JP2009053589A - Liquid crystal display and method for driving liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display using a VA mode liquid crystal, in which viewing angle characteristics of luminance and chromaticity are improved. <P>SOLUTION: When liquid crystal elements 22A, 22B in each pixel 20 using a VA mode liquid crystal are driven to display, the display driving of each pixel 20 is spatially divided into two to carry out division driving. This disperses changes in the gamma characteristics when the display screen is viewed in an oblique direction and improves viewing angle characteristics of the luminance compared with an operation without division driving. The maximum difference in driving voltages applied to the liquid crystal elements 22A, 22B in each division driving is controlled to be different from one another for the different pixels corresponding to R, G and B. The gamma characteristics when the display screen is viewed in an oblique direction can be individually adjusted for each of the pixels corresponding to R, G and B. Thus, coloring in an intermediate tone is decreased when the display screen is viewed in an oblique direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device composed of vertically aligned (VA) mode liquid crystal and a driving method of such a liquid crystal display device.

  In recent years, a liquid crystal display device adopting, for example, a VA (Vertical Alignment) mode using a vertically aligned liquid crystal has been proposed as a display monitor for a liquid crystal television, a notebook personal computer, a car navigation system, and the like. In this VA mode, liquid crystal molecules have a negative dielectric anisotropy, that is, the property that the dielectric constant in the major axis direction of the molecule is smaller than that in the minor axis direction, and is wider than that of the TN (Twisted Nematic) mode. A viewing angle can be realized.

  However, in a liquid crystal display device using a VA mode liquid crystal, there is a problem that the luminance varies depending on whether the display screen is viewed from the front direction or from an oblique direction. FIG. 18 shows the relationship between the gradation of the video signal (0 to 255 gradations) and the luminance ratio (luminance ratio with respect to the luminance at 255 gradations) in the liquid crystal display device using the VA mode liquid crystal. is there. As indicated by the arrow P101 in the figure, the luminance characteristics are significantly different when viewed from the front direction (Ys (0 °)) and when viewed from the 45 degree direction (Ys (45 °)). It can be seen that (the brightness fluctuates in the direction of increasing). Such a phenomenon is called “Shirachacha”, “Wash out”, “Color Shift” or the like, and is regarded as the biggest defect in a liquid crystal display device using a VA mode liquid crystal.

  Therefore, as a measure for improving such a “shattering” phenomenon, a unit pixel is separated into a plurality of sub-pixels, and the threshold value of each sub-pixel is changed (multi-pixel structure). It has been proposed (for example, Patent Documents 1 to 3). These multi-pixel structures shown in Patent Documents 1 to 3 are called the HT (halftone gray scale) method by capacitive coupling, and the potential difference between the two sub-pixels is determined by the capacitance ratio. Yes.

  FIG. 19 shows an example of the relationship between the gradation of the video signal and the display mode of each sub-pixel in the multi-pixel structure. In the process of increasing the gradation from 0 gradation (black display state) to 255 gradation (white display state) (increasing luminance), first, the luminance of a part (one sub-pixel) of the pixel is increased. Subsequently, it can be seen that the luminance of the other part of the pixel (the other sub-pixel) increases. According to such a multi-pixel structure, for example, as indicated by an arrow P102 in FIG. 18, the luminance characteristic (Ym (45 °)) in the 45 ° direction in the multi-pixel structure is 45 ° in the normal pixel structure. It can be seen that the “shattering” phenomenon is improved as compared with the luminance characteristic in the direction (Ys (45 °)).

  In addition to such a multi-pixel structure, in a normal pixel structure, a unit frame for display driving is temporally divided into a plurality of (for example, two) sub-frames, and a desired luminance is set to a high-luminance sub-frame. By dividing and expressing using frames and low-brightness subframes, the effect of “slack” can be improved by obtaining a halftone effect as in the case of the multi-pixel structure. I know it.

Japanese Patent Laid-Open No. 2-12 US Pat. No. 4,840,460 Japanese Patent No. 3076938

  However, when such a halftone technique is used, when the display screen is viewed from an oblique direction (for example, 45 ° direction), the values of chromaticity x and y are halftone as shown in FIG. 20, for example. In both cases, there is a problem in that both colors increase and have a peak, so that they appear yellow in a halftone. That is, by using the halftone technique as described above, the viewing angle characteristic of luminance is improved, but conversely, the viewing angle characteristic of chromaticity is deteriorated.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a liquid crystal display device and a liquid crystal display device capable of improving the viewing angle characteristics of luminance and chromaticity in a liquid crystal display device using a VA mode liquid crystal. It is to provide a method for driving a display device.

  The liquid crystal display device of the present invention is based on a video signal with respect to a plurality of pixels which are arranged in a matrix as a whole and have liquid crystal elements composed of liquid crystal in a vertical alignment (VA) mode, and the liquid crystal elements of each pixel. Drive means for performing display drive by applying a voltage. Here, the pixel is composed of pixels corresponding to R (Red), G (Green), or B (Blue). The driving means divides the display drive for each pixel into a plurality of spatially or temporally based on the video signal to perform the divided drive, and the difference in voltage applied to the liquid crystal element at the time of each divided drive. The division driving is performed so that the maximum value of the pixel is different for each of the pixels corresponding to R, G, and B.

