JP2004012969A - Liquid crystal display - Google Patents

Abstract

A liquid crystal display device capable of removing a ghost even when using a TN type liquid crystal having a slow response speed and capable of displaying a high-quality moving image by an interlaced TV signal.
A first electrode and a second electrode are disposed on a substrate so as to oppose each other with the liquid crystal interposed therebetween for driving the liquid crystal, and are disposed on a side opposite to the substrate on which the liquid crystal is disposed. A backlight; a first polarizing means disposed on a side of the first electrode opposite to a side facing the liquid crystal; a second polarizing means disposed between the substrate and the backlight; And a first reflection disposed between the first polarizing means and the liquid crystal and arranged so that the direction of the transmitted linearly polarized light is parallel to the direction of the transmitted linearly polarized light of the first polarizing plate. The liquid crystal display device includes a polarizing plate. .
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to improvement in image quality of a liquid crystal display device, and more particularly, to improvement in moving image quality in an active matrix type liquid crystal display device displaying an interlaced television signal.
[0002]
[Prior art]
2. Description of the Related Art A liquid crystal display device (hereinafter, referred to as an LCD) has features such as high definition, low power consumption, and space saving, and is entirely used for a cathode ray tube (CRT) in various applications such as a computer monitor and a television display device. Hereinafter, it is described as CRT.). However, LCDs are not sufficient in image quality in displaying moving images as compared with CRTs. Therefore, improvement in moving image quality is required. In particular, when applied to television display devices, moving images based on current television signals can be displayed. It is necessary to be able to display with high image quality.
[0003]
[Problems to be solved by the invention]
The problem with LCD moving image display is that, first, when displaying an image with a partially bright portion in a dark background, it is possible to display a sharp bright point with less power compared to the surroundings. The second is that the definition of the moving image is poor.
[0004]
First, the reason for not displaying a partial bright spot with low power is that the principle of drawing is not light emission for each pixel, but panel transmittance of light emitted from a backlight with uniform brightness on the back side is applied to each pixel. This is caused by adjusting the retardation of the liquid crystal that changes with the voltage. That is, the maximum luminance is limited by the maximum luminance of the backlight and the maximum transmittance of the panel. For this reason, in the case of a conventional liquid crystal display device using a backlight having a uniform luminance in a plane and a liquid crystal panel having a uniform transmittance, the maximum luminance at each location on the screen is limited to a certain value regardless of the image to be displayed. I will. For this reason, when there is a white point on a dim background, it is necessary to increase the luminance of the entire backlight in order to increase the luminance of the white point, so that the power supplied to the backlight increases.
On the other hand, in the case of a CRT, when there is a white point on a dim background, it is only necessary to increase the cathode power at the timing of drawing the white point to increase the brightness of the white point. Yes.
[0005]
Next, it is said that the reason why the definition of the moving image is poor is as follows. First, as shown in FIG. 9A, when displaying a screen in which a white object 50 moves in a certain direction on a black background, the LCD displays an object as shown in FIG. 9B. “Motion blur” occurs in which 50 outlines are blurred and perceived. Also, as shown in FIG. 9C, a “ghost” in which the afterimage 51 of the object 50 before movement is perceived also occurs. Note that, for example, the description “white → black” in the figure indicates that the screen changes from white to black as the object 50 moves.
[0006]
One of the problems in displaying a moving image is that the response time of the liquid crystal to a signal is long. In a twisted nematic type (hereinafter referred to as a TN type) or a super swissed nematic type (hereinafter referred to as an STN type) LCD generally used at present, an electric field is applied to a liquid crystal. The electro-optical response time required until the arrangement of the liquid crystal molecules changes to reach the desired light transmittance is several times longer than 16.7 msec, which is the field cycle of a general television signal, so that the movement within one field period is possible. The optical response of the part is not completed. For this reason, the delay in the optical response of the liquid crystal is visually recognized as “motion blur” or “ghost”.
[0007]
It is also said that the LCD is of a hold type that continues to emit light until rewritten with image information of the next frame, which is a cause of poor display quality for moving images. In a thin film transistor type (hereinafter, referred to as a TFT type) LCD, which is widely used as an LCD, a charge stored by applying an electric field to a liquid crystal is held at a relatively high rate until the next electric field is applied. . For this reason, as shown in FIG. 10A, each pixel of the LCD continues to emit light until it is rewritten by applying an electric field based on the image information of the next frame. On the other hand, in a CRT type display device that performs display by emitting a phosphor by scanning an electron beam, as shown in FIG. 10B, the light emission of each pixel is substantially impulse-shaped. Therefore, the LCD has a lower time-frequency characteristic of image display light than a CRT, and accordingly, a spatial frequency characteristic is also reduced to cause blurring of a viewed image.
[0008]
For example, Japanese Patent Application Laid-Open No. H11-202286 discloses that a backlight is divided and driven in order to improve image quality in displaying moving images on an LCD. FIG. 11 is a block diagram showing the configuration of the apparatus. The backlight 54 arranged on the rear surface of the liquid crystal panel is divided into a plurality of light emitting areas 54a to 54d, and each light emitting area 54a is provided with a certain time delay for an image writing operation of the liquid crystal panel in a corresponding area. The lighting control circuit 60 and the inverter 61 cause the discharge lamps 56 to 54d to emit light sequentially.
