JP3986334B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device such as a liquid crystal monitor or a liquid crystal television.
[0002]
[Prior art]
In recent years, the technological progress of liquid crystal display devices has been remarkable, and it has been used for notebook computers, monitors, liquid crystal TVs, portable information devices, mobile phones, etc., with the advantage of being able to save space and power saving due to the thinness of the device, It forms a big market.
[0003]
This liquid crystal display device has a structure in which a polarizing plate is mounted on the light incident side and light emitting side of an element (liquid crystal panel) sandwiching liquid crystal between a pair of glass substrates, polarized by the polarizing plate and incident on the liquid crystal panel. Image display is enabled by modulating the linearly polarized light that has been modulated by the liquid crystal layer of each pixel.
[0004]
The basic operation principle of the liquid crystal panel is shown in FIG. FIG. 2 shows a normally white liquid crystal panel, in which the polarizing axes of two polarizing sheets sandwiching the liquid crystal are arranged so as to be orthogonal to each other, and the transmittance is minimized by applying a sufficient applied voltage. is there.
[0005]
In FIG. 2, 5 is a liquid crystal panel, 5a is an incident side polarizing sheet, 5b is an output side polarizing sheet, 5c is a liquid crystal part, 5d is a liquid crystal molecule, and the liquid crystal molecules 5d that are rotated and aligned in a spiral shape by applying voltage are converted into light. Is sandwiched between two polarizing films 5a and 5b whose polarization directions are orthogonal to each other.
[0006]
FIG. 2A is a principle diagram of light transmission (On display) of a liquid crystal panel. When no voltage is applied, the liquid crystal panel 5c is rotated and oriented in a spiral shape, and incident light is first oscillated in one direction by the polarizing film 5a. The polarized light is twisted by 90 ° along the gap between the liquid crystal molecules 5d, and the polarized light is transmitted through the polarizing film 5b.
[0007]
FIG. 2b shows the principle of light blocking (off display) of the liquid crystal panel. When a voltage is applied to the liquid crystal panel, the liquid crystal molecules 5d are twisted and stand upright, so that the light polarized by the polarizing film 5a changes the polarization direction. Without passing through the liquid crystal panel, the polarized light is blocked.
[0008]
In addition, halftone display is expressed by applying an appropriate voltage that is intermediate between On display and Off display to the liquid crystal panel. In the color display method, one pixel is composed of three dots each having a red, green, and blue filter, and the necessary colors are displayed by controlling each dot.
[0009]
FIG. 6 shows a circuit block of the liquid crystal display device. In FIG. 6, 1 is a Y / C separation circuit, 2 is a video chroma circuit, 3 is an A / D converter, 4 is a liquid crystal controller, 5 is a liquid crystal panel, 6 is a fluorescent tube driving circuit, 7 is a backlight, and 8 is a microcomputer. , 11 are gradation circuits.
[0010]
The input video signal is input to the Y / C separation circuit 1 and separated into a luminance signal and a color signal. The luminance signal and the color signal are converted into R, G, and B which are the three primary colors of light by the video chroma circuit 2, and the analog RGB signal is converted into a digital RGB signal by the A / D converter 3, and the liquid crystal Input to the controller 4.
[0011]
In the liquid crystal panel 5, RGB signals from the liquid crystal controller 4 are input at a predetermined timing, and RGB gradation voltages from the gradation circuit 11 are supplied to display an image.
[0012]
The microcomputer 8 controls the entire system including these processes.
Although the basic configuration and basic operation of the liquid crystal display device are as described above, in order to obtain faithful color reproduction such as color video display and high contrast, it is necessary to deal with the wavelength dependence of each component of the liquid crystal panel. For example, various proposals have been made as countermeasures for wavelength dependence of liquid crystals.
[0013]
In JP-A-5-323311, in general, in the TN mode, the liquid crystal panel is arranged so that the outgoing light after passing through the liquid crystal layer becomes linearly polarized light whose polarization axis is orthogonal to the incident linearly polarized light when no voltage is applied. design.
[0014]
The condition at this time is usually that the optical retardation Δn · d / λ (Δn = refractive index anisotropy of liquid crystal, d = thickness of liquid crystal layer, λ = wavelength of light) is approximately 0.9. In this case, in the case of the normally black mode in which the display mode is black when no voltage is applied, the display near black uses a relatively large region with an optical phase difference of about 1. The wavelength dependence is large, and the chromaticity changes drastically in the halftone near black, resulting in a very poor display quality.
