WO2007108436A1

WO2007108436A1 - Liquid crystal display device

Info

Publication number: WO2007108436A1
Application number: PCT/JP2007/055502
Authority: WO
Inventors: Akihiro Yamamoto; Masumi Kubo; Yohichi Naruse; Takashi Ochi
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2006-03-20
Filing date: 2007-03-19
Publication date: 2007-09-27

Abstract

A liquid crystal display device has a plurality of pixels and each pixel (P) has a plurality of sub-pixels with respective liquid crystal layers to which independently controllable voltages are applied. Each sub-pixel has a first sub-pixel (SP1) and a second sub-pixel (SP2), the area of which is larger than or equal to that of the first sub-pixel (SP1). Until a prescribed first gray scale, a voltage in accordance with a gray scale to be displayed is applied only to the first sub-pixel but a voltage in accordance with a gray scale to be display is applied at least to the second sub-pixel when a prescribed second gray scale or more which is higher than the first gray scale is to be displayed.

Description

Specification

Liquid crystal display

Technical field

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having excellent viewing angle characteristics.

Background art

A liquid crystal display device is a flat display device having excellent features such as high definition, thinness, light weight, and low power consumption. In recent years, liquid crystal display devices have been improved in display performance, production capacity, and price for other display devices. As the competitiveness increases, the market scale is rapidly expanding.

[0003] A liquid crystal display device of the twisted 'nematic' mode (TN mode), which has been common in the past, has a problem in display performance, particularly viewing angle characteristics. Specifically, when the display surface of a TN mode liquid crystal display device is observed from an oblique direction, the contrast ratio of the display is remarkably reduced, and multiple gradations up to black strength white can be clearly observed when observed from the front. When the image was observed from an oblique direction, the problem was that the brightness difference between the gradations became very unclear. In addition, the gradation characteristics of the display were reversed, and a phenomenon in which darker parts were observed brighter when viewed from the front (so-called gradation inversion phenomenon) was also a problem.

[0004] In recent years, the in-plane 'switching' mode (IPS mode) described in Patent Document 1 and the multi-domain described in Patent Document 2 are liquid crystal display devices that have improved viewing angle characteristics in these TN mode liquid crystal display devices. A “vertical” aligned mode (MVA mode), an axially symmetric alignment mode (ASM mode) described in Patent Document 3, a liquid crystal display device described in Patent Document 4, and the like have been developed.

[0005] All of these novel mode (wide viewing angle mode) liquid crystal display devices solve the above-mentioned specific problems relating to viewing angle characteristics. In other words, when the display surface is observed from an oblique direction, problems such as a significant decrease in display contrast ratio and inversion of display gradation do not occur.

[0006] Under the circumstances where the display quality of liquid crystal display devices is improving! Today, the problem with viewing angle characteristics is that the γ characteristics during frontal observation and the γ characteristics during oblique observation are different. γ The problem of viewing angle dependence of characteristics has become newly apparent. Here, the γ characteristic is the gradation dependence of the display brightness. The fact that the γ characteristic differs between the front direction and the diagonal direction means that the gradation display state differs depending on the observation direction. This is especially a problem when displaying or when displaying TV broadcasts.

[0007] The problem of viewing angle dependence of γ characteristics is more prominent in MVA mode and ASM mode than in IPS mode. On the other hand, in the IPS mode, it is difficult to produce a panel with a high contrast ratio in front view with high productivity compared to the MVA mode and ASM mode. From these points, it is desirable to improve the viewing angle dependency of the γ characteristics, especially in liquid crystal display devices in MVA mode and ASM mode.

[0008] Therefore, the applicant of Patent Document 5 discloses a liquid that can improve the viewing angle dependency of γ characteristics, in particular, white floating characteristics, by dividing one pixel into a plurality of sub-pixels having different brightness. A crystal display device and a driving method are disclosed. In this specification, such display or driving may be referred to as area gradation display, area gradation driving, multi-pixel display, or multi-pixel driving.

[0009] In Patent Document 5, an auxiliary capacitor is provided for each of a plurality of subpixels in one pixel, and an auxiliary capacitor counter electrode (connected to the CS bus line) constituting the auxiliary capacitor is electrically connected to each subpixel. By changing the voltage supplied to the auxiliary capacitor counter electrode (referred to as the auxiliary capacitor counter voltage) by changing the effective voltage applied to the liquid crystal layers of the plurality of sub-pixels by changing the capacity. A liquid crystal display device is disclosed.