[0009]
FIG. 12 is a timing chart showing the relationship between the optical response of the liquid crystal and the backlight emission timing in such a liquid crystal display device. In FIG. 12, the upper part shows the writing voltage to the liquid crystal, the middle part shows the optical response of the liquid crystal, and the lower part shows the light emission timing of the backlight. An example in which an interlace signal that is a current television signal is displayed will be described. When displaying an interlaced signal, the display period of one frame (= 1 screen) is divided into an even field and an odd field, only the even rows (2n rows, n is a positive integer) are scanned in the even fields, and the odd fields are scanned in the odd fields. Only the rows ((2n + 1) rows) are scanned.
[0010]
First, in the even-numbered field, the liquid crystal optical response 64 of the pixel on the 2nth row rewritten from the black signal to the white signal shows a large increase in luminance during the field period immediately after the rewriting, and thereafter, over several fields, complete white Display. In the subsequent odd-numbered fields, the liquid crystal optical response 65 of the pixel in the (2n + 1) th row rewritten from the black signal to the white signal shows the same behavior as the pixel in the 2nth row with a shift of one field period (about 16 msec).
[0011]
As shown in the lower part of FIG. 11, the backlight is turned on only in a predetermined period after a predetermined delay time has elapsed since the rewriting of the image signal in each of the even field and the odd field. As a result, the progress of the change in the liquid crystal optical response is hardly seen by the viewer, and the light emission of each pixel becomes close to an impulse, so that the image quality in moving image display is improved.
[0012]
However, in the above-described conventional liquid crystal display device, of the above-described problems in displaying moving images, although “moving image blur” is improved, “ghost” cannot be sufficiently eliminated. As shown in FIG. 9C, the cause of the ghost is based on the difference in the liquid crystal response time between the area 52 where the black image is replaced with the white image and the area 53 where the white image is replaced with the white image. This may cause a contrast difference. However, since the response time of a general TN type liquid crystal is several times longer than the field period, as shown in FIG. 12, the liquid crystal optical response 64 corresponding to the area 52 where the black image is rewritten to the white image, and the white image There is a brightness difference between the liquid crystal optical response 66 corresponding to the area 53 to be rewritten to the white image even during the period when the backlight is turned on. The luminance difference completely disappears a few fields after rewriting. Therefore, no matter how short the lighting period of the backlight is limited, a ghost remains.
[0013]
Therefore, according to the present invention, ghost can be removed even by using a TN-type liquid crystal having a low response speed, and a sharp and high-quality moving image can be displayed with low power consumption based on an interlaced television signal. An object is to provide an active matrix type liquid crystal display device.
[0014]
[Means for Solving the Problems]
A liquid crystal display device according to a first configuration of the present invention includes a first electrode and a second electrode disposed on a substrate so as to face each other with the liquid crystal interposed therebetween for driving the liquid crystal, and a substrate on which the liquid crystal is disposed. A backlight disposed on a side opposite to the side of the first electrode, a first polarizing means disposed on a side opposite to a side of the first electrode facing the liquid crystal, and a backlight including the substrate and the backlight. The second polarizer disposed between the first polarizer and the liquid crystal is disposed between the first polarizer and the liquid crystal so that the direction of transmitted linear polarized light is parallel to the direction of transmitted linear polarized light of the first polarizer. And a first reflective polarizing plate provided in alignment.
[0015]
A liquid crystal display device according to a second configuration of the present invention includes a color filter between the liquid crystal and the first polarizing means, and includes the first reflective polarizer between the color filter and the liquid crystal. I have.
[0016]
In the liquid crystal display device according to the third configuration of the present invention, the direction of the transmitted linearly polarized light is aligned between the backlight and the second polarizing plate so as to be parallel to the direction of transmitting the linearly polarized light of the polarizing plate. And a second reflective polarizing plate provided.
[0017]
A liquid crystal display device according to a fourth configuration of the present invention includes an image display unit having pixels arranged in a matrix and switch means connected to each pixel, and selecting the pixels for each line while driving the switch means. A row drive circuit for scanning one screen, and a column drive circuit for writing an interlaced pixel signal composed of an even field and an odd field to pixels on a selected line in synchronization with the scanning, and In, while writing an image signal to the pixels of the even-numbered line, writing an erasing signal for adjusting the potential of each pixel to the pixels of the odd-numbered line, and writing the image signal to the pixels of the odd-numbered line in the odd-numbered field, The erase signal is written to the.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing a planar luminance distribution and a cross-sectional structure of one pixel of a liquid crystal cell of a liquid crystal display device according to Embodiment 1 of the present invention.
FIG. 1A shows the luminance distribution of one pixel, and a, b, and c show the divided R, G, and B color sub-pixels (hereinafter, referred to as sub-pixels). I have. This screen shows a case where the sub-pixels a and b display black (transmittance is 0) and the sub-pixel c displays white (transmittance is maximum).
In FIG. 1B, reference numeral 101 denotes a first polarizing plate (first polarizing means) on the display surface side, which is attached on a first glass substrate 102, and a color filter is provided on the back side of the first glass substrate 102. (Hereinafter referred to as CF.) 103, a first reflective polarizing plate 104, and a first transparent electrode 105 are sequentially arranged. Reference numeral 106 denotes a liquid crystal held in a cell formed by the first glass substrate 102 and the second glass substrate 108. Here, for example, as the first reflective polarizing plate 104, a DBEF sheet manufactured by Sumitomo 3M Limited can be used.
On the front side of the second glass substrate 108 facing the liquid crystal 106, second transparent electrodes 107a, 107b, 107c are formed corresponding to the CF 103 divided into sub-pixels of the CF 103. On the back side of the second glass substrate 108, a second polarizing plate (second polarizing means) 109 and a second reflecting polarizing plate 111 are sequentially arranged, and further behind this, a backlight 110 is located. The light source 112 is disposed on the side surface, and the reflection plate 113 is disposed on the back side.