  A driving method of a liquid crystal display device of the present invention includes a plurality of pixels that are arranged in a matrix as a whole and have liquid crystal elements formed of liquid crystal in a vertical alignment (VA) mode, and these pixels are R (Red: Red: This is applied to a liquid crystal display device constituted by pixels corresponding to red (red), G (green) or B (blue), and a voltage based on a video signal is applied to the liquid crystal element of each pixel. When performing display drive by applying, the display drive for each pixel is divided into a plurality of spatially or temporally divided drives based on the video signal, and applied to the liquid crystal element during each divided drive. The division drive is performed so that the maximum value of the difference between the voltages to be applied is different for each pixel corresponding to R, G, and B.

  In the liquid crystal display device and the driving method of the liquid crystal display device of the present invention, the display drive for each pixel is spatially or temporally based on the video signal when the display drive for the liquid crystal element of each pixel using VA mode liquid crystal is performed. Therefore, the gamma characteristic when the display screen is viewed from an oblique direction (representing the relationship between the gradation of the video signal and the luminance) is compared with the case where the division driving is not performed. Variations in characteristics) (variations when viewing the display screen from the front) are dispersed. In addition, since the maximum value of the voltage difference applied to the liquid crystal element in each divided drive is different for each pixel corresponding to R, G, B, the maximum value of the voltage difference is R, G, Unlike the conventional case where the pixels corresponding to B are equal to each other, the gamma characteristics when the display screen is viewed from an oblique direction can be individually adjusted for each pixel corresponding to R, G, and B.

In the liquid crystal display device of the present invention, the driving means satisfies the following expression among the pixels corresponding to R, G, and B, with the maximum value of the voltage difference applied to the liquid crystal element in each divided drive. Thus, it is preferable to perform division driving. When configured in this way, it is possible to perform adjustment such that the luminance increase ratios in the pixels corresponding to R, G, and B are substantially equal in the gamma characteristics when the display screen is viewed from an oblique direction. Therefore, coloring to yellow in a halftone when the display screen is viewed from an oblique direction is reduced.
(Maximum value at the pixel corresponding to R) ≧ (Maximum value at the pixel corresponding to G) ≧ (Maximum value at the pixel corresponding to B)

  According to the liquid crystal display device or the driving method of the liquid crystal display device of the present invention, when the display driving for the liquid crystal element of each pixel using the VA mode liquid crystal, the display driving for each pixel is made spatially or temporally plural. Compared to the case where the division driving is not performed, the gamma characteristic variation when the display screen is viewed from an oblique direction can be dispersed and the luminance viewing angle characteristic can be dispersed. Can be improved. In addition, since the maximum value of the difference in voltage applied to the liquid crystal element in each divided drive is different for each pixel corresponding to R, G, B, the display screen is viewed from an oblique direction. In this case, it is possible to individually adjust the gamma characteristic for each pixel corresponding to R, G, and B, and it is possible to reduce halftone coloring when the display screen is viewed from an oblique direction. Therefore, it is possible to improve viewing angle characteristics of luminance and chromaticity in a liquid crystal display device using a VA mode liquid crystal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an overall configuration of a liquid crystal display device (liquid crystal display device 1) according to an embodiment of the present invention. The liquid crystal display device 1 includes a liquid crystal display panel 2, a backlight unit 3, an image processing unit 41, a multi-pixel conversion unit 43, a reference voltage generation unit 45, a data driver 51, a gate driver 52, a timing, A control unit 61 and a backlight control unit 63 are provided. Note that the driving method of the liquid crystal display device according to the present embodiment is embodied by the liquid crystal display device of the present embodiment, and will be described below.

  The backlight unit 3 is a light source that irradiates light to the liquid crystal display panel 2, and includes, for example, a CCFL (Cold Cathode Fluorescent Lamp), an LED (Light Emitting Diode), and the like. The

  The liquid crystal display panel 2 is based on the video signal Din by modulating the light emitted from the backlight unit 3 based on the drive voltage supplied from the data driver 51 in accordance with the drive signal supplied from the gate driver 52 described later. The video display is performed, and includes a plurality of pixels 20 arranged in a matrix as a whole. Each pixel 20 is a pixel provided with a color filter (not shown) for R, G, B corresponding to R (Red :), G (Green: Green) or B (Blue: Blue), R, G, B color pixels that emit display light). In each pixel 20, a pixel circuit including two subpixels (subpixels 20A and 20B described later) is formed. The detailed configuration of this pixel circuit will be described later (FIGS. 2 and 3).

  The image processing unit 41 generates a video signal D1 that is an RGB signal by performing predetermined image processing on the external video signal Din.

  The multi-pixel conversion unit 43 converts the video signal D1 supplied from the image processing unit 41 into two video signals D2a and D2b for each sub-pixel by using a look-up table (LUT) described later (multi-pixel). The video signal D2a and D2b are supplied to the timing control unit 61. This LUT associates the gradation of the luminance level of the video signal D1 and the gradation of the luminance level of the video signal corresponding to each sub-pixel for each video signal of the pixels corresponding to R, G, and B. Is. Details of the LUT will be described later (FIGS. 4 to 8).

