JP2004302312A - Illumination device and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination device for a liquid crystal display which has a comparatively simple constitution and wherein an animation blur and image quality deterioration are eliminated without increasing its cost. <P>SOLUTION: This illumination device is so constituted as to have a light source by which the region to be irradiated of a liquid crystal panel is synchronized with a scanning signal of a display image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lighting device for a liquid crystal display device, and more particularly to a lighting device for a reflective liquid crystal display device that improves the quality of a moving image.
[0002]
[Prior art]
The liquid crystal panel of the liquid crystal display device does not emit light by itself, and therefore needs some illumination.
There are reflective, transmissive, and transflective types of illumination methods for liquid crystal display devices. Among them, a reflective liquid crystal display device has a reflective plate provided on the back surface of the liquid crystal panel or inside the liquid crystal panel, and is provided from the outside. Display is performed using the reflection of light. However, since it has no built-in illumination means, it can take advantage of the inherent low power consumption of liquid crystal, but has the disadvantage that it is difficult to see in dark places.
[0003]
Furthermore, current liquid crystal display devices have a problem of moving image blur and tailing phenomenon when displaying moving images. In particular, in an active matrix type liquid crystal display device in which each pixel includes a TFT (Thin Film Transistor) as a switching element, gradation data written in each pixel is held in principle for one frame period. In such a hold-type display method, when a moving image is displayed, image quality degradation may occur in which a blurring or tailing phenomenon of an image is visually recognized without being able to follow a quick image change.
[0004]
That is, the liquid crystal used in the TFT type liquid crystal panel includes modes such as TN (Twisted Nematic), MVA (Multi-domain Vertical Alignment), and IPS (In Plane Switching), but the response speed is relatively low at about 25 ms. It is. The response at halftone is even slower, dropping to around 100 ms. Therefore, the motion of the object in the moving image is delayed over several frames, so that the image quality is deteriorated.
[0005]
For this reason, in the scan backlight method, for example, the screen is divided into four parts, the writing of the liquid crystal panel is completed, and the backlight is turned on only for the blocks that have passed a relatively long time, thereby providing half-bright luminance which is in the middle of response. Pixels that are not displayed are not displayed, and the visual response is improved.
As a method for compensating for the disadvantage that it is difficult to see in a dark place, there is a light guide plate type front light illumination or a tilt-up type front light illumination.
[0006]
FIG. 7 shows a configuration example of a reflection type liquid crystal display device in which a light guide plate type front light is arranged on a conventional liquid crystal panel. Here, reference numeral 1 denotes a light source, 2 denotes a reflection plate, 3 denotes a light guide plate, and 4 denotes a reflection type liquid crystal panel.
As can be seen, the front light is composed of a light source and a light guide plate, and the light emitted from the light source travels through the light guide plate while being repeatedly reflected, and reaches the surface of the liquid crystal panel uniformly. As a light source, a cold cathode tube or a light emitting diode is generally used, and a reflector having a high-reflectance film formed on an inner surface is provided on the back side of the light source in order to increase the efficiency of light quantity.
[0007]
This type of illumination can illuminate the display area, but when used with outside light without using a front light, there is a problem in that the reflectance of the panel is reduced. Further, the light guide plate is made of an acrylic resin or the like, and the weight of the light guide plate depends on the area. Therefore, the light guide plate cannot take advantage of the thin and lightweight characteristics of the reflective liquid crystal display device.
[0008]
For this reason, for a notebook personal computer of, for example, about 12 inches, a front light type liquid crystal display device is hardly practically used, and a transmission type liquid crystal display device is mainly used.
In the case of transmissive backlights, Nitto Denko is a trade name of DBEF (a product name of a reflective polarizing film manufactured by Sumitomo 3M), PCF (Polarization Conversion Film), or a film using a polarization separation function, which can increase light use efficiency. ) Can be realized between the polarizing plate of the liquid crystal panel and the backlight, thereby achieving an improvement in luminance of nearly 40% at the maximum.
[0009]
However, this method is not effective in the case of a conventional reflection type front light because a polarizing plate is provided between the reflection plate and the light guide plate.