[0019]
Here, the first reflective polarizing plate 104 is provided such that the direction of the transmitted linearly polarized light is parallel to the direction of the transmitted linearly polarized light of the first polarizing plate 101, and the first reflective polarizing plate 104 and the second polarizing plate The polarizing plate 109 is arranged at an angle at which the directions of the transmitted linearly polarized light are orthogonal to each other. The second polarizing plate 109 and the second reflecting polarizing plate 111 are arranged such that the directions of the transmitted linearly polarized light are parallel to each other.
The liquid crystal 106 is a TN type liquid crystal, and is driven by an electric field applied between the second transparent electrodes 107 a to 107 c and the first transparent electrode 105 that are divided into pixels. When the retardation becomes 0 and no voltage is applied, the optical properties, thickness, alignment processing, and applied voltage value of the liquid crystal 106 are adjusted so that the retardation increases and the angle of linearly polarized light incident on the liquid crystal 106 is rotated by 90 degrees. It is decided.
[0020]
In this case, the sub-pixels a and b are set to perform black display with a low transmittance with a voltage applied thereto, and the sub-pixel c is configured to perform white display with a high transmittance with no voltage applied.
In the liquid crystal display device thus formed, light from the light source 112 emitted from the backlight 110 becomes linearly polarized light by the second reflection polarizing plate 111 and the second polarizing plate 109 and enters the liquid crystal 106. Here, the linearly polarized light P entering the liquid crystal cell at the position corresponding to the sub-pixel c is rotated by 90 degrees due to the retardation of the liquid crystal 106 to which no voltage is applied, and reaches the first reflective polarizing plate 104. Then, the light passes through it without being reflected, is colored by absorbing and removing light of an extra wavelength by the CF 103, and further passes through the first polarizing plate and is visually recognized by an observer.
On the other hand, the linearly polarized light Q entering the liquid crystal cell 106 corresponding to the sub-pixel b reaches the first reflective polarizing plate 104 in the same direction because the retardation of the liquid crystal 106 to which the voltage is applied is 0 because the retardation is 0. The light is reflected by the one-reflection polarizing plate 104, further passes through the second polarizing plate 109, returns to the backlight 110, is reflected by the reflecting plate 113, and emits again as backlight R. At this time, since the light does not pass through the CF 103, there is no absorption loss, and most of the light that has entered the liquid crystal corresponding to the sub-pixel b returns to the backlight again. For this reason, when the background is entirely dark, the luminance of the backlight 110 is effectively increased, and the luminance of the sub-pixel c can be increased in proportion to the effective luminance of the backlight.
[0021]
At this time, since the second reflective polarizer 111 is provided between the backlight 110 and the second polarizer 109, the light U reflected by the bottom surface of the backlight 110 and traveling toward the second reflective polarizer 111 is second reflected polarized light. The reflected light V is reflected by the plate 111, returns to the backlight 110, is reflected by the bottom surface of the backlight 110, and the reflected light V is transmitted through the second reflective polarizing plate 111 and the second polarizing plate 109 because the polarization plane is rotated. Through the second reflective polarizing plate 111 and the second polarizing plate 109 (the polarizing planes are arranged so as to be parallel to each other) and introduced into the second transparent electrode 107c corresponding to the sub-pixel c. , Will be reused. If there is no second reflective polarizing plate 111, the light U is absorbed by the second polarizing plate 109. Accordingly, the absorption of light is further reduced by the second reflective polarizing plate 111, and the effective reuse of light is promoted. Therefore, the effect of increasing the luminance of the sub-pixel c, which is a white point surrounded by a black background, is further enhanced.
According to the first embodiment described above, in the image where the entire background is dark and there are locally bright spots, the light that should be absorbed by the first polarizing plate 101 at the pixel corresponding to the dark background portion is CF Since the light is returned to the backlight 110 by the first reflective polarizer 104 before the light is absorbed by the light emitting device, the brightness of the backlight substantially increases, and thus the brightness of a locally bright portion increases.
[0022]
Embodiment 2 FIG.
FIG. 2 is a schematic diagram showing a planar luminance distribution and a cross-sectional structure of one pixel of a liquid crystal cell of a liquid crystal display device according to a second embodiment of the present invention.
FIG. 2A shows the luminance distribution of one pixel, and a, b, and c show each divided sub-pixel. This screen shows a case where the sub-pixels a and b display black and the sub-pixel c displays white.
In FIG. 2B, the same reference numerals as those in FIG. 1B indicate the same or corresponding parts. That is, the first polarizing plate 101, the first glass substrate 102, the first transparent electrode 104, the liquid crystal 106, the second transparent electrodes 107a to 107c, the second glass substrate 108, the second polarizing plate 109, the backlight 110, the light source 112, The reflection plate 113 has the same configuration as that of FIG. In FIG. 1B, the color filter CF 103 and the first reflective polarizer 104 are arranged between the first glass substrate 102 and the first transparent electrode 105, whereas in the second embodiment, The difference is that it is arranged between the first polarizing plate 101 and the first glass substrate 102 and does not include the second reflective polarizing plate 111 in the first embodiment.
