JP2008122536A - Liquid crystal display device, method for driving liquid crystal display device, and television receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a liquid crystal display device with high display quality in which contrast is improved by stacking two or more liquid crystal panels and luminance irregularity of liquid crystal panels is improved. <P>SOLUTION: The liquid crystal display device 100 comprises optically stacked liquid crystal panels (a first panel and a second panel), in which image data based on the same image source are sent to the respective liquid crystal panels. In a plurality of liquid crystal panels stacked, a color liquid crystal panel is placed as the outermost surface liquid crystal panel, while a monochromatic liquid crystal panel is placed as at least another liquid crystal panel. The monochromatic liquid crystal panel is equipped with a grayscale correcting unit 423 (a correcting means) to correct a grayscale value to a threshold or lower than that when an inputted grayscale value of a pixel within a pixel unit exceeds the threshold. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device with improved contrast and a television receiver including the same.

  As a technique for improving the contrast of the liquid crystal display device, there are various techniques as disclosed in the following Patent Documents 1 to 7.

  Patent Document 1 discloses a technique for improving the contrast ratio by appropriately adjusting the content and specific surface area of the yellow pigment in the pigment component of the color filter. Accordingly, it is possible to improve the problem that the contrast ratio of the liquid crystal display device is lowered due to the pigment molecules of the color filter scattering and depolarizing the polarized light. According to the technique disclosed in Patent Document 1, the contrast ratio of the liquid crystal display device is improved from 280 to 420.

  Patent Document 2 discloses a technique for improving the contrast ratio by increasing the transmittance and polarization degree of a polarizing plate. According to the technique disclosed in Patent Document 2, the contrast ratio of the liquid crystal display device is improved from 200 to 250.

  Further, Patent Document 3 and Patent Document 4 disclose a technique for improving contrast in a guest-host system using the light absorption of a dichroic dye.

  Patent Document 3 describes a method for improving contrast by a structure in which a guest-host liquid crystal cell has two layers and a quarter-wave plate is sandwiched between the two layers of cells. Patent Document 3 discloses that no polarizing plate is used.

  Patent Document 4 discloses a liquid crystal display element of a type in which a dichroic dye is mixed with liquid crystal used in a dispersion type liquid crystal system. In this patent document 4, there is a description that the contrast ratio is 101.

  However, the techniques disclosed in Patent Document 3 and Patent Document 4 have a lower contrast than other methods, and in order to further improve the contrast, the light absorption of the dichroic dye is increased, the dye content is increased, Although it is necessary to increase the thickness of the guest host liquid crystal cell, there are new problems such as technical problems, reduced reliability, and poor response characteristics.

  Patent Document 5 and Patent Document 6 disclose a contrast improving method using an optical compensation method, in which a liquid crystal display panel and a liquid crystal panel for optical compensation are provided between a pair of polarizing plates.

  In Patent Document 5, the contrast ratio of the display cell, the differential optical compensation liquid crystal cell, and the retardation is improved from 14 to 35 in the STN method.

  In Patent Document 6, a contrast ratio is improved from 8 to 100 by installing an optical compensation liquid crystal cell for compensating the wavelength dependency of a TN liquid crystal display cell during black display.

  However, with the techniques disclosed in the above patent documents, a contrast ratio improvement effect of 1.2 times to 10 times is obtained, but the absolute value of the contrast ratio is about 35 to 420.

As a technique for improving contrast, for example, Patent Document 7 discloses a composite liquid crystal display device in which two liquid crystal panels are overlapped so that each polarizing plate forms a crossed Nicol. Yes. Patent Document 7 describes that a contrast ratio of one panel is 100, and the contrast ratio can be expanded to about 3 to 4 digits by superimposing two panels.
JP 2001-188120 A (publication date: July 10, 2001) JP 2002-90536 A (publication date: March 27, 2002) Japanese Unexamined Patent Publication No. 63-25629 (Publication Date: February 3, 1988) JP-A-5-2194 (Publication date: January 8, 1993) JP-A 64-49021 (Publication date: February 23, 1989) Japanese Patent Laid-Open No. 2-23 (Publication date: January 5, 1990) Japanese Patent Laid-Open No. 5-88197 (Publication date: April 9, 1993)

  By the way, a liquid crystal display device may be used as a broadcast monitor or the like. In that case, there is a problem if there is uneven brightness in the liquid crystal display device. This luminance unevenness often occurs due to the gap unevenness of the liquid crystal cell sealed between the substrates, and lowers the display quality.

  The present invention has been made in view of the above-described problems, and the object thereof is to overlap two or more liquid crystal panels to improve contrast, to improve luminance unevenness of the display panel, and to improve display quality. It is to realize a high liquid crystal display device.

  In order to solve the above problems, a liquid crystal display device according to the present invention is configured by optically superposing a plurality of liquid crystal panels, and outputs image data based on the same video source to each of the liquid crystal panels. An upper limit value of a gradation value determined for each pixel unit composed of at least one pixel based on output luminance obtained by irradiating a light source in a state where the plurality of liquid crystal panels are overlapped with each other. Is a color liquid crystal panel as the outermost liquid crystal panel, and a black and white liquid crystal panel is arranged as at least one other liquid crystal panel, and the image on the black and white liquid crystal panel is arranged. Correction means for correcting the gradation value to be equal to or less than the threshold value when the gradation value corresponding to the pixel in the pixel unit obtained from the source exceeds the threshold value; It is characterized by that example.

  Further, in order to solve the above-described problem, the liquid crystal display device driving method according to the present invention includes a plurality of liquid crystal panels stacked, and image data based on the same video source is provided to each of the liquid crystal panels. A driving method of a liquid crystal display device for outputting, wherein a level determined for each pixel unit consisting of at least one pixel based on output luminance obtained by irradiating a light source with the plurality of liquid crystal panels overlaid. When a color liquid crystal panel is arranged as the outermost liquid crystal panel and a black and white liquid crystal panel is arranged as at least one other liquid crystal panel among the plurality of superimposed liquid crystal panels, with the upper limit value of the tone value as a threshold value, In the liquid crystal panel, when a gradation value corresponding to a pixel in the pixel unit obtained from the video source exceeds the threshold value, the gradation value is set to the threshold value. It is characterized by performing the process for correcting down.

  According to the above configuration, when a gradation value corresponding to a pixel in the pixel unit obtained from the video source in the monochrome liquid crystal panel exceeds the threshold value, the gradation value is corrected to be equal to or less than the threshold value. Therefore, it is possible to suppress the luminance of pixels whose luminance is higher than necessary in the monochrome liquid crystal panel.

  As described above, in the liquid crystal display device of the present invention composed of a plurality of liquid crystal panels, the gradation value is corrected not in the color liquid crystal panel arranged on the outermost surface but in the black and white liquid crystal panel arranged on the light source side. In the entire liquid crystal display device formed by superimposing the liquid crystal panels, the luminance is suppressed in units of pixels whose luminance is higher than necessary. As a result, with respect to the display image obtained when a plurality of liquid crystal panels are overlaid, the brightness disparity at each position on the display screen can be reduced, and the brightness generated due to the non-uniform thickness of the liquid crystal cell. Unevenness can be improved.

  In the present invention, in a liquid crystal display device having a configuration including a color liquid crystal panel and a black and white liquid crystal panel, luminance unevenness correction is performed using only the black and white liquid crystal panel. This is because, when luminance unevenness correction is performed on the color liquid crystal panel side, the ratio of each color, such as RGB, changes and color changes occur, but if luminance unevenness correction is performed only on a black and white panel, no color change occurs. This is because luminance unevenness can be effectively improved. On the monochrome liquid crystal panel side, the high gradation region has a substantially constant value (maximum gradation value), and it is only necessary to provide a threshold value in this portion to correct luminance unevenness. Since it is not necessary to correct the gradation value, it can be easily performed as compared with the case where the gradation value is corrected on the color liquid crystal panel side.

  Furthermore, according to the present invention, by constructing two or more liquid crystal panels that are optically overlapped, the panel transmittance is reduced, so that the black luminance is extremely low and a high-contrast image can be displayed. .

  In the liquid crystal display device according to the aspect of the invention, it is preferable that the threshold value is set based on a pixel unit having the lowest relative luminance based on a relative luminance with other pixel units obtained in the pixel unit.

  According to the above configuration, the threshold value is determined in accordance with the pixel unit having the lowest relative luminance based on the relative luminance with the other pixel units, thereby further reducing the variation in luminance occurring in the display panel. be able to. Thereby, the brightness nonuniformity of the whole display apparatus can be improved effectively.