[0015]
On the other hand, in the normally white mode, white is displayed in a region where the optical phase difference is large. At this time, even if wavelength dependence occurs, the change in chromaticity is small, and the optical phase difference is small near black. Further, since the wavelength dependence itself is reduced, a uniform and good display without chromaticity change can be obtained. Therefore, a normally white mode TN liquid crystal display device is generally used.
[0016]
However, in order to obtain a display with a high contrast ratio in the normally white mode, it is necessary to reduce the light transmittance in the black display as much as possible. In the normally white mode, the liquid crystal molecules are applied to the substrate surface by applying a voltage. However, in reality, the liquid crystal molecules in the vicinity of the substrate interface have strong interaction with the substrate even when a voltage is applied, and do not stand up completely. As a result, an optical phase difference occurs, the polarization state of the light changes, and a true black display is unlikely to occur.
[0017]
As this correspondence, a liquid crystal panel in which a liquid crystal is sandwiched between a pair of light-transmitting electrode substrates, a polarizing plate disposed on both sides of the liquid crystal panel, and a liquid crystal panel disposed between the polarizing plate and the liquid crystal panel. And an optical retardation film having an optical retardation that corrects the optical anisotropy of the liquid crystal with respect to incident light when a predetermined driving voltage is applied.
[0018]
In Japanese Patent Laid-Open No. 7-159770, a multi-gap color filter composed of R, G, and B filters having different thicknesses is installed on a first polarizing plate on which backlight light is incident. A second polarizing plate is disposed in parallel to face the first polarizing plate. The gap between the first and second alignment films between the multi-gap color filter and the second polarizing plate is filled with liquid crystal having a refractive index anisotropy Δn = 0.094 to form a multi-gap liquid crystal layer. is doing.
[0019]
The thicknesses of the liquid crystal layers on the R, G, and B filters are 5.6 μm, 5.0 μm, and 4.8 μm, respectively. This is expressed as retardation Δn · d, which is 0.53 μm, 0.47 μm, and 0.45 μm, respectively. In this way, in the multi-gap type liquid crystal panel, it is a proposal to improve the contrast as well as the chromaticity of the display color.
[0020]
In JP-A-9-325314, a liquid crystal cell in which a nematic liquid crystal layer twisted and aligned at 120 ° or more is sandwiched between a pair of substrates, and an optically anisotropic body are disposed between the pair of polarizing plates. This is a method of eliminating the coloration of the liquid crystal cell by an optical anisotropic body.
[0021]
[Problems to be solved by the invention]
However, in the liquid crystal display device, the optical characteristics when the pixel is turned on / off are the On display when the polarization axis of the polarizing film is parallel, and the Off display is when the polarization axis of the polarizing film is orthogonal. Also strongly affected by optical properties.
[0022]
Usually, when the polarizing axes of the polarizing film are arranged orthogonally, the transmittance of light having a short wavelength is higher than that of light having a long wavelength. For example, in the case of an iodine-based polarizing sheet often used in a liquid crystal TV, the polarizing axis is When black display is made by arranging them orthogonally, dark blue (high color temperature), which is the color of iodine, is displayed instead of black. That is, when shifting from On display to Off display or halftone display, the color tone shifts in the blue direction.
[0023]
FIG. 7 shows an example of measuring the change in chromaticity when displaying white (On) to gray to black (Off) on a liquid crystal display device. When the voltage is gradually applied to the liquid crystal panel and the brightness decreases, it can be confirmed that the screen color gradually shifts from white to blue.
[0024]
The present invention has been made in view of such a situation, and an object of the present invention is to correct a change in display color when a voltage applied to a liquid crystal panel is varied due to the characteristics of a polarizing film and the method of arranging the polarization axis. It is an invention.
[0025]
[Means for Solving the Problems]
According to a first aspect of the present invention, in a transmissive liquid crystal display device having a backlight, a backlight device having a variable light source chromaticity, a backlight control means, a luminance level detection means for an input video signal, and a polarizing sheet. and a storage means for holding a voltage applied versus wavelength transmission characteristic of the liquid crystal panel in which liquid crystal is sandwiched Te, the backlight control means, the correction to be extracted from the detected luminance level and said memory means by said brightness level detecting means A signal is added to control the light emission chromaticity of the backlight.