  The reference voltage generation unit 45 supplies the data driver 51 with a reference voltage Vref used when performing D / A (digital / analog) conversion described later. Specifically, the reference voltage Vref is composed of a plurality of reference voltages from a black voltage (a voltage having a luminance level of 0 gradation described later) to a white voltage (for example, a voltage having a luminance level of 255 gradation described later). Has been. In this embodiment, the reference voltage Vref is common among pixels corresponding to R, G, and B. The reference voltage generation unit 45 is configured by, for example, a resistance tree structure in which a plurality of resistors are connected in series.

  The gate driver 52 drives each pixel 20 in the liquid crystal display panel 2 line-sequentially along a scanning line (not shown) (a gate line G to be described later) according to timing control by the timing control unit 61.

  The data driver 51 supplies a drive voltage based on the video signals D2a and D2b supplied from the timing control unit 61 to each pixel 20 (more specifically, each subpixel in each pixel 20) of the liquid crystal display panel 2. To do. More specifically, the data driver 51 performs D / A conversion on the video signals D2a and D2b using the reference voltage Vref supplied from the reference voltage generation unit 45, so that the video signal that is an analog signal is obtained. (The driving voltage) is generated and output to each pixel 20.

  The backlight drive unit 62 controls the lighting operation of the backlight unit 3. The timing control unit 61 controls the driving timing of the gate driver 52 and the data driver 51 and supplies the video signals D2a and D2b to the data driver 51.

  Next, the configuration of the pixel circuit formed in each pixel 20 will be described in detail with reference to FIGS. 2 and 3. FIG. 2 shows a circuit configuration example of the pixel circuit in the pixel 20. FIG. 3 shows a planar configuration example of the pixel electrode in the liquid crystal element in the pixel circuit.

  The pixel 20 includes two sub-pixels 20A and 20B and has a multi-pixel structure. The sub-pixel 20A includes a liquid crystal element 22A that is a main capacitive element, an auxiliary capacitive element 23A, and a thin film transistor (TFT) element 21A. Similarly, the sub-pixel 20B includes a liquid crystal element 22B as a main capacitor, an auxiliary capacitor 23B, and a TFT element 21B. Further, the pixel 20 includes a gate line G for line-sequentially selecting a pixel to be driven and a driving voltage (supplied from the data driver 51) for each of the sub-pixels 20A and 20B with respect to the pixel to be driven. Drive data) and one auxiliary capacitance line Cs which is a bus line for supplying a predetermined reference potential to the counter electrode side of the auxiliary capacitance elements 23A and 23B. And are connected.

  The liquid crystal element 22A functions as a display element that performs an operation for display (emits display light) according to a drive voltage supplied to one end from the data line DA via the TFT element 21A. Similarly, the liquid crystal element 22B functions as a display element that performs an operation for display (emits display light) in accordance with a drive voltage supplied to one end from the data line DB via the TFT element 21B. Yes. Each of the liquid crystal elements 22A and 22B includes a liquid crystal layer (not shown) made of VA mode liquid crystal and a pair of electrodes (not shown) sandwiching the liquid crystal layer. One (one end) side (reference numeral P1A, P1B side in FIG. 2) of the pair of electrodes is connected to the sources of the TFT elements 21A, 21B and one ends of the auxiliary capacitance elements 23A, 23B, and the other (the other end). The side is grounded. In addition, an electrode on one side of the pair of electrodes (reference P1A, P1B side in FIG. 2) is a pixel electrode 220 having a planar shape as shown in FIG. 3, for example, and is a pixel on the sub-pixel 20A side. An electrode and a pixel electrode on the side of the sub-pixel 20B (consisting of 20B-1 and 20B-2) are configured.

  The auxiliary capacitance elements 23A and 23B are capacitance elements for stabilizing the accumulated charges of the liquid crystal elements 22A and 22B. One end (one electrode) of the auxiliary capacitance element 23A is connected to one end of the liquid crystal element 22A and the source of the TFT element 21A, and the other end (counter electrode) is connected to the auxiliary capacitance line Cs. One end (one electrode) of the auxiliary capacitance element 23B is connected to one end of the liquid crystal element 22B and the source of the TFT element 21B, and the other end (counter electrode) is connected to the auxiliary capacitance line Cs.

  The TFT element 21A is composed of a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor), the gate is connected to the gate line G, the source is connected to one end of the liquid crystal element 22A, and one end of the auxiliary capacitance element 23A. The drain is connected to the data line DA. The TFT element 21A functions as a switching element for supplying a driving voltage (driving voltage based on the video signal D2a) for the sub-pixel 20A to one end of the liquid crystal element 22A and one end of the auxiliary capacitive element 23A. Specifically, in accordance with a selection signal supplied from the gate driver 52 through the gate line G, the data line DA and one end of the liquid crystal element 22A and the auxiliary capacitance element 23A are selectively conducted. It has become.