In the liquid crystal display device of the present invention, when the relative luminance of the lowest pixel unit of relative brightness and X _n, the relative brightness of an arbitrary pixel units and X _m, the maximum tone value that each pixel can take the Y, optionally The threshold value M in pixel units of the following equation (1)
M = (X _n / X _m ) ^{(1 / γ)} × Y (1)
(Γ is the γ value indicating the gradation luminance characteristics of the liquid crystal panel)
Is preferably determined by:

  According to the above configuration, the threshold value for each pixel unit is determined based on the pixel unit having the lowest relative luminance. Therefore, since the gradation value when the luminance is higher than the relative luminance of the pixel unit having the lowest relative luminance exceeds the threshold value, it can be excluded from the display by the gradation correcting process by the correcting means. Thereby, it is possible to realize a liquid crystal display device with more excellent luminance uniformity.

  The maximum gradation value Y of the pixel having the lowest relative luminance is, for example, 255 (256) for an 8-bit signal and 63 (64) for a 6-bit signal.

  In addition, a television receiver according to the present invention includes a tuner unit that receives a television broadcast, and any one of the above-described liquid crystal display devices that displays the television broadcast received by the tuner unit. It is said.

  According to said structure, the television receiver which can implement | achieve the moving image display with high display quality can be provided.

  As described above, the liquid crystal display device according to the present invention has the gradation value when the gradation value corresponding to the pixel in the pixel unit obtained from the video source in the monochrome liquid crystal panel exceeds the threshold value. It is characterized by comprising a correction means for correcting the value below the threshold value.

  In addition, as described above, the driving method of the liquid crystal display device according to the present invention is such that, in the black and white liquid crystal panel, the gradation value corresponding to the pixel in the pixel unit obtained from the video source exceeds the threshold value. The gradation value is corrected to be equal to or less than the threshold value.

  Therefore, according to the present invention, with respect to a display image obtained when a plurality of liquid crystal panels are overlaid, the luminance disparity at each position on the display screen can be reduced, and the thickness of the liquid crystal cell is not uniform. Luminance unevenness caused by this can be improved. In addition, according to the present invention, by constructing two or more liquid crystal panels that are optically overlapped, the panel transmittance is reduced, so that the black luminance is extremely low and a high-contrast image can be displayed. . Therefore, a liquid crystal display device with high display quality can be realized.

  As shown in FIG. 8, a general liquid crystal display device is configured by attaching polarizing plates A and B to a liquid crystal panel including a color filter and a driving substrate. Here, an MVA (Multidomain Vertical Alignment) type liquid crystal display device will be described.

  As shown in FIG. 9, the polarization axes of the polarizing plates A and B are orthogonal to each other. When a threshold voltage is applied to the pixel electrode 208 (FIG. 8), the direction in which the liquid crystal is tilted is aligned with the polarizing plates A and B. The polarization axis of B and the azimuth angle are set to 45 degrees. At this time, since the polarization axis rotates when the incident polarized light passing through the polarizing plate A passes through the liquid crystal layer of the liquid crystal panel, light is emitted from the polarizing plate B. In addition, when only a voltage equal to or lower than the threshold voltage is applied to the pixel electrode, the liquid crystal is aligned perpendicular to the substrate, and the deflection angle of incident polarized light does not change, so that black display is obtained. In the MVA method, a high viewing angle is realized by dividing the direction in which the liquid crystal tilts when a voltage is applied into four (multidomain).

  However, in the case of the two polarizing plate configuration, there is a limit to the improvement in contrast. Accordingly, the inventors of the present application have found that the shutter performance is improved in both the front and oblique directions by adopting a configuration with three polarizing plates (each set in crossed Nicols) with respect to two liquid crystal display panels.

  The principle of contrast improvement will be described below.

Specifically, the inventors of this application
(1) About the front direction Leaked light was generated from the transmission axis direction of crossed Nicol due to depolarization in the panel (scattering of CF, etc.). It was found that the leakage light can be cut by matching the third polarizing plate absorption axis with respect to the leakage light in the transmission axis direction of the polarizing plate.

(2) Diagonal direction It has been found that the change in the amount of leakage light is insensitive to the collapse of the polarizing plate Nicol angle φ, that is, it is difficult for black to float with respect to the spread of Nicol angle φ at an oblique viewing angle.

  From the above, the present inventors have found that the contrast is greatly improved in the liquid crystal display device. In the following, the principle of contrast improvement will be described below with reference to FIGS. Here, the description will be made assuming that the two-polarizing plate configuration is the configuration (1) and the three-polarizing plate configuration is the configuration (2). The improvement in the contrast in the oblique direction is essentially caused by the configuration of the polarizing plate. Therefore, here, the description is modeled only by the polarizing plate without using the liquid crystal panel.

  FIG. 10A assumes the case where there is one liquid crystal display panel in the configuration (1), and shows an example in which two polarizing plates 101a and 101b are arranged in crossed Nicols. b) is a diagram showing an example in which three polarizing plates 101a, 101b, and 101c are arranged in crossed Nicols in the configuration (2). That is, in the configuration (2), since it is assumed that there are two liquid crystal display panels, there are two pairs of polarizing plates arranged in crossed Nicols. FIG. 10C is a diagram showing an example in which the polarizing plates 101a and 101b facing each other are arranged in crossed Nicols, and polarizing plates having the same polarization direction are overlapped on the outer sides of the respective polarizing plates. FIG. 10C shows the configuration of four polarizing plates, but the polarizing plates in a crossed Nicol relationship are a pair that assumes a case where one liquid crystal display panel is sandwiched. .

  The transmittance when the liquid crystal display panel performs black display is modeled as the transmittance when the polarizing plate without the liquid crystal display panel is arranged in crossed Nicols, that is, the cross transmittance, and is referred to as black display. The transmittance when white display is modeled as the transmittance when the polarizing plate without the liquid crystal display panel is arranged in parallel Nicol, that is, the parallel transmittance, is called white display when viewed from the front. FIGS. 11A to 11D show examples of the relationship between the wavelength of the transmission spectrum and the transmittance and the relationship between the wavelength of the transmission spectrum and the transmittance when the polarizing plate is viewed obliquely. It is a graph. The modeled transmittance corresponds to the ideal value of the transmittance for white display and black display in a system in which polarizing plates are arranged in a crossed Nicol manner and the liquid crystal display panel is held.

  FIG. 11A is a graph when the relationship between the wavelength of the transmission spectrum and the cross transmittance when the polarizing plate is viewed from the front is compared between the configuration (1) and the configuration (2). From this graph, it can be seen that the transmittance characteristics in the front of the black display tend to be similar between the configuration (1) and the configuration (2).

  FIG. 11B is a graph when the relationship between the wavelength of the transmission spectrum and the parallel transmittance when the polarizing plate is viewed from the front is compared between the configuration (1) and the configuration (2). From this graph, it can be seen that the transmittance characteristics in the front of white display tend to be similar between the configuration (1) and the configuration (2).

  FIG. 11C shows the relationship between the wavelength of the transmission spectrum and the cross transmittance when the polarizing plate is viewed obliquely (azimuth angle 45 ° −polar angle 60 °), and the above configurations (1) and (2). It is a graph at the time of comparing by. From this graph, the transmittance characteristics in the oblique black display show that the transmittance is almost 0 in the most wavelength range in the configuration (2), and a little light is transmitted in the most wavelength region in the configuration (1). It can be seen that In other words, it can be seen that light leakage occurs at an oblique viewing angle when black is displayed in the two-polarizer configuration (a worsening of black tightening), and conversely, an oblique viewing angle is displayed when black is displayed in the three-polarizer configuration. It can be seen that light leakage (deterioration of black tightening) is suppressed.

  FIG. 11 (d) shows the relationship between the wavelength of the transmission spectrum and the parallel transmittance when the polarizing plate is viewed obliquely (azimuth angle 45 ° −polar angle 60 °), and the above configurations (1) and (2). It is a graph at the time of comparing by. From this graph, it can be seen that the transmittance characteristics of the white display in the oblique direction tend to be similar between the configuration (1) and the configuration (2).

  From the above, at the time of white display, as shown in FIG. 11 (b) and FIG. 11 (d), there is almost no difference depending on the number of polarizing plates, that is, the number of Nicol cross pairs of polarizing plates, As can be seen from FIG.

