JP2006119204A - Liquid crystal display device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device having excellent display quality and capable of suppressing dropping of production yield and to provide its driving method. <P>SOLUTION: The liquid crystal display device provided with a liquid crystal display panel constituted by holding a liquid crystal layer between a pair of substrates and provided with a plurality of color pixels and a panel driving part applying voltage corresponding to a display image to each color pixel of the liquid crystal panel is characterized in that when each relative luminous efficiency in a main wavelength of a color which each pixel displays has a relation of a display color of a first color pixel more than a display color of a second color pixel more thana display color of a third color pixel, the panel driving part sets voltage applied to each color pixel so as to satisfying a relation of the display color of the third color pixel equal to or more than the display color of the second color pixel more than the display color of the first color pixel in the same gradation in a dark display region of specification luminance of each color pixel specified by the luminance obtained in the maximum gradation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly to a liquid crystal display device having a configuration capable of improving display unevenness in a screen and a driving method thereof.

  Usually, a color display device includes a red pixel that displays red, a green pixel that displays green, and a blue pixel that displays blue. In such a display device, the voltage-transmittance characteristics of these color pixels are set to be substantially equal and adjusted so as to display a natural color image with little color shift from the bright display area to the dark display area. Yes.

Similarly, in a liquid crystal display device, a technique for displaying a color image with little color misregistration from a bright display area to a dark display area by independently setting voltages to be applied to each color pixel is disclosed (for example, (See Patent Document 1).
JP 2003-255908 A

  In the liquid crystal display device, there may be a problem that in-plane uniformity is deteriorated due to various causes in the manufacturing process. Such in-plane non-uniformity is likely to be visually recognized as display unevenness when an image is displayed, and there is a risk of deterioration in yield in the manufacturing process and display quality as a display device. In addition, in a large liquid crystal display device in which the diagonal size of the screen exceeds several tens of centimeters, the in-plane uniformity may be further deteriorated.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a liquid crystal display device that is excellent in display quality and can suppress a decrease in manufacturing yield, and a driving method thereof.

A liquid crystal display device according to a first aspect of the present invention provides:
A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates and having a plurality of color pixels;
Driving means for applying a voltage corresponding to a display image to each color pixel of the liquid crystal panel;
With
The relative visibility at the dominant wavelength of the color displayed by each color pixel is
When the relationship of the display color of the first color pixel> the display color of the second color pixel> the display color of the third color pixel,
In the same gradation of the dark display area, the driving means has the normalized luminance of each color pixel normalized by the luminance obtained at the maximum gradation.
The voltage applied to each color pixel is set so as to satisfy the relationship of display color of the third color pixel ≧ display color of the second color pixel> display color of the first color pixel.

The driving method of the liquid crystal display device according to the second aspect of the present invention is as follows:
A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates and having a plurality of color pixels;
Driving means for applying a voltage corresponding to a display image to each color pixel of the liquid crystal panel,
The relative visibility at the dominant wavelength of the color displayed by each color pixel is
A method of driving a liquid crystal display device, wherein the display color of the first color pixel> the display color of the second color pixel> the display color of the third color pixel,
The drive means, for each color pixel, the normalized luminance of each color pixel normalized by the luminance obtained at the maximum gradation, in the same gradation of the dark display area,
A voltage set so as to satisfy the relationship of display color of the third color pixel ≧ display color of the second color pixel> display color of the first color pixel is applied.

  According to the present invention, it is possible to provide a liquid crystal display device excellent in display quality and capable of suppressing a decrease in manufacturing yield and a driving method thereof.

  A liquid crystal display device and a driving method thereof according to an embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a liquid crystal display device using an OCB (Optically Compensated Bend) mode method will be described as an example of the liquid crystal display device. However, the present invention can also be applied to liquid crystal display devices in other display modes. Needless to say.

  As shown in FIG. 1, the OCB type liquid crystal display device includes a liquid crystal panel 1 having a liquid crystal layer 30 sandwiched between a pair of substrates, that is, an array substrate 10 and a counter substrate 20, and the liquid crystal panel 1 on the back surface. A backlight 50 for illuminating from is provided. The liquid crystal panel 1 is, for example, a transmission type, and is configured to be able to transmit backlight light from the backlight 50 arranged on the array substrate 10 side to the counter substrate 20 side. Further, the liquid crystal panel 1 includes an effective display unit 2 that substantially displays an image. The effective display unit 2 is composed of display pixels PX (R, G, B) arranged in a matrix.

