JP4566579B2 - Driving method of liquid crystal display device - Google Patents

Description

  The present invention relates to a driving method of a liquid crystal display device that displays a desired image by controlling the tilt angle of liquid crystal molecules with respect to a substrate surface for each pixel.

  A liquid crystal display device is advantageous in that it is thin and lightweight, can be driven at a low voltage, and has low power consumption, and is used in various electronic devices. In particular, an active matrix type liquid crystal display device in which a TFT (Thin Film Transistor) is provided for each pixel is superior to a CRT (Cathode-Ray Tube) in terms of display quality. Widely used in displays such as computers.

  Conventional TN (Twisted Nematic) type liquid crystal display devices have poor viewing angle characteristics compared to CRTs, and contrast and color tone change greatly when the screen is viewed from the front and obliquely. There was a drawback of end. For this reason, various techniques for improving viewing angle characteristics have been developed and put into practical use. As a liquid crystal display device using this type of technology, for example, Japanese Patent Application Laid-Open No. 11-242225 (Patent Document 1) discloses an MVA having a plurality of regions (domains) in which alignment directions of liquid crystal molecules are different from each other in one pixel. A (Multi-domain Vertical Alignment) type liquid crystal display device is described.

  1A and 1B are schematic cross-sectional views showing the basic structure of an MVA liquid crystal display device. A pixel electrode 11 is formed on the first substrate 10, and a protrusion (bank) 12 is formed on the pixel electrode 11 as a domain regulating structure. The surface of the pixel electrode 11 and the protrusion 12 is covered with a vertical alignment film 13.

  Further, a color filter 21 is formed on the second substrate 20 (lower side in FIG. 1A), and a counter electrode (common electrode) 22 is formed on the color filter 21. Further, a protrusion 23 is formed on the counter electrode 22 as a domain regulating structure. As shown in FIG. 1A, the protrusion 23 on the second substrate 20 side is disposed between the protrusions 12 on the first substrate 10 side. The surfaces of the protrusions 23 and the counter electrode 22 are covered with a vertical alignment film 24.

  The first substrate 10 and the second substrate 20 are disposed so that the surfaces on which the alignment films 13 and 24 are formed are opposed to each other, and a vertical alignment type liquid crystal (a dielectric anisotropy is negative) between the substrates 10 and 20. The liquid crystal layer 30 made of the liquid crystal is encapsulated. The first substrate 10, the second substrate 20 and the liquid crystal layer 30 constitute a liquid crystal panel 40. The thickness (cell gap) of the liquid crystal layer 30 is kept constant by a spacer (not shown) disposed between the substrates 10 and 20. In addition, polarizing plates (not shown) are arranged above and below the liquid crystal panel 40 with their absorption axes orthogonal to each other.

  In the liquid crystal display device thus configured, the liquid crystal molecules 30 a are aligned perpendicularly to the surfaces of the alignment films 13 and 24 when no voltage is applied between the pixel electrode 11 and the counter electrode 22. Accordingly, as shown in FIG. 1A, the liquid crystal molecules 30a in the vicinity of the protrusions 12 and 23 are oriented obliquely with respect to the substrate surface, but most of the liquid crystal molecules 30a are oriented perpendicular to the substrate surface. In this case, the light that has entered the liquid crystal layer 30 from the lower side of the substrate 10 through the one polarizing plate passes through the liquid crystal layer 30 without changing the polarization direction, and is blocked by the polarizing plate on the substrate 20. . That is, in this case, the display is dark.

  On the other hand, when a voltage higher than the voltage (threshold voltage) between the pixel electrode 11 and the counter electrode 22 is applied, the voltage between the pixel electrode 11 and the counter electrode 22 is changed as shown in FIG. The liquid crystal molecules 30a are aligned in an oblique direction with respect to the electric field. In this state, the light that has entered the liquid crystal layer 30 through the polarizing plate from the lower side of the substrate 10 changes its polarization direction in the liquid crystal layer 30 and passes through the polarizing plate on the substrate 20. That is, in this case, the display is bright.