  However, at the time of black display, as shown in FIG. 11C, in the case of the configuration (1) in which the crossed Nicols pair is 1, the black tightening deteriorates at an oblique viewing angle, and the configuration in which the crossed Nicols pair is 2 In the case of (2), it can be seen that deterioration of black tightening at an oblique viewing angle is suppressed.

  For example, when the wavelength of the transmission spectrum is 550 nm, the relationship of transmittance when viewed from the front and obliquely (azimuth angle 45 ° −polar angle 60 °) is as shown in Table 1 below.

  Here, in Table 1, “parallel” indicates parallel transmittance, and indicates the transmittance during white display. Further, the cross indicates a cross transmittance, and indicates a transmittance during black display. Therefore, parallel / cross indicates contrast.

  From Table 1, the front contrast in configuration (2) is about twice that in configuration (1), and the diagonal contrast in configuration (2) is about 22 times that in configuration (1). It can be seen that the contrast is greatly improved.

  The viewing angle characteristics during white display and black display will be described below with reference to FIGS. 12 (a) to 12 (c). Here, the case where the azimuth angle with respect to the polarizing plate is 45 ° and the wavelength of the transmission spectrum is 550 nm will be described.

  FIG. 12A is a graph showing the relationship between polar angle and transmittance during white display. From this graph, the transmittance of the configuration (2) is generally lower than that of the configuration (1), but the viewing angle characteristics (parallel viewing angle characteristics) in this case are the configurations (2) and configurations. It can be seen that (1) has a similar tendency.

  FIG. 12B is a graph showing the relationship between polar angle and transmittance during black display. From this graph, it can be seen that, in the case of the configuration (2), the transmittance at an oblique viewing angle (around polar angle ± 80 °) is suppressed. On the contrary, in the case of the configuration (1), it can be seen that the transmittance at an oblique viewing angle is increased. That is, the configuration (1) is more markedly worse in black tightening at an oblique viewing angle than the configuration (2).

  FIG. 12C is a graph showing the relationship between polar angle and contrast. From this graph, it can be seen that the contrast of the configuration (2) is much better than that of the configuration (1). The reason why the vicinity of 0 degree in the configuration 2 in FIG. 12C is flat is that the black transmittance is so small that the calculation is not possible due to the loss of digits, and the actual curve is smooth.

  Next, the change in the amount of leakage light becomes insensitive to the collapse of the polarizing plate Nicol angle φ, that is, the deterioration of black tightening is less likely to occur with respect to the spread of the Nicol angle φ at an oblique viewing angle. This will be described below with reference to (a) and (b). Here, as shown in FIG. 13A, the polarizing plate Nicol angle φ is an angle in a state where the polarization axes of the polarizing plates facing each other are in a twisted relationship. FIG. 13A is a perspective view of a polarizing plate in which crossed Nicols are arranged, and the Nicol angle φ changes from 90 ° (corresponding to the collapse of the Nicol angle).

  FIG. 13B is a graph showing the relationship between the Nicol angle φ and the cross transmittance. Calculation is performed using an ideal polarizer (parallel Nicol transmittance 50%, crossed Nicol transmittance 0%). From this graph, it can be seen that the degree of change in the transmittance with respect to the change in the Nicol angle φ is smaller in the configuration (2) than in the configuration (1) during black display. That is, it can be understood that the three-polarizing plate configuration is less susceptible to the change in the Nicol angle φ than the two-polarizing plate configuration.

  Next, the thickness dependency of the polarizing plate will be described below with reference to FIGS. 14 (a) to 14 (c). Here, as shown in FIG. 10C, the thickness of the polarizing plate is adjusted by superposing polarizing plates with the same polarization axis one by one on the polarizing plates arranged in a pair of crossed Nicols (3 ). FIG. 10C shows an example in which the polarizing plates 101a and 101b having the polarization axis in the same polarization direction are superimposed on the pair of polarizing plates 101a and 101b arranged in crossed Nicols. In this case, in addition to the two polarizing plates arranged in a pair of crossed Nicols, the structure has two polarizing plates. Similarly, if the number of polarizing plates to be superimposed increases, the cross pair is −3, −4,. In the graphs shown in FIGS. 14A to 14C, each value is measured at an azimuth angle of 45 ° and a polar angle of 60 °.

  FIG. 14A is a graph showing the relationship between the polarizing plate thickness and the transmittance (cross transmittance) of a pair of polarizing plates arranged in crossed Nicols during black display. For comparison, this graph shows the transmittance in the case of having two pairs of polarizing plates arranged in crossed Nicols.

  FIG. 14B is a graph showing the relationship between the thickness and the transmittance (parallel transmittance) of the polarizing plates arranged in a pair of crossed Nicols during white display. For comparison, this graph shows the transmittance in the case of having two pairs of polarizing plates arranged in crossed Nicols.

  From the graph shown in FIG. 14 (a), it can be seen that if the polarizing plates are superimposed, the transmittance during black display can be reduced, but from the graph shown in FIG. 14 (b), if the polarizing plates are superimposed, It turns out that the transmittance | permeability at the time of white display becomes small. That is, in order to suppress the deterioration of black tightening at the time of black display, the transmittance at the time of white display is lowered only by overlapping the polarizing plates.

  Moreover, the graph which shows the relationship between the thickness of the polarizing plate arrange | positioned at a pair of crossed Nicols, and contrast becomes as shown in FIG.14 (c). For comparison, this graph shows the contrast when two pairs of crossed Nicols polarizing plates are provided.

  As described above, from the graphs shown in FIGS. 14A to 14C, the configuration of the polarizing plates arranged in two pairs of crossed Nicols suppresses the deterioration of black tightening at the time of black display and at the time of white display. It can be seen that a decrease in transmittance can be prevented. Moreover, since the two pairs of crossed Nicols polarizing plates are composed of a total of three polarizing plates, it can be seen that the thickness of the entire liquid crystal display device is not increased and the contrast can be greatly improved.

  FIGS. 15A and 15B specifically show the viewing angle characteristics of the crossed Nicols transmittance. FIG. 15A is a diagram showing the crossed Nicols viewing angle characteristics of the configuration (1), that is, the configuration of two crossed Nicol pairs of polarizing plates, and FIG. 15B is the configuration (2). That is, it is a view showing the crossed Nicols viewing angle characteristics of the two pairs of crossed Nicols polarizing plates.

  From the diagrams shown in FIGS. 15 (a) and 15 (b), it can be seen that in the configuration of two crossed Nicols, black tightening deterioration (equivalent to an increase in transmittance during black display) is hardly observed (especially 45 °). , 135 °, 225 °, 315 ° direction).

  Further, FIGS. 16A and 16B specifically show the contrast viewing angle characteristics (parallel / cross luminance). FIG. 16A is a diagram showing the contrast viewing angle characteristics of the configuration (1), that is, the configuration of two crossed Nicol polarizing plates, and FIG. 16B is the configuration (2). That is, it is a diagram showing the contrast viewing angle characteristics of the three crossed Nicols polarizing plate three-piece configuration.

  From the diagrams shown in FIGS. 16A and 16B, it can be seen that the contrast of the two pairs of crossed Nicols is improved as compared with the structure of the pair of crossed Nicols.

Here, a liquid crystal display device using the above-described principle of improving contrast will be described below with reference to FIGS.
Here, for simplicity, the case where two liquid crystal panels are used will be described.

  FIG. 1 is a diagram showing a schematic cross section of a liquid crystal display device 100 according to the present embodiment.

  As shown in FIG. 1, the liquid crystal display device 100 is configured by alternately bonding a first panel, a second panel, and polarizing plates A, B, and C.

  FIG. 2 is a diagram showing the arrangement of the polarizing plate and the liquid crystal panel in the liquid crystal display device 100 shown in FIG. In FIG. 2, polarizing plates A and B and polarizing plates B and C are configured so that their polarization axes are orthogonal to each other. That is, the polarizing plates A and B and the polarizing plates B and C are arranged in crossed Nicols.

  Among the liquid crystal panels provided in the liquid crystal display device 100, the liquid crystal panel (first liquid crystal panel) on the outermost surface (the side closest to the observer) is a color liquid crystal panel and is provided on the backlight (light source) side. The liquid crystal panel (second liquid crystal panel) is a monochrome liquid crystal panel.

  The first panel is formed by enclosing liquid crystal between a pair of transparent substrates (color filter substrate 220 and active matrix substrate 230). On the other hand, the second panel is not provided with a color filter, and is formed by sealing liquid crystal between the counter substrate 220 ′ and the active matrix substrate 230. The first panel and the second panel have a state in which the polarized light incident on the polarizing plate A from the light source is rotated by about 90 degrees, a state in which the polarized light is not rotated, Means for arbitrarily changing the intermediate state is provided.