Patent Document 1: Japanese Patent Publication No. 63-21907

Patent Document 2: Japanese Patent Laid-Open No. 11-242225

Patent Document 3: Japanese Patent Laid-Open No. 10-186330

Patent Document 4: Japanese Patent Laid-Open No. 2002-55343

Patent Document 5: Japanese Patent Application Laid-Open No. 2004-62146 (US Pat. No. 6,695,8791) Disclosure of Invention

Problems to be solved by the invention

However, there is a limit to the effect of improving the viewing angle dependency of the γ characteristic by the conventional multi-pixel driving technique described in Patent Document 5 described above. This is a sub-picture that each pixel has Elementary subpixels (bright subpixels) exhibiting higher luminance than the luminance corresponding to the gradation to be displayed and subpixels (dark subpixels) exhibiting lower luminance than the luminance corresponding to the gradation to be displayed. This is because the voltage applied to the liquid crystal layer of the bright subpixel and the voltage applied to the liquid crystal layer of the dark subpixel are restricted by capacitive coupling rather than being independent of each other.

The present invention has been made in view of the above points, and an object of the present invention is to provide a liquid crystal display device in which the viewing angle dependency of the γ characteristic is improved. Independently from the conventional multi-pixel driving described above, Alternatively, a novel multi-pixel driving technology that can be used in combination is provided.

Means for solving the problem

[0012] The liquid crystal display device of the present invention is a liquid crystal display device having a plurality of pixels, and each of the plurality of pixels has a plurality of voltages that can be controlled independently of each other. The plurality of subpixels includes a first subpixel and a second subpixel having an area larger than or equal to the first subpixel, and up to a predetermined first gradation. When a voltage corresponding to the gradation to be displayed is applied only to the liquid crystal layer of the first sub-pixel, and a gradation greater than a predetermined second gradation higher than the first gradation is to be displayed. A voltage corresponding to a gradation to be displayed is applied to at least the liquid crystal layer of the second subpixel.

In one embodiment, the area of the first subpixel is smaller than the area of the second subpixel.

[0014] In one embodiment, the plurality of sub-pixels further include a third sub-pixel having a larger area than or equal to the second sub-pixel, and a predetermined third higher than the second gray level. When gradations higher than the gradation are to be displayed, a voltage corresponding to the gradation to be displayed is applied to at least the liquid crystal layer of the third subpixel.

[0015] In one embodiment, the area of the first subpixel is smaller than the area of the third subpixel.

The invention's effect

[0016] According to the present invention, the viewing angle dependency of the y characteristic can be improved. In addition, the viewing angle dependency of the y characteristic can be further improved by combining with the conventional multi-pixel drive technology using capacitive division. Brief Description of Drawings

[0017] [Fig. L] (a) is a graph showing a voltage-luminance (transmittance) curve (V—T force curve) of a liquid crystal display device in a vertical alignment mode, and (b) is a graph in (a). This is a graph obtained by standardizing the V-T curve shown with each maximum brightness as 100.

FIG. 2 is a diagram schematically showing the structure of one pixel P of the liquid crystal display device according to the embodiment of the present invention.

FIG. 3 (a) and (b) are graphs schematically showing gradation display characteristics of a liquid crystal display device according to an embodiment of the present invention.

[FIG. 4] (a) to (c) are diagrams illustrating an example of a multi-pixel structure according to an embodiment of the present invention and how to apply a voltage to the liquid crystal layer of each sub-pixel.

FIGS. 5 (a) to 5 (d) are diagrams illustrating another example of a multi-pixel structure according to an embodiment of the present invention and a method of applying a voltage to the liquid crystal layer of each sub-pixel.

[FIG. 6] (a) to (d) are diagrams illustrating another example of a multi-pixel structure according to an embodiment of the present invention and a method of applying a voltage to the liquid crystal layer of each sub-pixel.

[FIG. 7] (a) to (g) are diagrams illustrating another example of a multi-pixel structure according to an embodiment of the present invention and a method of applying a voltage to the liquid crystal layer of each sub-pixel.

[FIG. 8] (a) to (e) are diagrams illustrating another example of a multi-pixel structure according to an embodiment of the present invention and a method of applying a voltage to the liquid crystal layer of each sub-pixel.

[FIG. 9] (a) to (i) are diagrams illustrating another example of a multi-pixel structure according to an embodiment of the present invention and a method of applying a voltage to the liquid crystal layer of each sub-pixel.

Explanation of symbols

[0018] P pixel

SP1, SP2 Kajihoromoto 1

BEST MODE FOR CARRYING OUT THE INVENTION

First, the viewing angle dependence of the γ characteristic of the liquid crystal display device will be described. Here, a vertical alignment mode liquid crystal display device in which the effect of the present invention is remarkably obtained is illustrated, but there is no particular limitation on the applicable display mode.