In addition, the first reflective polarizing plate 104 is provided so that the direction of the transmitted linearly polarized light is parallel to the direction of transmitting the linearly polarized light of the first polarizing plate 101, and the first reflective polarizing plate 104 and the second polarizing plate The polarizing plate 109 is arranged at an angle at which the directions of the transmitted linearly polarized light are orthogonal to each other, as in the first embodiment. The liquid crystal 106 is a TN type liquid crystal, and is driven by an electric field applied between the second transparent electrodes 107a to 107c and the first transparent electrode 105 divided so as to correspond to the sub-pixels, in a state where a voltage is applied. As in the first embodiment, the retardation becomes zero when no voltage is applied and the retardation is increased so that the angle of the linearly polarized light is rotated by 90 degrees.
[0023]
Here, the sub-pixels a and b are set so that a voltage is applied and black display with a low transmittance is displayed, and the sub-pixel c is displayed with no voltage applied and a white display with a high transmittance is displayed. The light from the light source 112 emitted from the backlight 110 becomes linearly polarized light by the second polarizing plate 109 and enters the liquid crystal 106. Here, the linearly polarized light P entering the liquid crystal cell at the position corresponding to the sub-pixel c is rotated by 90 degrees by the retardation of the liquid crystal 106 to which no voltage is applied, and reaches the first reflective polarizing plate 104. Pass through this without being reflected, light of an extra wavelength is absorbed by the CF 103, and passes through the first polarizing plate 101 to be visually recognized by an observer.
On the other hand, the linearly polarized light Q entering the liquid crystal cell corresponding to the sub-pixel b reaches the first reflective polarizing plate 104 in the same direction because the retardation of the liquid crystal 106 to which the voltage is applied is 0, and the first reflected polarized light The light is reflected by the plate 104, further passes through the second polarizing plate 109, returns to the backlight 110, is reflected by the reflection plate 113, and emits light from the backlight 110 again. This backlight light R passes through the second transparent electrode 107c corresponding to the sub-pixel c and the CF 103. Therefore, when the background is entirely dark, the luminance of the backlight 110 is effectively increased, and the luminance of the sub-pixel c can be increased in proportion to the luminance of the backlight.
[0024]
If the second reflective polarizer 111 of the first embodiment is provided between the backlight 110 and the second polarizer 109, the same as in the first embodiment, the Can be further reduced, and the higher luminance of the sub-pixel c by the first reflective polarizer 104 can be increased. In particular, the effect of increasing the luminance of a white display pixel, such as the sub-pixel c, in which a black display with low transmittance is surrounded by pixels in the vicinity, is large.
[0025]
Here, in the case of the second embodiment, the configuration of the liquid crystal cell surrounded by the first glass substrate 102 and the second glass substrate 108 is the same as that of the conventional monochrome LCD, so that the cell gap in the manufacturing process is uniform. Conversion is easy.
Here, as a method of realizing color display, there is a field sequential color display method of realizing a three-source color light source and a corresponding black-and-white display field in contrast to an area color mixing method using CF. Is also effective in the field sequential type color display method since there is no light absorption by CF. The same applies to the first embodiment and the following third and fourth embodiments.
[0026]
Embodiment 3 FIG.
FIG. 3 is a schematic diagram showing a planar luminance distribution and a cross-sectional structure of one pixel of a liquid crystal cell according to Embodiment 3 of the present invention. 2 denote the same or corresponding parts. Note that the backlight 110, the light source 112, and the reflection plate 113 are not described.
In the liquid crystal display device according to the second embodiment, when the thickness of the first glass substrate 102 is larger than the pixel size, the distance between the second transparent electrode 107 and the CF 103 increases, so that light emitted from the backlight 110, that is, When the light P and R shown in FIG. 2B are not perpendicular but inclined with respect to the liquid crystal layer 106, they enter the adjacent sub-pixel b as shown in FIG. 3 and cause color blur.
Therefore, as shown in FIG. 3, in the third embodiment, a slit 115 that forms a narrow opening between the liquid crystal 106 and the second polarizing plate 109 at a position facing the center of each sub-pixel of the CF 103 with the liquid crystal interposed therebetween. Is disposed. This slit reflection plate 116 is formed on the surface of the second glass substrate 108 on the liquid crystal 106 side in FIG.
[0027]
FIG. 4 is a characteristic diagram for explaining the shape of the slit 115 for suppressing the color fringing due to the pixel structure.
In FIG. 4, the sub-pixel horizontal division is a structure in which the CF 103 is divided into three sub-pixels in the horizontal direction such that the shape of the sub-pixel becomes a horizontally long rectangle. The structure is rotated by degrees. The BL half-luminance angle in FIG. 4 is an angle at which the luminance of the backlight (BL) becomes の of the front luminance. In cases (1) to (6), ± 25 degrees in the horizontal direction and ± 10 degrees in the vertical direction. Degree. The distance T is the distance between the CF 103 and the slit reflector 116. The required width is the distance W (shown in FIG. 3) from the end of the slit 115 to the end of the pixel for the left and right, and the distance H from the end of the slit 115 to the adjacent sub-pixel for the up and down. The required gap width ratio is W / T on the left and right and H / T on the upper and lower sides. The pixel size is the length of the left and right and top and bottom of the sub-pixels a, b, and c, and is indicated by M and N in FIG. The slit size has a length U in the horizontal direction (longitudinal direction) of the slit 115 on the left and right, and a length V in the vertical direction of the slit 115 on the left and right. The slit area ratio is a ratio between the area of the sub-pixels a, b, and c and the area of the slit 115. Case (1) is the case where the distance T is 400 (μm), the required gap width ratio (W / T) on the left and right is 0.293, and the required gap width ratio (H / T) on the upper and lower sides is 0.116. The left and right pixel size M is 300 μm, the upper and lower pixel size N is 100 μm, the distance T is 400 μm, the required width W is 117.4 μm, the required upper and lower width H is 46.6 μm, Is 65.2 μm, the upper and lower slit sizes V are 6.8 μm, and the slit area ratio representing the aperture ratio of the slit is 0.01. Case (2) shows a case where T is 200 μm, and case (3) shows a case where T is 100 μm.