[0026]
According to a second aspect of the present invention, there is provided a transmissive liquid crystal display device having a backlight, a backlight device having a variable light source chromaticity, a backlight control means, a luminance level detection means for an input video signal, and a polarizing sheet . and a storage means for holding the wavelength transmission characteristics, the backlight control means, emission chromaticity of the backlight by adding the correction signal extracted from the detected luminance level and said memory means by said brightness level detecting means It is characterized by controlling.
[0027]
The invention according to claim 3 of the present application is characterized in that the backlight device with variable light source chromaticity comprises a plurality of light sources having different emission colors.
[0028]
The invention according to claim 4 of the present application is characterized in that the backlight device with variable light source chromaticity has a constant light emission intensity and only variable chromaticity.
[0029]
The invention according to claim 5 of the present application is a luminance level detection means for an input video signal, a white balance adjustment means, a storage means for holding applied voltage versus wavelength transmission characteristics of a liquid crystal panel in which liquid crystal is sandwiched between polarizing sheets. the a, and performs white balance adjustment by the correction signal extracted from the detected luminance level and said memory means by said brightness level detecting means.
[0030]
According to claim 6 of the present invention includes a luminance level detecting means of the input video signal, and white balance adjusting means, and storage means for holding the wavelength transmission characteristic of the polarizing sheet, detected by said luminance level detection means White balance adjustment is performed using the luminance level and the correction signal extracted from the storage means.
[0031]
The invention according to claim 7 of the present application is characterized in that the wavelength transmission characteristic is stored in a lookup table.
[0032]
The invention according to claim 8 of the present application is characterized by having a look-up table for storing a plurality of wavelength transmission characteristics, a means for specifying one of the wavelength transmission characteristic of the plurality of.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the liquid crystal display device of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same part as a prior art example, and the description is abbreviate | omitted.
[0034]
As a first embodiment, a liquid crystal display device using a side edge type backlight device will be described with reference to FIGS. In FIG. 1, 7a is a first lamp, 7b is a second lamp, 9 is a luminance level detection circuit, and 10 is a look-up table.
[0035]
The basic processing until the input video signal is input to the Y / C separation circuit 1 and displayed on the liquid crystal panel 5 via the video chroma circuit 2, A / D converter 3, and liquid crystal controller 4 is shown in FIG. Since it is the same as the liquid crystal display device of the conventional example, the description is omitted.
[0036]
On the other hand, the luminance signal separated from the video signal by the Y / C separation circuit 1 is also input to the luminance level detection circuit 9 where the average luminance level of the entire screen is detected and input to the microcomputer 8.
[0037]
The control luminance signal detection level is not limited to the average luminance level, and the maximum luminance level, the minimum luminance level, and a combination level thereof can be used. It is also possible to detect a level by giving weight to a specific area and / or a specific area of the screen.
[0038]
FIG. 3 is a cross-sectional view of a side-edge type backlight device. In FIG. 3, 5a is input morphism side polarizing sheet, 5b exits elevation side polarizing sheet, 5c LCD, 7a a first ramp, 7b a second lamp, 7d indicates a light guide plate, 7e reflection sheet, 7f is It is a diffusion sheet.
[0039]
The light emitted from the lamps 7a and 7b proceeds on the principle of total reflection in the light guide plate 7d made of highly transparent acrylic or the like as in the case of the optical fiber.
Dots for diffusing light are formed on the back surface of the light guide plate 7d by printing or the like, and a part of the light that has traveled by total reflection is diffused by these dots, and the front direction (liquid crystal panel side) of the light guide plate 7d. And the liquid crystal panel 5 is uniformly irradiated by the diffusion sheet 7f.
[0040]
In-plane brightness distribution, that is, brightness unevenness control, is performed by adjusting the density and distribution of dots on the back surface of the light guide plate 7d, but even the diffusion sheet 7f can control brightness unevenness in a minute area. It is. The reflection sheet 7e is arranged to return light leaking from the back surface or the like into the light guide plate.
[0041]
The backlight 7 is composed of a first lamp 7 a having a long light spectrum in the long wavelength region and a second lamp 7 b having a strong light spectrum in the short wavelength region, and is driven by a fluorescent tube by a control signal from the control microcomputer 8. The circuit 6 is controlled so that the total light emission intensity of the backlight 7 is constant, and the light emission intensity of each of the first lamp 7a and the second lamp 7b is variable.