[0020] FIG. 1 (a) shows a liquid crystal including a liquid crystal layer having a nematic liquid crystal material force having a negative dielectric anisotropy. The voltage-luminance (transmittance) curve (VT curve) of a display device, a so-called vertical alignment mode liquid crystal display device is shown. The curve attached to the front in the figure is the VT curve when observed from the normal direction of the display surface. In the figure, the curve with left / right direction and polar angle 60 ° is the azimuth direction force, the horizontal axis is placed within the polarization axis (transmission axis) of the polarizing plate placed in crossed Nicols, and the polar angle The V-T curve is shown when the display surface normal force angle is observed from 60 °. This curve will be explained as a typical VT curve at an oblique viewing angle. The vertical axis of the VT curve shown in Fig. 1 (a) is the absolute luminance (arbitrary unit).

[0021] As can be seen from FIG. 1 (a), at the oblique viewing angle, the maximum luminance obtained is smaller than the front viewing angle. On the other hand, the voltage at which the luminance starts to rise is lower in the oblique viewing angle than in the front viewing angle.

[0022] The V—T curve shown in Fig. 1 (a) is standardized with the maximum luminance as 100, and the vertical axis is the normalized luminance (hereinafter referred to as “normalized V—T curve”). Is shown in Fig. 1 (b). As shown in Fig. 1 (b), on the higher voltage side (high gradation side) than a certain voltage (about 4.2V), the V-T curve at the front viewing angle and the V-T curve at the oblique viewing angle are almost the same. On the other hand, on the low voltage side of the voltage (about 4.2V), the normalized luminance at an oblique viewing angle is large. The fact that the normalized brightness at the oblique viewing angle is higher than the normalized brightness at the front viewing angle is a cause of the phenomenon that the display at the oblique viewing angle looks whitish (so-called “white floating”).

[0023] The inventor found that the normalized VT curve shown in FIG. 1 (b) matches the curve of the front viewing angle and the curve of the oblique viewing angle in the region where the normalized luminance is about 70. Focused on. In other words, in this example, if the gradation display is performed using only the range where the applied voltage is 4.2 V or higher or the normalized luminance is about 70 or higher, the “whitening” does not occur. However, if display is performed with normal pixels (one type of voltage applied to the liquid crystal layer), the display will be performed with a normalized luminance in the range of about 70 to 100, so a contrast ratio cannot be obtained.

In the liquid crystal display device according to the embodiment of the present invention, each pixel has a plurality of sub-pixels whose voltages applied to the respective liquid crystal layers can be controlled independently of each other. The voltage applied to the liquid crystal layer of each sub-pixel is used in accordance with the gradation to be displayed by the pixel, so that the above “white floating” in the standard 匕 V-T curve of each sub-pixel does not occur and the range is used. Next, the voltage applied to the liquid crystal layer of each sub-pixel is set. Conventional multi-pixel structure using capacitive division In a liquid crystal display device with a structure, the voltage applied to the liquid crystal layer of the sub-pixel cannot be controlled independently of each other. Therefore, a V-T curve having a certain relationship is added to thereby average the viewing angle characteristics. In contrast, in the liquid crystal display device according to the embodiment of the present invention, the normalized VT curve of each sub-pixel makes maximum use of the range where the oblique viewing angle and the front viewing angle match. It becomes possible to do.

For example, if each pixel has a first subpixel SP1 and a second subpixel SP2, if S is the area of the first subpixel SP1 and S is the area of the second subpixel SP2, then S ≤ S And pre-determined

(SP1) (SP2) (SP1) (SP2)

Up to the first gray level, a voltage corresponding to the gray level to be displayed is applied only to the liquid crystal layer of the first sub-pixel SP1, and the second gray level higher than the first gray level is determined. When a tone is to be displayed, a voltage corresponding to the tone to be displayed is applied to at least the liquid crystal layer of the second subpixel SP2. In other words, in the gradation range from the lowest gradation (black) to the first gradation, gradation display is performed only with the first subpixel, and in the gradation range over the second gradation, the second subpixel SP2 Apply a voltage according to the gradation to be displayed on the liquid crystal layer. When displaying the highest gradation, a voltage corresponding to the highest gradation is applied to both the first sub-pixel SP1 and the second sub-pixel SP2. The “voltage according to the gradation to be displayed” is independent of the voltage for the first subpixel SP1 and the voltage for the second subpixel SP2. When a voltage is applied to the liquid crystal layer of both the first sub-pixel SP1 and the second sub-pixel SP2 in order to display a gray level that is greater than or equal to the second gray level, the voltage is applied to the liquid crystal layer of the first sub-pixel SP1. The voltage VSP1 and the voltage VSP2 applied to the liquid crystal layer of the second sub-pixel SP2 are not necessarily the same, but a certain combination is set.