[0028]
The sub-pixel vertical division is a structure in which one pixel is divided into three in the vertical direction so that the shape of the sub-pixel becomes a vertically long rectangle in the CF 103 division, that is, a structure as shown in FIG. is there.
In this case, the left and right and up and down of the pixel size are opposite to the sub-pixel horizontal division, and the left and right are represented by V in FIG. The same applies to the left and right and top and bottom of the required width. The required width of the left and right is H and the required width of the top and bottom is W. Further, the required gap width ratio on the left and right is H / T, and the required gap width ratio on the top and bottom is W / T.
For example, when a high-vision compatible LCD-TV of about 30 inches is considered, the pixel size is about 0.3 mm, and the short side length of each sub-pixel is about 0.1 mm. The light distribution of the backlight 110 for the liquid crystal monitor is represented by a half-value BL luminance angle, which is a light emission angle at which the luminance becomes の of the front, and the horizontal direction is ± 25 degrees and the vertical direction is about ± 10 degrees. It is common. Here, considering the refractive index of glass or an optical film of 1.5, as shown in FIG. 4, the CF 103 is divided horizontally so that the shape of the sub-pixel becomes a horizontally long rectangle, unlike the related art. When the distance T between the CF 103 and the vertical width of the CF 103 is 400 μm, which is four times the vertical width of 100 μm, in order to prevent color bleeding, the slit size must be reduced to about 65 × about 7 μm. The ratio of the slit area to the sub-pixel area is only about 0.01, that is, about 1%, as shown in FIG. Bright display is not possible with the slit structure as in case (1).
[0029]
When the distance T between the slit reflector 116 and the CF 103 is set to 200 μm, which is twice as large as the vertical width 100 μm, which is the width of the CF 103 in the short direction, the slit size for preventing color bleeding is about 182 × about 53 μm. The slit area ratio can be increased to about 0.33, that is, about 33%. This is smaller than the current aperture ratio of the pixel in the TFT array substrate of 60 to 80%, but is an allowable value in consideration of the reuse of the light reflected by the slit reflector 116.
[0030]
Further, when the distance T between the slit reflector 116 and the CF 103 is set to 100 μm, which is about the same as the vertical width 100 μm which is the width of the CF 103 in the short direction, the slit size for preventing color bleeding is about 241 × about 76 μm. The slit area ratio increases to about 0.62, that is, about 62%. This is a value comparable to the current pixel aperture ratio of 60 to 80% on the TFT array substrate. It is also possible to further reduce the color blur by making the slit 115 smaller.
[0031]
Therefore, it is desirable that the distance T between the slit reflection plate 116 and the CF 103 is about twice or less, or about the same or less, the length of the short side of each sub-pixel in the normally rectangular CF 103. In the case where the slit 115 is configured in this manner, in FIG. 3, light P from a backlight (not shown) passes through only the opposing CF and does not pass through CF of another adjacent color. The occurrence of bleeding can be suppressed. The light S is reflected by the slit reflector 115 and does not reach CFs of other colors.
The distance between the slit reflector 115 and the CF 103 is set to be equal to or less than the narrowest width of the CF 103. According to this configuration, since there is less leakage light passing through the CF 103 of another adjacent color, there is an effect that color blur does not occur.
[0032]
The lower part of FIG. 4 shows an example of calculation in the case of the conventional sub-pixel vertical division of the CF 103 as in the related art. In this case, when the distance T between the slit reflector 116 and the CF 103 is 100 μm, which is approximately the same as the vertical width 100 μm, which is the width of the CF 103 in the short direction (case (6)), the slit area ratio is 0.38, The aperture ratio is about 38%, which is lower than that in case (3) of the sub-pixel horizontal division described above, resulting in dark screen luminance.
As described above, the sub-pixel horizontal division is more advantageous as the configuration of the slit for suppressing color fringing.
[0033]
According to the third embodiment described above, the slit reflector 116 having the narrow aperture slit 115 is provided between the liquid crystal 106 and the second polarizing plate 109 at a position facing the center of the CF 103 with the liquid crystal interposed therebetween. The distance between the slit reflecting plate 116 and the CF 103 is set to be equal to or less than twice the narrowest width of the CF 103, preferably equal to or less than the same. Light that has passed through the opening slit corresponding to each color CF can be less likely to enter another adjacent CF, so that color bleeding is suppressed. At this time, if the three primary color sub-pixels forming one square pixel are divided into three parts in a rectangular shape that is long in the horizontal direction, the color is applied to the backlight having a wider light distribution angle in the horizontal direction than in the vertical direction. Bleeding can be suppressed.
At this time, the second reflective polarizing plate 111 (provided between the backlight and the second polarizing plate 109 such that the direction of the transmitted linearly polarized light is parallel to the direction of the linearly polarized light transmitted through the second polarizing plate 109. The arrangement of (described in Embodiment 1)) increases the efficiency of reuse of the backlight light as described in Embodiment 1, and further enhances the effect of increasing the local white luminance.
[0034]
Embodiment 4 FIG.