  Similarly, the TFT element 21B is composed of a MOS-FET, the gate is connected to the gate line G, the source is connected to one end of the liquid crystal element 22B and one end of the auxiliary capacitance element 23B, and the drain is connected to the data line DB. ing. The TFT element 21B functions as a switching element for supplying a driving voltage for the sub-pixel 20B (a driving voltage based on the video signal D2b) to one end of the liquid crystal element 22B and one end of the auxiliary capacitive element 23B. Specifically, in accordance with a selection signal supplied from the gate driver 52 via the gate line G, the data line DB and one end of the liquid crystal element 22B and the auxiliary capacitance element 23B are selectively conducted. It has become.

  Next, the LUT used in the multi-pixel conversion unit 43 will be described in detail with reference to FIGS. In the characteristic diagrams described below, as an example, the luminance level gradation is set from 0/255 gradation (black display state) to 255/255 gradation (white display state). .

  For example, as shown in FIG. 4, the LUT uses the gradation of the luminance level (corresponding to the straight line LO in the figure) of the video signal D1 supplied to the multi-pixel conversion unit 43 as the video signal D2a for the sub-pixel 20A. Luminance level gradation (corresponding to the curves Ra, Ga, Ba in the figure) and the luminance level gradation of the video signal D2b for the sub-pixel 20B (corresponding to the curves Rb, Gb, Bb in the figure). It is for dividing. In other words, the display driving for each pixel 20 is spatially divided into two for each of the sub-pixels 20A and 20B based on the video signal D1, and is used for the division driving. The curves Ra and Rb in the figure are used for the video signal D1 of the pixel corresponding to R, and the curves Ga and Gb are used for the video signal D1 of the pixel corresponding to G. The curves Ba and Bb are used for the video signal D1 of the pixel corresponding to B.

For example, as shown in FIG. 5, in this LUT, the maximum value of the difference between the drive voltage applied to the liquid crystal element 22A of the sub-pixel 20A and the drive voltage applied to the liquid crystal element 22B of the sub-pixel 20B is In order to make the pixels corresponding to R, G, and B different from each other, the gradation of the luminance level of the video signal corresponding to the sub-pixel 20A and the level of the luminance level of the video signal corresponding to the sub-pixel 20B. The maximum values of the tone and the difference ("A gradation-B gradation" on the vertical axis in the figure) are different for each pixel corresponding to R, G, and B. That is, the maximum value Rmax of the difference Ra-b at the pixel corresponding to R, the maximum value Gmax of the difference Ga-b at the pixel corresponding to G, and the maximum value of the difference Ba-b at the pixel corresponding to B Bmax is different from each other. Specifically, the maximum value Rmax of the difference Ra-b at the pixel corresponding to R, the maximum value Gmax of the difference Ga-b at the pixel corresponding to G, and the difference Ba at the pixel corresponding to B The following equation (1) is satisfied between the maximum value Bmax of -b.
(Maximum value Rmax of difference Ra-b at the pixel corresponding to R) ≧ (maximum value Gmax of difference Ga-b at the pixel corresponding to G) ≧ (maximum of difference Ba-b at the pixel corresponding to B Value Bmax) (1)

The LUT is created as follows. That is, first, as in the LUT shown in FIG. 6, for example, the curves Ra0, Ga0, Ba0 and the curves Rb0, Gb0, Bb0 corresponding to R, G, B correspond to R, G, B. Each pixel is created based on an LUT that is different from each other and satisfies the following expressions (2) and (3). Specifically, based on the LUT as shown in FIG. 6, for example, the wavelength dependency of the transmittance (I / I0) as shown in FIG. 7 (light in the wavelength region of R (for example, the wavelength is 620 nm) Transmittance IR of light in the G wavelength region (for example, light having a wavelength of 550 nm), and transmittance IB of light in the wavelength region of B (for example, light having a wavelength of 460 nm). However, in consideration of the change in the horizontal axis (Δnd; the birefringence of the liquid crystal (corresponding to the voltage applied to the liquid crystal element)) in FIG. As described above, the chromaticity x, y in the front direction of the display screen of the liquid crystal display panel 2 is flat with respect to the change in the gradation of the luminance level of the video signal D1 (the chromaticity curves x0, y0 are respectively As shown by the arrows in the figure, the chromaticity curves x1 and y1 , By adjusting the curve Ra0, Ga0, Ba0 and curve Rb0, Gb0, BB0, is LUT shown in FIG. 4 is created.
Ra0 ≧ Ga0 ≧ Ba0 (2)
Rb0 ≧ Gb0 ≧ Bb0 (3)

  Here, the multi-pixel conversion unit 43, the timing control unit 61, the reference voltage generation unit 45, the data driver 51, and the gate driver 52 correspond to a specific example of “driving means” in the present invention. Further, the LUT shown in FIG. 4 corresponds to a specific example of “first LUT” in the present invention.

  Next, the operation of the liquid crystal display device 1 of the present embodiment having such a configuration will be described in detail.

  First, the basic operation of the liquid crystal display device 1 will be described with reference to FIGS.