The liquid crystal display device according to the embodiment of the present invention can be obtained by making the configuration of each subpixel the same as that of a conventional pixel. For example, in the case of a TFT-type liquid crystal display device, one TFT is provided for each sub-pixel, and one gate bus line and one source bus line are provided. At this time, a pixel division structure using conventional capacity division (for example, a pixel division structure described in Patent Document 5) can be applied to each sub-pixel.

FIG. 2 schematically shows the structure of one pixel P of the liquid crystal display device according to the embodiment of the present invention. The pixel P includes three subpixels, that is, a first subpixel SP1, a second subpixel SP2, and a third subpixel SP3. Here, if the areas of the first subpixel SP1, the second subpixel SP2, and the third subpixel SP3 are S, S, and S, respectively, S <S <S of

3) Satisfied the relationship.

When such a pixel division structure is adopted, for example, a gradation display characteristic as schematically shown in FIG. 3 can be obtained. In FIG. 3, the horizontal axis represents the display gradation at the front viewing angle (frontal gradation), and the vertical axis represents the gradation display characteristics at the oblique viewing angle (left-right direction 'polar angle 60 °). Here, a 256 gradation display from OZ255 gradation (black) to 255Z255 gradation (white) is exemplified. As shown in FIG. 3, in a display gradation of a certain gradation or more, the display gradation is the same between the oblique viewing angle and the front viewing angle, that is, “whitening” does not occur. On the other hand, the display gradation at the oblique viewing angle is larger than the display gradation at the front viewing angle within a range below a certain gradation. The range where the display gradation of the oblique viewing angle is relatively large is the range where the normalized luminance is about 70 or less within the range where display is performed using only one sub-pixel (see Fig. 1 (b)). ). As can be seen from this, in order to prevent the occurrence of “whitening” in the widest possible gradation range, the area S of the first sub-pixel SP1 that performs gradation display with only one sub-pixel is reduced.

(SP1) is preferable. For the same reason, when the third subpixel SP3 is provided, the area S of the third subpixel SP3 is preferably larger than the area S of the second subpixel SP2.

(SP3) (SP2)

[0029] The number of sub-pixels constituting each pixel (hereinafter, also referred to as "division number"!) And the area ratio of sub-pixels (the area of other sub-pixels relative to the area of the smallest sub-pixel (S)) Ratio of S / S, S / S

By setting (SPl) (SP2) (SP1) (SP3) (also referred to as “splitting ratio”, such as S), gradation display as shown in Fig. 3 (a)

P1)

Characteristics can be obtained. Here, when the number of divisions or the division ratio deviates from the optimum value, as shown in FIG. 3B, the display gradation of the oblique viewing angle becomes relatively high even in the intermediate gradation.

[0030] Next, how to determine the number of divisions and the division ratio will be described.

[0031] Here, the normalized luminance 0 to: within the normalized luminance range of A or more of LOO, the normalized V-T curve at the oblique viewing angle and the normalized V-T curve at the front viewing angle coincide with each other. Consider optimal conditions for combining pixels. In the example shown in Fig. 1 (a), the normalized luminance is about 70 or more, and the normalized V-T curve is the same between the oblique viewing angle and the front viewing angle, so A is about 70. .

Note that the relationship between the normalized luminance and the gradation is related by the γ value of the display device, typically γ = 2.2. Assuming that AZ100 is represented by a, the number of pixel division is N, the area of each subpixel is S, S, '"S, and the relationship S ≤ S ≤---≤ S is satisfied,

(SPl) (SP2) (SPN) (SPl) (SP2) (SPN) The divisors N and S can be obtained as follows. N is 1 or more and N or less

(SPn)

It is an integer.

[0033] (I) When 0 <A≤50 is set, it is possible to prevent whitening (see FIG. 3 (b)) in the intermediate gradation with the division number N = 2. Therefore, N = 2 is the lowest number of divisions. In this case, the minimum value of the sub-pixel area of the nth division or more is S. For example, in the case of two divisions, S

(SPn-1) (S

= S is the minimum value S min of S. The maximum value S max is

P2) (SP1) (SP2) (SP2) (SPn) (SPn) is given by equation (1).

[Number 1]

n-1

'»(SPn) max― / / j S (SPk) I

[0034] (II) When setting 50 <A <100,

{S / a ^(N_1) }-(l -a) ≥ S -a

(SP1) (SP1)

N is required, i.e.

