixed colors can be obtained.

[0005]

However, in such a color filter-less color liquid crystal display device, although there have been many proposals relating to control of liquid crystal cells, practical proposals relating to backlights have been made. rare. For example, when the light source of red (R), green (G), and blue (B) is a cold cathode tube, the rising and falling characteristics (hereinafter, falling characteristics) of the red (R) light source are particularly poor. For,
When the duty ratio of each pulse light emission is set to 1/3 of the maximum, red color overlaps with other colors, causing color blur. Therefore, in order to eliminate color blur, the duty ratio must be 1
It is necessary to make it smaller than / 3, and the reduction of the luminance is inevitable. A practical solution to the problem caused by the falling characteristics of the light source has not yet been proposed.

The present invention has been made by paying attention to such a conventional technique, and provides a structure capable of solving a problem caused by the falling characteristic of a light source in a backlight.

[0007]

According to the first aspect of the present invention,
A backlight for a color liquid crystal display device in which independent light sources of three primary colors that sequentially and periodically emit pulses are arranged on at least one end surface of one light guide plate and a color filter is not used in a liquid crystal cell, wherein Among them, the red (R) light source is a rare gas discharge tube, the other light source is a cold cathode tube, and a control circuit for making the temperature characteristics of the rare gas discharge tube the same as that of the cold cathode tube is provided.

According to the first aspect of the present invention, since the red (R) light source is a rare gas discharge tube, the fall characteristic of red is good, and the duty ratio of the emission pulse can be set to 1/3 of the maximum. No overlap with other colors occurs. Therefore, the color blur can be prevented and the luminance can be improved. Also,
Since the control circuit for making the temperature characteristics of the rare gas discharge tube the same as that of the cold cathode tube is provided, excellent performance can be obtained in a wide temperature range without being affected by a temperature change.

In the invention according to claim 2, the rare gas discharge tube is a neon tube.

According to the second aspect of the present invention, since the rare gas discharge tube is a neon tube which can be easily formed, a light source having substantially the same diameter as that of the cold cathode tube can be formed, and the arrangement in the reflecting mirror can be achieved. Easy. According to the third aspect of the invention, the color light of the cold cathode tube is emitted from the phosphor.

According to the third aspect of the present invention, since green and blue colors are emitted from the phosphors of the respective cold cathode tubes, a color filter on the light source side provided for coloring can be eliminated, and the number of parts can be reduced. Can be achieved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, a color liquid crystal display device according to this embodiment includes a liquid crystal cell 1 forming one pixel of a liquid crystal panel, a backlight 2, a high-speed liquid crystal drive circuit 3, inverters 4, 5, and so on. , And 6.

In the liquid crystal cell 1, a liquid crystal (STN) 8 is sealed between two glass substrates 7, and the liquid crystal 8 is turned on through a transparent conductive film (ITO film) 9 in which the liquid crystal 8 is arranged in a matrix.
A known device that is turned off can be used. The liquid crystal cell 1 has a simple structure because it is for monochrome and does not require a color filter or a thin film transistor.

The transparent conductive film (ITO film) 9 of the liquid crystal cell 1
Are connected to the high-speed liquid crystal drive circuit 3. Also,
This high-speed liquid crystal drive circuit 3 has three primary colors (red (R)
It has three terminals of green (G) and blue (B), and a terminal for the red (R) light source 12 is connected to the inverter 6 via the control circuit 19 and is connected to the other blue (B). The terminals for the color light source 11 and the green (G) light source 10 are connected to respective inverters 4 and 5. The control circuit 19 controls the temperature characteristics of the red (R) light source 12. The output terminals of the inverters 4, 5, 6 are connected to one ends of the light sources 10, 11, 12 in the backlight 2,
The other ends of 1 and 12 are grounded.

The backlight 2 includes one light guide plate 13,
It comprises a reflector 14, three light sources 10, 11 and 12, a diffusion sheet 15, a halftone dot (dot pattern) 16, a reflection sheet 17, and an auxiliary reflection sheet 18.