  In the liquid crystal display device 1, as shown in FIG. 1, the video signal Din supplied from the outside is subjected to image processing by the image processing unit 41, and the video signal D 1 for each pixel 20 is generated. The video signal D1 is supplied to the multi-pixel conversion unit 43. In the multi-pixel conversion unit 43, the supplied video signal D1 is converted into two video signals D2a and D2b for the sub-pixels 20A and 20B by using the above-described LUT (multi-pixel conversion). These two video signals D2a and D2b are supplied to the data driver 51 via the timing control unit 61, respectively. In the data driver 51, D / A conversion is performed on the video signals D2a and D2b using the reference voltage Vref supplied from the reference voltage generation unit 45, and two video signals that are analog signals are generated. Based on these two video signals, a line-sequential display driving operation is performed for each pixel 20 by driving voltages to the sub-pixels 20A and 20B in each pixel 20 output from the gate driver 52 and the data driver 51. Specifically, as shown in FIGS. 2 and 3, the TFT elements 21A and 21B are turned on / off according to a selection signal supplied from the gate driver 52 via the gate line G, and the data line By selectively conducting between DA and DB and the liquid crystal elements 22A and 22B and the auxiliary capacitance elements 23A and 23B, the driving voltage based on the two video signals supplied from the data driver 51 is changed to the liquid crystal elements 22A and 22B. Then, it is supplied to the auxiliary capacitance elements 23A and 23B, and a display driving operation is performed.

  Then, in the pixel 20 in which the data lines DA and DB are connected to the liquid crystal elements 22A and 22B and the auxiliary capacitance elements 23A and 23B, the illumination light from the backlight unit 30 is modulated in the liquid crystal display panel 2 and the display light is displayed. Is output as Thereby, video display based on the video signal Din is performed in the liquid crystal display device 1.

  Next, with reference to FIGS. 2 and 6 to 12 in addition to FIGS. 1 to 4, characteristic portions of the driving operation of the liquid crystal display device of the present invention will be described in detail in comparison with a comparative example. Here, FIG. 9 to FIG. 11 are for explaining the LUT in the conventional liquid crystal display device according to the comparative example.

  First, in the liquid crystal display device 1 of the present embodiment, by using the LUT shown in FIG. 4, the video signal D1 is displayed when the liquid crystal elements 22A and 22B of each pixel 20 using the VA mode liquid crystal are displayed. Based on the above, the display drive for each pixel 20 is spatially divided into two and divided drive is performed. Specifically, each pixel 20 includes two sub-pixels 20A and 20B, and video signals D3a and D3b (not shown; supplied from the data driver 51) obtained by performing multi-pixel conversion on the video signal D1. Display drive for each pixel 20 is divided into two spatially for each of the sub-pixels 20A and 20B, and divided drive is performed. Therefore, compared with the case where such division driving is not performed, the gamma characteristic when the display screen is viewed from an oblique direction (for example, the 45 ° direction) (the relationship between the gradation of the luminance level of the video signal D1 and the luminance). (Variation from the case where the display screen is viewed from the front) is dispersed. As a result, for example, as in the case of the luminance characteristic Ym (45 °) in FIG. 18, the luminance is compared with the case where the division driving by the multipixel structure is not performed (for example, the luminance characteristic Ys (45 °) in FIG. 18) Viewing angle characteristics are improved.

  On the other hand, since the liquid crystal display device according to the comparative example similarly performs the division driving by the multi-pixel structure, the luminance viewing angle characteristic is improved as compared with the case where the division driving by the multi-pixel structure is not performed. . However, in this comparative example, instead of the LUT of the present embodiment shown in FIG. 4, for example, the LUT (curves Ra100, Ga100, Ba100 for each pixel corresponding to R, G, B shown in FIG. 9). By using the sub pixel 20A) and the curves Rb100, Gb100, and Bb100 (for the sub pixel 20B)), division driving by a multi-pixel structure is performed. Specifically, in this LUT, for example, as shown in FIG. 10, the luminance level gradation of the video signal D3a corresponding to the sub-pixel 20A and the luminance level gradation of the video signal D3b corresponding to the sub-pixel 20B The maximum difference is the same for the pixels corresponding to R, G, and B. That is, the maximum value Rmax100 of the difference Ra-b100 at the pixel corresponding to R, the maximum value Gmax100 of the difference Ga-b100 at the pixel corresponding to G, and the maximum value of the difference Ba-b100 at the pixel corresponding to B Bmax100 is equal to each other. Note that the LUT according to this comparative example is similar to the LUT shown in FIG. 11 (the curves RGBa0, RGBb0 for each pixel corresponding to R, G, B are common to the pixels corresponding to R, G, B). From this point onward, it is created in the same manner as the LUT of the present embodiment shown in FIG.

  Here, in the liquid crystal display device according to the comparative example using such an LUT, as described above, the luminance level gradation of the video signal D3a corresponding to the sub-pixel 20A and the video signal D3b corresponding to the sub-pixel 20B. Since the maximum value of the gradation and difference of the luminance level is the same for each of the pixels corresponding to R, G, and B, the display screen is slanted, for example, as indicated by reference numeral P2 in FIG. In the gamma characteristic when viewed from the direction (for example, 45 ° direction), the increase rate of the luminances YR100 and YG100 in the pixels corresponding to R and G compared to the increase rate of the luminance YB100 in the pixels corresponding to B Becomes larger. Therefore, for example, as shown in FIG. 20, when the display screen is viewed from an oblique direction (for example, 45 ° direction), the values of chromaticity x and y both increase in a halftone and have a peak. , It will appear yellow in the middle tone.