N that satisfies is required.

[0035] At this time, the area S of the sub-pixel in the n-th division (n is an integer satisfying 1 <η≤Ν) is S

(SPn) (SP1) Za ⁽ⁿ — is ^ϋ

, Say! / Convert and S / a! / I will meet you.

(SPn-l)

[0036] At this time, the minimum value S of the sub-pixel area of the m-th division (m is an integer of m> N) is S

(SPm) min (SP, and the maximum value S of S is given by the following equation (2).

m-1) (SPm) (SPm) max

[Equation 2]

Next, an example of a multi-pixel structure according to an embodiment of the present invention and how to apply a voltage to the liquid crystal layer of each sub-pixel will be described with reference to FIGS. Each of FIGS. 4 to 9 shows the area of the subpixel (the area of the first subpixel is 1) and the range of the voltage Vx applied to the liquid crystal layer of each subpixel. It is shown for each method of voltage application (distribution method). [0038] The voltage Vx means the voltage corresponding to the gradation to be displayed in the entire pixel, the voltage displaying the lowest gradation (black) is 0, and the voltage displaying the highest gradation (white) is 1. . However, in an actual display device, a voltage below the threshold voltage may be applied when displaying the lowest gradation (black) (for example, the V-T curve shown in Fig. 1 (a) is approximately 0.5V black voltage force is also started). The square in the figure indicates the size of the subpixel, and the area of the hatched portion schematically represents the magnitude of the applied voltage. The hatched portion is on the top with respect to the lower side of the square indicating the subpixel. The larger the voltage, the larger the applied voltage. The magnitude of the applied voltage is relative to each subpixel. When the entire subpixel is hatched, a voltage for displaying the maximum gradation is applied to the liquid crystal layer of the subpixel. Indicates that The broken line shown in the rectangle indicating the sub-pixel indicates the highest voltage level at which the viewing angle dependence occurs in the normalized VT curve.

First, with reference to FIGS. 4 to 7, a case where A = 50, that is, a case where the normalized luminance is 50 or more and the normalized VT curve has no viewing angle dependency will be described.

[0040] Figures 4 (a) to 4 (c) show examples of a two-part structure (number of divisions N = 2). The area ratio between the first sub-pixel SP1 (left side in the figure) and the second sub-pixel SP2 (right side in the figure) is 1: 1.

[0041] As shown in FIG. 4 (a), in the case of black display (Vx = 0), no voltage is applied to any sub-pixel.

[0042] Next, as shown in FIG. 4B, the voltage range of 0Z2 <Vx≤lZ2 (until the normalized luminance of the first subpixel SP1 reaches 100), the liquid crystal of the first subpixel SP1 Apply voltage only to the layer. At this time, in the region where the normalized luminance of the first sub-pixel SP1 is less than 50 (the range indicated by the arrow in the figure), the normalized luminance of the entire pixel is 25 because the normalized VT curve has a viewing angle dependency. The whitening occurs until (136Z2 55 gradation).

[0043] Next, as shown in FIG. 4 (c), in the voltage range of lZ2 <Vx≤2Z2 (that is, the range where the normalized luminance of the entire pixel exceeds 50), the first subpixel SP1 and the second subpixel Apply the same voltage to SP2, each with a normalized brightness exceeding 50.

[0044] Figs. 5 (a) to (d) show other examples of a two-divided structure (number of divisions N = 2). The area ratio of the first subpixel SP1 (left side in the figure) and the second subpixel SP2 (right side in the figure) is 1: 2.

[0045] As shown in Fig. 5 (a), in the case of black display (Vx = 0), voltage is applied to any sub-pixel. Not.

[0046] Next, as shown in FIG. 5 (b), in the voltage range of OZ3 <Vx≤lZ3 (until the normalized luminance of the first subpixel SP1 reaches 100), the liquid crystal layer of the first subpixel SP1 Apply voltage only to. At this time, in the region where the normalized luminance of the first sub-pixel SP1 is less than 50 (the range indicated by the arrow in the figure), the normalized luminance of the entire pixel is 16 because the normalized VT curve has a viewing angle dependency. . Whitening occurs until 7 (1 13Z255 gradation).

Next, as shown in FIG. 5 (c), in the voltage range of lZ3 <Vx≤2Z3 (until the normalized luminance of the second subpixel SP2 reaches 100), the liquid crystal layer of the second subpixel SP2 Apply voltage only to.