FIG. 5 is a block diagram showing a liquid crystal display device according to Embodiment 4 of the present invention. The liquid crystal display device 201 includes an image display unit 202, a vertical drive circuit (row drive circuit) 203, and a horizontal drive circuit (column drive circuit) 204, and a plurality of discharge lamps (described as lamps) on the back of the image display unit 202. .) A backlight including A1 to A8 is provided. In the image display unit 202, the pixels as described in Embodiment Modes 1 to 3 are arranged in a matrix, and a switching element such as a thin film transistor (hereinafter, referred to as a TFT) is connected to each pixel to form a liquid crystal panel. I have. In FIG. 4, pixels and TFTs are omitted, but the fourth embodiment has a pixel structure as in the first to third embodiments.
[0035]
The vertical drive circuit 203 sends timing signals A and B to the gate driver 205 connected to the TFT gate electrode of each line via a gate wiring, the gate driver 205 and the source driver 206, and sends the lighting signal C to the backlight lighting circuit 207. And scans one screen while driving each TFT line by line based on a synchronization signal D supplied from the outside. The horizontal drive circuit 204 includes a source driver 206 that receives and drives the timing signal B from the control circuit 208, and writes a signal to a pixel on a line selected by the horizontal drive circuit 204.
[0036]
The horizontal drive circuit 204 is supplied with an interlaced image signal E and an erasing signal F for erasing the image signal held in the pixel and erasing the potential of each pixel. A signal switching circuit 209 is provided in the horizontal drive circuit 204. The signal switching circuit 209 switches the input to the source driver 206 between the image signal E and the erase signal F based on the signal G from the control circuit 208. To switch. The erase signal F is, for example, a black display signal having a voltage level equal to or higher than the maximum voltage level of the image signal E. In general, the response speed of the TN liquid crystal is high when a high voltage is applied. Therefore, if the erase signal F is a black display signal having a high voltage level, it is advantageous for erasing the previous image. Further, when the state of the previous voltage application is the black level, there is an advantage that a decrease in contrast is suppressed.
[0037]
The liquid crystal display device 201 displays an interlaced image signal 209 supplied from the outside. In the interlaced image signal 209, one frame is divided into an even-numbered field and an odd-numbered field. The image information to be written to the pixels of the line is included, and the signal of the odd field includes the image information to be written to the pixels of the odd line. Therefore, when displaying an interlaced image signal by a general liquid crystal display device, interlaced scanning is performed in which only even lines are scanned in even fields and only odd lines are scanned in odd fields.
[0038]
However, the liquid crystal display device 201 according to the fourth embodiment performs sequential scanning in which all lines are line-sequentially scanned in both the even field and the odd field, and performs the writing of the image signal E and the erasing signal F for each line. Are written alternately. The alternate writing of the image signal E and the erasing signal F can be performed by the signal switching circuit 209 alternately switching between the image signal E and the erasing signal F for each line.
[0039]
FIG. 6 is a timing chart schematically showing the operation of the liquid crystal display device 201. As shown in the upper part of FIG. 6, in the even field, the image signal E is written when the even (= 2n) line is selected, and the erase signal F is written when the odd (= 2n + 1) line is selected. . In the odd field, the image signal E is written when the odd line is selected, and the erase signal F is written when the even line is selected.
[0040]
By writing the image signal E and the erase signal F at such timing, the optical response of the liquid crystal becomes as shown in the middle part of FIG. In the liquid crystal optical response 4 of the even line on the 2nth line, the gradation changes in accordance with the image signal E written in the even field, and the image signal E written in the subsequent odd field is erased to display black. This operation is alternately repeated for each field. On the other hand, the liquid crystal optical response 5 of the odd-numbered line in the (2n + 1) -th row, on the other hand, has a black display by erasing the previous erasure signal F in the even-numbered field and the image signal E written in the subsequent odd-numbered field. The gray scale changes according to.
[0041]
As described above, before writing the image signal E, the image information is erased to make a uniform black display, so that the optical response time of each pixel can be made uniform regardless of the display image of the previous frame. For example, even if a pixel that performed black display and a pixel that performed white display in the previous frame were simultaneously rewritten to different gray scales, after all of the pixels once changed to black display, the next gray scale was displayed. Since the tone signal is written, there is almost no difference in luminance due to the difference in liquid crystal response. Therefore, "ghost" can be almost eliminated. At this time, since the first reflective polarizing plate 104 is provided as described in Embodiment Modes 1 to 3, even when the erase signal is a black signal, the backlight which is incident on the pixel on the gate line to which the erase signal is written is applied. Light is not absorbed by the CF 103 or the first polarizing plate 101, but is reflected by the first reflective polarizing plate 104 and returns to the backlight, so that the backlight brightness is increased. Therefore, a decrease in average screen brightness can be suppressed. .
[0042]
Further, in the fourth embodiment, in order to further suppress “ghost” and also “motion blur”, as shown in the lower part of FIG. The backlight is turned on after a certain delay time t (FIG. 6) has elapsed from the writing of E.
[0043]
As shown in FIG. 4, the image display unit 202 is divided into eight display blocks B1 to B8 in the pixel line direction, and lamps A1 to A8 are arranged in parallel for each display area. The lamps A1 to A8 are sequentially turned on by the backlight lighting circuit 207 according to the timing signal C sent from the control circuit 208. Further, as shown in FIG. 7, the lamps A1 to A8 arranged in the backlight 110 are separated from each other by a light shielding wall 210 so that light does not leak to the display block of tonnage. Note that a plurality of lamps A1 to A8 are provided for each display block, and eight lamps are provided in the fourth embodiment to improve the luminance.
[0044]
FIG. 8 is a waveform diagram showing lighting timing of the backlight including the lamps A1 to A8.
