WO2012118069A1

WO2012118069A1 - Liquid crystal display device

Info

Publication number: WO2012118069A1
Application number: PCT/JP2012/054903
Authority: WO
Inventors: 貢祥平田; 歳久内田
Original assignee: シャープ株式会社
Priority date: 2011-03-01
Filing date: 2012-02-28
Publication date: 2012-09-07

Abstract

A liquid crystal display device (100) is provided with a liquid crystal panel (1) and a drive circuit (2). Four or more pixels, which constitute a color display pixel (CP), and which respectively display different colors, include a first type pixel in which the width in the row direction is a predetermined first width (W1), and a second type pixel, in which the width in the row direction is a second width (W2) that is smaller than the first width (W1). The drive circuit (2) is capable of performing undershoot drive when a display gradation level shifts to a highest gradation level from a lowest gradation level. The drive circuit (2) does not perform the undershoot drive when the display gradation levels of all of the four or more pixels constituting the color display pixel (CP) shift to the highest gradation level from the lowest gradation level, and when the display gradation level of the pixel adjacent to the second type pixel in the row direction remains at the lowest gradation level, and the display gradation level of the second type pixel shifts to the highest gradation level from the lowest gradation level, the drive circuit performs the undershoot drive with respect to the second type pixel.

Description

Liquid crystal display

The present invention relates to a liquid crystal display device, and more particularly to a multi-primary color liquid crystal display device that performs display using four or more primary colors.

The display characteristics of liquid crystal display devices have been improved, and the use for television receivers is progressing. Although the viewing angle characteristics of liquid crystal display devices have been improved, further improvements are desired. In particular, there is a strong demand for improving the viewing angle characteristics of a liquid crystal display device using a vertical alignment type liquid crystal layer (sometimes referred to as a VA mode liquid crystal display device).

VA mode liquid crystal display devices currently used in large display devices such as televisions employ an alignment division structure in which a plurality of liquid crystal domains are formed in one pixel in order to improve viewing angle characteristics. . As a method of forming the alignment division structure, the MVA mode is the mainstream. The MVA mode is disclosed in Patent Document 1, for example.

In the MVA mode, a plurality of liquid crystal domains having different alignment directions (tilt directions) in each pixel (typically) are provided by providing an alignment regulating structure on each liquid crystal layer side of a pair of substrates facing each other with a vertical alignment type liquid crystal layer interposed therebetween. Specifically, four types of orientation directions are formed. As the alignment regulating structure, slits (openings) provided in the electrodes and ribs (projection structure) are used, and the alignment regulating force is exhibited from both sides of the liquid crystal layer.

However, when slits or ribs are used, unlike the case where the pretilt direction is defined by the alignment film used in the conventional TN mode, the slits and ribs are linear, so that the alignment regulating force on the liquid crystal molecules is within the pixel. In this case, there is a problem that the response speed is distributed. In addition, since the light transmittance of the region where the slits and ribs are provided is lowered, there is also a problem that display luminance is lowered.

In order to avoid the above-described problem, it is preferable to form an alignment division structure in the VA mode liquid crystal display device by defining the pretilt direction with the alignment film. The applicant of the present application has proposed a VA mode liquid crystal display device in which an alignment division structure is formed as described above in Patent Document 2.

In the liquid crystal display device disclosed in Patent Document 2, a quadrant alignment structure is formed by defining a pretilt direction with an alignment film. That is, when a voltage is applied to the liquid crystal layer, four liquid crystal domains are formed in one pixel. Such a quadrant alignment structure is sometimes simply referred to as a 4D structure.

Further, in the liquid crystal display device disclosed in Patent Document 2, a pretilt direction defined by one alignment film of a pair of alignment films opposed via a liquid crystal layer and a pretilt defined by the other alignment film are provided. The directions differ from each other by approximately 90 °. Therefore, when a voltage is applied, the liquid crystal molecules are twisted. Thus, the VA mode in which the liquid crystal molecules are twisted by using a pair of vertical alignment films provided so that the pretilt directions (alignment processing directions) are orthogonal to each other is a VATN (Vertical Alignment Twisted Nematic) mode or RTN. Also called (Reverse Twisted Nematic) mode. As already described, since the 4D structure is formed in the liquid crystal display device of Patent Document 2, the applicant of the present application calls the display mode of the liquid crystal display device of Patent Document 2 as the 4D-RTN mode.

As a specific method for defining the pretilt direction of the liquid crystal molecules in the alignment film, as described in Patent Document 2, a method of performing photo-alignment treatment is considered promising. Since the photo-alignment treatment can be performed in a non-contact manner, there is no generation of static electricity due to friction unlike the rubbing treatment, and the yield can be improved.

In recent years, in addition to the improvement in viewing angle characteristics as described above, it is desired to expand the color reproduction range (displayable color range) of a liquid crystal display device. In a general liquid crystal display device, one color display pixel is composed of three pixels that display red, green, and blue, which are the three primary colors of light, thereby enabling color display. On the other hand, as disclosed in Patent Document 3, a method for widening the color reproduction range of a liquid crystal display device by increasing the number of primary colors used for display to four or more has been proposed.

For example, as in the liquid crystal display device 600 shown in FIG. 16, one color display pixel CP is configured by four pixels of a red pixel R, a green pixel G, a blue pixel B, and a yellow pixel Y, thereby reducing the color reproduction range. Can be wide. Alternatively, as in the liquid crystal display device 700 illustrated in FIG. 17, one color display pixel CP may be configured by five pixels of the red pixel R, the green pixel G, the blue pixel B, the cyan pixel C, and the yellow pixel Y. Then, as in the liquid crystal display device 800 shown in FIG. 18, one color display pixel CP is constituted by six pixels of a red pixel R, a green pixel G, a blue pixel B, a cyan pixel C, a magenta pixel M, and a yellow pixel Y. May be. By using four or more primary colors, the color reproduction range can be made wider than that of a conventional liquid crystal display device that performs display using three primary colors. A liquid crystal display device that performs display using four or more primary colors is called a multi-primary color liquid crystal display device.

In the multi-primary color liquid crystal display device, the size of some of the plurality of pixels constituting the color display pixel may be set differently from the size of other pixels. For example, Patent Document 4 proposes a liquid crystal display device in which a red pixel has the largest size among a plurality of pixels constituting a color display pixel.

Japanese Patent Laid-Open No. 11-242225 International Publication No. 2006/132369 JP-T-2004-529396 International Publication No. 2007/148519

The inventor of the present application examined the adoption of a 4D-RTN mode for a multi-primary color liquid crystal display device. As a result, it was found that when the 4D-RTN mode is adopted in the multi-primary color liquid crystal display device having a specific configuration, the display quality is deteriorated. Specifically, if one color display pixel contains a pixel with a width different from that of the other pixels, the response speed is significantly reduced when performing monochrome display with a relatively small pixel. I understood that.

Here, taking the liquid crystal display device 900 shown in FIG. 19 as an example, the above-described decrease in response speed will be described more specifically. The color display pixel CP of the liquid crystal display device 900 includes a red pixel R, a green pixel G, a blue pixel B, and a yellow pixel Y. In the liquid crystal display device 900, as shown in FIG. 19, the widths of the red pixel R and the blue pixel B are relatively large, and the widths of the green pixel G and the yellow pixel Y are relatively small.

FIG. 20 shows an example of response speed when the 4D-RTN mode is used for the liquid crystal display device 900. In FIG. 20, the voltage corresponding to the highest gradation is applied to all the pixels constituting the color display pixel CP from the black display state (the state where all the pixels constituting the color display pixel CP display the lowest gradation). The relationship between the time (msec) and the luminance level when the (maximum gradation voltage) is applied is shown (curve indicated as “black → white” in the figure). In FIG. 20, when the highest gradation voltage is applied only to the red pixel R from the black display state, when the highest gradation voltage is applied only to the green pixel G from the black display state, the blue pixel B is changed from the black display state. The relationship between time (msec) and the luminance level is also shown when the highest gradation voltage is applied only to the pixel and when the highest gradation voltage is applied only to the yellow pixel Y from the black display state (each in the figure). "Black → red", "black → green", "black → blue", "black → yellow"). In the example shown in FIG. 20, one vertical scanning period is about 8.3 msec (that is, double speed driving).