  The first panel and the second panel have a function of displaying an image with a plurality of pixels. The display method having such a function includes a TN (TwistedNematic) method, a VA (Vertical Alignment) method, an IPS (InPlain Switching) method, an FFS (Fringe Field Switching) method, or a combination of these methods. The method is suitable. Here, the description will be made using the MVA (Multidomain Vertical Alignment) method, but since the IPS method and the FFS method are also normally black methods, there are sufficient effects. The driving method uses active matrix driving by TFT (ThinFilmTransistor). Details of the manufacturing method of MVA are disclosed in Japanese Patent Laid-Open No. 2001-83523.

  The first and second panels in the liquid crystal display device 100 have the same structure except for the color filters, and as described above, the color filter substrate 220 (or the counter substrate 220 ′) and the active matrix substrate 230 that face each other. And a columnar resin structure provided on a plastic bead or the color filter substrate 220 (or the counter substrate 220 ′) as a spacer (not shown) to maintain a constant substrate interval. . Liquid crystal is sealed between a pair of substrates (color filter substrate 220 (or counter substrate 220 ') and active matrix substrate 230), and a vertical alignment film 225 is formed on the surface of each substrate in contact with the liquid crystal. As the liquid crystal, a nematic liquid crystal having negative dielectric anisotropy is used.

  The color filter substrate 220 is obtained by forming a color filter 221, a black matrix 224, and the like on a transparent substrate 210. An alignment control protrusion 222 that defines the alignment direction of the liquid crystal is formed.

  As shown in FIG. 3, the active matrix substrate 230 includes a TFT element 203, a pixel electrode 208, and the like formed on a transparent substrate 210, and further has an alignment control slit pattern 211 that defines the alignment direction of the liquid crystal. The black matrix 224 for shielding the alignment regulating protrusions 222 and unnecessary light for reducing the display quality shown in FIG. 3 is a diagram in which a pattern formed on the color filter substrate 220 is projected onto the active matrix substrate 230. When a voltage equal to or higher than the threshold is applied to the pixel electrode 208, the liquid crystal molecules are tilted in a direction perpendicular to the protrusions 222 and the slit pattern 211. In the present embodiment, the protrusion 222 and the slit pattern 211 are formed so that the liquid crystal is oriented in the direction of 45 ° azimuth with respect to the polarization axis of the polarizing plate.

  Further, the counter substrate 220 ′ constituting the second liquid crystal panel is obtained by forming the counter electrode 223, the black matrix 224, etc. on the transparent substrate 210.

  The first and second panels are arranged with their respective black matrices so that the positions seen from the vertical direction coincide.

  As described above, in the liquid crystal display device according to the present embodiment, the liquid crystal panel (first liquid crystal panel) located on the outermost surface is the color liquid crystal panel among the two stacked liquid crystal panels, and the back surface thereof. The liquid crystal panel (second liquid crystal panel) provided is a monochrome liquid crystal panel. As described above, by using the second liquid crystal panel as a monochrome liquid crystal panel, it is possible to simplify materials and processes. In addition, when the two liquid crystal panels are both color liquid crystal panels, the correct color is obtained due to the parallax between the first panel and the second panel, or due to the displacement of the color filters of the first panel and the second panel. It is not displayed or moire occurs. Therefore, as in the present embodiment, the first panel is a color liquid crystal panel and the second panel is a black and white liquid crystal panel, thereby preventing color display from being performed correctly and moiré from occurring. be able to.

  FIG. 4 shows an outline of a drive system of the liquid crystal display device 100 having the above configuration.

  The driving system includes a display controller 400 necessary for displaying an image on the liquid crystal display device 100. As a result, appropriate image data based on the input signal is output to the liquid crystal display device 100.

  The display controller 400 includes first and second panel drive circuits (1) and (2) for driving the first panel and the second panel with predetermined signals, respectively. The display controller 400 includes a signal distribution unit 401 that distributes the video source signal to the liquid crystal display drive units (1) and (2) (first and second panel drive circuits (1) and (2)). . Details of the display controller 400 will be described later.

  Here, the input signal represents not only a video signal from a TV receiver, VTR, DVD, etc., but also a signal obtained by processing these signals.

  Accordingly, the display controller 400 transmits a signal that can display an appropriate image on the liquid crystal display device 100 to each panel.

  FIG. 5 shows the connection relationship between the first and second panels and the respective panel drive circuits. In FIG. 5, the polarizing plate is omitted.

  The first panel drive circuit (1) is connected to a terminal (1) provided on a circuit board (1) of the first panel via a driver (TCP) (1). In other words, the driver (TCP) (1) is connected to the first panel, connected by the circuit board (1), and connected to the panel drive circuit (1).

  Since the connection of the second panel drive circuit (2) in the second panel is the same as that in the first panel, the description thereof is omitted.

  Next, the operation of the liquid crystal display device 100 having the above configuration will be described.

  The pixels of the first panel are driven based on the display signal, and the corresponding pixels of the second panel corresponding to the positions of the pixels of the first panel and the positions viewed from the vertical direction of the panel are the first panel. It is driven in response to In the case where the part (constituent part 1) composed of the polarizing plate A, the first panel, and the polarizing plate B is in a transmissive state, the part composed of the polarizing plate B, the second panel, and the polarizing plate C (constituent part) 2) is also in a transmissive state, and when the component 1 is in a non-transmissive state, the component 2 is also driven in a non-transmissive state.

  The same image signal may be input to the first and second panels, or separate signals associated with each other may be input to the first and second panels.

  Here, a method for manufacturing the active matrix substrate 230 and the color filter substrate 220 will be described.

  First, a method for manufacturing the active matrix substrate 230 will be described.

  First, as shown in FIG. 3, on the transparent substrate 210, a scanning signal wiring (gate wiring, gate line, gate voltage line or gate bus line) 201 and auxiliary capacitance wiring 202 are formed by sputtering to form Ti / A metal such as an Al / Ti laminated film is formed, a resist pattern is formed by photolithography, dry etching is performed using an etching gas such as a chlorine-based gas, and the resist is peeled off. As a result, the scanning signal wiring 201 and the auxiliary capacitance wiring 202 are simultaneously formed on the transparent substrate 210.

  Thereafter, a gate insulating film made of silicon nitride (SiNx) or the like, an active semiconductor layer made of amorphous silicon or the like, a low-resistance semiconductor layer made of amorphous silicon or the like doped with phosphorus or the like is formed by CVD, and then a data signal wiring (Source wiring, source line, source voltage line or source bus line) 204, drain lead-out wiring 205, auxiliary capacitance forming electrode 206 are formed by depositing a metal such as Al / Ti by sputtering, and by photolithography A resist pattern is formed, dry etching is performed using an etching gas such as a chlorine-based gas, and the resist is peeled off. As a result, the data signal wiring 204, the drain lead wiring 205, and the auxiliary capacitance forming electrode 206 are formed at the same time.

  The auxiliary capacitance is formed between the auxiliary capacitance wiring 202 and the auxiliary capacitance forming electrode 206 with a gate insulating film of about 4000 mm sandwiched therebetween.

  Thereafter, the TFT element 203 is formed by dry etching the low resistance semiconductor layer using chlorine gas or the like for source / drain separation.

  Next, an interlayer insulating film 207 made of acrylic photosensitive resin or the like is applied by spin coating, and a contact hole (not shown) for electrically contacting the drain lead-out wiring 205 and the pixel electrode 208 is formed by photolithography. Form. The film thickness of the interlayer insulating film 207 is about 3 μm.

  Further, the pixel electrode 208 and a vertical alignment film (not shown) are formed in this order.

  As described above, the present embodiment is an MVA type liquid crystal display device, and the slit pattern 211 is provided in the pixel electrode 208 made of ITO or the like. Specifically, a film is formed by sputtering, a resist pattern is formed by photolithography, and etching is performed with an etchant such as ferric chloride to obtain a pixel electrode pattern as shown in FIG.

  Thus, the active matrix substrate 230 is obtained.