[0048] Next, as shown in FIG. 5 (d), in the voltage range where Vx exceeds 2Z3 (the range where the normalized luminance of the entire pixel exceeds 67), the first subpixel SP1 and the second subpixel SP2 Is used. At this time, the highest gradation voltage is applied to the liquid crystal layer of the first subpixel SP1, the normalized luminance of the first subpixel SP1 is 100, and the first subpixel SP1 whose area is 1Z3 as a whole. By applying the highest gradation voltage to the pixel, the entire pixel displays a gradation that is one third of the highest gradation. A voltage for displaying a gradation exceeding this is applied to the liquid crystal layer of the second sub-pixel SP2.

[0049] Figs. 6 (a) to (d) show examples of a three-division structure (division number N = 3). The area ratio of the first subpixel SP1 (left side in the figure), the second subpixel SP2 (center in the figure), and the third subpixel SP3 (right side in the figure) is 1: 1: 1.

[0050] As shown in FIG. 6 (a), in the case of black display (Vx = 0), no voltage is applied to any sub-pixel.

[0051] Next, as shown in FIG. 6 (b), in the voltage range of OZ3 and Vx≤lZ3 (until the normalized luminance of the first subpixel SP1 reaches 100), the liquid crystal layer of the first subpixel SP1 Apply voltage only to. At this time, in the region where the normalized luminance of the first sub-pixel SP1 is less than 50 (the range indicated by the arrow in the figure), the normalized luminance of the entire pixel is 16 because the normalized VT curve has a viewing angle dependency. . Whitening occurs until 7 (1 13Z255 gradation).

[0052] Next, as shown in FIG. 6 (c), in the voltage range of l / 3 <Vx≤l.5Z3 (the normalized luminance of the entire pixel is 50 or less), the first subpixel SP1 and the first subpixel SP1 From the state in which a voltage with a normalized luminance of 50 is applied to the liquid crystal layer of the 2nd subpixel SP2, the standard value is applied to the 1st subpixel SP1. A voltage with a luminance exceeding 50 is applied.

Next, as shown in FIG. 6 (d), in the voltage range where Vx exceeds 1.5Z3, the first subpixel SP

1. The second subpixel SP2 and the third subpixel SP3 are equally used. In other words, a voltage with a normalized luminance exceeding 50 is equally applied to each sub-pixel.

[0054] FIGS. 7A to 7G show other examples of a three-division structure (number of divisions N = 3). The area ratio of the first subpixel SP1 (left side in the figure), the second subpixel SP2 (center in the figure), and the third subpixel SP3 (right side in the figure) is 1: 2: 6.

As shown in FIG. 7 (a), in the case of black display (Vx = 0), no voltage is applied to any sub-pixel.

Next, as shown in FIG. 7B, in the voltage range of OZ9 <Vx ≦ lZ9, a voltage is applied only to the liquid crystal layer of the first subpixel SP1. That is, a voltage is applied only to the first subpixel SP1 until the normalized luminance of the first subpixel SP1 reaches 100. At this time, the region where the normalized luminance of the first subpixel SP1 is less than 50 (the range indicated by the arrow in the figure) is dependent on the viewing angle of the normalized VT curve, so 5.6 (69Z255 gradation Whitening will occur until).

[0057] Next, as shown in FIG. 7 (c), in the voltage range of l / 9 <Vx≤l.5Z9, a voltage with a normalized luminance exceeding 50 is applied only to the liquid crystal layer of the second sub-pixel SP2. Apply normalized brightness up to 100.

[0058] Next, as shown in FIG. 7 (d), in the voltage range of 1.5Z9 <Vx≤3Z9, the normalized luminance is applied to the liquid crystal layers of the first subpixel SP1 and the second subpixel SP2, respectively. A voltage exceeding 50 is applied.

Next, as shown in FIG. 7 (e), in the voltage range of 3Z9 <Vx≤4Z9, a voltage with a normalized luminance exceeding 50 is applied only to the liquid crystal layer of the third subpixel SP3.

Next, as shown in FIG. 7 (f), in the voltage range of 4Z9 <Vx≤6Z9, the voltage with the normalized luminance of 100 is applied to the liquid crystal layer of the first subpixel SP1. A voltage with a normalized luminance exceeding 50 is applied to the liquid crystal layer of the 3 sub-pixel SP3.

[0061] Next, as shown in FIG. 7 (g), in the voltage range of 6Z9 <Vx≤9Z9, the normalized luminance is 100 in each liquid crystal layer of the first subpixel SP1 and the second subpixel SP2. With the voltage applied, a voltage with a normalized luminance exceeding 50 is applied to the liquid crystal layer of the third subpixel SP3. Next, the case where A = 67, that is, the case where the normalized luminance is 67 or more and the normalized VT curve has no viewing angle dependency will be described with reference to FIGS. 8 and 9.