  By adjusting the voltage applied to the pixel electrode 11, bright, dark, and intermediate gradations can be displayed. Further, by controlling the voltage applied to the pixel electrode for each pixel, a desired image is displayed on the liquid crystal display device.

  In the MVA type liquid crystal display device described above, when a voltage is applied, due to the influence of the initial alignment of the liquid crystal molecules 30a in the vicinity of the protrusions 12 and 23, as shown in FIG. The inclination directions of the liquid crystal molecules 30a are different on both sides. When multi-domain is achieved in this way, light leakage in an oblique direction with respect to the substrate surface is suppressed, so that viewing angle characteristics are remarkably improved.

  In the above example, the case where the protrusions 12 and 23 are used as the domain regulating structure has been described. However, a slit provided on at least one of the pixel electrode 11 and the counter electrode 22 or a substrate surface (electrode or A depression (groove) provided in the insulating film thereon may be used as a domain regulating structure.

  FIG. 2 shows an example in which slits 11a and 22a are provided in the electrodes 11 and 22 as domain regulating structures, respectively. In a state where no voltage is applied, the liquid crystal molecules 30a are aligned in a direction perpendicular to the substrate surface. On the other hand, when a voltage is applied between the pixel electrode 11 and the counter electrode 22, an electric field is generated obliquely toward the center of the slits 11a and 22a at the edges of the slits 11a and 22a, and the liquid crystal molecules 30a are inclined. The direction is determined. Therefore, as shown in FIG. 2, the tilt directions of the liquid crystal molecules 30a are different on both sides of the slits 11a and 22a, and multi-domain is achieved.

In the above example, the case where the domain regulating structure is provided on both the pair of substrates 10 and 20 has been described. However, the domain regulating structure may be provided only on one of the substrates.
Japanese Patent Laid-Open No. 11-242225

  However, in the above-described conventional MVA type liquid crystal display device, a phenomenon that a portion with low luminance becomes whitish when the screen is viewed from an oblique direction (hereinafter referred to as discolor) occurs.

  In view of the above, an object of the present invention is to provide a driving method of a liquid crystal display device that can suppress a phenomenon that a portion with low luminance becomes whitish when the screen is viewed in an oblique direction (white-brown), and display performance is further improved. That is.

In the present invention, in a driving method of a liquid crystal display device that displays an image by controlling a voltage applied to a liquid crystal for each pixel, one frame period is divided into a first period and a second period, and the first and second periods are divided. The voltage applied during the first period is individually controlled, and the voltage applied during the first period is determined by determining the voltage applied during the first period in accordance with an image signal and controlling the voltage applied during the second period. Divides the range of the applied voltage in the first period into the first, second, and third ranges from the lowest voltage, and the second range is a transmittance when the screen is viewed from an oblique direction. Is a voltage range higher than the transmittance when viewed from the front, and when the applied voltage in the first period is in the first range, the applied voltage in the second period is set to 0 V, and the first When the applied voltage in the period is in the third range, the applied voltage in the second period The same city as the applied voltage of the first period, the applied voltage of the second period when the range applied voltage is the second of the first period, the transmittance and the diagonal direction when the screen is viewed from the front Is set so as to minimize the difference from the transmittance when viewed from above .

The lengths of the first period and the second period may be the same, and the lengths of the first period and the second period may be different.

  Examples of liquid crystal display devices to which the present invention can be applied include MVA (Multi-domain Vertical Alignment) type liquid crystal display devices, VA (Vertical Alignment) type liquid crystal display devices, and TN (Twisted Nematic) type liquid crystal display devices.

  Hereinafter, the present invention will be described in more detail.

  The inventors of the present application have studied the mechanism of occurrence of white tea. In FIG. 3, the horizontal axis represents the applied voltage, and the vertical axis represents the transmittance. When the screen of the conventional MVA type liquid crystal display device is viewed from the front (normal direction of the liquid crystal panel), TV (transmission) is shown. It is a figure which shows the result of having simulated the rate-applied voltage) characteristic and the TV characteristic when it sees from the diagonal direction (upper 60 degree direction). As can be seen from FIG. 3, when a voltage in the vicinity of the threshold (in this example, about 1.8 V to 3.0 V) is applied, the transmittance when viewed from an oblique direction is the transmission when viewed from the front. When a voltage higher than that is applied, the transmittance when viewed from an oblique direction is lower than the transmittance when viewed from the front.