This is because, in the case of a backlight, the polarized light reflected by the DBEF or PCF returns to the backlight, and contributes to the luminance again after repeated reflection in the light guide plate. However, in the case of the reflective light guide plate, This is because the reflected light passes through the light guide plate and is emitted to the front side of the display device, so that the contrast is reduced and the display quality is significantly reduced.
[0010]
In addition, a scan backlight is attracting attention as a means for improving a response speed problem that a liquid crystal display device is inferior to other flat displays such as a PDP (Plasma Display) and an organic EL (Electro Luminescence). It can be applied only to a transmissive liquid crystal display device, and cannot be applied to a reflective liquid crystal display device whose image quality is gradually improved.
[0011]
On the other hand, FIG. 8 shows a configuration example of a reflection type liquid crystal display device in which a tilt-up type front light is arranged on a conventional liquid crystal panel. Here, reference numeral 5 denotes a support for supporting the reflection plate 2 and the light source 1. Note that the tilt-up front light is a device that houses the light when the liquid crystal panel is not illuminated, illuminates and illuminates when illuminating the liquid crystal panel, and uses the liquid crystal panel from the liquid crystal display surface side without using a light guide plate. Means a type of front light that emits light.
[0012]
However, this method has not been established due to the problem that it is difficult to uniformly irradiate the entire liquid crystal panel.
In order to solve these problems, for example, a plurality of fluorescent tubes, a light guide plate covering the plurality of fluorescent tubes, a display panel disposed on the light emitting side of the light guide plate, and a driving unit for sequentially lighting the fluorescent tubes are provided. A display device, and a reflective display panel; and a microlens array disposed on a light incident side of the reflective display panel, wherein a light diffusion region is formed in a part of a pixel electrode of the reflective display panel. The disclosed display device is disclosed. However, this display device not only requires a large number of fluorescent tubes (light emitting elements), but also has a problem that the configuration is complicated and the cost is high (for example, see Patent Document 1).
[0013]
On the other hand, in a transmissive liquid crystal display device, an illuminating unit is arranged on the back surface of a liquid crystal panel, and the liquid crystal panel functions as an optical shutter. Further, the illumination device is classified into two types, ie, EL illumination and FL (Fluorescent Lamp) illumination, depending on the difference in the illumination means. Further, FL lighting can be classified into a sidelight type and a direct type according to its structure.
However, in the case of a transmissive liquid crystal display device, since a large number of light sources are required, it is a problem to reduce power consumption.
[0014]
In order to solve the problem of moving image blur and tailing phenomenon, it is necessary to improve the moving image display characteristics by avoiding a certain degree of moving image contour deterioration by using a liquid crystal display device that controls the lighting time of the light source. However, when the number of fluorescent tubes increases, the emission time of each fluorescent tube in one scanning cycle is shortened, the luminance efficiency is reduced, and sufficient luminance cannot be obtained. There is a problem that it is difficult to similarly apply to the light source of the type.
[0015]
To solve this problem, for example, when the light source blinks in synchronization with the start time of the scanning signal of the display image and when the same level of the luminance signal is supplied, the display luminance of the liquid crystal panel becomes the time integral of the luminance value between frames. There is disclosed a liquid crystal display device in which moving image contour deterioration is eliminated by making the values equal.
Here, since the liquid crystal panel needs to be of the impulse type rather than the hold type, it is blinked as an impulse type synchronized with display data (image data) or scanning signal data of the liquid crystal panel.
[0016]
However, in order to control the lighting time of the light source and not to lower the luminance efficiency at the same time, a large number of linear lamps are required as a light source to compose, so that the configuration is complicated, and there is a problem that the cost is high (for example, Patent Document 1). 2).
In addition, the transflective liquid crystal display device has a transflective reflector having a combination of reflectivity and transmissivity attached to the back surface of the liquid crystal panel, and further arranged illuminating means behind it, and turns on the illumination in a bright place. It is used as a transmission type. However, in order to increase the visibility when used as a reflection type, it is necessary to increase the reflectance and also to increase the transmittance as a liquid crystal. However, this results in a decrease in contrast and poor visibility. Therefore, it is difficult to combine the properties of both the reflection type and the transmission type.