  Note that reference numerals 212 a, 212 b, 212 c, 212 d, 212 e, and 212 f shown in FIG. 3 indicate electrical connection portions of slits formed in the pixel electrode 208. At the electrical connection portion in the slit, the orientation is disturbed and an orientation abnormality occurs. However, for the slits 212a to 212d, the time during which the positive potential supplied to the gate wiring is applied to operate the TFT element 203 in the on state is usually on the order of microseconds, and the TFT element 203 is operated in the off state. For this reason, since the time during which the negative potential supplied to the gate wiring is applied is usually on the order of milliseconds, the time during which the negative potential is applied is dominant. For this reason, when the slits 212a to 212d are positioned on the gate wiring, in addition to the alignment abnormality, impurity ions contained in the liquid crystal gather due to the gate minus DC application component, so that it may be visually recognized as display unevenness. Therefore, since it is necessary to provide the slits 212a to 212d in a region that does not overlap with the gate wiring in a plan view, it is preferable to hide the slits 212a to 212d with the black matrix 224 as shown in FIG.

  Next, a method for manufacturing the color filter substrate 220 will be described.

  The color filter substrate 220 includes a color filter layer composed of three primary colors (red, green, blue), a color filter 221 and a black matrix (BM) 224, a counter electrode 223, a vertical alignment film 225, and a transparent substrate 210. A protrusion 222 for controlling the orientation is provided.

  First, a negative acrylic photosensitive resin liquid in which carbon fine particles are dispersed is applied onto the transparent substrate 210 by spin coating, and then dried to form a black photosensitive resin layer. Subsequently, the black photosensitive resin layer is exposed through a photomask and then developed to form a black matrix (BM) 224. At this time, in the regions where the first colored layer (for example, red layer), the second colored layer (for example, green layer), and the third colored layer (for example, blue layer) are formed, the first colored layer opening, The BM is formed so that an opening for the second colored layer and an opening for the third colored layer (each opening corresponds to each pixel electrode) are formed. More specifically, as shown in FIG. 3, a BM pattern that shields an abnormal alignment region generated in the slits 212a to 212d of the electrical connection portions of the slits 212a to 212f formed in the pixel electrode 208 is formed in an island shape. In addition, a light shielding portion (BM) is formed on the TFT element 203 in order to prevent an increase in leakage current that is photoexcited when external light enters the TFT element 203.

  Next, after applying a negative acrylic photosensitive resin liquid in which a pigment is dispersed by spin coating, drying is performed, and exposure and development are performed using a photomask to form a red layer.

  Thereafter, the second color layer (for example, the green layer) and the third color layer (for example, the blue layer) are similarly formed, and the color filter 221 is completed.

  Further, a counter electrode 223 made of a transparent electrode such as ITO is formed by sputtering, and then a positive type phenol novolac photosensitive resin solution is applied by spin coating, followed by drying, and exposure and development using a photomask. To form a protrusion 222 for controlling vertical alignment. Further, columnar spacers (not shown) for defining the cell gap of the liquid crystal panel are formed by applying an acrylic photosensitive resin liquid, exposing, developing and curing with a photomask.

  Thus, the color filter substrate 220 is formed.

  In the present embodiment, the case of a BM made of resin is shown, but a BM made of metal may be used. The colored layers of the three primary colors are not limited to red, green, and blue, and may include colored layers such as cyan, magenta, and yellow, and may include a white layer.

  The counter substrate 220 ′ constituting the second panel is a configuration that does not include the color filter 221 in the color filter substrate 220, and is performed by each process except the process of forming the color filter from the manufacture of the color filter substrate 220 described above. Can be manufactured. Moreover, you may manufacture using the manufacturing method generally of the opposing board | substrate of the liquid crystal panel for monochrome displays.

  A method for manufacturing a liquid crystal panel (first panel, second panel) using the color filter substrate 220 and the active matrix substrate 230 manufactured as described above will be described below.

  First, the vertical alignment film 225 is formed on the surface of the color filter substrate 220 and the active matrix substrate 230 that are in contact with the liquid crystal. Specifically, baking is performed as a degassing process before the alignment film is applied, and then substrate cleaning and alignment film application are performed. After the alignment film is applied, alignment film baking is performed. After the alignment film is applied and washed, further baking is performed as a degassing process. The vertical alignment film 225 defines the alignment direction of the liquid crystal 226.

  Next, a method for sealing liquid crystal between the active matrix substrate 230 and the color filter substrate 220 will be described.

  As for the liquid crystal sealing method, for example, an injection port is provided for injecting a part of the thermosetting sealing resin around the substrate, the liquid injection is performed by immersing the injection port in a liquid crystal in a vacuum, and opening to the atmosphere, and then UV curing is performed. You may carry out by methods, such as a vacuum injection method, which seals an injection port with resin etc. However, the vertical alignment liquid crystal panel has a drawback that the injection time is very long as compared with the horizontal alignment panel. Here, explanation will be given by the liquid crystal dropping bonding method.

  A UV curable seal resin is applied around the active matrix substrate side, and liquid crystal is dropped onto the color filter substrate by a dropping method. An optimum amount of liquid crystal is regularly dropped on the inner part of the seal so as to obtain a desired cell gap by liquid crystal by a liquid crystal dropping method.

  Further, in order to bond the active filter substrate and the color filter substrate on which the seal drawing and liquid crystal dropping were performed as described above, the atmosphere in the bonding apparatus was reduced to 1 Pa, and the substrates were bonded under this reduced pressure. After that, the atmosphere is set to atmospheric pressure, the seal portion is crushed, and a desired gap of the seal portion is obtained.

  Next, with respect to the structure having a desired cell gap in the seal portion, UV irradiation is performed with a UV curing device to temporarily cure the seal resin. Further, baking is performed to finally cure the sealing resin. At this time, the liquid crystal spreads inside the sealing resin and the liquid crystal is filled in the cell. A liquid crystal panel is completed by dividing the structure into liquid crystal panel units after baking is completed.

  In the present embodiment, the first panel and the second panel are manufactured by the same process.

  Subsequently, a mounting method of the first panel and the second panel manufactured by the above-described manufacturing method will be described.

  Here, after cleaning the first panel and the second panel, a polarizing plate is attached to each panel. Specifically, as shown in FIG. 4, polarizing plates A and B are attached to the front and back surfaces of the first panel, respectively. Moreover, the polarizing plate C is affixed on the back surface of the second panel. In addition, you may laminate | stack an optical compensation sheet etc. on a polarizing plate as needed.

  Next, a driver (liquid crystal driving LSI) is connected. Here, the connection of the driver by the TCP (Tape Career Package) method will be described.

  For example, as shown in FIG. 5, after temporarily crimping an ACF (ArisotoropiConduktiveFilm) to the terminal portion (1) of the first panel, the TCP (1) on which the driver is placed is punched from the carrier tape and positioned on the panel terminal electrode. Combine, heat, and press-fit. Thereafter, the circuit board (1) for connecting the drivers TCP (1) and the input terminal (1) of the TCP (1) are connected by ACF.

  Next, the two panels are bonded together. The polarizing plate B is provided with an adhesive layer on both sides. The surface of the second panel is washed, the laminate of the adhesive layer of the polarizing plate B attached to the first panel is peeled off, precisely aligned, and the first panel and the second panel are bonded together. At this time, since bubbles may remain between the panel and the adhesive layer, it is desirable to bond them under vacuum.

  As another bonding method, an adhesive that cures at room temperature or below the heat resistance temperature of the panel, such as an epoxy adhesive, is applied to the periphery of the panel, a plastic spacer is sprayed, and fluorine oil is sealed, for example. Also good. A liquid that is optically isotropic, has a refractive index comparable to that of a glass substrate, and is as stable as liquid crystal is desirable.

  In addition, in this embodiment, as described in FIG. 4 and FIG. 5, the present invention can be applied to the case where the terminal surface of the first panel and the terminal surface of the second panel are at the same position. Moreover, the direction of the terminal with respect to the panel and the bonding method are not particularly limited. For example, a mechanical fixing method may be used regardless of adhesion.

  In order to reduce parallax due to the thickness of the inner glass, it is better to make the inner substrates facing each other of the two panels as thin as possible.

  When a glass substrate is used, a thin substrate can be used from the beginning. The possible substrate thickness varies depending on the production line and the size of the liquid crystal panel, but 0.4 mm glass can be used as the inner substrate.

There are also methods for polishing and etching glass. There are known techniques for etching glass (Patent Publications such as Japanese Patent Nos. 3524540 and 3523239). For example, a chemical working solution such as a 15% hydrofluoric acid aqueous solution is used. Portions that are not to be etched such as terminal surfaces are coated with an acid-resistant protective material, soaked in the chemical working solution and etched into the glass, and then the protective material is removed. The glass is thinned to about 0.1 mm to 0.4 mm by etching.
After the two panels are bonded together, the liquid crystal display device 100 is obtained by integrating with a lighting device called a backlight.