FIG. 20 shows that the response speed is lower in the case of monochromatic display than in the case of white display. In particular, in the case of green display and yellow display, the response speed is significantly reduced. For this reason, the trailing of the color close to the primary color is severe and the display quality is degraded.

As described above, when the 4D-RTN mode is adopted in the multi-primary color liquid crystal display device, the response speed is remarkably reduced in pixels having relatively small widths (green pixel G and yellow pixel Y in the example of FIG. 20). . Therefore, a colored tail with high visibility occurs, and the display quality deteriorates.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a multi-primary color liquid crystal display device in which a plurality of pixels constituting a color display pixel include pixels having different widths from other pixels. The object is to suppress a reduction in display quality caused by a reduction in response speed in a pixel having a small width when the RTN mode is employed.

The liquid crystal display device according to the present invention has a plurality of pixels arranged in a matrix having a plurality of rows and a plurality of columns, and four or more pixels displaying different colors constitute a color display pixel. A device, a liquid crystal panel having a vertical alignment type liquid crystal layer, and a first substrate and a second substrate facing each other with the liquid crystal layer interposed therebetween, and display on each of the plurality of pixels for each vertical scanning period A drive circuit for supplying a voltage, and the four or more pixels constituting the color display pixel include a first type pixel having a predetermined first width in a row direction, and a row. And a second type pixel having a second width smaller than the first width in the direction along the direction, and the driving circuit is configured to change the display gradation from the lowest gradation to the highest gradation. Display voltage for displaying the highest gradation. An undershoot voltage having a magnitude between a display voltage for displaying the lowest gradation and a display voltage for performing the highest gradation is supplied in the vertical scanning period before the vertical scanning period. Undershoot driving can be performed, and when the display gray level of all the four or more pixels constituting the color display pixel transitions from the lowest gray level to the highest gray level, the drive circuit can perform undershoot driving. Without performing the undershoot driving, the display gradation of the pixel of the second type is the lowest gradation while the display gradation of the pixel adjacent to the second type pixel in the row direction remains the lowest gradation. When transitioning from 1 to the maximum gradation, the undershoot drive is performed on the second type pixel.

In a preferred embodiment, the driving circuit applies the second type pixel along the row direction when the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation. Even when the difference between the absolute value of the display voltage for displaying the target gradation of the adjacent pixel and the absolute value of the display voltage for displaying the maximum gradation is 6 V or more, the second type Undershoot drive is performed on the pixel.

In a preferred embodiment, the undershoot voltage is not less than 0.5 times and not more than 0.9 times the display voltage for displaying the highest gradation.

Alternatively, the liquid crystal display device according to the present invention includes a plurality of pixels arranged in a matrix having a plurality of rows and a plurality of columns, and four or more pixels displaying different colors constitute a color display pixel. A liquid crystal display device comprising: a liquid crystal panel having a vertical alignment type liquid crystal layer; a first substrate and a second substrate facing each other with the liquid crystal layer interposed therebetween; and a plurality of pixels each having a vertical scanning period A drive circuit that supplies a display voltage to the four or more pixels constituting the color display pixel, the first type of pixels having a predetermined first width in the row direction; And a second type pixel having a second width smaller than the first width in the row direction, and all the display floors of the four or more pixels constituting the color display pixel Tone transition from lowest to highest Display gray level of a pixel adjacent to the second type pixel in the row direction rather than the absolute value of the display voltage supplied to the second type pixel in the vertical scanning period immediately after the start of transition Is supplied to the second type pixel in the vertical scanning period immediately after the start of transition when the display gray level of the second type pixel transitions from the lowest gray level to the highest gray level. The absolute value of the display voltage is small.

In a preferred embodiment, the second type pixel is supplied to the second type pixel in a vertical scanning period immediately after the start of transition when the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation. The absolute value of the display voltage includes the absolute value of the display voltage for displaying the target gradation of the pixel adjacent in the row direction to the second type pixel and the display voltage for displaying the maximum gradation. When the difference from the absolute value of 6V is 6V or more is smaller than when it is less than 6V.

In a preferred embodiment, the four or more pixels constituting the color display pixel include a red pixel that displays red, a green pixel that displays green, and a blue pixel that displays blue.

In a preferred embodiment, the four or more pixels constituting the color display pixel further include a yellow pixel for displaying yellow.

In a preferred embodiment, the red pixel and the blue pixel are each the first type pixel, and at least one of the green pixel and the yellow pixel is the second type pixel.

In a preferred embodiment, the four or more pixels constituting the color display pixel are four pixels of the red pixel, the green pixel, the blue pixel, and the yellow pixel, and the green pixel and the yellow pixel. Both pixels are the second type of pixel.

In a preferred embodiment, the first substrate has a first alignment film provided on the surface on the liquid crystal layer side, and the second substrate is provided on the surface on the liquid crystal layer side. Each of the plurality of pixels has a predetermined tilt direction of the liquid crystal molecules in the layer surface of the liquid crystal layer and in the vicinity of the center in the thickness direction when a voltage is applied to the liquid crystal layer. A first liquid crystal domain that is a direction, a second liquid crystal domain that is a second direction, a third liquid crystal domain that is a third direction, and a fourth liquid crystal domain that is a fourth direction, and the first direction The second direction, the third direction, and the fourth direction are four directions in which the difference between any two directions is approximately equal to an integral multiple of 90 °.

In a preferred embodiment, the first liquid crystal domain, the second liquid crystal domain, the third liquid crystal domain, and the fourth liquid crystal domain are respectively adjacent to other liquid crystal domains and arranged in a matrix of 2 rows and 2 columns. ing.

In a preferred embodiment, the first liquid crystal domain, the second liquid crystal domain, the third liquid crystal domain, and the fourth liquid crystal domain are arranged so that the tilt direction differs by approximately 90 ° between adjacent liquid crystal domains.

In a preferred embodiment, when the horizontal azimuth angle on the display surface is 0 °, the first direction is approximately 45 °, approximately 135 °, approximately 225 °, or approximately 315 °.

In a preferred embodiment, the liquid crystal panel further includes a pair of polarizing plates that are opposed to each other via the liquid crystal layer and are arranged so that their transmission axes are substantially orthogonal to each other, the first direction, The second direction, the third direction, and the fourth direction form an angle of about 45 ° with the transmission axis of the pair of polarizing plates.

In a preferred embodiment, the liquid crystal layer includes liquid crystal molecules having negative dielectric anisotropy, a pretilt direction defined by the first alignment film, and a pretilt direction defined by the second alignment film; Differ from each other by approximately 90 °.

In a preferred embodiment, a pretilt angle defined by the first alignment film and a pretilt angle defined by the second alignment film are substantially equal to each other.

In a preferred embodiment, each of the first alignment film and the second alignment film is a photo-alignment film.

According to the present invention, when a 4D-RTN mode is adopted in a multi-primary color liquid crystal display device in which a plurality of pixels constituting a color display pixel include pixels having different widths from other pixels, Decrease in display quality due to a decrease in response speed can be suppressed.