[0017]
On the other hand, for example, at least one light source capable of changing light emission luminance, at least one light emission region for emitting light from the light source, a maximum lighting state in which the light emission region emits light at a predetermined maximum luminance, and a lower state than the maximum luminance An illuminating device for illuminating a display area of an active matrix type liquid crystal display device having a light source control system for switching between an intermediate lighting state in which light is emitted at a predetermined intermediate luminance is disclosed (for example, see Application No. 2002-314955). .
[0018]
In this illumination device, the backlight type can improve the moving image blur and the trailing phenomenon at the time of displaying the moving image, but has a problem that the configuration becomes complicated and the cost increases.
[0019]
[Patent Document 1]
JP-A-2000-321993 (pp. 19-21, FIG. 1 and FIG. 36)
[0020]
[Patent Document 2]
JP 2001-108962 A (Page 9, FIG. 3)
[0021]
[Problems to be solved by the invention]
Accordingly, it is an object of the present invention to provide a lighting device for a reflective liquid crystal display device which is easy to see even in a dark place, has a relatively simple structure, eliminates blurring of moving images at no cost, and can be made thin.
[0022]
[Means for Solving the Problems]
The above-mentioned object is achieved according to claim 1 of the present invention by providing an illuminating device having a light source whose illuminated area of a liquid crystal panel is synchronized with a scanning signal of a display image.
In other words, the illumination device is configured such that a region to be illuminated by the light source on the liquid crystal panel moves in synchronization with a scanning signal of a display image. With this configuration, it is possible to illuminate the liquid crystal panel in synchronization with the scanning signal, thereby improving moving image blur and tailing at the time of displaying a moving image. At the same time, only one light source is required. It can be thin. In addition, the above-mentioned object is achieved according to claim 2 of the present invention, in which the light source is a lighting device according to claim 1 which has a light-shielding mechanism around which a rotation speed is variable.
[0023]
That is, a light blocking mechanism having a variable rotation speed is configured around the light source. With this configuration, the rotation speed of the light shielding mechanism is periodically changed so that the illumination that moves the liquid crystal panel in synchronization with the scanning signal of the display image changes the amount of light according to the distance between the light source and the liquid crystal panel. Thus, the light amount can be set according to the illumination position, and a change in the irradiation intensity due to a change in the light irradiation area according to the distance between the light source and the liquid crystal panel can be suppressed.
[0024]
For example, in the case of a point light source, the light becomes dark in inverse proportion to the square of the distance in principle, so that the correction is performed by changing the luminance of the light source according to the irradiation position. For example, when the light source is an LED, it can be easily realized by changing the current.
According to a third aspect of the present invention, the light source has a reflecting mirror between the light source and the liquid crystal panel, and the reflecting body is a polyhedron having a variable rotation speed. The illumination device according to claim 1, wherein an illuminated region of the liquid crystal panel is moved by rotation.
[0025]
That is, the light source is configured so as to have a reflecting mirror made of a polyhedron and having a variable rotation speed between the light source and the liquid crystal panel. With this configuration, the rotation speed of the reflecting mirror is periodically changed so that the illumination moving the liquid crystal panel in synchronization with the scanning signal of the display image changes the amount of light according to the distance between the light source and the liquid crystal panel. By changing it, the light amount can be set according to the irradiation position.
[0026]
According to a fourth aspect of the present invention, there is provided a liquid crystal display, comprising: a first polarizing plate and a second polarizing plate between the light source and the liquid crystal panel; The polarization angles of the plate and the second polarizer coincide with each other, and of the irradiation light emitted by the light source, polarized light that intersects with the polarization direction of the first polarizer is the first polarizer. This is achieved by an illumination device that reflects and returns to the light source.
[0027]
That is, by keeping the polarization angles of the first polarizing plate and the second polarizing plate interposed between the light source and the liquid crystal panel, the first polarizing plate of the irradiation light emitted by the light source can be adjusted. It is possible to enhance the light use efficiency by reflecting the polarized light intersecting with the polarization direction of the first polarizing plate and returning to the light source, and by emitting the light repeatedly when the polarization angle is matched by repeating the reflection. it can.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.