  On the other hand, in the liquid crystal display device 1 of the present embodiment, in the LUT shown in FIG. 4, as shown in FIG. 5, the gradation of the luminance level of the video signal D3a corresponding to the sub-pixel 20A and the sub-pixel 20B The maximum value of the gradation and difference of the luminance level of the video signal D3b corresponding to is different for each pixel corresponding to R, G, and B. Specifically, the maximum value Rmax of the difference Ra-b at the pixel corresponding to R, the maximum value Gmax of the difference Ga-b at the pixel corresponding to G, and the difference Ba-b at the pixel corresponding to B The above-mentioned formula (1) is satisfied with the maximum value Bmax. Therefore, the gamma characteristic when the display screen is viewed from an oblique direction can be individually adjusted for each pixel corresponding to R, G, and B.

  Thus, for example, as indicated by reference numeral P3 in FIG. 12B, the gamma characteristic when the display screen is viewed from an oblique direction (for example, 45 ° direction), the comparative example shown in FIG. As compared with the case of, the increase rate of the luminance YR, YG, YB in the pixels corresponding to R, G, B is substantially equal (the increase rate of the luminance YB in the pixel corresponding to B is larger). Adjustment) becomes possible. Therefore, for example, as indicated by arrows and chromaticity curves x2 and y2 in FIG. 13, compared to the chromaticity curves x100 and y100 according to the comparative example, the display screen turns to yellow in a halftone when viewed from an oblique direction. The coloring is reduced.

  As described above, in the present embodiment, when the display drive for the liquid crystal elements 22A and 22B of each pixel 20 using the VA mode liquid crystal is performed, the display drive for each pixel 20 is divided into two spatially divided drives. As compared with the case where such a division drive is not performed, the variation of the gamma characteristic when the display screen is viewed from an oblique direction can be dispersed, and the viewing angle characteristic of the luminance can be improved. it can. Further, since the maximum value of the difference between the drive voltages applied to the liquid crystal elements 22A and 22B at the time of each divided drive is made different for each pixel corresponding to R, G and B, the display screen is slanted. The gamma characteristic when viewed from the direction can be individually adjusted for each pixel corresponding to R, G, and B, and coloring in a halftone when the display screen is viewed from an oblique direction can be reduced. . Therefore, it is possible to improve viewing angle characteristics of luminance and chromaticity in a liquid crystal display device using a VA mode liquid crystal.

  Specifically, each pixel 20 is composed of two sub-pixels 20A and 20B, and display drive for each pixel 20 is performed based on the video signals D3a and D3b obtained by performing multi-pixel conversion on the video signal D1. Since each of 20A and 20B is spatially divided into two and divided driving is performed, the above-described effect can be obtained.

  Further, by using an LUT that associates the video signal D1 with the video signals D3a and D3b corresponding to the sub-pixels 20A and 20B, the luminance levels of the video signals D3a and D3b corresponding to the sub-pixels 20A and 20B can be obtained. Since the maximum value (Rmax, Gmax, Bmax) of the gradation difference is different for each pixel corresponding to R, G, B, as described above, the liquid crystal element 22A is used in each divided drive as described above. , 22B can be made different from each other for each pixel corresponding to R, G, B.

  Further, the maximum value Rmax of the difference Ra-b at the pixel corresponding to R, the maximum value Gmax of the difference Ga-b at the pixel corresponding to G, and the maximum value of the difference Ba-b at the pixel corresponding to B Since the above equation (1) is satisfied with respect to Bmax, it is possible to adjust so that the increase ratios of the luminances YR, YG, and YB in the pixels corresponding to R, G, and B are substantially equal. When the display screen is viewed from an oblique direction, it is possible to reduce coloring to yellow in a halftone.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to this embodiment, and various modifications can be made.

  For example, in the above-described embodiment, one gate line G and two data lines DA and DB are connected in each pixel 20 like the pixel 20 and sub-pixels 20A and 20B shown in FIG. The multi-pixel structure in the case has been described. For example, as in the pixel 20-1 and the sub-pixels 20A-1 and 20B-1 illustrated in FIG. 14, two gate lines GA, GB and The present invention can also be applied to a multi-pixel structure in which one data line D is connected.

  In the above embodiment, as shown in FIG. 1, the reference voltage Vref supplied from the reference voltage generation unit 45 to the data driver 51 is common among the pixels corresponding to R, G, and B. In addition, as shown in FIG. 4, by using the LUT in which the video signal D1 and the video signals D3a and D3b corresponding to the sub-pixels 20A and 20B are associated with each other, the liquid crystal element 22A is used in each divided drive. , 22B, the maximum value of the difference in drive voltage applied to each pixel corresponding to R, G, B has been described. For example, as in the liquid crystal display device 1A shown in FIG. A reference voltage used when D / A converting the video signal D1 supplied from the image processing unit 41 into video signals D3a and D3b (not shown) in the data driver 51 is a sub-voltage. The pixels 20A and 20B and the pixels corresponding to R, G, and B are different from each other (the reference voltage Vrefr for the pixel corresponding to R, the reference voltage Vrefg for the pixel corresponding to G, and the pixel corresponding to B The reference voltage Vrefb is different for each of the sub-pixels 20A and 20B), and is applied to the liquid crystal elements 22A and 22B of the sub-pixels 20A and 20B as in the above embodiment. The maximum value of the drive voltage difference may be different for each pixel corresponding to R, G, and B. Even in such a configuration, it is possible to obtain the same effect as the above embodiment. In this case as well, a multi-pixel structure as shown in FIG. 14 can be applied.