It is a figure which shows the example of the pixel which has a 4-partition alignment structure. 2A and 2B are diagrams for explaining a method for dividing the alignment of the pixel shown in FIG. 1, in which FIG. 1A shows a pretilt direction on the TFT substrate side, FIG. 1B shows a pretilt direction on the CF substrate side, and FIG. A tilt direction and a dark region when a voltage is applied to the layer are shown. It is a figure for demonstrating the other alignment division | segmentation method of a pixel, (a) shows the pretilt direction by the side of a TFT substrate, (b) shows the pretilt direction by the side of a CF substrate, (c) is a voltage to a liquid crystal layer. A tilt direction and a dark region when is applied are shown. It is a figure for demonstrating the other alignment division | segmentation method of a pixel, (a) shows the pretilt direction by the side of a TFT substrate, (b) shows the pretilt direction by the side of a CF substrate, (c) is a voltage to a liquid crystal layer. A tilt direction and a dark region when is applied are shown. It is a figure for demonstrating the other alignment division | segmentation method of a pixel, (a) shows the pretilt direction by the side of a TFT substrate, (b) shows the pretilt direction by the side of a CF substrate, (c) is a voltage to a liquid crystal layer. A tilt direction and a dark region when is applied are shown. It is a figure which shows typically the liquid crystal display device 100 in suitable embodiment of this invention. It is a figure which shows typically the liquid crystal display device 100 in suitable embodiment of this invention. It is a figure which shows typically the liquid crystal panel 1 with which the liquid crystal display device 100 is provided, and is a top view which shows the area | region corresponding to one color display pixel (four pixels). FIG. 9 is a diagram schematically illustrating a liquid crystal panel 1 included in the liquid crystal display device 100, and is a cross-sectional view taken along line 9A-9A ′ in FIG. It is a graph which shows the response speed (relationship between time (msec) and a luminance level) at the time of undershoot drive. It is a figure which shows typically the liquid crystal display device 100 in suitable embodiment of this invention. It is a figure which shows typically the liquid crystal display device 200 in suitable embodiment of this invention, and is a top view which shows the area | region corresponding to one color display pixel (four pixels). It is a figure which shows typically the liquid crystal display device 300 in suitable embodiment of this invention. It is a figure which shows typically the liquid crystal display device 400 in suitable embodiment of this invention. It is a figure which shows typically the liquid crystal display device 500 in suitable embodiment of this invention. It is a figure which shows the conventional liquid crystal display device 600 typically. It is a figure which shows the conventional liquid crystal display device 700 typically. It is a figure which shows the conventional liquid crystal display device 800 typically. It is a figure which shows the conventional liquid crystal display device 900 typically. 20 is a graph showing a response speed (relationship between time (msec) and luminance level) when a 4D-RTN mode is used in the liquid crystal display device 900 shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. The present invention is widely used when a 4D-RTN mode is employed in a multi-primary color liquid crystal display device. As described above, the 4D-RTN mode is an RTN mode (VATN mode) in which a four-division alignment structure (4D structure) is formed in each pixel, and a liquid crystal display device employing the 4D-RTN mode has a vertical alignment. A liquid crystal layer of the type is provided.

In the present specification, the “vertical alignment type liquid crystal layer” refers to a liquid crystal layer in which liquid crystal molecules are aligned at an angle of about 85 ° or more with respect to the substrate surface (or the surface of the alignment film) when no voltage is applied. The liquid crystal molecules contained in the vertical alignment type liquid crystal layer have negative dielectric anisotropy. By combining a vertically aligned liquid crystal layer and a pair of polarizing plates arranged in crossed Nicols so as to face each other through the liquid crystal layer (that is, each transmission axis is arranged substantially perpendicular to each other) The normally black mode is displayed.

In the specification of the present application, “pixel” refers to a minimum unit for expressing a specific gradation in display, and a unit for expressing each gradation of primary colors (red, green, blue, etc.) used for display. (Also referred to as “dots”). A combination of a plurality of pixels constitutes (defines) one “color display pixel” which is a minimum unit for performing color display. In addition, a “sub-pixel” is a unit that is included in one pixel and that can display different luminances. A predetermined luminance (gradation) with respect to a display voltage input to one pixel is expressed by the plurality of sub-pixels. A display by sub-pixels.

The “pretilt direction” is the alignment direction of the liquid crystal molecules defined by the alignment film, and indicates the azimuth angle direction in the display surface. Further, the angle formed by the liquid crystal molecules with the surface of the alignment film at this time is referred to as “pretilt angle”. In addition, performing the process for expressing the ability to define the pretilt direction in a predetermined direction on the alignment film is expressed as “giving a pretilt direction to the alignment film” in the present specification, and the alignment film The pretilt direction defined by is sometimes simply referred to as “the pretilt direction of the alignment film”.

A quadrant alignment structure can be formed by changing the combination of the pretilt directions by a pair of alignment films facing each other through the liquid crystal layer. The pixel divided into four has four liquid crystal domains.

Each liquid crystal domain is characterized by a tilt direction (also referred to as “reference alignment direction”) of liquid crystal molecules in the layer plane of the liquid crystal layer and in the thickness direction near the center when a voltage is applied to the liquid crystal layer. The tilt direction (reference orientation direction) has a dominant influence on the viewing angle dependency of each domain. This tilt direction is also the azimuth direction. The reference of the azimuth angle direction is the horizontal direction of the display surface, and the counterclockwise direction is positive (when the display surface is compared to a clock face, the 3 o'clock direction is azimuth angle 0 ° and the counterclockwise direction is positive). The tilt directions of the four liquid crystal domains are four directions (for example, 12 o'clock direction, 9 o'clock direction, 6 o'clock direction, and 3 o'clock direction) in which the difference between any two directions is approximately equal to an integral multiple of 90 °. By setting to, the viewing angle characteristics are averaged and a good display can be obtained. Also, from the viewpoint of uniformity of viewing angle characteristics, it is preferable that the areas occupied by the four liquid crystal domains in the pixels are substantially equal to each other. Specifically, the difference between the area of the largest liquid crystal domain and the area of the smallest liquid crystal domain among the four liquid crystal domains is preferably 25% or less of the largest area.

A vertical alignment type liquid crystal layer exemplified in the following embodiment includes liquid crystal molecules having negative dielectric anisotropy (nematic liquid crystal material having negative dielectric anisotropy), and a pretilt direction defined by one alignment film. The pretilt direction defined by the other alignment film is substantially 90 ° different from each other, and the tilt direction (reference alignment direction) is defined in the middle of these two pretilt directions. When a voltage is applied to the liquid crystal layer, the liquid crystal molecules take a twist alignment according to the alignment regulating force of the alignment film. A chiral agent may be added to the liquid crystal layer as necessary.

The pretilt angles defined by each of the pair of alignment films are preferably substantially equal to each other. Since the pretilt angles are substantially equal, an advantage that display luminance characteristics can be improved is obtained. In particular, by making the difference in pretilt angle within 1 °, the tilt direction (reference alignment direction) of the liquid crystal molecules near the center of the liquid crystal layer can be stably controlled, and the display luminance characteristics can be improved. . This is because when the difference in the pretilt angle exceeds 1 °, the tilt direction varies depending on the position in the liquid crystal layer, and as a result, the transmittance varies (that is, a region having a transmittance lower than the desired transmittance is formed). This is probably because

The pretilt direction is imparted to the alignment film by a photo-alignment process. By using a photo-alignment film containing a photosensitive group, the variation in the pretilt angle can be controlled to 1 ° or less. The photosensitive group preferably contains at least one photosensitive group selected from the group consisting of a 4-chalcone group, a 4'-chalcone group, a coumarin group, and a cinnamoyl group.

(Embodiment 1)
Prior to the description of the present embodiment, the method of aligning and dividing pixels in the 4D-RTN mode, and the problems when the 4D-RTN mode is adopted in the multi-primary color liquid crystal display device (the response speed decreases when performing monochromatic display) Explain why.

FIG. 1 shows a pixel P1 having a quadrant alignment structure (4D structure). For the sake of simplicity, FIG. 1 shows a substantially square pixel P1 corresponding to a substantially square pixel electrode, but the shape of the pixel is not limited. For example, the pixel P1 may be substantially rectangular.

The pixel P1 has four liquid crystal domains D1, D2, D3, and D4 as shown in FIG. In FIG. 1, the areas of the liquid crystal domains D1, D2, D3, and D4 are equal to each other, and the example shown in FIG. 1 is an example of the most preferable 4D structure in view angle characteristics. The four liquid crystal domains D1, D2, D3 and D4 are arranged in a matrix of 2 rows and 2 columns.

If the respective tilt directions (reference alignment directions) of the liquid crystal domains D1, D2, D3, and D4 are t1, t2, t3, and t4, these are the difference between any two directions is approximately equal to an integral multiple of 90 ° 4 There are two directions. When the horizontal azimuth (3 o'clock direction) on the display surface is 0 °, the tilt direction t1 of the liquid crystal domain D1 is about 225 °, the tilt direction t2 of the liquid crystal domain D2 is about 315 °, and the tilt direction t3 of the liquid crystal domain D3. Is approximately 45 °, and the tilt direction t4 of the liquid crystal domain D4 is approximately 135 °. That is, the liquid crystal domains D1, D2, D3, and D4 are arranged such that their tilt directions differ by approximately 90 ° between adjacent liquid crystal domains.