[0063] FIGS. 8 (a) to 8 (e) show examples of a two-divided structure (number of divisions N = 2). The area ratio between the first subpixel SP1 (left side in the figure) and the second subpixel SP2 (right side in the figure) is 2: 3.

[0064] As shown in FIG. 8 (a), in the case of black display (Vx = 0), no voltage is applied to any sub-pixel.

[0065] Next, as shown in FIG. 8 (b), in the voltage range of OZ5 <Vx≤2Z5 (until the normalized luminance of the first subpixel SP1 reaches 100), the liquid crystal layer of the first subpixel SP1 Apply voltage only to. At this time, the region where the normalized luminance of the first sub-pixel SP1 is less than 67 (the range indicated by the arrow in the figure) has a viewing angle dependency on the normalized VT curve, so that the normalized luminance of the entire pixel is 26 . Whitening occurs until 7 (1 40Z255 gradation).

[0066] Next, as shown in FIG. 8 (c), in the voltage range of 2Z5 <Vx≤3Z5 (until the normalized luminance of the second subpixel SP2 reaches 100), the liquid crystal of the second subpixel SP2 Apply voltage only to the layer. Whitening does not occur in this voltage range.

[0067] Next, as shown in FIG. 8 (d), in the voltage range of 3Z5 <Vx≤4Z5, the first subpixel SP2 is applied with the voltage corresponding to the normalized luminance 67 and the first subpixel is applied. Voltage is applied to the liquid crystal layer of pixel SP1 until the normalized luminance reaches 100. At this time, whitening occurs when the voltage range applied to the liquid crystal layer of the first sub-pixel SP1 is less than the normalized luminance 67, so that the normalized luminance of the entire pixel is 60 or more and less than 66.7 (202Z255 Whitening occurs in the range of gradation to 212Z255.

Next, as shown in FIG. 8 (e), in the voltage range of 4Z5 <Vx≤5Z5, the voltage with the normalized luminance of 100 is applied to the liquid crystal layer of the first subpixel SP1. A voltage with the normalized luminance of the second subpixel SP2 exceeding 67 is applied to the liquid crystal layer of the second subpixel SP2. Whitening does not occur even in this voltage range.

[0069] Figs. 9 (a) to (i) show examples of a three-division structure (division number N = 3). The area ratio of the first subpixel SP1 (left side in the figure), the second subpixel SP2 (center in the figure), and the third subpixel SP3 (right side in the figure) is 4: 6: 9.

[0070] As shown in Fig. 9 (a), in the case of black display (Vx = 0), voltage is applied to all sub-pixels. Not.

Next, as shown in FIG. 9B, in the voltage range of OZ19 and Vx≤4Zl9 (until the normalized luminance of the first subpixel SP 1 reaches 100), the liquid crystal of the first subpixel SP1 Apply voltage only to the layer. At this time, the region where the normalized luminance of the first subpixel SP1 is less than 67 (the range indicated by the arrow in the figure) has a viewing angle dependency on the normalized VT curve. The whitening occurs until (10 5Z255 gradation).

[0072] Next, as shown in FIG. 9 (c), in the voltage range of 4Z19 and Vx≤6Zl9 (until the normalized luminance of the second subpixel SP2 becomes 100), the second subpixel SP2 A voltage that exceeds the standardized luminance power S67 is applied only to the liquid crystal layer.

[0073] Next, as shown in FIG. 9 (d), in the voltage range of 6Z19 and Vx≤9Zl9 (until the normalized luminance of the third subpixel SP3 becomes 100), the third subpixel SP3 A voltage that exceeds the standardized luminance power S67 is applied only to the liquid crystal layer.

[0074] Next, as shown in FIG. 9 (e), in the voltage range of 9Z19 and Vx≤10Zl9, each subpixel is normalized to the liquid crystal layer of each of the first subpixel SP1 and the third subpixel SP3. A voltage with a normalized luminance exceeding 67 is applied to the liquid crystal layer of the first sub-pixel SP1 with a voltage at which the luminance becomes 67 applied.

[0075] Next, as shown in FIG. 9 (f), in the voltage range of 10Z19 and Vx≤12Zl9, the normalized luminance of each subpixel is set in each liquid crystal layer of the second subpixel SP2 and the third subpixel SP3. A voltage with a normalized luminance exceeding 67 is applied to the liquid crystal layer of the second sub-pixel SP2 in a state in which a voltage of becomes 67 is applied.