  The array substrate 10 is formed using an insulating substrate 11 having optical transparency such as glass. The array substrate 10 includes a switch element 12, a pixel electrode 13, an alignment film 14 and the like on one main surface of an insulating substrate 11. The switch element 12 is disposed in each display pixel PX, and includes a TFT (Thin Film Transistor), a MIM (Metal Insulated Metal), or the like. The pixel electrode 13 is disposed in each display pixel PX and is electrically connected to the switch element 12. The pixel electrode 13 is formed of a light-transmitting conductive member such as ITO (Indium Tin Oxide). The alignment film 14 is disposed so as to cover the entire main surface of the insulating substrate 11, and is formed of a light transmissive material.

  The counter substrate 20 is formed using an insulating substrate 21 having optical transparency such as glass. The counter substrate 20 includes a counter electrode 22 and an alignment film 23 on one main surface of an insulating substrate 21. The counter electrode 22 is disposed in common in all the display pixels PX in the effective display portion 2, and is formed of a conductive member having light transmissivity, such as ITO. The alignment film 23 is disposed so as to cover the entire main surface of the insulating substrate 21 and is made of a light-transmitting material.

  In the color display type liquid crystal display device, the liquid crystal panel 1 displays a plurality of types of display pixels, for example, a red pixel PXR that displays red (R), a green pixel PXG that displays green (G), and blue (B). It has a blue pixel PXB. That is, the red pixel PXR includes a red color filter CFR that transmits light having a red main wavelength. The green pixel PXG includes a green color filter CFG that transmits light having a green main wavelength. The blue pixel PXB includes a blue color filter CFB that transmits light having a blue main wavelength. These color filters CF (R, G, B) are arranged on the main surface of the array substrate 10 or the counter substrate 20, but are arranged on the array substrate 10 in the example shown in FIG. 1.

  The array substrate 10 and the counter substrate 20 having the above-described configuration are arranged in a state where a predetermined gap is maintained with a spacer (not shown), and are bonded together by a sealing material. The liquid crystal layer 30 is sealed in the gap between the array substrate 10 and the counter substrate 20. The liquid crystal molecules 31 included in the liquid crystal layer 30 can be selected from materials having positive dielectric anisotropy and optically positive uniaxiality.

  Such an OCB type liquid crystal display device optically compensates for the retardation of the liquid crystal layer 30 including the liquid crystal molecules 31 bend-aligned as shown in FIG. 1 in a predetermined display state in which a voltage is applied to the liquid crystal layer 30. An optical compensation element 40 is provided. As shown in FIG. 2, the optical compensation element 40 includes a first compensation element 40A disposed on one main surface of the liquid crystal panel 1, that is, the outer surface on the array substrate 10, and the other main surface of the liquid crystal panel 1, that is, a counter substrate. And a second compensation element 40B disposed on the outer surface of the 20 side.

  For example, the first compensation element 40A includes a polarizing plate 41A and a plurality of optical elements 42A and 43A that function as retardation plates. Similarly, the second compensation element 40B includes a polarizing plate 41B and a plurality of optical elements 42B and 43B that function as retardation plates. The optical elements 42A and 42B mainly function as retardation plates having retardation (phase difference) in the thickness direction. The optical elements 43A and 43B mainly function as retardation plates having retardation (phase difference) in the in-plane direction.

  As shown in FIG. 3, the alignment films 14 and 23 have been subjected to parallel alignment processing (that is, have been rubbed in the direction indicated by the arrow A in the figure). Thereby, the orthogonal projection (liquid crystal alignment direction) of the optical axis of the liquid crystal molecules 31 is parallel to the arrow A in the figure. In a state where an image can be displayed, that is, in a state where a predetermined bias is applied, the liquid crystal molecules 31 are arranged in the cross section of the liquid crystal layer 30 defined by the arrow A as shown in FIG. A bend arrangement between 20 and 20.