Here, the pair of polarizing plates facing each other through the liquid crystal layer are arranged so that the transmission axes (polarization axes) are substantially orthogonal to each other. More specifically, one transmission axis is the display surface. Are arranged so that the other transmission axis is substantially parallel to the vertical direction of the display surface. Therefore, the tilt directions t1, t2, t3, and t4 form an angle of about 45 ° with the transmission axis of the pair of polarizing plates. Hereinafter, unless otherwise indicated, the arrangement of the transmission axes of the polarizing plates is the same as that described above.

The 4D structure of the pixel P1 shown in FIG. 1 can be obtained as shown in FIG. FIGS. 2A, 2B, and 2C are diagrams for explaining the alignment dividing method of the pixel P1 shown in FIG. 2A shows the pretilt directions PA1 and PA2 of the alignment film provided on the TFT substrate (lower substrate), and FIG. 2B is provided on the color filter (CF) substrate (upper substrate). The pretilt directions PB1 and PB2 of the alignment film are shown. FIG. 2C shows the tilt direction when a voltage is applied to the liquid crystal layer. In these figures, the orientation direction of the liquid crystal molecules as viewed from the observer side is schematically shown, and the liquid crystal molecules are aligned so that the bottom end of the liquid crystal molecules shown in a conical shape is close to the observer. Indicates that the camera is tilted.

As shown in FIG. 2A, the area on the TFT substrate side (area corresponding to one pixel P1) is divided into two parts on the left and right, and the vertical alignment of each area (left area and right area). Orientation treatment is performed so that pretilt directions PA1 and PA2 antiparallel to the film are given. Specifically, photo-alignment processing is performed by obliquely irradiating ultraviolet rays from the direction indicated by the arrow. When the left region is irradiated with light, the right region is shielded by the light shielding portion of the photomask, and when the right region is irradiated with light, the left region is similarly shielded.

As shown in FIG. 2B, the area on the CF substrate side (area corresponding to one pixel P1) is vertically divided into two areas, and each area (upper area and lower area) is perpendicular to each other. Alignment processing is performed so that pretilt directions PB1 and PB2 antiparallel to the alignment film are provided. Specifically, photo-alignment processing is performed by obliquely irradiating ultraviolet rays from the direction indicated by the arrow. When the upper region is irradiated with light, the lower region is shielded by the light shielding portion of the photomask, and when the lower region is irradiated with light, the upper region is similarly shielded. Yes.

As shown in FIGS. 2A and 2B, the alignment-divided pixel P1 can be formed as shown in FIG. 2C by bonding together the TFT substrate and the CF substrate that have been subjected to the alignment treatment. it can. As can be seen from FIGS. 2A, 2B and 2C, for each of the liquid crystal domains D1 to D4, the pretilt direction of the alignment film of the TFT substrate and the pretilt direction of the alignment film of the CF substrate are approximately 90 to each other. The tilt direction (reference orientation direction) is defined in the middle direction between these two pretilt directions. Further, for each of the liquid crystal domains D1 to D4, the combination of the pretilt directions by the upper and lower alignment films is different from that of the other liquid crystal domains, and thereby, four tilt directions are realized in one pixel P1.

In the pixel P1 in the 4D-RTN mode, when a certain halftone (or the highest gradation) is displayed, a region DR darker than the gradation to be displayed is formed as shown in FIG. The dark region DR includes a cross-shaped dark line (cross-shaped portion) CL located at the boundary between the liquid crystal domains D1, D2, D3, and D4, and a linear dark line (in the vicinity of the edge of the pixel electrode, extending substantially parallel to the edge). A straight portion) SL and is generally bowl-shaped as a whole.

The cross-shaped dark line CL is formed by aligning the liquid crystal molecules so that the alignment is continuous between the liquid crystal domains so as to be parallel or orthogonal to the transmission axis of the polarizing plate at the boundary between the liquid crystal domains. Further, the linear dark line SL near the edge indicates that the azimuth angle direction perpendicular to the edge of the pixel electrode to which the liquid crystal domain is adjacent and inward of the pixel electrode is more than 90 ° with respect to the tilt direction (reference alignment direction) of the liquid crystal domain. If there is an edge portion that forms a corner of the shape, it is formed. This is because the tilt direction of the liquid crystal domain and the direction of the alignment regulating force due to the oblique electric field generated at the edge of the pixel electrode have components opposite to each other. This is considered to be oriented in parallel or orthogonal.

Note that the method of aligning and dividing one pixel into four liquid crystal domains D1 to D4 (that is, the arrangement of the liquid crystal domains D1 to D4 in the pixel) is not limited to the examples of FIGS.

For example, the alignment-divided pixel P2 is formed as shown in FIG. 3C by bonding the TFT substrate and the CF substrate that have been subjected to the alignment treatment as shown in FIGS. 3A and 3B. Can do. The pixel P2, like the pixel P1, has four liquid crystal domains D1 to D4. The tilt directions of the liquid crystal domains D1 to D4 are the same as the liquid crystal domains D1 to D4 of the pixel P1.

However, in the pixel P1, the liquid crystal domains D1 to D4 are arranged in the order of upper left, lower left, lower right, and upper right (that is, counterclockwise from the upper left), whereas in the pixel P2, the liquid crystal domains D1 to D4 are They are arranged in the order of lower right, upper right, upper left, and lower left (that is, counterclockwise from the lower right). This is because the pretilt direction is opposite between the left and right regions of the TFT substrate and the upper and lower regions of the CF substrate in the pixel P1 and the pixel P2.

Also, the alignment-divided pixel P3 as shown in FIG. 4 (c) is formed by bonding the TFT substrate and the CF substrate that have been subjected to the alignment treatment as shown in FIGS. 4 (a) and 4 (b). Can do. The pixel P3 has four liquid crystal domains D1 to D4 like the pixel P1. The tilt directions of the liquid crystal domains D1 to D4 are the same as the liquid crystal domains D1 to D4 of the pixel P1.

However, in the pixel P3, the liquid crystal domains D1 to D4 are arranged in the order of upper right, lower right, lower left, and upper left (that is, clockwise from the upper right). This is because the pretilt direction is opposite between the left and right regions of the TFT substrate between the pixel P1 and the pixel P3.

Further, by aligning the TFT substrate and the CF substrate that have been subjected to the alignment treatment as shown in FIGS. 5A and 5B, the pixel P4 that is divided in alignment as shown in FIG. 5C is formed. Can do. The pixel P4 has four liquid crystal domains D1 to D4 like the pixel P1. The tilt directions of the liquid crystal domains D1 to D4 are the same as the liquid crystal domains D1 to D4 of the pixel P1.

However, in the pixel P4, the liquid crystal domains D1 to D4 are arranged in the order of lower left, upper left, upper right, and lower right (that is, clockwise from the lower left). This is because the pretilt direction is opposite between the upper region and the lower region of the CF substrate between the pixel P1 and the pixel P4.

As described above, various arrangements can be adopted as the arrangement of the liquid crystal domains D1 to D4 in the pixel. As shown in FIGS. 2 to 5, when the arrangement of the liquid crystal domains D1 to D4 is different, the generation pattern of the dark line SL in the vicinity of the edge is different, so that the overall shape of the dark region DR is different. In the pixels P1 and P2 shown in FIGS. 2 and 3, the dark region DR has a substantially bowl shape, whereas in the pixels P3 and P4 shown in FIGS. 4 and 5, the dark region DR has an approximately 8 character shape. (Eight-letter shape inclined from the vertical direction).

Next, in a multi-primary color liquid crystal display device (for example, the liquid crystal display device 900 shown in FIG. 19) simply adopting the 4D-RTN mode, refer to FIG. 20 when performing monochromatic display with pixels having a relatively small width. However, the reason why the response speed is significantly reduced as described above will be described.