[Example 1]
FIG. 1 is an explanatory diagram showing the principle of the present invention. Here, an example is shown in which the sectional view of the reflection type liquid crystal panel is divided into eight and two blocks are rewritten. That is, FIG. 1a shows the fifth and sixth blocks from the left, 1b shows the seventh and eighth blocks from the left, 1c shows the first and second blocks from the left, and 1d shows the left and right blocks. And the third and fourth blocks are rewritten. These correspond to the lapse of 1/4 frame time, respectively.
[0029]
FIG. 2 is a diagram showing a main cross section and the like of a lighting device of a reflection type liquid crystal display device using the tilt-up front light according to the present invention. FIG. 2a shows a tilt-up front light used as an example of a light source. FIG. 2B is a cross-sectional view, FIG. 2B is a view showing how the direction of irradiation light is moved by the rotation of the light shielding mechanism 6, and FIG. 2C is a cross-sectional view of the reflective liquid crystal display device. Reference numeral 6 denotes a light shielding mechanism having a slit that rotates around the light source, 7 denotes a micro motor, and 8 denotes a housing of the liquid crystal display device. Note that the same reference numerals as those in the conventional example are denoted by the same reference numerals.
[0030]
The light shielding mechanism 6 is configured to rotate in synchronization with rewriting of the liquid crystal panel. With this configuration, when the light shielding mechanism 6 rotates, the position of the slit changes with the rotation, so that light extracted from the slit in the opening of the reflector 2 scans the liquid crystal panel 4. Thus, the illuminated area can be moved.
[0031]
Further, by forming a film having a high reflectivity on the inside of the light shielding mechanism 6 by plating, for example, similarly to the reflection plate 2, the light use efficiency can be increased.
When four slits are attached to the light shielding mechanism 6 as in the example shown in FIG. 2A, for example, the micro motor 7 shown in FIG. In order to rewrite the liquid crystal panel, rotation is performed 15 times per second, that is, at 900 revolutions per minute. The light shielding mechanism 6 is configured to synchronize with the timing of rewriting the liquid crystal panel.
[0032]
The light source 1 is preferably a line light source arranged in parallel to the long side direction of the liquid crystal panel so as to facilitate scanning.
[Example 2]
FIG. 3 shows a second illumination device of a reflection type liquid crystal display device having a reflecting mirror that rotates between a light source and a liquid crystal panel, and an illuminated area of the liquid crystal panel is moved by the light source when the reflecting mirror rotates. It is a figure showing an example.
[0033]
Reference numeral 9 denotes a reflecting mirror having a rotation axis parallel to the longitudinal direction of the linear light source 1. Here, a reflector having a regular hexagonal cross section is shown as an example.
With the configuration of this embodiment, unlike the tilt-up type front light, the direction is changed by applying light from a light source to a rotating reflecting mirror. By doing so, the lighting device attached to the support can have a simpler configuration.
[0034]
The configuration of the reflector is not limited to the illustrated shape, and various modifications are possible, such as a configuration in which a reflecting mirror attached to an elastic body is driven by a cam mechanism instead of a rotating reflecting mirror.
Note that the irradiation intensity changes because the light irradiation area of the liquid crystal panel changes depending on the distance between the reflecting mirror 9 and the liquid crystal panel (not shown). For example, a point light source darkens in inverse proportion to the square of the distance, and a line light source darkens in proportion to the distance.
[0035]
For this reason, FIG. 4 shows an example of a configuration in which the illumination intensity is made uniform by using a correction optical system such as a lens or a reflecting mirror so that the luminance of the light source is changed according to the illumination position. Here, reference numeral 12 indicates a correction lens.
That is, when irradiating a distant place, by converging the light, the irradiation range can be narrowed and the luminance can be made uniform.
[0036]
FIG. 5 is a diagram illustrating a method of adjusting the irradiation light amount. When the light source is a cold-cathode tube, as shown here, the pulse of the voltage application and the frame period of the liquid crystal panel are matched, and the applied voltage pattern is made uniform in the amount of emitted light, so that the The amount of irradiation light can be adjusted.