  Here, the specific example of the illuminating device suitable for this invention is demonstrated below. However, this invention is not restricted to the form of the illuminating device given below, It can change suitably.

  In the liquid crystal display device 100 of the present invention, the backlight is required to have an ability to provide a larger amount of light than a conventional panel according to the display principle. Moreover, since short wavelength absorption becomes more prominent even in the wavelength region, it is necessary to use a blue light source having a shorter wavelength on the illuminating device side. An example of a lighting device that satisfies these conditions is shown in FIG.

  In the liquid crystal display device 100 according to the present invention, a hot cathode lamp is used this time in order to obtain the same luminance as the conventional one. The hot cathode lamp is characterized in that the amount of light can be output about six times that of a cold cathode lamp used in general specifications.

  Taking a 37 inch diagonal WXGA as an example of a standard liquid crystal display device, 18 lamps having an outer diameter of 15 mm are arranged on a housing made of aluminum. In this housing, a white reflective sheet using a foamed resin is disposed in order to efficiently use the light emitted from the lamp in the back direction. A driving power source for the lamp is disposed on the rear surface of the housing, and the lamp is driven by power supplied from a household power source.

Next, a milky white resin plate is required for erasing the lamp image in the direct type backlight in which a plurality of lamps are arranged in the housing. This time, a plate member based on polycarbonate, which is 2mm thick and absorbs warp and heat deformation, is placed in the housing on the lamp, and the optical sheet to obtain the predetermined optical effect on its upper surface, specifically this time Arranges a diffusion sheet, a lens sheet, a lens sheet, and a polarization reflection sheet from the bottom. With this specification, it is possible to obtain a backlight luminance of about 10 times that of a general specification of 18 cold-cathode lamps of φ4 mm, two diffusion sheets and a polarizing reflection sheet. Thereby, the 37-inch liquid crystal display device of the present invention can obtain a luminance of about 400 cd / m ² .

  However, since the amount of heat generated by this backlight is five times that of the conventional one, fins for radiating heat to the air and a fan for forcing the air flow are installed on the back of the back chassis.

  The mechanism member of the present lighting device also serves as a main mechanism member of the entire module, and the mounted panel is disposed in the backlight, and a liquid crystal display controller including a panel drive circuit and a signal distributor, a light source power source, In some cases, a household general power supply is attached to complete the liquid crystal module. The liquid crystal display device of the present invention is obtained by disposing the mounted panel on the backlight and installing a frame body for pressing the panel.

  In the present embodiment, a direct illumination device using a hot cathode tube is shown, but a projection method or an edge light method may be used according to the application, and the light source is a cold cathode tube, LED, OEL, electron beam fluorescent tube. Or a combination of optical sheets can be selected as appropriate.

  Furthermore, as another embodiment, as a method for controlling the alignment direction of the vertically aligned liquid crystal molecules of the liquid crystal, in the embodiment described above, a slit is provided in the pixel electrode of the active matrix substrate, and a protrusion for alignment control on the color filter substrate side. However, they may be reversed, or a structure in which slits are provided on the electrodes of both substrates, or an MVA type liquid crystal panel in which alignment control protrusions are provided on the electrode surfaces of both substrates. I do not care.

  In addition, instead of the MVA type, a method using a vertical alignment film in which pretilt directions (alignment processing directions) defined by a pair of alignment films are orthogonal to each other may be used. In addition, a VA mode in which liquid crystal molecules are twisted alignment may be used, which may be referred to as a VATN (Vertical Alignment Twisted Nematic) mode. The VATN method is more preferable in the present invention because there is no decrease in contrast due to light leakage at the alignment control projection. The pretilt is formed by optical alignment or the like.

  Here, a specific example of a driving method in the display controller of the liquid crystal display device 100 having the above configuration will be described below with reference to FIG. Here, the case of input 8 bits (255 gradations) and liquid crystal driver 8 bits will be described.

  In the panel drive circuit (1) of the display controller unit, the input signal (video source) is subjected to drive signal processing such as γ conversion and overshoot to the 8-bit floor for the source driver (source drive means) of the first panel. Output key data.

  On the other hand, the panel drive circuit (2) performs signal processing such as γ conversion and overshoot, and outputs 8-bit grayscale data to the source driver (source drive means) of the second panel. In the liquid crystal display device 100 of the present embodiment, since the second panel is a monochrome liquid crystal panel, a monochrome panel conversion process (that is, a luminance value conversion process) is performed before the γ conversion.

  The first panel, the second panel, and the output image that is output as a result are 8 bits, correspond one-to-one with the input signal, and are faithful to the input image.

  Further, in the liquid crystal display device 100 according to the present embodiment, the gradation value corresponding to the pixel in the pixel unit obtained from the input video source signal is the threshold value on the second panel side which is a monochrome liquid crystal panel. When the value exceeds the threshold value, correction processing is performed to correct the gradation value to be equal to or less than the threshold value. Here, the threshold value is an upper limit value of a gradation value determined in pixel units of at least one pixel based on output luminance obtained when a light source is irradiated in a state where a plurality of liquid crystal panels are overlapped. This correction processing will be described in detail in the first embodiment.

[Embodiment 1]
As shown in FIG. 1, the liquid crystal display device according to the present embodiment is configured by optically superposing two liquid crystal panels, and each of the liquid crystal panels is an image based on the same video source signal. Output data. Of the two liquid crystal panels, the first panel is a color liquid crystal panel, and the second panel is a monochrome liquid crystal panel. The black-and-white liquid crystal panel (second panel) has a pixel level in the input pixel unit based on a threshold value of gradation values determined in pixel units consisting of at least one pixel based on output luminance. When the tone value exceeds the threshold value, correction means (in this embodiment, a gradation correction unit 423) is provided to correct the gradation value to be equal to or less than the threshold value.

  The correction means is provided in the display controller 400 in the liquid crystal display device. FIG. 17 shows the configuration in the display controller 400 shown in FIG. 4 more specifically. As shown in FIG. 17, the display controller 400 includes a signal distribution unit 401 that distributes the same video source signal to the first panel display unit 411 and the second panel display unit 421, respectively. In addition, as a block for processing the video source signal distributed for the first panel, a liquid crystal display driving unit (1) 410 is provided, and for the video source signal distributed for the second panel. A liquid crystal display drive unit (2) 420 is provided as a block for processing.

  The liquid crystal display driving unit (1) 410 includes a gradation conversion unit (1) 412 that performs gradation conversion on the gradation value of the input video source signal. Although not shown, in the liquid crystal display drive unit (1), in addition to the gradation conversion unit (1) 412, a video signal (first panel signal) for displaying an image on the first panel is displayed. Various processing units are provided for creating the.

  In the liquid crystal display driving unit (2) 420, a luminance value converting unit 426 for converting the luminance value of the input video source signal for displaying a black and white image, and a gradation with respect to the gradation value of the input video source signal A gradation conversion unit (2) 422 for performing conversion, a gradation correction unit 423 (correction unit) for further correcting the gradation value subjected to gradation conversion, a memory 425, and the like are provided. Although not shown, in the liquid crystal display drive unit (2), in addition to these processing units, a video signal (second panel signal) for displaying an image on the second panel is created. Various processing circuits are provided for this purpose.

  In the memory 425, correction data 424 used when the gradation correction unit 423 performs gradation correction is stored. The display controller 400 further includes a threshold value determination unit 430 that determines a threshold value of a gradation value based on luminance data of the display panel (data in which each pixel is associated with detected luminance of the pixel). . This luminance data is obtained by measuring the luminance of the display panel using a luminance detector or the like.

  Here, the threshold value of the gradation value is a gradation determined for each pixel position based on the output luminance obtained when the light source is irradiated with the first and second liquid crystal panels superimposed. This is the upper limit value. A method for determining the threshold will be described later.

  The correction data is obtained by storing the threshold value determined for each pixel in association with each pixel.

  In this embodiment, a plurality of adjacent pixels (for example, 2 to 4 pixels) are set as one pixel unit, and the threshold value of the gradation value is determined in this pixel unit. Without limitation, a threshold value may be determined for each pixel. However, if a plurality of pixels are used as one pixel unit, the amount of memory to be stored can be reduced. In this case, the threshold values of the pixels existing in one pixel unit have the same value, but the gradation value to be input is different for each pixel, so that gradation correction is performed for each pixel.