Further, in the above embodiment, each pixel 20 is constituted by two sub-pixels 20A and 20B, and the display drive for each pixel 20 is spatially divided into two for each of the sub-pixels 20A and 20B. As described above, for example, an ordinary single-structure pixel 20-2 (having one liquid crystal element 22, one auxiliary capacitance element 23, and one TFT element 21 as shown in FIG. For example, as shown in FIG. 17, a display driving unit frame (one frame period) is temporally divided into two subframe periods SFA and SFB in the gate line G and one data line D). Multi-pixel structure by dividing and expressing desired luminance by using high luminance sub-frame SFA and low luminance sub-frame SFB If a may be obtained the effects of halftone similarly. Specifically, based on the video signal D1, the display drive for each pixel 20-2 is divided into two in time for each subframe period SFA, SFB, and divided drive is performed, and each subframe period SFA, SFB is performed. In FIG. 5, the maximum value of the difference in drive voltage applied to the liquid crystal element 22 is different for each pixel corresponding to R, G, and B. As a technique for making the maximum value of the drive voltage difference in each subframe period SFA, SFB different for each pixel corresponding to R, G, B in this way, similarly to the LUT shown in FIG. The LUT (second LUT) in which the video signal D1 and the video signals corresponding to the subframe periods SFA and SFB are associated with each other may be used, and the liquid crystal display device 1A shown in FIG. Similarly to the case, the reference voltage used when D / A converting the video signal D1 may be set to be different for each subframe period SFA, SFB and for each pixel corresponding to R, G, B. . Even when configured as described above, it is possible to obtain the same effects as those of the above-described embodiment. Also in these cases, the maximum value of the difference between the drive voltages applied to the liquid crystal element 22 in each subframe period SFA, SFB satisfies the following expression (4), as in the above expression (1). It is preferable to do so. This is because, similarly to the above-described embodiment, it is possible to reduce coloring in yellow in a halftone when the display screen is viewed from an oblique direction.
(Maximum value at pixel corresponding to R) ≧ (maximum value at pixel corresponding to G) ≧ (maximum value at pixel corresponding to B) (4)

  In the above embodiment, the planar shape of the pixel electrode 220 is specifically described, but the planar shape of the pixel electrode is not limited to that shown in FIG.

  Further, the number of sub-pixels in each pixel 20 and the number of sub-frame periods in one frame period are not limited to two cases as described above, and may be three or more.

1 is a block diagram illustrating an overall configuration of a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a circuit diagram illustrating a detailed configuration of a pixel illustrated in FIG. 1. It is a top view showing the detailed structure of the pixel electrode in the liquid crystal element shown in FIG. FIG. 6 is a characteristic diagram illustrating an example of an LUT (lookup table) used in the multi-pixel conversion unit illustrated in FIG. 1. FIG. 5 is a characteristic diagram illustrating an example of a difference in gradation of a video signal between sub-pixels in the LUT illustrated in FIG. 4 for each color. FIG. 5 is a characteristic diagram illustrating an example of an LUT for each color that is a basis for creating the LUT illustrated in FIG. 4. It is a characteristic view showing an example of the relationship between the birefringence (applied voltage to a liquid crystal element) of each color light, and the transmittance | permeability with respect to a liquid crystal element. FIG. 5 is a characteristic diagram illustrating an example of a relationship between a gradation of a video signal and chromaticity in a front direction of a liquid crystal display panel, which is considered when the LUT illustrated in FIG. 4 is created. It is a characteristic view showing LUT concerning a comparative example. FIG. 10 is a characteristic diagram illustrating a difference in gradation of a video signal between sub-pixels for each color in the LUT according to the comparative example illustrated in FIG. 9. FIG. 10 is a characteristic diagram illustrating an example of an LUT serving as a basis for creating the LUT according to the comparative example illustrated in FIG. 9. It is a characteristic view showing an example of the relationship between the gradation of the video signal which concerns on embodiment and a comparative example, and the luminance ratio in the 45 degree direction of a liquid crystal display panel. It is a characteristic view showing an example of the relationship between the gradation of the video signal which concerns on embodiment and a comparative example, and chromaticity in the 45 degree direction of a liquid crystal display panel. It is a circuit diagram showing the detailed structure of the pixel which concerns on the modification of this invention. It is a block diagram showing the whole structure of the liquid crystal display device which concerns on the other modification of this invention. It is a circuit diagram showing the detailed structure of the pixel which concerns on the other modification of this invention. FIG. 17 is a timing chart for explaining a subframe period in display driving according to the modification shown in FIG. 16. It is a characteristic view showing an example of the relationship between the gradation of the video signal in the conventional liquid crystal display device and the luminance ratio in the front direction and 45 ° direction of the liquid crystal display panel. It is a top view showing an example of the relationship between the gradation of the video signal in the conventional multi-pixel structure, and the display mode of each sub pixel. It is a characteristic view showing an example of the relationship between the gradation of the video signal in the conventional liquid crystal display device, and the chromaticity in the 45 degree direction of a liquid crystal display panel.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1A ... Liquid crystal display device, 2 ... Liquid crystal display panel, 20, 20-1, 20-2 ... Pixel, 20A, 20A-1, 20B, 20B-1 ... Sub pixel, 21, 21A, 21B ... TFT element, 22, 22A, 22B ... Liquid crystal element, 220 ... Pixel electrode, 23, 23A, 23B ... Auxiliary capacitance element, 3 ... Backlight part, 41 ... Image processing part, 43 ... Multi-pixel conversion part, 45, 45A ... Reference voltage generation , 51 ... Data driver, 52 ... Gate driver, 61 ... Timing controller, 62 ... Backlight drive unit, Din ... Video signal, D1, D2a, D2b ... Video signal, Vref, Vrefr, Vrefg, Vrefb ... Reference voltage, G, GA, GB ... gate lines, D, DA, DB ... data lines, Cs ... auxiliary capacitance lines, SFA, SFB ... subframe periods.