Next, as shown in FIG. 9 (g), in the voltage range of 12719 <¥ ≤15 19, the voltage at which the normalized luminance of the second subpixel SP2 becomes 100 in the liquid crystal layer of the second subpixel SP2 With voltage applied, a voltage with a normalized luminance exceeding 67 is applied to the liquid crystal layer of the third subpixel SP3.

Next, as shown in FIG. 9 (h), in the voltage range of 15Z19 and Vx≤16Zl9, a voltage at which the normalized luminance of the second subpixel SP2 becomes 100 is applied to the liquid crystal layer of the second subpixel SP2. With the voltage applied to the liquid crystal layer of the third subpixel SP3 and a voltage with a normalized luminance of 67 for each subpixel applied, a voltage with a normalized luminance exceeding 67 is applied to the liquid crystal layer of the first subpixel SP1. Apply.

Next, as shown in FIG. 9 (i), in the voltage range of 16Z19 and Vx≤19Zl9, the first sub-pixel A voltage with a normalized luminance exceeding 67 is applied to the liquid crystal layer of the third sub-pixel SP3 with a voltage at which the normalized luminance of each sub-pixel is 100 applied to the liquid crystal layer of the SP1 and the second sub-pixel SP2. Apply.

[0079] Normalized V—T curve where the luminance A that does not depend on the viewing angle is different. Based on the design guidelines described above, the number of divisions and the division ratio (the area of each subpixel is denoted by S. )

(SPn)

Table 1 shows the results. Table 1 holds for 2 to 5 divisions. Table 1 shows gradations at which whitening occurs in pixels having each pixel division structure. For each divided structure, “min” and “max” indicate the minimum and maximum configurations of the subpixel area after the second subpixel, respectively. The division structure specified by the numerical value marked with * in Table 1 indicates that there is an area where whitening occurs in the halftone area as shown in Fig. 3 (b).

[0080] [Table 1]

* At this division number, bumps occur in the halftone.

Table 2 also shows the preferred split ratio for the number of divisions N = 3 or 4 with regard to the viewing angle dependence of the VT curve of the liquid crystal display device in the MVA mode (see Fig. 1) in consideration of mass productivity. The results are shown together. The numerical range described in the VT characteristic is the relative transmittance corresponding to A described above. [0082] [Table 2]

However, low gradation whitening varies depending on each parameter.

[0083] As described above, the number of divisions and the division ratio of the pixel division structure are set, and the voltage applied to each subpixel is set to the maximum in the range where the normalized V-T curve of each subpixel has no viewing angle dependency. By supplying it to be used for the above, it is possible to effectively suppress the whitening of the entire pixel and reduce the viewing angle dependency of the γ characteristic.

[0084] In the above description, the V-repulsive force at the left / right direction and the polar angle of 60 ° is used as the oblique viewing angle characteristic. However, depending on the viewing angle characteristic required for the liquid crystal display device to which the present invention is applied. It can be changed as appropriate. For example, if the V-Τ curve with a 45 ° polar angle 45 ° coincides with the V-Τ curve at the front viewing angle, there are sufficient applications. In this case, the value of Α can be around 50.

Further, by applying the conventional pixel division structure described in Patent Document 4 or the like to each sub-pixel, the viewing angle dependency of the γ characteristic can be further reduced.

Industrial applicability

[0086] According to the present invention, a liquid crystal display device excellent in viewing angle characteristics is provided. The present invention is particularly suitably applied to large liquid crystal display devices such as liquid crystal televisions.

Claims

The scope of the claims

[1] A liquid crystal display device having a plurality of pixels,

Each of the plurality of pixels has a plurality of subpixels in which voltages applied to the respective liquid crystal layers can be controlled independently of each other,

The plurality of sub-pixels include a first sub-pixel and a second sub-pixel having an area larger than or equal to the first sub-pixel,

Up to a predetermined first gradation, a voltage corresponding to the gradation to be displayed is applied only to the liquid crystal layer of the first subpixel,

Applying a voltage corresponding to the gradation to be displayed to at least the liquid crystal layer of the second sub-pixel when displaying a gradation equal to or higher than a predetermined second gradation higher than the first gradation; Liquid crystal display device.

[2] The liquid crystal display device according to [1], wherein an area of the first sub-pixel is smaller than an area of the second sub-pixel.

[3] The plurality of sub-pixels further include a third sub-pixel having a larger area than or equal to the second sub-pixel,

Applying a voltage corresponding to the gradation to be displayed to at least the liquid crystal layer of the third sub-pixel when displaying a gradation equal to or higher than a predetermined third gradation higher than the second gradation; A liquid crystal display device according to claim 1 or 2.

4. The liquid crystal display device according to claim 3, wherein an area of the first subpixel is smaller than an area of the third subpixel.