  The phenomenon that the transmittance increases when viewed from an oblique direction when the applied voltage is low is recognized as a color change. That is, when examining the gradation histogram of the three primary colors of red (R), green (G), and blue (B) of the image, the luminance difference between red, green, and blue decreases when the screen is viewed from an oblique direction. The result screen becomes whitish. In this way, white brown is generated.

  The applicant of the present application has proposed a liquid crystal display device in which a plurality of regions having different threshold values of TV characteristics are provided in one pixel in order to suppress the browning. Such a liquid crystal display device can be realized, for example, by dividing the pixel electrode into a plurality of subpixel electrodes and capacitively coupling the subpixel electrodes. It can also be realized by partially forming a dielectric film on at least one of the pixel electrode and the counter electrode.

  FIG. 4 shows the applied voltage on the horizontal axis and the transmissivity on the vertical axis, as seen from the front of the two regions (first region and second region) in one pixel formed as described above. It is a figure which shows TV characteristic at the time of seeing, and TV characteristic when it sees from the diagonal direction. Here, the lower region of the TV characteristic is defined as the first region, and the higher threshold voltage is defined as the second region.

  In FIG. 4, the solid line indicates the TV characteristics when viewed from the front in the first region and the second region, and the broken line is viewed from an oblique direction (up to 60 °) in the first region and the second region. The TV characteristics are shown. The TV characteristic of one pixel is a characteristic obtained by synthesizing the TV characteristics of the first region and the second region. In FIG. 4, the characteristics obtained by synthesizing the TV characteristics of the first and second regions are indicated by a one-dot chain line.

  From the comparison between the TV characteristics shown by the one-dot chain line and the TV characteristics shown in FIG. 3, the transmittance when viewed from the front when the applied voltage is low and the transmittance when viewed from an oblique direction are obtained. It can be seen that the difference becomes smaller and white browning is suppressed. Hereinafter, such a method for preventing white-browning by a plurality of regions having different TV characteristics will be referred to as an HT (halftone gray scale) method.

  However, in the above-described HT method, the manufacturing process of the liquid crystal display device increases and the manufacturing cost increases. In addition, in the HT method using capacitive coupling, a driving voltage is increased, so that a high-breakdown-voltage driver IC is required and an aperture ratio is reduced.

  Therefore, in the present invention, the browning is suppressed by devising the driving method without changing the basic structure of the pixel portion.

(First embodiment)
FIG. 5 is a plan view showing a pixel portion of a liquid crystal display device to which the driving method of the present invention is applied, and FIG. 6 is a schematic sectional view of the pixel portion.

  As shown in FIG. 6, this liquid crystal display device includes a pair of glass substrates 110 and 120, and a vertically aligned liquid crystal (liquid crystal having negative dielectric anisotropy) sealed between the glass substrates 110 and 120. A liquid crystal panel 140 including the liquid crystal layer 130. The space | interval of the glass substrate 110 and the glass substrate 120 is maintained constant by the spacer (not shown) arrange | positioned between both. On both sides of the liquid crystal panel 140, polarizing plates 141a and 141b are disposed with their absorption axes orthogonal to each other. A backlight (not shown) is disposed on one side of the liquid crystal panel 140.

  As the liquid crystal constituting the liquid crystal layer 130, for example, a negative type liquid crystal manufactured by Merck can be used. The thickness (cell thickness) of the liquid crystal layer 130 is, for example, 4 μm.

  As shown in FIG. 5, a plurality of gate bus lines 111 extending in the horizontal direction and a plurality of data bus lines 113 extending in the vertical direction are formed on one glass substrate 110 at predetermined intervals. . The gate bus lines 111 are arranged at a pitch of 300 μm, for example, and the data bus lines 113 are arranged at a pitch of 100 μm, for example. The gate bus line 111 and the data bus line 113 are electrically separated by a first insulating film (not shown). A plurality of rectangular areas partitioned by the gate bus lines 111 and the data bus lines 113 are pixel areas. Further, on the glass substrate 110, an auxiliary capacity bus line 112 that crosses the center of each pixel region is formed in parallel with the gate bus line 111.