The decrease in response speed is due to alignment failure that occurs when a voltage is applied. When the display gradation of the pixel transitions from the lowest gradation to the highest gradation, that is, the voltage applied to the liquid crystal layer is a voltage corresponding to the highest gradation (for example, about 0 V). 7V), some of the liquid crystal molecules are subjected to the alignment regulating force due to the oblique electric field generated at the edge of the pixel electrode, and are different from the original alignment directions (tilt directions t1 to t4 shown in FIG. 1). Falls in the direction. At this time, the direction in which the liquid crystal molecules are tilted is parallel to or perpendicular to the transmission axis of the polarizing plate. Therefore, the liquid crystal molecules tilted in such a direction cause a decrease in transmittance. In a pixel having a small width, the influence of the pixel electrode edge on the entire pixel becomes large, and thus a decrease in transmittance increases.

In the case of performing monochromatic display, as shown in FIG. 20, the luminance level once increases to some extent immediately after voltage application, and then gradually increases. This gradual increase in luminance level is due to the fact that liquid crystal molecules that fall in a direction different from the original orientation due to the edge of the pixel electrode rotate slowly in the liquid crystal layer plane (in the plane parallel to the substrate). The process of returning to the orientation of is shown.

In the case of white display, since all the pixels are in a lighting state, voltages applied to the liquid crystal layer have opposite polarities between two adjacent pixels (typically, dot inversion driving is performed in a liquid crystal display device). ). Accordingly, since the equipotential surface between the pixel electrodes (showing an oblique electric field generated at the edge of the pixel electrode) becomes steep, the liquid crystal molecules existing near the edge of the pixel electrode are perpendicular to the substrate surface. Oriented at a close angle. Therefore, since the energy required for the rotation of the liquid crystal molecules is small, the liquid crystal molecules quickly return to the original alignment.

In the case of monochromatic display, only a pixel of a certain color is in a lighting state, so that a pixel adjacent to the pixel is in a black display state (for example, a state where a voltage of about 0.2 V is applied to the liquid crystal layer). Accordingly, since the equipotential surface between the pixel electrodes is gentle, the liquid crystal molecules existing in the vicinity of the edge of the pixel electrode are tilted so as to form a relatively large angle with respect to the substrate normal direction. Therefore, since the energy required for the rotation of the liquid crystal molecules is large, the time required for the liquid crystal molecules to return to the original alignment is long. In a pixel having a small width, since the existence ratio of such liquid crystal molecules is high, a decrease in response speed becomes remarkable, and a colored tail with high visibility occurs.

In the liquid crystal display device according to the present invention, it is possible to suppress a decrease in response speed due to the alignment failure as described above. Hereinafter, specific embodiments of the liquid crystal display device according to the present invention will be described.

FIG. 6 shows a liquid crystal display device 100 according to this embodiment. As shown in FIG. 6, the liquid crystal display device 100 includes a plurality of pixels arranged in a matrix having a plurality of rows and a plurality of columns. The plurality of pixels include a red pixel R that displays red, a green pixel G that displays green, a blue pixel B that displays blue, and a yellow pixel Y that displays yellow. These four pixels (red pixel R, green pixel G, blue pixel B, and yellow pixel Y) that display different colors constitute (specify) a color display pixel CP that is a minimum unit for performing color display. Thus, the liquid crystal display device 100 is a multi-primary color liquid crystal display device that performs display using four primary colors (red, green, blue, and yellow).

In the example shown in FIG. 6, the red pixel R, the green pixel G, the blue pixel B, and the yellow pixel Y are arranged in one row and four columns in the color display pixel CP. In the example shown in FIG. 6, the red pixel R, the green pixel G, the blue pixel B, and the yellow pixel Y are arranged in this order from the left side to the right side in the color display pixel CP.

In the liquid crystal display device 100, as shown in FIG. 6, the width W2 along the respective row directions of the green pixel G and the yellow pixel Y is larger than the width W1 along the respective row directions of the red pixel R and the blue pixel B. Is small. In other words, the four pixels constituting the color display pixel CP have “first type” pixels (red pixels R and R) having a predetermined first width (width W1 in FIG. 6) along the row direction. Blue pixel B) and “second type” pixels (green pixel G and yellow pixel) having a second width (width W2 in FIG. 6) smaller than the first width in the row direction. Y). In the example illustrated in FIG. 6, the first type pixel and the second type pixel are adjacent to each other along the row direction, and are alternately arranged along the row direction.

Since the width W1 of the red pixel R and the blue pixel B and the width W2 of the green pixel G and the yellow pixel Y are in the above-described relationship (W1> W2), each area of the red pixel R and the blue pixel B is green. It is larger than each area of the pixel G and the yellow pixel Y. When the area of the red pixel R is larger than that of the yellow pixel Y, as in the liquid crystal display device disclosed in Patent Document 4, it is brighter red (high brightness) than when each pixel has the same area. Can be displayed.

In addition, the liquid crystal display device 100 performs display in the 4D-RTN mode. Each pixel of the liquid crystal display device 100 has, for example, the same quadrant alignment structure as any of the pixels P1 to P4 shown in FIGS.

Subsequently, a more specific configuration of the liquid crystal display device 100 will be described. As shown in FIG. 7, the liquid crystal display device 100 includes a liquid crystal panel 1 and a drive circuit 2. The liquid crystal panel 1 has a plurality of pixels already described. The drive circuit 2 supplies a display voltage to each of the plurality of pixels every one vertical scanning period. Typically, one vertical scan period is about 16.7 msec. For the purpose of improving blurring and blurring of moving images, one vertical scanning period is approximately 8.3 msec when performing double speed driving, and one vertical scanning period is approximately 4.2 msec when performing quadruple speed driving. is there. The display voltage supplied to each pixel is not limited to the voltage (grayscale voltage) corresponding to the gradation to be displayed, but an overshoot voltage for improving response characteristics, pseudo impulse drive (black insertion drive), or the like. Including all voltages supplied to the pixel, such as a black display voltage for.

8 and 9 show examples of the specific structure of the liquid crystal panel 1. FIG. 8 is a plan view showing a region corresponding to one color display pixel CP (that is, four pixels) of the liquid crystal panel 1. FIG. 9 is a cross-sectional view showing a region corresponding to two pixels (red pixel R and green pixel G), and is a cross-sectional view taken along line 9A-9A 'in FIG.

The liquid crystal panel 1 includes a vertical alignment type liquid crystal layer 30, an active matrix substrate (hereinafter referred to as “TFT substrate”) 10 and a counter substrate (hereinafter referred to as “color filter substrate”) that face each other with the liquid crystal layer 30 interposed therebetween. 20).

The liquid crystal layer 30 includes liquid crystal molecules having negative dielectric anisotropy (that is, Δε <0). The liquid crystal molecules of the liquid crystal layer 30 are aligned substantially perpendicular to the substrate surface when no voltage is applied to the liquid crystal layer 30.

The TFT substrate 10 includes a pixel electrode 11 provided in each of a plurality of pixels, a plurality of scanning wirings (gate bus lines) 12 extending in the row direction, and a plurality of signal wirings (source bus lines) 13 extending in the column direction. Have The TFT substrate 10 further has a plurality of storage capacitor lines (CS bus lines) 14 extending in the row direction.

The pixel electrode 11 is connected to a TFT (Thin Film Transistor) 15 provided in each pixel. The TFT 15 is supplied with a scanning signal from the corresponding scanning wiring 12 and supplied with a display signal (signal voltage) from the corresponding signal wiring 13.

The scanning wiring 12 is provided on an insulating transparent substrate (for example, a glass substrate) 10a. In addition, auxiliary capacitance wiring 14 is also provided on the transparent substrate 10a. Here, the auxiliary capacitance line 14 is formed of the same conductive film as the scanning line 12.

A gate insulating film 16 is provided so as to cover the scanning wiring 12 and the auxiliary capacitance wiring 14. A signal wiring 13 is provided on the gate insulating film 16. An auxiliary capacitance electrode 17 is also provided on the gate insulating film 16. Here, the auxiliary capacitance electrode 17 is formed of the same conductive film as the signal wiring 13. The auxiliary capacitance electrode 17 is electrically connected to the drain electrode of the TFT 15 via the connection electrode 17a.