  At this time, the polarizing plate 41A is arranged so that its transmission axis faces the direction indicated by the arrow B in the drawing. Further, the polarizing plate 41B is arranged so that the transmission axis thereof faces the direction indicated by the arrow C in the drawing. That is, the transmission axes of the polarizing plates 41A and 41B form an angle of 45 ° with respect to the liquid crystal alignment direction A, and are orthogonal to each other. Thus, the arrangement in which the transmission axes of the polarizing plates are orthogonal to each other is called crossed Nicol, and the birefringence amount (retardation amount) of the object between the pair of polarizing plates is effectively 0 or an integral multiple of the wavelength. Light is not transmitted and a black image is displayed. Conversely, if the birefringence amount (retardation amount) of the object between the pair of polarizing plates is effectively λ / 2 with respect to the incident light having the wavelength λ, the light is transmitted and a white image (or color image) is displayed. Is done.

  The optical elements 43A and 43B compensate for the influence of retardation remaining in the liquid crystal layer 30 when the screen is observed from the front direction in a specific voltage application state (for example, a state where a high voltage is applied to display a black image). . The optical elements 42A and 42B compensate for the influence of retardation of the liquid crystal layer 30 when the screen is observed from an oblique direction in a specific voltage application state (for example, a state where a high voltage is applied to display a black image). . As a result, viewing angle characteristics and display quality can be improved in the OCB type liquid crystal display device.

  As shown in FIG. 4, the liquid crystal display device applies a voltage corresponding to a display image to each display pixel PX (R, G, B) of the liquid crystal panel 1 having the above-described configuration (supplying a video signal). A panel driving unit 60 functioning as a driving unit.

  That is, the panel drive unit 60 is electrically connected to the liquid crystal panel 1 via a flexible printed circuit board or the like. The panel driving unit 60 can display the red pixel PXR, the green pixel PXG, and the blue pixel PXB with optimal brightness for each gradation of the display image based on the input video data. Apply an optimized voltage.

  More specifically, since the voltage applied to the counter electrode 22 is common to each display pixel, the panel driving unit 60 optimizes the voltage applied to the pixel electrode 13. The panel driving unit 60 outputs the voltage VR set for the red pixel at the timing when the switch element 12 of the red pixel PXR is turned on, and for the green pixel at the timing when the switch element 12 of the green pixel PXG is turned on. The set voltage VG is output, and the voltage VB set for the blue pixel is output at the timing when the switch element 12 of the blue pixel PXB is turned on. Each voltage V (R, G, B) output from the panel drive unit 60 is written to the pixel electrode 13 from the corresponding signal line X via the switch element 12.

  By the way, in the manufacturing process of the liquid crystal display device, display unevenness may occur due to the generated in-plane non-uniformity. This display unevenness is worsened as the cause of the deterioration of in-plane uniformity is larger. In addition, the degree of deterioration of the display unevenness seems to deteriorate as the condition is more visible. That is, the degree of deterioration of display quality is determined by the interaction between the cause of occurrence of display unevenness and the visibility of display unevenness.

  As a result of various examinations on conditions under which display unevenness is easily visible, it has been found that there is a brightness region where display unevenness is easily visible. That is, it has been found that in the liquid crystal display device, display unevenness is easily visible in a relatively dark dark display region. Therefore, by making the display unevenness in the dark display region difficult to see, it is possible to improve display quality deterioration due to in-plane non-uniformity, and to secure a margin in the manufacturing process.

Example 1
In the liquid crystal display device according to the first embodiment, the relative visibility at the dominant wavelength of the color displayed by each color pixel is
When the relationship of the display color of the first color pixel> the display color of the second color pixel> the display color of the third color pixel is satisfied, the panel driving unit 60 determines that the normalized luminance of each color pixel normalized by the maximum luminance is dark. In the same gradation of the display area,
The voltage applied to each color pixel is set so as to satisfy the relationship of the display color of the third color pixel ≧ the display color of the second color pixel> the display color of the first color pixel.

Note that the dark display area is a gradation area whose normalized luminance is 5% or less of the maximum luminance. For example, when the maximum luminance of the liquid crystal display device is 500 cd / m ² , the dark display area corresponds to a gradation area of 25 cd / m ² or less (although the lower limit gradation of the dark display area is not particularly set). For example, it is possible to set the gradation so that the normalized luminance is about 0.3% of the maximum luminance).