As the light guide plate 13, a transparent resin plate or a molded product having six smooth transparent surfaces can be used. As the transparent resin, an acrylic plate, a polyester plate, a vinyl chloride plate and the like are preferable. The cross-sectional area (i.e., thickness) of one end surface (light incident surface) of the light guide plate 13 is an important factor for effectively introducing light from the light sources 10, 11, 12;
Although a large amount of light can enter the light guide plate 13, if it is too thick, it takes up space, which is against the weight and size reduction of the electronic device, and also leads to light loss. Backlight 2 of this embodiment
Since only one light guide plate 13 is required, the structure is simple, which is advantageous in reducing the size and thickness of the device.

Back surface of light guide plate 13 (surface on the side opposite to liquid crystal cell 1)
Are white halftone dots 16. Dot 16
Is for scattering light, and is formed by printing an ink in which a filler having a high refractive index is mixed with an organic resin in a dot shape. The halftone dots 16 are light sources 10, 11,
The surface density increases as the distance from the center 12 and the auxiliary reflection sheet 18 increases (closer to the center position), contributing to the uniformity of luminance.

The reflecting mirror 14 is attached to one end face of the light guide plate 13. The reflecting mirror 14 has a curved cross section opened at one end surface. On the inner surface of the reflecting mirror 14, a silver mirror surface having a high reflectance is formed in order to efficiently introduce light from the light sources 10, 11, and 12 into the light guide plate 13 and prevent the light from leaking outside. However, a reflecting member in which a white material or the like is kneaded in a synthetic resin (for example, PET) may be used. Further, the reflecting mirror 14 is not limited to a linear shape as shown in FIG. 2, and may be formed in an L shape. In this case, the reflecting mirror 14
It goes without saying that these openings are opened at the two end faces of the light guide plate 13, respectively.

Light sources 10, 11, and 12 use cold cathode tubes for green (G) and blue (B) colors, and use a "rare gas discharge tube" for red (R) color. Neon (Ne)
Use a tube. The neon tube is easy to form, can form a light source having substantially the same diameter as the cold-cathode tube, and can be easily arranged in the reflecting mirror 14. The green (G) light source 10 and the blue (B) light source 11 emit light from the phosphor itself coated on the inner surface of the cold cathode tube to display pure colors of green and blue, and do not require a color filter. . The light sources 10, 11, and 12 are continuously lit with a pulse cycle synchronized with the driving timing of the liquid crystal, and do not require an optical shutter or the like.

The proportion of the three primary colors that perceive the brightness of the human eye,
That is, three primary colors, red (R) and green (G), were obtained by visual experiment of luminance.
-It is adjusted by the inverters 4, 5, and 6 so that blue (B) becomes 1.5: 3.5: 1. Therefore, CIE (C
A green (G) light source 1 that requires the most luminance when adjusting to the center of a so-called white area adopted by the International Commission on Illumination, which is abbreviated as “ommission Internationalization Leclairage”.
0 is disposed closest to the light guide plate 13.

The reflection sheet 17 is made of a synthetic resin (for example, PE
T) is a sheet of a white high-reflectance material obtained by kneading a white material or the like into T), and is arranged in contact with the halftone dot 16 side of the light guide plate 13 via a fine air layer.

The same applies to the auxiliary reflection sheet 18 provided on the other end surface. By providing the auxiliary reflection sheet 18, it is possible to prevent the luminance from declining in portions far from the light sources 10, 11, and 12, and to achieve uniform luminance.

The diffusion sheet 15 is a roughened surface in which the sheet surface is roughened like a satin finish, and is for scattering and transmitting light transmitted from the light guide plate 13.