An interlayer insulating film 18 is provided so as to cover the signal wiring 13 and the auxiliary capacitance electrode 17. A pixel electrode 11 is provided on the interlayer insulating film 18. Here, the pixel electrode 11 is connected to the auxiliary capacitance electrode 17 in the contact hole CH formed in the interlayer insulating film 18, and is electrically connected to the TFT 15 via the auxiliary capacitance electrode 17 and the connection electrode 17a. . The same signal voltage is supplied to the pixel electrode 11 and the auxiliary capacitance electrode 17 via the TFT 15. Further, the portion of the auxiliary capacitance line 14 facing the auxiliary capacitance electrode 17 (overlapping via the gate insulating film 16) functions as an auxiliary capacitance counter electrode constituting the auxiliary capacitance. A storage capacitor counter voltage (CS voltage) is supplied to the storage capacitor wiring (storage capacitor counter electrode) 14.

An alignment film 19 is formed on the outermost surface of the TFT substrate 10 (the surface on the liquid crystal layer 30 side). The alignment film 19 is given a pretilt direction by a photo-alignment process. That is, the alignment film 19 is a photo-alignment film.

The counter substrate 20 has a counter electrode 21 that faces the pixel electrode 11. The counter electrode 21 is provided on an insulating transparent substrate (for example, a glass substrate) 20a. An alignment film 29 is formed on the outermost surface of the counter substrate 20 (the surface on the liquid crystal layer 30 side). The alignment film 29 is given a pretilt direction by a photo-alignment process. That is, the alignment film 29 is a photo-alignment film.

Although not shown here, the counter substrate 20 further includes a color filter layer and a light shielding layer (black matrix). The color filter layer corresponds to the red pixel R, the green pixel G, the blue pixel B, and the yellow pixel Y, a red color filter that transmits red light, a green color filter that transmits green light, and blue light. A blue color filter that transmits light and a yellow color filter that transmits yellow light are included.

The liquid crystal panel 1 further includes a pair of

polarizing plates

41 and 42. The pair of

polarizing plates

41 and 42 are opposed to each other with at least the liquid crystal layer 30 therebetween, and are arranged so that their transmission axes (polarization axes) are substantially orthogonal to each other. The tilt directions of the four liquid crystal domains D1 to D4 included in each pixel form an angle of approximately 45 ° with the transmission axes of the pair of

polarizing plates

41 and 42.

As described above, the liquid crystal display device 100 according to this embodiment is a multi-primary color liquid crystal display device that performs display in the 4D-RTN mode.

The driving circuit 2 included in the liquid crystal display device 100 has a vertical line before a vertical scanning period for supplying a display voltage for displaying the highest gradation when the display gradation changes from the lowest gradation to the highest gradation. In the scanning period (typically, the vertical scanning period immediately after the transition), the display voltage for displaying the lowest gradation (the lowest gradation voltage) and the display voltage for performing the highest gradation display (the highest gradation voltage) ) Can be supplied. In the present specification, such a display voltage is referred to as an “undershoot voltage”. In addition, the above-described driving that transiently supplies an undershoot voltage (voltage having an absolute value smaller than the original value) is referred to as “undershoot driving”.

Since the drive circuit 2 performs undershoot driving, the voltage applied to the liquid crystal layer 30 immediately after the transition of the display gradation becomes lower than the original (that is, the torque for depressing the liquid crystal molecules becomes weak), so that the original orientation direction The number of liquid crystal molecules that fall in a different direction from that of the liquid crystal becomes smaller, and the occurrence of alignment defects can be suppressed. Therefore, as a result, the luminance level can be quickly reached the target value.

Fig. 10 shows an example of response speed when undershoot drive is performed. FIG. 10 shows that when only the red pixel R is shifted to the highest gradation from the black display state (the state where all the pixels constituting the color display pixel CP display the lowest gradation), only the green pixel G is the highest. The time when the undershoot voltage is supplied during the vertical scanning period immediately after the transition in the case of transitioning to the gradation, the case of transitioning only the blue pixel B to the maximum gradation, and the case of transitioning only the yellow pixel Y to the maximum gradation. The relationship between (msec) and the luminance level is shown (curves indicated as “black → red”, “black → green”, “black → blue”, “black → yellow” in the figure). Here, one vertical scanning period is about 8.3 msec (that is, double speed driving). Each pixel can perform 256 gradation display (that is, the lowest gradation is 0 and the highest gradation is 255), and the display voltage corresponding to 240 gradations is used as the undershoot voltage.

10 and 20, it can be seen that the response speed is improved for all of the red pixel R, the green pixel G, the blue pixel B, and the yellow pixel Y by performing the undershoot drive. However, when a driving method in which undershoot driving is performed only for the green pixel G and the yellow pixel Y, in which the response speed is significantly reduced due to the occurrence of alignment failure, the white display state (the color display pixel CP is configured from the black display state). When the display state is switched to a state in which all the pixels to be displayed are in the highest gradation), the response is delayed only for the green pixel G and the yellow pixel Y, so the displayed color is colored magenta. End up. Further, when a driving method in which undershoot driving is performed for all of the red pixel R, green pixel G, blue pixel B, and yellow pixel Y is adopted, the display is switched from the black display state to the white display state. The response speed of all the pixels becomes slow (a curve expressed as “black → white” in FIG. 10), and the level of tailing deteriorates. As described above, high-quality display cannot be performed even by simply using undershoot driving.

The driving circuit 2 of the liquid crystal display device 100 according to the present embodiment performs undershoot driving when all the display gradations of the four pixels constituting the color display pixel CP transition from the lowest gradation to the highest gradation. First, the display gradation of the pixel (here, the red pixel R or the blue pixel B, which is the first type pixel) adjacent to the second type pixel (the green pixel G or the yellow pixel Y) in the row direction. When the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation while maintaining the lowest gradation, undershoot driving is performed on the second type pixel. Therefore, in the liquid crystal display device 100, when the display state is switched from the black display state to the white display state, the undershoot drive is not performed, and the display from the black display state to the single color display state by the second type pixel is performed. When the state is switched, undershoot driving is performed for the second type pixel.

Typically, undershoot driving is performed in the vertical scanning period immediately after the transition of the display gradation, in the liquid crystal display device 100 in this embodiment, all the display floors of the four pixels constituting the color display pixel CP are displayed. In the row direction of the second type pixel, the absolute value of the display voltage supplied to the second type pixel in the vertical scanning period immediately after the start of transition when the tone transitions from the lowest gradation to the highest gradation. In the vertical scanning period immediately after the start of transition when the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation while the display gradation of the adjacent pixels remains at the lowest gradation. It can also be said that the absolute value of the display voltage supplied to the pixel of the type is small.

As described above, in the liquid crystal display device 100, when monochromatic display is performed with the second type pixel (pixel having a relatively small width), undershoot driving is performed with respect to the second type pixel. Accordingly, it is possible to suppress a decrease in response speed in the second type pixel, and thus it is possible to suppress the occurrence of colored tailing. In the liquid crystal display device 100, undershoot driving is not performed when white display is performed. Therefore, the response speed at the time of white display does not decrease, and the tailing level does not deteriorate. As described above, the liquid crystal display device 100 according to this embodiment performs selective undershoot driving for a specific pixel, thereby realizing high-quality display.

It should be noted that not only when monochrome display by the second type pixel is performed but also when display close to monochrome display is performed (that is, when the second type pixel transitions to the highest gradation and the adjacent pixels are low). In such a case, it is preferable to perform undershoot driving on the second type pixel even in such a case. Specifically, when the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation, the driving circuit 2 detects the pixel adjacent to the second type pixel along the row direction. Even when the difference between the absolute value of the display voltage for displaying the target gradation and the absolute value of the display voltage for displaying the maximum gradation is 6 V or more, the second type pixel is used. It is preferable to perform undershoot driving. In other words, the absolute value of the display voltage supplied to the second type pixel in the vertical scanning period immediately after the start of transition when the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation is The difference between the absolute value of the display voltage for displaying the target gradation of the pixel adjacent to the second type pixel in the row direction and the absolute value of the display voltage for displaying the maximum gradation is It is preferable that the case of 6V or more is smaller than the case of less than 6V.