  By the way, when the first panel is a color liquid crystal panel and the second panel is a black and white liquid crystal panel as in the present embodiment, when RGB gradation signals are input to the second panel for performing black and white display, Unless the light is parallel light, color display is not performed correctly due to the parallax between the first panel and the second panel. Therefore, as shown in FIG. 20, it is desirable to input signals based on the same video source signal to the pixels of the second panel corresponding to RGB. In consideration of luminance efficiency, control can be performed so that RGB input pixel maximum gradation data of an input signal at a corresponding position becomes gradation data indicated by a calculation result reflecting the maximum gradation. desirable. FIG. 21 is a diagram for explaining the above in more detail. At this time, as shown in FIG. 22, the minimum unit pixel on the structure of the second panel may be one pixel corresponding to RGB.

  Further, the pixel size of the second panel may be increased as shown in FIG. In FIG. 23, the pixel size is doubled in the gate scanning direction and RGB × 2 in the signal direction and 6 times the pixel size. This is advantageous in terms of aperture ratio.

  Next, a video source signal processing method in the liquid crystal display driving units (1) and (2) will be described.

  First, the gradation conversion (γ conversion) performed in the gradation conversion unit (1) 412 and the gradation conversion unit (2) 422 will be described.

Here, the γ conversion refers to a process of changing a γ value for an input signal based on the gradation luminance characteristic (γ characteristic) of the display panel. In the case of a display, the γ value is expressed as i = k × E ^γ <k: constant> as input signal (gradation) E and output (luminance) i, and logi = logk + γ · logE, and the slope of the log · log graph It becomes.

Since the γ value of the TV signal is defined by G = 0.45, generally the γ of the display is about G _out = 2.2. However, in an actual display device such as a liquid crystal display device, black does not have a luminance of 0 and signal processing such as saturation adjustment rarely has the same γ for all gradations, and is generally 1.8. It is distributed continuously to about 2.6.

  Therefore, γ is not a constant straight line in all gradations but a curve, and γ is defined as a tangential slope in each gradation. However, in actual use, a minute gradation region (such as between one gradation) is used. Is approximated by the slope of the straight line.

In the present embodiment, the first panel display unit 411 (color panel) has a γ value obtained in a state where the first panel and the second panel are overlapped to be about G _out = 2.2. The γ ₁ value of the image data output from the first panel) is set to G ₁ = 1.8 to 2.5, and the image data output from the second panel display unit 421 (second panel) which is a monochrome panel. it is preferred to a gamma ₂ values and _G 2 = 0.1 to 0.3.

The gradation conversion unit (1) 412 and the gradation conversion unit (2) 422 perform gradation conversion processing so that each γ value (γ ₁ value and γ ₂ value) falls within the above range. FIG. 19A shows the relationship between the gradation values before and after gradation conversion of the first panel (broken line) and the second panel (solid line). In this figure, G ₁ = about 0.2, G ₂ = about 2.4, and the γ value is slightly changed depending on the gradation.

  Next, the gradation correction process performed after the gradation conversion process in the second liquid crystal panel that performs monochrome display will be described below.

  This gradation correction processing is performed in order to improve luminance unevenness caused by the difference in the gap between the liquid crystal cells depending on the pixel position on the display panel.

  In the present embodiment, gradation correction processing is performed in the gradation correction unit 423. When this gradation correction is performed, correction data 424 stored in the memory 425 is used. First, a method for creating correction data will be described.

  The correction data is created by measuring the luminance of a display panel having a configuration in which the first panel and the second panel are overlaid in pixel units (here, 8 × 8 pixels are set as one pixel unit). . In the case of a display panel composed of 1024 (horizontal direction (x direction)) × 720 (vertical direction (y direction)) pixels, for example, the coordinates of the pixel at the upper left end of the display panel are ( 1, 1), the position of each pixel can be determined by (x, y) (x is an integer from 1 to 1024 and y is an integer from 1 to 720).

  FIG. 18 shows how the luminance of the display panel is detected in order to acquire the luminance data of each pixel. As shown in this figure, in a state where the first panel display unit 411 and the second panel display unit 421 are overlapped, a light source (light source of the liquid crystal display device 100) is irradiated from the second panel display unit 421 side, and the panel Is displayed in white. In this state, the luminance detector 450 is scanned in the direction of arrow A, for example, to detect the output luminance at each pixel position. Thereby, luminance data for each pixel position (x, y) (hereinafter, this data is referred to as pixel / luminance data) is obtained.

  The obtained pixel / luminance data is input to the threshold value determination unit 430 in the display controller 400. The threshold value determination unit 430 determines a threshold value for gradation correction processing in the second panel for each pixel based on the pixel / luminance data. The threshold value is determined based on the relative luminance for each pixel in the display panel.

In particular,
When the relative intensity of the lowest pixel unit of relative brightness and X _n, the relative brightness of an arbitrary pixel units and X _m, the maximum tone value that each pixel can take the Y,
The threshold value M in arbitrary pixel units is expressed by the following equation (1).
M = (X _n / X _m ) ^{(1 / γ)} × Y (1)
(Γ is the γ value indicating the gradation luminance characteristics of the liquid crystal panel)
Determined by

  Here, the maximum gradation value Y that each pixel can take is, for example, 255 (256) for an 8-bit signal and 63 (64) for a 6-bit signal.

For example, in the case of an 8-bit signal, if the relative luminance of the pixel with the highest luminance is 1 and the relative luminance of the pixel with the lowest luminance is 0.9, the threshold value of the pixel with the lowest luminance is 255. On the other hand, the threshold value of the brightest pixel is
M = (0.9 / 1.0) ^{(1 / γ)} × 255 = 242 (where γ = 2.2)
Accordingly, the threshold value of the pixel with the highest luminance is 242.

  As described above, since the threshold value is determined for each pixel, the correction data is created by associating the pixel position (x, y) with the threshold value of the pixel. The created correction data is transferred to the memory 425 in the liquid crystal display driver (2) 420. The correction data stored in the memory 425 is preferably a lookup table (LUT) in which the pixel position (x, y) and the threshold value of the pixel are associated with each other.

  Note that the threshold value determination method described here is an example, and the present invention is not limited to this. However, the threshold value is based on the relative luminance with other pixel units obtained in pixel units, in order to reduce the variation in luminance generated for each position of the display panel. It is preferable that the luminance is set as a reference.

  Next, the gradation correction process in the gradation correction unit 423 will be described. The gradation correction process is performed by referring to the correction data 424 created as described above. Specifically, when the gradation value of each pixel of the video source signal transmitted from the gradation conversion unit 422 exceeds the threshold value of the gradation value of the corresponding pixel in the correction data 424, the gradation value is Correct to threshold. The gradation correction unit 423 outputs the corrected threshold value as a gradation value.

  FIG. 19B shows the tone value of the original signal (the tone value before tone conversion) when tone correction processing is performed on the black and white liquid crystal panel, and after tone conversion and tone correction processing. The relationship with the gradation value is shown. As shown in FIG. 19B, among the gradation values of the monochrome panel signal shown in FIG. 19A, gradation values exceeding the threshold value are corrected to the threshold value.

  Thus, the threshold value is the upper limit value of the gradation value of each pixel that is corrected by the gradation correction unit 423.

  As described above, the gradation correction is performed by the correction unit described above, so that the luminance of the high luminance pixel can be lowered in accordance with the low luminance pixel. As a result, it is possible to improve luminance unevenness when a plurality of liquid crystal panels are stacked to display an image.

  In addition, since gradation correction is performed on the monochrome liquid crystal panel side, luminance unevenness can be improved by a simple process of providing an upper limit value and cutting the luminance exceeding the upper limit value. For example, Non-Patent Document 1 (Japanese Utility Model Publication No. 3-77795) is intended to improve luminance unevenness in a color display device. However, signal processing is complicated because each RGB signal needs to be corrected. (The memory is three times as large as that of black and white), and a coefficient signal indicating how much the luminance is lowered with respect to the input signal is stored. On the other hand, in the present invention, a color panel and a monochrome panel are superposed, and a method of cutting gradation values exceeding a threshold value on the monochrome panel side is adopted. Therefore, it is possible to improve luminance unevenness as the entire color display panel with a simple processing method.

  As described above, according to the present invention, when the second panel is a monochrome liquid crystal panel, the configuration of the second panel is simplified, the number of drivers can be reduced, and a plurality of color liquid crystal panels are stacked. Moire generated in the above can be suppressed. Therefore, it is possible to provide a liquid crystal display device that has a high contrast ratio, suppresses moire, and improves display quality.