Next, the operation of the color liquid crystal display device will be described. The high-speed liquid crystal drive circuit 3 outputs a pulse waveform synchronized with the liquid crystal drive timing. Red (R)
The pulse waveform for the color light source 10 has a duty set to １ ／ to avoid simultaneous lighting with other colors (mixing colors). Next, the pulses of the green (G) light source 10 and the blue (B) light source 11 are caused to rise just in a manner shifted by １ ／ cycle.

FIG. 3 shows the pulse waveform of each light source in the same phase. The two-dot chain line of the red (R) light source 12 indicates the case where the red (R) light source 12 is formed by a cold cathode tube. 2 shows the falling characteristic (time required to reach 10% from the steady state) dT. As described above, when the red (R) light source 12 is formed of a cold cathode tube, the fall characteristic dT is large, and when the duty ratio is set to 1/3 of the maximum, the color overlaps with other colors to cause color blur. However, in the present invention, the red (R) light source 1
Since 2 is a neon tube, the fall characteristic dt is as small (about 0.1 ms) as the other green (G) light sources 10 and blue (B) light sources 11. Therefore, even if the duty ratio of the light emission pulse is set to the maximum of 1/3, red does not overlap with other colors, color blur can be prevented, and luminance can be improved.

Further, in this embodiment, the control circuit 19 corrects and controls the difference in temperature characteristics between the red (R) light source 12 which is a neon tube and the other light sources 10 and 11 which are cold cathode tubes. doing. That is, the green (G) light source 10 and the blue (B) light source 11 using a cold cathode tube are easily affected by a temperature change (the high-temperature brightness increases and the low-temperature brightness decreases), whereas the neon tube uses a neon tube. As shown in FIG. 4, the red (R) light source always shows a constant luminance without being affected by the temperature as a relative value to the ambient temperature. The red (R) light source 12 was confirmed using a neon tube having a diameter of 4.8 mm and a length of 216 mm. Therefore, if both light sources are used without controlling the temperature characteristics, the relative brightness of the cold cathode fluorescent lamp is reduced at low temperatures and the display surface becomes reddish. I will.

Therefore, in this embodiment, the control circuit 1
9, the brightness of the neon tube (red (R) color light source 12)
Cold cathode tubes (green (G) light source 10, blue (B) light source 11)
The luminance is changed so as to be the same as the luminance. That is, the control circuit 19 controls the tube current of the red (R) light source 12,
The neon tube has the same temperature specification as the cold cathode tube. This control circuit 19 does not use a temperature sensor,
Active control is performed by detecting the relative starting voltage from the output of one inverter 5 of the cold cathode tube and feeding it back. Since this relative starting voltage also shows temperature characteristics,
If control is performed based on this relative starting voltage, there will be no variation in detection accuracy due to the installation position or installation state, such as a temperature sensor.

In this way, the color light generated from the light sources 10, 11, 12 is reflected directly or by the reflecting mirror 14,
Light enters the light guide plate 13 from one end surface of the light guide plate 13. The light that has entered the light guide plate 13 strikes the inner surface of the light guide plate 13 and repeats total reflection. Part of the light hits the halftone dot 16 on the back surface and is scattered, so that the light is emitted toward the liquid crystal cell 1. A part of the light hitting the halftone dot 16 is reflected in the light guide plate 13 and then hits the reflection sheet 17 to be guided to the liquid crystal cell 1 side.

Light entering the liquid crystal cell 1 from the light guide plate 13 passes through the diffusion sheet 15. The light passing through the diffusion sheet 15 becomes scattered light due to minute irregularities and satin patterns on the surface, so that the light sources 10, 11, 12 and the pattern of the halftone dots 16 are not directly seen, and an effect of uniformly illuminating the entire surface is obtained. Can be