In the above description, the display voltage corresponding to 240 gradations is exemplified as the undershoot voltage, but the undershoot voltage is not limited to this. However, if the undershoot voltage is too high (that is, too close to the maximum gradation voltage), the occurrence of orientation failure may not be sufficiently suppressed. If the undershoot voltage is too low, the rise of the luminance level is slow. Therefore, it may take a long time to reach the target luminance level. For this reason, the undershoot voltage is preferably set to an appropriate level that can sufficiently prevent the occurrence of alignment failure and can quickly reach the target luminance level. The display voltage is preferably 0.5 to 0.9 times, more preferably 0.7 to 0.8 times the display voltage for displaying the tone.

As described above, in the liquid crystal display device 100, it is possible to suppress a decrease in response speed when performing a monochrome display with a second type (that is, a relatively small width) of pixels.

In the above description, the case where the first type pixel and the second type pixel are alternately arranged along the row direction is illustrated, but the first type pixel and the second type pixel are illustrated as examples. The arrangement of the type pixels is not limited to this.

FIG. 11 shows another example of the arrangement of the first type pixel and the second type pixel. In the example shown in FIG. 11, a plurality of pixels in the color display pixel CP are arranged in the order of red pixel R, yellow pixel Y, green pixel G, and blue pixel B from the left side to the right side. That is, the first type pixel, the second type pixel, the second type pixel, and the first type pixel are arranged from the left side to the right side. In other words, a plurality of second type pixels (green pixel G and yellow pixel Y) are arranged in the color display pixel CP so as to be continuous in the row direction.

(Embodiment 2)
The liquid crystal display device in this embodiment can perform multi-pixel driving (pixel division driving). According to the multi-pixel driving, the problem that the γ characteristic (gamma characteristic) observed from the front direction is different from the γ characteristic observed from the oblique direction, that is, the viewing angle dependency of the γ characteristic is improved. Here, the γ characteristic is the gradation dependency of display luminance. In multi-pixel driving, one pixel is composed of a plurality of sub-pixels that can display different luminances, and a predetermined luminance corresponding to a display signal input to the pixels is displayed. In other words, multi-pixel driving is a technique for improving the viewing angle dependency of the γ characteristics of pixels by combining different γ characteristics of a plurality of sub-pixels.

FIG. 12 shows a liquid crystal display device 200 according to this embodiment. FIG. 12 is a plan view showing a region corresponding to one color display pixel (four pixels of red pixel R, green pixel G, blue pixel B, and yellow pixel Y) of the liquid crystal display device 200. Each pixel of the liquid crystal display device 200 has a plurality of sub-pixels sp1 and sp2 that can apply different voltages to the liquid crystal layer in each pixel. A plurality (specifically two) of sub-pixels sp1 and sp2 are arranged along the column direction. Although two subpixels sp1 and sp2 are illustrated here, each pixel may have three or more subpixels.

The pixel electrode 11 of each pixel has two

subpixel electrodes

11A and 11B so as to correspond to the two subpixels sp1 and sp2. The two

subpixel electrodes

11A and 11B are connected to the corresponding

TFTs

15A and 15B, respectively.

The gate electrodes of the two

TFTs

15A and 15B are connected to the common scanning wiring 12, and are on / off controlled by the same gate signal. The source electrodes of the two

TFTs

15A and 15B are connected to a common signal line 13.

An auxiliary capacitor is provided for each of the two sub-pixels sp1 and sp2. The auxiliary capacitance electrode 17 constituting the auxiliary capacitance of one subpixel sp1 is electrically connected to the drain electrode of the TFT 15A, and the auxiliary capacitance electrode 17 constituting the auxiliary capacitance of the other subpixel sp2 is connected to the drain of the TFT 15B. It is electrically connected to the electrode. Further, the storage capacitor counter electrode 14b constituting the storage capacitor of the sub-pixel sp1 is electrically connected to the storage capacitor line 14A, and the storage capacitor counter electrode 14b forming the storage capacitor of the sub-pixel sp2 is connected to the storage capacitor line 14B. Is electrically connected. Accordingly, the storage capacitor counter electrode 14b of the subpixel sp1 and the storage capacitor counter electrode 14b of the subpixel sp2 are independent from each other, and different voltages (CS voltages) are supplied from the

storage capacitor lines

14A and 14B, respectively. By changing the CS voltage supplied to the storage capacitor counter electrode 14b, the effective voltage applied to the liquid crystal layer 30 of the sub-pixel sp1 and the liquid crystal layer 30 of the sub-pixel sp2 is made different by using capacitive division. Accordingly, the display luminance can be different between the sub-pixel sp1 and the sub-pixel sp2.

Similarly to the liquid crystal display device 100, the liquid crystal display device 200 performs display in the 4D-RTN mode. That is, each pixel of the liquid crystal display device 200 has the same quadrant alignment structure as any of the pixels P1 to P4 shown in FIGS. From the viewpoint of viewing angle characteristics, it is more preferable that each of the sub-pixel sp1 and the sub-pixel sp2 has a quadrant alignment structure.

Also, as shown in FIG. 12, in the liquid crystal display device 200 as well, the green pixels G and the yellow pixels Y are arranged in the row directions rather than the widths of the red pixels R and the blue pixels B in the row directions. The width is small. That is, the red pixel R and the blue pixel B are “first type” pixels, and the green pixel G and the yellow pixel Y are “second type” pixels.

Furthermore, the liquid crystal display device 200 according to the present embodiment also performs selective undershoot driving for the second type of pixels, similarly to the liquid crystal display device 100 according to the first embodiment. For this reason, it is possible to suppress a decrease in response speed when performing monochrome display with the second type pixel, and thus it is possible to suppress the occurrence of colored tailing. Further, the response speed at the time of white display does not decrease, and the tailing level does not deteriorate. Therefore, the liquid crystal display device 200 in the present embodiment can also perform high-quality display.

(Other embodiments)
In the first and second embodiments, the case where the red pixel R and the blue pixel B are the first type pixels and the green pixel G and the yellow pixel Y are the second type pixels is exemplified. Is not limited to this. For example, only one of the green pixel G and the yellow pixel Y may be the second type pixel. Which pixel has a relatively large width (that is, which pixel has a relatively large area) may be appropriately determined in accordance with the application, specifications, and the like of the liquid crystal display device.

In the first and second embodiments, a configuration in which a plurality of pixels are arranged in one row and a plurality of columns in the color display pixel CP is illustrated. However, as in the liquid crystal display device 300 illustrated in FIG. A plurality of pixels may be arranged in a plurality of rows and a plurality of columns. In the example shown in FIG. 13, a red pixel R as a first type pixel and a green pixel G as a second type pixel are alternately arranged in a certain pixel row. Blue pixels B that are one type of pixels and yellow pixels Y that are a second type of pixels are alternately arranged. Therefore, four pixels are arranged in 2 rows and 2 columns in the color display pixel CP.

Furthermore, the number of the plurality of pixels constituting the color display pixel CP is not limited to four. The present invention is widely used in a liquid crystal display device in which the color display pixel CP includes four or more pixels that display different colors. For example, the color display pixel CP may be configured by five pixels, or may be configured by six pixels as in the liquid crystal display device 400 illustrated in FIG. In the example illustrated in FIG. 14, the color display pixel CP includes a cyan pixel C that displays cyan and a magenta pixel M that displays magenta in addition to the red pixel R, green pixel G, blue pixel B, and yellow pixel Y. .

Also, the type (combination) of the pixels constituting the color display pixel CP is not limited to the above example. For example, when the color display pixel CP is configured by four pixels, the color display pixel CP may be configured by the red pixel R, the green pixel G, the blue pixel B, and the cyan pixel C, or the red pixel R, the green pixel The color display pixel CP may be configured by G, the blue pixel B, and the magenta pixel M. Further, like the liquid crystal display device 500 shown in FIG. 15, the color display pixel CP may be configured by a red pixel R, a green pixel G, a blue pixel B, and a white pixel W that displays white. When the configuration shown in FIG. 15 is adopted, a color filter that is colorless and transparent (that is, transmits white light) is provided in a region corresponding to the white pixel W of the color filter layer of the counter substrate. In the configuration of FIG. 15, since the added primary color is white, the effect of widening the color reproduction range cannot be obtained, but the display luminance of one color display pixel CP can be improved.

In the liquid

crystal display devices

300, 400, and 500 shown in FIGS. 13, 14, and 15 as well, the liquid crystal display device 100 according to the first and second embodiments is performed by performing selective undershoot driving for the second type pixels. As with 200 and 200, high-quality display can be performed.