  That is, the liquid crystal display panel 1 includes a red pixel PXR, a green pixel PXG, and a blue pixel PXB as display pixels. The relationship of the relative visibility at the dominant wavelength of the colors displayed by these color pixels is as follows.

Display Color of Green Pixel> Display Color of Red Pixel> Display Color of Blue Pixel Therefore, for each color pixel, as shown in FIG. Then, the obtained characteristics are normalized by the luminance obtained at the maximum gradation. Usually, the entire display area of the bright display area and the dark display area is set so that the normalized luminances of the respective color pixels at the same gradation match. In this case, as described above, display unevenness due to in-plane non-uniformity is likely to be visually recognized in the dark display region.

For this reason, in the first embodiment, in the dark display region, the standardized luminance of each color pixel at the same gradation is set to be different. In other words, based on the relationship between the relative luminous sensitivities as described above, the luminance is set lower for the color having higher specific luminous efficiency. That is, as shown in FIG. 6, in the same gradation of the dark display area,
It is set so as to satisfy the relationship of normalized luminance of blue pixels ≧ normalized luminance of red pixels> normalized luminance of green pixels.

  The panel driving unit 60 corrects the input video data based on the setting as described above, and the voltage VB set for the blue pixel, the voltage VR set for the red pixel, and the voltage VG set for the green pixel. Is generated. Then, the panel driving unit 60 outputs a voltage set for the corresponding color pixel at the timing when the switch element of the corresponding color pixel is turned on.

  This makes it possible to set the relationship between gradation and standardized luminance as shown in FIG. 6, and even if display unevenness due to in-plane non-uniformity occurs in the manufacturing process, it is difficult to visually recognize it. It becomes possible to do. That is, in a dark display area where display unevenness is conspicuous, color misregistration is intentionally made to make display unevenness difficult to see.

  This is based on the following findings. For example, when the normalized luminance of a red pixel is 1%, the normalized luminance of a green pixel is 1%, and the normalized luminance of a blue pixel is 1% in a predetermined gradation of a dark display area, these total The luminance is 3%. Here, paying attention to the relationship of specific luminous efficiency, the distribution of the normalized luminance is lowered for the color having higher specific luminous sensitivity while keeping the total luminance the same (3%). For example, the normalized luminance of the red pixel is 1%, the normalized luminance of the green pixel is 0.8%, and the normalized luminance of the blue pixel is 1.2%. As a result, even if the total luminance is 3%, which is the same as the previous example, the standardized luminance of the color with high relative visibility is kept low, so the visibility of display unevenness is reduced compared to the previous example. can do.

(Example 2)
In Example 1 described above, it was confirmed that the visibility of display unevenness can be reduced by unbalanced the normalized luminances of the red pixel, the green pixel, and the blue pixel in the same gradation. Further, it was confirmed that the display unevenness is less noticeable as the normalized luminance of each color pixel becomes unbalanced.

  On the other hand, in the configuration of the first embodiment, in the case of monochrome display in which each color pixel is displayed with the same gradation, coloring occurs (magenta is colored slightly because blue is strong and green is weak). Further, while the brighter display feels more colored, the visibility of display unevenness tends to decrease, and the same is true for an excessively dark display. Therefore, it is desirable to set a well-balanced gradation-normalized luminance relationship that is limited to the dark display area and has little coloration and sufficiently low visibility of the display village.

Such a setting is
(1) When the normalized luminance of the blue pixel is C1 (au) and the normalized luminance of the green pixel is C3 (au) at the same gradation in the dark display area,
C3 (au) × 3 ≧ C1 (au) ≧ C3 (au) × 1.5
connection of,
(2) When the normalized luminance of the red pixel is C2 (au) and the normalized luminance of the green pixel is C3 (au) in the same gradation of the dark display area,
C3 (au) × 2 ≧ C2 (au) ≧ C3 (au) × 1
connection of,
It is realizable by satisfy | filling at least one of these.

  The panel driving unit 60 corrects the input video data based on the setting as described above, and the voltage VB set for the blue pixel, the voltage VR set for the red pixel, and the voltage VG set for the green pixel. Is generated. Then, the panel driving unit 60 outputs a voltage set for the corresponding color pixel at the timing when the switch element of the corresponding color pixel is turned on.