It is obvious that the same effect can be obtained by changing the voltage instead of the applied voltage pattern.
[0037]
Since writing of liquid crystal is performed at a constant speed, it is desirable that the irradiation position also moves at a constant speed on the surface of the liquid crystal panel. Therefore, when the reflecting mirror is rotated at a constant speed, the writing speed becomes faster as the irradiated position of the liquid crystal panel is farther and slower as the irradiated position is closer, so that the moving speed of the reflecting mirror is constant so that the moving speed of the irradiated position is constant. It is desirable that the rotation speed be changed periodically.
[0038]
[Example 3]
FIG. 6 is a diagram showing a third embodiment of the reflection type liquid crystal display device in which light emitted from the light source is separated in the polarization direction, and light whose polarization directions do not match is reflected toward the light source. Reference numeral 10 denotes a first polarizing plate, and 11 denotes a second polarizing plate.
The first polarizing plate 10 and the second polarizing plate 11 having a polarization plane coinciding with the polarization angle of the first polarizing plate 10 are arranged between the light source 1 and the reflective liquid crystal panel 4. When the polarized light that does not match the polarization direction of the first polarizing plate 10 of the irradiation light emitted by the light source is reflected by the first polarizing plate 10 and returned to the light source, and the reflection is repeated, the polarization angle matches. Light, the effect of increasing the light use efficiency is produced.
[0039]
The illumination device and the reflection type liquid crystal display device of the reflection type liquid crystal display device have been described above. However, the illumination device can be applied to a transmission type liquid crystal display device or a transflective type liquid crystal display device.
[0040]
【The invention's effect】
As described above, according to the present invention, the illuminating device that moves the liquid crystal panel in synchronization with the scanning signal by configuring the illuminated area of the liquid crystal panel to have the light source that synchronizes with the scanning signal of the display image It is possible to improve moving image blur and tailing at the time of displaying a moving image, and at the same time, it is possible to reduce the weight and thickness because only one light source is required.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing the principle of the present invention.
FIG. 2 is a diagram showing a main cross section and the like of an illumination device of a reflection type liquid crystal display device using a tilt-up type front light according to the present invention.
FIG. 3 is a diagram showing a second embodiment of the illumination device of the reflection type liquid crystal display device.
FIG. 4 is a diagram showing an example of a configuration for making uniform irradiation intensity by using a correction optical system.
FIG. 5 is a diagram showing a method for adjusting the irradiation light amount.
FIG. 6 is a diagram showing a third embodiment of the illumination device of the reflection type liquid crystal display device.
FIG. 7 is a diagram showing a configuration example of a reflection type liquid crystal display device in which a conventional light guide plate type front light is arranged.
FIG. 8 is a diagram showing a configuration example of a reflective liquid crystal display device in which a tilt-up type front light is arranged on a conventional liquid crystal panel.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 light source 2 reflector 3 light guide plate 4 reflective liquid crystal panel 5 support 6 light shielding mechanism 7 micro motor 8 liquid crystal display case 9 reflecting mirror 10 first polarizing plate 11 second polarizing plate 12 correction lens

Claims (5)

An illumination device, wherein an illuminated area of a liquid crystal panel has a light source synchronized with a scanning signal of a display image. 2. The lighting device according to claim 1, wherein the light source has a light shielding mechanism having a variable rotation speed around the light source. The light source has a reflecting mirror between the light source and the liquid crystal panel,
2. The lighting device according to claim 1, wherein the reflecting mirror is made of a polyhedron whose rotation speed is variable, and moves the irradiated area of the liquid crystal panel by rotating. Having a first polarizing plate and a second polarizing plate between the light source and the liquid crystal panel,
The polarization angles of the first polarizing plate and the second polarizing plate match,
The illumination according to claim 1, wherein, of the irradiation light emitted by the light source, polarized light that intersects the polarization direction of the first polarizing plate is reflected by the first polarizing plate and returns to the light source. apparatus. A liquid crystal display device comprising the lighting device according to claim 1.

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