Light sources 10, 11, 12 in the backlight 2
Is emitting pulses at high speed sequentially as described above,
In the liquid crystal cell 1, under the control of the high-speed liquid crystal drive circuit 3, the liquid crystal 8 opens at the same timing as the color to emit light. The color at the timing when the liquid crystal 8 opens is transmitted through the liquid crystal cell 1, and the color is displayed. The color mixture is performed by opening the liquid crystal 8 at the timing of another color. For example,
If the liquid crystal 8 is opened at both timings of the red (R) light source 12 and the green (G) light source 10, yellow, which is a mixed color of red (R) and green (G), is displayed. If three colors of red (R), green (G), and blue (B) are mixed, white is displayed. This is an afterimage color mixture that occurs because the pulses of the light sources 10, 11, and 12 are sufficiently faster than the afterimage time of the eyes. The white color adjustment is performed by adjusting the output current of the inverters 4, 5, and 6 to adjust the light amount (luminance) ratio of each of the light sources 10, 11, and 12.

According to the color liquid crystal display device of this embodiment, a color liquid crystal display device without using a color filter is possible, and the production of the liquid crystal cell 1 is easier than that of a conventional color liquid crystal display device using a color filter. . In addition, as for the backlight 2, while the TFT method requires only one white light source, the present embodiment uses three light sources 10, 11,.
12 is required, which is disadvantageous in terms of miniaturization and thinning. However, as described above, only one light guide plate 13 is required.
By adopting a structure in which the light sources 10, 11, and 12 are housed in the reflecting mirror 14, the backlight 2 can be reduced in size and thickness. Further, for the same reason, it is possible to reduce the cost by reducing the number of parts.

In this embodiment, the light sources 10, 11,
Although the duty of the 12 pulses is set to 1/3 of the maximum, it may be set to 1/3 or less depending on the relationship with the liquid crystal cell 1. Further, the rare gas discharge tube is not limited to a neon tube, and a xenon tube or the like can be used. Also, the reflecting mirror 14 may be a reflecting member made by kneading a white material or the like in a synthetic resin (for example, PET).

[0034]

According to the first aspect of the present invention, red (R)
Since the color light source is a rare gas discharge tube, the fall characteristics of red are good, and even if the duty ratio of the emission pulse is 1/3 of the maximum, no overlap with other colors occurs. Therefore, the color blur can be prevented and the luminance can be improved. Further, since a control circuit for making the temperature characteristics of the rare gas discharge tube the same as that of the cold cathode tube is provided, excellent performance can be obtained in a wide temperature range without being affected by a temperature change.

According to the second aspect of the present invention, since the rare gas discharge tube is a neon tube which can be easily formed, a light source having substantially the same diameter as that of the cold cathode tube can be formed, and the arrangement in the reflecting mirror can be reduced. Easy. According to the third aspect of the present invention, green and blue colors are emitted from the phosphors of the respective cold cathode tubes, so that a color filter on the light source side provided for coloring can be eliminated,
The number of parts can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a backlight for a color liquid crystal display device of the present invention.

FIG. 2 is an exploded perspective view showing a backlight.

FIG. 3 is a diagram showing pulse waveforms of respective colors at the same phase.

FIG. 4 is a temperature characteristic diagram of a neon tube.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal cell 10, 11 light source (cold cathode tube) 12 light source (neon tube as rare gas discharge tube) 13 light guide plate 15 diffusion sheet 16 halftone dot 17 reflection sheet 18 auxiliary reflection sheet 19 control circuit

Claims (3)

[Claims] 1. A backlight for a color liquid crystal display device in which independent light sources of three primary colors that emit pulses sequentially and periodically are arranged on at least one end face of one light guide plate and a color filter is not used in a liquid crystal cell. And a control circuit for setting the temperature characteristics of the rare gas discharge tube to be the same as that of the cold cathode tube, wherein the red (R) light source is a rare gas discharge tube and the other light source is a cold cathode tube. A backlight for a color liquid crystal display device, wherein the backlight is provided. 2. The backlight for a color liquid crystal display device according to claim 1, wherein the rare gas discharge tube is a neon tube. 3. A backlight for a color liquid crystal display device according to claim 1, wherein the color light of the cold cathode tube is emitted from a phosphor. Light.