  As a result, even if display unevenness due to in-plane non-uniformity occurs in the manufacturing process, it is possible to make it difficult to see in the dark display area and to reduce the degree of coloring. It becomes.

  As described above, according to this embodiment, when the liquid crystal display device is displayed in the gradation of the dark display region, the color is intentionally shifted, and the luminance distribution is higher for the color having higher relative sensitivity. Is set to keep it small. Thereby, even if in-plane non-uniformity occurs in the manufacturing process of the liquid crystal display device, the visibility of display unevenness caused by this can be reduced, and the display quality can be improved.

  In addition, in the case of a large-sized liquid crystal display device having a diagonal size exceeding several tens of centimeters, in-plane non-uniformity is likely to occur due to manufacturing margin restrictions. With such a configuration, the visibility of display unevenness can be reduced, and a reduction in manufacturing yield can be suppressed.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the gist of the invention in the stage of implementation. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

FIG. 1 is a cross-sectional view schematically showing a configuration of an OCB type liquid crystal display device as an embodiment of the present invention. FIG. 2 is a diagram schematically showing a configuration of an optical compensation element applied to the OCB type liquid crystal display device. FIG. 3 is a diagram showing the relationship between the optical axis direction and the liquid crystal alignment direction of each optical member constituting the optical compensation element shown in FIG. FIG. 4 is a diagram schematically showing a configuration for driving the liquid crystal display panel shown in FIG. FIG. 5 is a diagram illustrating an example of a relationship of luminance with respect to gradation obtained by measurement in each color pixel. FIG. 6 is a diagram illustrating an example of the relationship of the normalized luminance with respect to the gradation between the color pixels.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel 2 ... Effective display part 10 ... Array substrate 20 ... Opposite substrate 30 ... Liquid crystal layer 31 ... Liquid crystal molecule 40 ... Optical compensation element 50 ... Backlight 60 ... Panel drive part

Claims (6)

A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates and having a plurality of color pixels;
Driving means for applying a voltage corresponding to a display image to each color pixel of the liquid crystal panel;
With
The relative visibility at the dominant wavelength of the color displayed by each color pixel is
When the relationship of the display color of the first color pixel> the display color of the second color pixel> the display color of the third color pixel,
In the same gradation of the dark display area, the driving means has the normalized luminance of each color pixel normalized by the luminance obtained at the maximum gradation.
A voltage applied to each color pixel is set so as to satisfy a relationship of display color of third color pixel ≧ display color of second color pixel> display color of first color pixel.   The liquid crystal display device according to claim 1, wherein the dark display region is a gradation region in which the normalized luminance is 5% or less of the maximum luminance. In the same gradation in the dark display area, the driving means has a normalized luminance of the first color pixel as C1 (au) and a normalized luminance of the third color pixel as C3 (au). ,
C3 (au) × 3 ≧ C1 (au) ≧ C3 (au) × 1.5
The liquid crystal display device according to claim 1, wherein voltages applied to the first color pixel and the third color pixel are set so as to satisfy the relationship. In the same gradation in the dark display area, the driving means has a normalized luminance of the second color pixel as C2 (au) and a normalized luminance of the third color pixel as C3 (au). ,
C3 (au) × 2 ≧ C2 (au) ≧ C3 (au) × 1
The liquid crystal display device according to claim 1, wherein voltages applied to the first color pixel and the third color pixel are set so as to satisfy the relationship.   2. The optical compensation element according to claim 1, further comprising an optical compensation element that optically compensates for retardation of the liquid crystal layer including bend-aligned liquid crystal molecules in a predetermined display state where a voltage is applied to the liquid crystal layer. Liquid crystal display device. A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates and having a plurality of color pixels;
Driving means for applying a voltage corresponding to a display image to each color pixel of the liquid crystal panel,
The relative visibility at the dominant wavelength of the color displayed by each color pixel is
A method of driving a liquid crystal display device, wherein the display color of the first color pixel> the display color of the second color pixel> the display color of the third color pixel,
The drive means, for each color pixel, the normalized luminance of each color pixel normalized by the luminance obtained at the maximum gradation, in the same gradation of the dark display area,
A driving method of a liquid crystal display device, wherein a voltage set so as to satisfy a relationship of display color of third color pixel ≧ display color of second color pixel> display color of first color pixel is applied.

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