  The liquid crystal display device of the present invention is not necessarily limited to one constituted by two liquid crystal panels. That is, three or more liquid crystal panels may be used. In this case, the brightness of the black display can be further reduced and the contrast ratio can be further improved by setting the outermost liquid crystal panel as a color liquid crystal panel and the other liquid crystal panels as black and white panels. In this case, it is preferable that a correction unit is provided in each of the plurality of black and white liquid crystal panels. In order to easily perform the correction process, it is preferable that only one monochrome panel is provided.

[Embodiment 2]
A television receiver to which the liquid crystal display device of the present invention is applied will be described below with reference to FIGS.

  FIG. 24 shows a circuit block of a liquid crystal display device 601 for a television receiver.

  As shown in FIG. 24, the liquid crystal display device 601 includes a Y / C separation circuit 500, a video chroma circuit 501, an A / D converter 502, a liquid crystal controller 503, a liquid crystal panel 504, a backlight drive circuit 505, a backlight 506, a microcomputer. 507 and a gradation circuit 508 are provided.

The liquid crystal panel 504 has a two-panel configuration including a first liquid crystal panel and a second liquid crystal panel, and may have any of the configurations described in the above-described embodiments.
In the liquid crystal display device 601 having the above configuration, first, an input video signal of a television signal is input to the Y / C separation circuit 500 and separated into a luminance signal and a color signal. The luminance signal and the color signal are converted into R, G, and B which are the three primary colors of light by the video chroma circuit 501, and the analog RGB signal is converted into a digital RGB signal by the A / D converter 502, and the liquid crystal Input to the controller 503.

  In the liquid crystal panel 504, RGB signals from the liquid crystal controller 503 are input at a predetermined timing, and RGB gradation voltages from the gradation circuit 508 are supplied to display an image. The microcomputer 507 controls the entire system including these processes.

  Video signals are displayed based on various video signals such as video signals based on television broadcasts, video signals captured by cameras, video signals supplied via the Internet, video signals recorded on DVDs, etc. Is possible.

  25 receives a television broadcast and outputs a video signal, and the liquid crystal display device 601 displays an image (video) based on the video signal output from the tuner unit 600.

  When the liquid crystal display device having the above configuration is a television receiver, for example, as shown in FIG. 26, the liquid crystal display device 601 is sandwiched between the first housing 301 and the second housing 306. It has a configuration.

  The first housing 301 is formed with an opening 301 a that transmits an image displayed on the liquid crystal display device 601.

  The second housing 306 covers the back side of the liquid crystal display device 601. An operation circuit 305 for operating the liquid crystal display device 601 is provided, and a support member 308 is attached below. ing.

As described above, in the television receiver and the video monitor having the above-described configuration, by using the liquid crystal display device of the present invention as the display device, it is possible to display an image with high contrast, high response speed, and high display quality. It becomes possible.
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The liquid crystal display device of the present invention can be applied to a television receiver, a movie monitor, a broadcast monitor, and the like because luminance unevenness is improved and contrast can be greatly improved.

1 is a schematic cross-sectional view of a liquid crystal display device according to an embodiment of the present invention. It is a figure which shows the arrangement | positioning relationship between the polarizing plate and panel in the liquid crystal display device shown in FIG. FIG. 2 is a plan view of the vicinity of a pixel electrode of the liquid crystal display device shown in FIG. 1. It is a schematic block diagram of the drive system which drives the liquid crystal display device shown in FIG. It is a figure which shows the connection relation of the driver and panel drive circuit of the liquid crystal display device shown in FIG. It is a schematic block diagram of the backlight with which the liquid crystal display device shown in FIG. 1 is provided. FIG. 2 is a block diagram of a display controller that is a drive circuit that drives the liquid crystal display device shown in FIG. 1. It is a schematic sectional drawing of the liquid crystal display device of 1 sheet of liquid crystal panels. It is a figure which shows the arrangement | positioning relationship between the polarizing plate and panel in the liquid crystal display device shown in FIG. (A)-(c) is a figure explaining the principle of contrast improvement. (A)-(d) is a figure explaining the principle of contrast improvement. (A)-(c) is a figure explaining the principle of contrast improvement. (A) (b) is a figure explaining the principle of contrast improvement. (A)-(c) is a figure explaining the principle of contrast improvement. (A) (b) is a figure explaining the principle of contrast improvement. (A) (b) is a figure explaining the principle of contrast improvement. FIG. 8 is a block diagram showing a specific configuration of the display controller shown in FIG. 7. It is a schematic diagram which shows a mode that the brightness | luminance detection of a display panel is performed in order to acquire the brightness | luminance data of each pixel. (A) is a graph which shows the relationship of the gradation value before and after gradation conversion in the liquid crystal display drive part of each liquid crystal panel. (B) is a graph showing the gradation value when the gradation value exceeding the threshold value is corrected to the threshold value in the monochrome liquid crystal panel. (A) (b) is the schematic explaining the signal waveform of Embodiment 1. FIG. It is a figure explaining the signal waveform of Embodiment 1. FIG. 3 is an example of pixel sizes of a first panel and a second panel of Embodiment 1. 4 is an example of enlarging the pixels of the second panel of the first embodiment. It is a schematic block diagram of the television receiver provided with the liquid crystal display device of this invention. FIG. 25 is a block diagram illustrating a relationship between a tuner unit and a liquid crystal display device in the television receiver illustrated in FIG. 24. FIG. 26 is an exploded perspective view of the television receiver shown in FIG. 25.

Explanation of symbols

201 Scanning signal wiring 202 Auxiliary capacitance wiring 203 TFT element 204 Data signal wiring 205 Drain lead-out wiring 206 Auxiliary capacitance forming electrode 207 Interlayer insulating film 208 Pixel electrode 210 Transparent substrate 211 Slit patterns 212a to 212f Slit 220 Color filter substrate 220 ′ Counter substrate 221 Color filter 222 Protrusion 223 Counter electrode 224 Black matrix 225 Vertical alignment film 226 Liquid crystal 227 Transparent layer 228 Flattening film 230 Active matrix substrate 100 Liquid crystal display device 101a / 101b / 101c Polarizing plate 412 Gradation conversion section (1)
422 gradation conversion unit (2)
423 Tone correction unit (correction means)
424 Correction data 430 Threshold value determination unit 600 Tuner unit 601 Liquid crystal display device

Claims (5)

A liquid crystal display device configured by optically superposing a plurality of liquid crystal panels and outputting image data based on the same video source to each of the liquid crystal panels,
Based on the output luminance obtained when the light source is irradiated in a state where the plurality of liquid crystal panels are overlapped, the upper limit value of the gradation value determined for each pixel unit consisting of at least one pixel is set as a threshold value.
Among the plurality of stacked liquid crystal panels, a color liquid crystal panel is disposed as the outermost liquid crystal panel, and a monochrome liquid crystal panel is disposed as at least one other liquid crystal panel,
In the black-and-white liquid crystal panel, when a gradation value corresponding to a pixel in the pixel unit obtained from the video source exceeds the threshold value, correction means for correcting the gradation value below the threshold value is provided. A liquid crystal display device.   2. The liquid crystal display according to claim 1, wherein the threshold value is set based on a pixel unit having the lowest relative luminance based on a relative luminance with another pixel unit obtained in the pixel unit. apparatus. When the relative intensity of the lowest pixel unit of relative brightness and X _n, the relative brightness of an arbitrary pixel units and X _m, the maximum tone value that each pixel can take the Y,
The threshold value M in arbitrary pixel units is expressed by the following equation (1).
M = (X _n / X _m ) ^{(1 / γ)} × Y (1)
(Γ is the γ value indicating the gradation luminance characteristics of the liquid crystal panel)
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is determined by: A method of driving a liquid crystal display device, wherein a plurality of liquid crystal panels are optically overlapped and output image data based on the same video source to each of the liquid crystal panels,
Based on the output luminance obtained when the light source is irradiated in a state where the plurality of liquid crystal panels are overlapped, the upper limit value of the gradation value determined for each pixel unit consisting of at least one pixel is set as a threshold value.
When the color liquid crystal panel is arranged as the outermost liquid crystal panel among the plurality of liquid crystal panels overlaid and the monochrome liquid crystal panel is arranged as at least one other liquid crystal panel,
In the black-and-white liquid crystal panel, when a gradation value corresponding to a pixel in the pixel unit obtained from the video source exceeds the threshold value, processing for correcting the gradation value to be equal to or less than the threshold value is performed. For driving a liquid crystal display device.   A television set comprising: a tuner unit that receives a television broadcast; and the liquid crystal display device according to claim 1 that displays the television broadcast received by the tuner unit. Receiving machine.