Referring to FIG. 8, an even field will be described as an example. In the even-numbered field, the scanning is performed line-sequentially from the first row of the image display unit 202 while writing the erasing signal F to the odd-numbered line and writing the image signal E to the even-numbered line. When the image display unit 202 is divided into eight display blocks B1 to B8 in the line direction, one display block is scanned in about 2 msec, which is 1/8 of one field period.
[0045]
Description will be given focusing on the display block B1. The discharge lamp A1 that illuminates the display block B1 is such that the display block B1 has a scan period t ₁ After scanning during, a delay period t equal to the scanning period of 5 blocks ₂ , The lighting period t equal to the scanning period for two blocks ₃ Lights during The lamps A2 to A8 that illuminate the display blocks B2 to B8 perform the same operation while being delayed by one block scanning period. Also, in the odd field, the erase signal F is written to the even line and the image signal E is written to the odd line. Other than this write operation, the operation is the same as that of the even field.
[0046]
In the liquid crystal display device driven in this manner, the potentials of all the pixels are made equal to the potential of the erase signal F before the writing of the image signal E, and the response of the liquid crystal after the writing of the image signal E is stabilized to a certain extent. Since only the backlight is turned on, “ghost” is further suppressed. In addition, since the lighting period of the backlight is limited, the light emission state of the impulse type is obtained, so that a sharp image without “motion blur” can be obtained.
[0047]
In the fourth embodiment, the backlight lighting time of each display block is about 4 msec, and the backlight lighting time ratio is about 1/4. The backlight lighting time ratio is determined by the delay period t ₂ Can be adjusted by changing the setting, and may be appropriately set in consideration of the balance between the moving image display and the screen luminance. From the viewpoint of displaying moving images, it is preferable to set the lighting time ratio small so that light is emitted after the optical response of the liquid crystal is stabilized, while it is preferable to set the lighting time ratio large from the viewpoint of screen brightness.
[0048]
Further, from the viewpoint of erasing “ghost”, the erasing signal is preferably a black signal, and its voltage is preferably as high as possible. In the case of a general normally white driving TN type liquid crystal display element, the response speed of the liquid crystal is faster in the change from white gradation to black gradation than in the opposite change, and in the liquid crystal display element, In general, the higher the applied voltage, the faster the response speed. The faster the response of the liquid crystal, the more quickly the state of the liquid crystal is stabilized when an erase signal is written. In this case, in the conventional LCD, the light incident on the pixel on which the erasure signal F is written is absorbed by the first polarizing plate 101 on the emission side, so that black display is performed. With the configuration, light incident on the pixel to which the erasing signal F has been written can be returned to the backlight 10 by the first reflective polarizing plate 104 without loss, and the light is returned to the adjacent pixel to which the image signal E has been written. Since it can be used, there is an effect of suppressing a decrease in the average luminance of the screen.
Further, as a countermeasure against burn-in due to impurities in the liquid crystal, it is preferable that the polarity of the erase signal F applied to each pixel is inverted for each frame.
In the fourth embodiment, it is preferable that the erase signal written to each pixel is a black gradation signal. This is because in the case of a general normally white driving TN type liquid crystal display element, the response speed of the liquid crystal is faster in the change from white gradation to black gradation than in the opposite change. The faster the response of the liquid crystal, the sooner the state of the liquid crystal becomes stable when an erase signal is written.
[0049]
Further, in order to further improve the moving image quality, a light source is provided on the back of the image display unit, the light source being capable of illuminating the image display unit by dividing the image display unit into a plurality of display areas in a row direction. Is characterized in that the display area is illuminated for a predetermined period delayed from the end of scanning of each divided display area.
[0050]
Before writing the image signal, the potentials of all the pixels are adjusted to the potential of the erasing signal, and the illumination is performed only during a period in which the response of the liquid crystal after the writing of the image signal is stabilized to some extent, so that "ghost" is further suppressed. In addition, since the illumination period is limited, the light emission state of the impulse type is obtained, so that a sharp image without “motion blur” can be obtained.
[0051]
In the fourth embodiment, the erase signal F is written by switching the image signal E and the erase signal F line by line by the signal switching circuit 209, but the writing method of the erase signal F is not limited to this. For example, before the image signal E is supplied to the source driver, data processing is performed by an appropriate program, or the image signal E is stored in a memory for each frame. The writing of the signal F may be performed.
For example, consider a case where the liquid crystal display device of the fourth embodiment is used for a liquid crystal television. An image signal of a TV is generally of an interlaced type. If the image signal E is an even field where the image signal E is sent only for the even-numbered scanning lines and the odd-numbered scanning line does not have the image signal E, it corresponds to the odd-numbered scanning line Progressive image data is created by assigning the same erase signal F to the pixels on the gate line of the liquid crystal display device to be processed. In the case of an odd field, the progressive image data is generated on the gate line of the liquid crystal display device corresponding to the even-numbered scanning line. Pixels are assigned equal erasure signals to generate progressive image data, image data of a pair of even-odd gate lines is temporarily stored in a line memory, and sequentially sent to a liquid crystal display device as progressive image data for display. .
According to such a display, a frame memory for storing the image data of the previous field becomes unnecessary, and the cost can be reduced. In addition, there is an effect of improving image quality in that problems of contour blur and flicker associated with creation of a progressive image are eliminated.