Claims (9)

A plurality of pixels arranged in a matrix as a whole and having a liquid crystal element formed of a liquid crystal in a vertical alignment (VA) mode;
Drive means for performing display drive by applying a voltage based on the video signal to the liquid crystal element of each pixel,
The pixel is composed of pixels corresponding to R (Red), G (Green) or B (Blue),
The driving means divides display driving for each pixel into a plurality of spatially or temporally based on the video signal to perform divided driving, and a difference in voltage applied to the liquid crystal element in each divided driving. The liquid crystal display device is characterized in that the division drive is performed so that the maximum value of each of the pixels corresponding to R, G, and B is different from each other. The driving means performs the division driving so that the maximum value of the voltage difference applied to the liquid crystal element in each division driving satisfies the following expression between the pixels corresponding to the R, G, and B. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is performed.
(Maximum value at pixel corresponding to R) ≧ (maximum value at pixel corresponding to G) ≧ (maximum value at pixel corresponding to B) The pixel includes a plurality of sub-pixels each having the liquid crystal element,
The driving unit performs division driving by dividing the display driving for each pixel into a plurality of spatially subpixels based on the video signal, and the difference in voltage applied to the liquid crystal element of each subpixel. 2. The liquid crystal display device according to claim 1, wherein divisional driving is performed so that a maximum value is different for each pixel corresponding to R, G, and B. 3. The drive means uses a first LUT (look-up table) in which the video signal and the video signal corresponding to each sub-pixel are associated with each other, whereby a difference in luminance level of the video signal corresponding to each sub-pixel is obtained. 4. The liquid crystal display device according to claim 3, wherein the division driving is performed so that the maximum value of the pixel is different for each of the pixels corresponding to R, G, and B. 5. In the driving means, a reference voltage used when the video signal is D / A (digital / analog) converted into a voltage applied to the liquid crystal element is a pixel corresponding to each of the sub-pixels and the R, G, B. By setting differently for each pixel, the division drive is performed so that the maximum value of the difference in voltage applied to the liquid crystal element of each sub-pixel is different for each pixel corresponding to the R, G, B. The liquid crystal display device according to claim 3, wherein the liquid crystal display device is performed. A unit frame period of display driving for each pixel is composed of a plurality of subframe periods,
The driving means divides the display drive for each pixel into a plurality of times in each subframe period based on the video signal and performs the divided drive, and the voltage applied to the liquid crystal element in each subframe period. 2. The liquid crystal display device according to claim 1, wherein divisional driving is performed such that a maximum value of the difference is different for each pixel corresponding to the R, G, and B. 3. The drive means uses a second LUT (look-up table) in which the video signal and the video signal corresponding to each subframe period are associated with each other, whereby a difference in luminance level of the video signal in each subframe period. The liquid crystal display device according to claim 6, wherein the division driving is performed so that a maximum value of each of the pixels corresponding to the R, G, and B is different from each other. In the driving means, a reference voltage used when D / A (digital / analog) conversion of the video signal into a voltage applied to the liquid crystal element corresponds to the subframe period and the R, G, B. By setting each pixel to be different from each other, the division is performed so that the maximum value of the difference in voltage applied to the liquid crystal element in each subframe period is different for each pixel corresponding to the R, G, and B. It drives. The liquid crystal display device of Claim 6 characterized by the above-mentioned. A plurality of pixels which are arranged in a matrix as a whole and have a liquid crystal element composed of liquid crystal in a vertical alignment (VA) mode are provided, and these pixels are R (Red: Red), G (Green: Green) or B A driving method applied to a liquid crystal display device constituted by pixels corresponding to (Blue),
When display driving is performed by applying a voltage based on a video signal to the liquid crystal element of each pixel, the display driving for each pixel is divided into a plurality of spatially or temporally divided driving based on the video signal. And performing the division driving so that the maximum value of the difference in voltage applied to the liquid crystal element in each division driving is different for each pixel corresponding to the R, G, B. A method for driving a liquid crystal display device.

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