Further, in the above description, the color display pixel CP includes only the first type pixel and the second type pixel, that is, there are two types of pixel widths along the row direction in the color display pixel CP. However, the width of the pixel along the row direction may be three or more types. For example, the color display pixel CP includes a first type pixel whose width along the row direction is a predetermined first width, and a second width whose width along the row direction is smaller than the first width. In addition to the second type of pixels, the pixel further includes a “third type” pixel having a width along the row direction smaller than the first width and larger than the second width. Also good.

According to the present invention, when a 4D-RTN mode is adopted in a multi-primary color liquid crystal display device in which a plurality of pixels constituting a color display pixel include pixels having different widths from other pixels, Decrease in display quality due to a decrease in response speed can be suppressed. The liquid crystal display device according to the present invention is suitably used for applications that require high quality display such as television receivers.

10 Active matrix substrate (TFT substrate)
10a, 20a Transparent substrate 11

Pixel electrode

11A, 11B Subpixel electrode 12 Scanning wiring 13

Signal wiring

14, 14A, 14B Auxiliary capacitance wiring 14a Branch portion 14b Auxiliary

capacitance counter electrode

15, 15A, 15B Thin film transistor (TFT)
16 Gate insulating film 17 Auxiliary capacitor electrode 18

Interlayer insulating film

19, 29 Alignment film 20 Counter substrate (color filter substrate)
21 counter electrode 29 alignment film 30

liquid crystal layer

41, 42

polarizing plate

100, 200, 300, 400, 500 liquid crystal display device CP color display pixel P1, P2, P3, P4 pixel R red pixel G green pixel B blue pixel Y yellow pixel C Cyan pixel M Magenta pixel W White pixel sp1, sp2 Sub-pixel D1 to D4 Liquid crystal domain DR Dark region SL Linear dark line CL Cross-shaped dark line

Claims

A liquid crystal display device having a plurality of pixels arranged in a matrix having a plurality of rows and a plurality of columns, wherein four or more pixels displaying different colors constitute a color display pixel,
A liquid crystal panel having a vertically aligned liquid crystal layer and a first substrate and a second substrate facing each other with the liquid crystal layer interposed therebetween;
A drive circuit that supplies a display voltage to each of the plurality of pixels for each vertical scanning period;
The four or more pixels constituting the color display pixel include a first type pixel whose width along the row direction is a predetermined first width, and a width along the row direction that is the first width. A second type of pixel having a second width less than
When the display gray level transitions from the lowest gray level to the highest gray level, the driving circuit performs the lowest step in the vertical scanning period before the vertical scanning period for supplying the display voltage for performing the highest gray level display. Undershoot drive for supplying an undershoot voltage having a magnitude between a display voltage for displaying a tone and a display voltage for displaying a maximum gradation can be performed.
Furthermore, the drive circuit does not perform the undershoot drive when all the display gradations of the four or more pixels constituting the color display pixel transition from the lowest gradation to the highest gradation. When the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation while the display gradation of the pixel adjacent to the second type pixel in the row direction remains the lowest gradation. Is a liquid crystal display device that performs the undershoot drive on the second type of pixel.
When the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation, the drive circuit performs a target gradation of a pixel adjacent to the second type pixel in the row direction. Undershoot driving for the second type of pixel even when the difference between the absolute value of the display voltage for performing display and the absolute value of the display voltage for performing display of the highest gradation is 6 V or more The liquid crystal display device according to claim 1.
3. The liquid crystal display device according to claim 1, wherein the undershoot voltage is not less than 0.5 times and not more than 0.9 times a display voltage for displaying a maximum gradation.
A liquid crystal display device having a plurality of pixels arranged in a matrix having a plurality of rows and a plurality of columns, wherein four or more pixels displaying different colors constitute a color display pixel,
A liquid crystal panel having a vertically aligned liquid crystal layer and a first substrate and a second substrate facing each other with the liquid crystal layer interposed therebetween;
A drive circuit that supplies a display voltage to each of the plurality of pixels for each vertical scanning period;
The four or more pixels constituting the color display pixel include a first type pixel whose width along the row direction is a predetermined first width, and a width along the row direction that is the first width. A second type of pixel having a second width less than
All the display gradations of the four or more pixels constituting the color display pixel are supplied to the second type pixel in the vertical scanning period immediately after the start of transition when transitioning from the lowest gradation to the highest gradation. The display gradation of the pixel of the second type is the lowest level while the display gradation of the pixel adjacent to the second type pixel in the row direction remains at the lowest gradation. A liquid crystal display device in which an absolute value of a display voltage supplied to the second type pixel is small in a vertical scanning period immediately after the start of transition when transitioning from a gray level to a maximum gray level.
The absolute value of the display voltage supplied to the second type pixel in the vertical scanning period immediately after the start of transition when the display gradation of the second type pixel transitions from the lowest gradation to the highest gradation is: The difference between the absolute value of the display voltage for displaying the target gradation of the pixel adjacent to the second type pixel in the row direction and the absolute value of the display voltage for displaying the maximum gradation is The liquid crystal display device according to claim 4, wherein the case of 6V or more is smaller than the case of less than 6V.
6. The liquid crystal display according to claim 1, wherein the four or more pixels constituting the color display pixel include a red pixel that displays red, a green pixel that displays green, and a blue pixel that displays blue. apparatus.
The liquid crystal display device according to claim 6, wherein the four or more pixels constituting the color display pixel further include a yellow pixel for displaying yellow.
The red pixel and the blue pixel are each the first type of pixel,
The liquid crystal display device according to claim 7, wherein at least one of the green pixel and the yellow pixel is the second type pixel.
The four or more pixels constituting the color display pixel are four pixels of the red pixel, the green pixel, the blue pixel, and the yellow pixel,
The liquid crystal display device according to claim 8, wherein both the green pixel and the yellow pixel are the second type pixels.
The first substrate has a first alignment film provided on the surface on the liquid crystal layer side,
The second substrate has a second alignment film provided on the surface on the liquid crystal layer side,
Each of the plurality of pixels has a first direction in which a tilt direction of liquid crystal molecules in the layer surface of the liquid crystal layer and in the vicinity of the center in the thickness direction when a voltage is applied to the liquid crystal layer is a predetermined first direction. A liquid crystal domain, a second liquid crystal domain in the second direction, a third liquid crystal domain in the third direction, and a fourth liquid crystal domain in the fourth direction, wherein the first direction, the second direction, 10. The liquid crystal display device according to claim 1, wherein the third direction and the fourth direction are four directions in which a difference between any two directions is substantially equal to an integral multiple of 90 °.
11. The first liquid crystal domain, the second liquid crystal domain, the third liquid crystal domain, and the fourth liquid crystal domain are adjacent to other liquid crystal domains and are arranged in a matrix of 2 rows and 2 columns. Liquid crystal display device.
12. The liquid crystal display according to claim 11, wherein the first liquid crystal domain, the second liquid crystal domain, the third liquid crystal domain, and the fourth liquid crystal domain are arranged so that the tilt direction differs by approximately 90 ° between adjacent liquid crystal domains. apparatus.
The liquid crystal display device according to claim 12, wherein the first direction is approximately 45 °, approximately 135 °, approximately 225 °, or approximately 315 ° when the horizontal azimuth angle on the display surface is 0 °.
The liquid crystal panel further includes a pair of polarizing plates that are opposed to each other through the liquid crystal layer and are arranged so that their transmission axes are substantially orthogonal to each other,
The liquid crystal display device according to claim 10, wherein the first direction, the second direction, the third direction, and the fourth direction form an angle of about 45 ° with the transmission axis of the pair of polarizing plates.
The liquid crystal layer includes liquid crystal molecules having negative dielectric anisotropy,
The liquid crystal display device according to claim 10, wherein a pretilt direction defined by the first alignment film and a pretilt direction defined by the second alignment film differ from each other by approximately 90 °.
16. The liquid crystal display device according to claim 10, wherein a pretilt angle defined by the first alignment film and a pretilt angle defined by the second alignment film are substantially equal to each other.
The liquid crystal display device according to claim 10, wherein each of the first alignment film and the second alignment film is a photo-alignment film.