[0052]
【The invention's effect】
A liquid crystal display device according to a first configuration of the present invention includes a first electrode and a second electrode disposed on a substrate so as to face each other with the liquid crystal interposed therebetween for driving the liquid crystal, and a substrate on which the liquid crystal is disposed. A backlight disposed on a side opposite to the side of the first electrode, a first polarizing means disposed on a side opposite to a side of the first electrode facing the liquid crystal, and a backlight including the substrate and the backlight. The second polarizer disposed between the first polarizer and the liquid crystal is disposed between the first polarizer and the liquid crystal so that the direction of transmitted linear polarized light is parallel to the direction of transmitted linear polarized light of the first polarizer. The display quality of the liquid crystal display screen can be improved by including the first reflective polarizer provided in alignment.
[0053]
The liquid crystal display device according to a second configuration of the present invention, in the first configuration, further includes a color filter between the liquid crystal and the first polarizing unit, and the color filter is disposed between the color filter and the liquid crystal. The display quality of the liquid crystal display screen can be improved by providing the one reflection polarizing plate.
[0054]
In the liquid crystal display device according to a third configuration of the present invention, in the first configuration, the direction of linearly transmitted light between the backlight and the second polarizing plate transmits the linearly polarized light of the polarizing plate. The display quality of the liquid crystal display screen can be improved by providing the second reflective polarizer provided so as to be parallel to the direction.
[0055]
A liquid crystal display device according to a fourth configuration of the present invention is the liquid crystal display device according to the first configuration, wherein the image display unit includes pixels arranged in a matrix and switch means connected to each pixel; A row drive circuit that selects one pixel for each line to scan one screen, and a column drive that writes an interlaced pixel signal composed of even and odd fields to the pixels of the selected line in synchronization with the scan. In the even-numbered field, an image signal is written to the pixels of the even-numbered lines, while the erase signal for aligning the potential of each pixel is written to the pixels of the odd-numbered lines, and the image signal is written to the pixels of the odd-numbered lines in the odd-numbered fields. On the other hand, the erase signal is written to the pixels on the even-numbered lines while writing, so that the pixels are input to the black display pixels by the first reflective polarizer. Was light without loss can be returned to the backlight, for recycling, it is possible to mow suppress a decrease in the average brightness of the screen by writing the erase signal.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a cross-sectional structure of a liquid crystal cell of a liquid crystal display device according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing a cross-sectional structure of a liquid crystal cell of a liquid crystal display according to a second embodiment of the present invention.
FIG. 3 is a schematic diagram showing a cross-sectional structure of a liquid crystal cell of a liquid crystal display according to a third embodiment of the present invention.
FIG. 4 is a characteristic diagram for explaining a shape of a slit for suppressing color fringing due to a pixel structure in a liquid crystal display device according to a third embodiment of the present invention.
FIG. 5 is a block diagram showing a driving circuit of a liquid crystal display according to a fourth embodiment of the present invention.
FIG. 6 is a timing chart schematically showing an operation of a liquid crystal display device according to a fourth embodiment of the present invention.
FIG. 7 is a side view showing a structure of a backlight constituting a liquid crystal display device according to Embodiment 4 of the present invention.
FIG. 8 is a waveform diagram for explaining a backlight lighting timing of a liquid crystal display device according to a fourth embodiment of the present invention.
FIG. 9 is a schematic diagram showing a state of image quality abnormality in a conventional moving image display.
FIG. 10 is a schematic diagram showing emission signals of a conventional TFT-LCD and CRT.
FIG. 11 is a schematic diagram showing a configuration of a conventional liquid crystal display device.
FIG. 12 is a timing chart showing an operation of the conventional liquid crystal display device.
[Explanation of symbols]
101 first polarizing plate, 103 CF, 104 first reflective polarizing plate, 105 first transparent electrode, 106 liquid crystal, 107 second transparent electrode, 108 second glass substrate, 109 second polarizing plate, 110 backlight, 111 second Reflective polarizer, 116 slit reflector, 202 image display unit, 203 vertical drive circuit, 204 horizontal drive circuit, 205 gate driver, 206 source driver, 207 backlight lighting circuit, 208 control circuit.

Claims (4)

A first electrode and a second electrode disposed on a substrate so as to face each other with the liquid crystal interposed therebetween to drive the liquid crystal; and a backlight disposed on a side opposite to the substrate on which the liquid crystal is disposed. The backlight, a first polarizer disposed on the opposite side of the first electrode to the liquid crystal, a second polarizer disposed between the substrate and the backlight, A first reflective polarizer disposed between the first polarizer and the liquid crystal and arranged so that the direction of the transmitted linear polarized light is parallel to the direction of the transmitted linear polarized light of the first polarizer. Liquid crystal display device equipped. The liquid crystal display device according to claim 1, further comprising a color filter between the liquid crystal and the first polarizing means, and the first reflective polarizing plate between the color filter and the liquid crystal. A second reflective polarizer is provided between the backlight and the second polarizer, the second reflective polarizer being provided so that the direction of transmitted linearly polarized light is parallel to the direction of transmitting linearly polarized light of the polarizer. The liquid crystal display device according to claim 1. An image display unit having pixels arranged in a matrix and switch means connected to each pixel, a row drive circuit for selecting the pixels for each line while driving the switch means and scanning one screen, and In synchronization with scanning, the pixel of the selected line, a column drive circuit that writes an interlaced pixel signal consisting of an even field and an odd field, and in the even field, while writing an image signal to the pixels of the even line, 2. The erasure signal according to claim 1, wherein an erasure signal for aligning the potential of each pixel is written to the pixels of the odd-numbered line, and in the odd-numbered field, an image signal is written to the pixels of the odd-numbered line, and the erasure signal is written to the pixels of the even-numbered line. Liquid crystal display.

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