[0042]
The look-up table 10 stores the wavelength transmission characteristics of the voltage applied to the liquid crystal panel 5 based on the material of the polarizing sheets 5a and 5b and the polarization axis arrangement. It is also possible to store the wavelength transmission characteristics of a plurality of applied voltages in the look-up table 10 and select them according to the conditions of the polarizing sheets 5a and 5b to be used.
[0043]
Next, an example of the chromaticity control operation of the light source will be described. The input video signal is input to the Y / C separation circuit 1, and the separated luminance signal is also input to the luminance level detection circuit 9. The average luminance level detected by the luminance level detection circuit 9 is input to the microcomputer 8, and the microcomputer 8 refers to the look-up table 10 and outputs a light source control signal for the input average luminance level to the fluorescent tube driving circuit 6. .
[0044]
In the fluorescent tube driving circuit 6, the first lamp 7a and the second lamp are set based on the light source control signal from the microcomputer 8 so that the total light emission intensity of the backlight 7 is constant and the predetermined light source chromaticity is obtained. The driving voltage is supplied to 7b.
[0045]
Now, when the average luminance level detected by the luminance level detection circuit 9 is lowered, the color tone of the output light of the liquid crystal panel 5 is shifted in the blue direction due to the wavelength transmission characteristics of the polarizing sheets 5a and 5b. The microcomputer 8 outputs a control signal to the fluorescent tube driving circuit 6 so that the light emission chromaticity of the backlight 7 is shifted in the red direction, and the lamp 7a and the lamp 7b are driven at a predetermined voltage. Is shifted in the red direction, so that the change in the chromaticity of the liquid crystal display screen due to the change in the average luminance level of the input video signal is corrected.
[0046]
That is, the backlight 7 has a strong reddish color tone when the lamp 7a has a high emission intensity, and a strong blue tone with the lamp 7b having a high emission intensity.
[0047]
Since the display brightness level of the screen is low and the light transmitted through the liquid crystal panel is color-shifted due to the characteristics of the polarizing film, the backlight emission color is adjusted in the direction to correct this. By shifting, the display color as the liquid crystal display device can be kept appropriate.
[0048]
In the present embodiment, two light sources have been described, but it is naturally possible to realize with three or more light sources.
[0049]
Next, a second embodiment will be described with reference to FIGS. FIG. 4 is a block diagram of a liquid crystal display device having a direct type backlight device. The basic functions of each block are the same as in the first embodiment, and the operations other than the operation of the gradation circuit 11 are omitted. FIG. 5 is a cross-sectional view of the direct type backlight device. In FIG. 5, 7g is a polarizing sheet, 7h is a diffuser, 7i is a fluorescent tube, and 7j is a reflector.
[0050]
The white light from the plurality of fluorescent tubes 7i driven by the fluorescent tube driving circuit 6 reaches the diffusion plate 7h as direct light from the fluorescent tubes 7i or reflected light from the reflecting plate. Since the luminance directly above 7i becomes high, the luminance is uneven on the liquid crystal display surface as it is, so that the luminance on the liquid crystal display surface can be made uniform by inserting the diffusion plate 7h.
[0051]
Next, an example of the chromaticity control operation of the direct type backlight device will be described. As in the first embodiment, the input video signal is input to the Y / C separation circuit 1, and the separated luminance signal is also input to the luminance level detection circuit 9.
[0052]
The average luminance level detected by the luminance level detection circuit 9 is input to the microcomputer 8, and the microcomputer 8 refers to the lookup table 10 and outputs a gradation correction signal for the input average luminance level to the gradation circuit 11. . The gradation circuit 11 supplies the RGB gradation voltage to the liquid crystal panel after correcting the voltage based on the gradation correction signal from the microcomputer 8.
[0053]
Now, when the average brightness level detected by the brightness level detection circuit 9 is lowered, the color tone of the output light of the liquid crystal panel 5 is shifted in the blue direction from the wavelength transmission characteristics of the polarizing sheets 5a and 5b. The microcomputer 8 corrects the gradation circuit 11 so as to increase the RG gradation voltage level, thereby maintaining the white balance at the time of low luminance.
[0054]
In the present embodiment, the method for obtaining the white balance with the correction voltage from the gradation circuit 11 has been described. However, the microcomputer 8 refers to the LUT 10 and supplies the correction signal to the video chroma circuit 2. Naturally, it is possible to achieve white balance.
[0055]
In this embodiment, the direct-type backlight type liquid crystal display device has been described. However, correction by signal processing is naturally possible even in a side-edge type backlight system.
[0056]
In this way, it is possible to maintain the display color of the liquid crystal display device properly by maintaining the correction characteristics that match the light transmission characteristics of the liquid crystal panel and correcting the backlight control and signal processing according to the input video signal. Become.
[0057]
According to the inventions according to claims 1 to 3, 5 and 6 of the present application, it is possible to correct a change in chromaticity of a display screen due to wavelength transmission characteristics in a liquid crystal panel .
[0058]
According to the invention of claim 4 of the present application, the backlight device with variable light source chromaticity has a constant emission intensity and only the chromaticity is changed, thereby further ensuring display quality.
[0059]
According to according to claim 7 of the present invention, by having a look-up table that stores the wavelength transmission characteristics, also change the correction characteristics is facilitated, thereby enabling highly accurate chromaticity correction.
[0060]
According to according to claim 8 of the present invention, a look-up table for storing a plurality of wavelength transmission characteristics, to have a means for designating one of the characteristic, only the liquid crystal panel portion of the other type and replacement The display unit and the processing / control device main unit can be freely replaced.
[Brief description of the drawings]
FIG. 1 is a functional block diagram of a liquid crystal display device according to the present invention.
FIG. 2 is a basic operation principle diagram of a liquid crystal panel.
FIG. 3 is a configuration diagram of a backlight device according to the present invention.
FIG. 4 is a functional block diagram of a liquid crystal display device according to the present invention.
FIG. 5 is a configuration diagram of a backlight device according to the present invention.
FIG. 6 is a functional block diagram of a conventional liquid crystal display device.
FIG. 7 is a graph showing changes in display brightness and chromaticity of a liquid crystal display device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Y / C separation circuit 2 Video chroma circuit 3 A / D converter 4 Liquid crystal controller 5 Liquid crystal panel 6 Fluorescent tube drive circuit 7 Backlight 8 Control microcomputer 9 Luminance level detection circuit 10 Look-up table 11 Gradation circuit

Claims (8)

In a transmissive liquid crystal display device having a backlight,
A backlight device with variable light source chromaticity;
Backlight control means;
Means for detecting the luminance level of the input video signal;
Storage means for holding applied voltage versus wavelength transmission characteristics of a liquid crystal panel in which liquid crystal is sandwiched between polarizing sheets;
The backlight control unit, a liquid crystal display device, characterized in that by adding the correction signal extracted from the detected luminance level and said memory means by said brightness level detecting means for controlling the light emission chromaticity of the backlight. In a transmissive liquid crystal display device having a backlight,
A backlight device with variable light source chromaticity;
Backlight control means;
Means for detecting the luminance level of the input video signal;
And a storage means for holding the wavelength transmission characteristic of the polarizing sheet,
The backlight control unit, a liquid crystal display device, characterized in that by adding the correction signal extracted from the detected luminance level and said memory means by said brightness level detecting means for controlling the light emission chromaticity of the backlight.   3. The liquid crystal display device according to claim 1, wherein the backlight device having variable light source chromaticity comprises a plurality of light sources having different emission colors.   3. The liquid crystal display device according to claim 1, wherein the light source chromaticity-variable backlight device has a constant light emission intensity and a variable chromaticity only. 4. Means for detecting the luminance level of the input video signal;
White balance adjustment means,
Storage means for holding applied voltage versus wavelength transmission characteristics of a liquid crystal panel in which liquid crystal is sandwiched between polarizing sheets;
The liquid crystal display device and performs white balance adjustment by the correction signal extracted from the detected luminance level and said memory means by said brightness level detecting means. Means for detecting the luminance level of the input video signal;
White balance adjustment means,
And a storage means for holding the wavelength transmission characteristic of the polarizing sheet,
The liquid crystal display device and performs white balance adjustment by the correction signal extracted from the detected luminance level and said memory means by said brightness level detecting means. 7. The liquid crystal display device according to claim 1, wherein the wavelength transmission characteristic is stored in a lookup table. And a look-up table for storing a plurality of wavelength transmission characteristics, a liquid crystal display device according to any one of claims 1 to 6, characterized in that it comprises means for designating one of the wavelength transmission characteristic of said plurality of .

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