  A storage capacitor electrode 114, a TFT 115, and a pixel electrode 116 made of a transparent conductor such as ITO (Indium-Tin Oxide) are provided for each pixel region. The auxiliary capacitance electrode 114 and the TFT 115 are covered with a second insulating film (not shown), and the pixel electrode 116 is formed on the second insulating film.

  In the liquid crystal display device shown in FIGS. 5 and 6, a part of the gate bus line 111 is used as the gate electrode of the TFT 115. Further, the drain electrode of the TFT 115 is connected to the data bus line 113, and the source electrode is connected to the pixel electrode 116 through a contact hole provided in the second insulating film. Further, the auxiliary capacitance electrode 114 is formed between the auxiliary capacitance bus line 112 and the pixel electrode 116 via a first insulating film and a second insulating film, respectively, and is provided on the second insulating film. It is electrically connected to the pixel electrode 116 through a contact hole.

  The pixel electrode 116 is provided with a plurality of slits 116a as a domain regulating structure. These slits 116 a are arranged along a plurality of zigzag lines that obliquely intersect the data bus line 113 and bend at the intersections between the gate bus line 111 and the auxiliary capacitor bus line 112. The width of the slit 116a is, for example, 10 μm. The surface of the pixel electrode 116 is covered with a vertical alignment film 118 made of polyimide, for example. As the vertical alignment film 118, for example, a vertical alignment film manufactured by JSR Corporation can be used.

  On the other glass substrate 120 (lower side in FIG. 6), a color filter 121, a counter electrode (common electrode) 123 made of a transparent conductor such as ITO, and a domain regulating protrusion (bank) 124 are formed. Has been. As shown in FIG. 5, the protrusions 124 are disposed between adjacent slit rows in the horizontal direction.

  These protrusions 124 are formed using, for example, a photoresist. The width of the protrusion 124 is, for example, 10 μm, and the height is, for example, 1.4 μm. The interval between the protrusion 124 and the slit 116a is, for example, 25 μm. The surfaces of the counter electrode 123 and the protrusion 124 are covered with a vertical alignment film 128 made of polyimide, for example.

  Hereinafter, the substrate 110 on which the TFT 115, the pixel electrode 116, and the like are formed is referred to as a TFT substrate, and the substrate 120 on which the counter electrode 123 and the like are formed and disposed to face the TFT substrate is referred to as a counter substrate.

  Although not shown in FIGS. 5 and 6, at least one of the TFT substrate and the counter substrate is formed with a black matrix for shielding the area between the pixels and the TFT formation area. The color filter 121 may be provided on the TFT substrate side.

  FIG. 7 is a block diagram illustrating a driving circuit of the liquid crystal display device according to the first embodiment. This drive circuit is composed of a controller unit 100, a reference power supply circuit unit 101, a data driver 102, a gate driver 103, and a display unit 104 composed of a set of a plurality of pixels.

  The controller unit 100 receives an image signal (for example, a red (R) signal, a green (G) signal, and a blue (B) signal) and a synchronization signal (for example, a horizontal synchronization signal and a vertical synchronization signal) from a device such as a computer. A timing signal is generated and output to the reference power supply circuit unit 101, the data driver 102, and the gate driver 103.

  The reference power supply circuit unit 101 outputs a reference voltage to the data driver 102 according to the timing signal from the controller unit 100. The data driver 102 inputs an image signal and a timing signal from the controller unit 100 and a reference voltage from the reference power supply circuit unit 101, and supplies a data signal to the data bus line 113 of the display unit 104 at a predetermined timing. The gate driver 103 generates a scanning signal from the timing signal input from the controller unit 100 and supplies the scanning signal to the gate bus line 111 of the display unit 104 in order.

  The TFT 115 is turned on when a scanning signal is supplied to the gate bus line 111, and transmits the data signal supplied to the data bus line 113 to the pixel electrode 116. In this way, a voltage is applied to the pixel electrode 116.

  Note that part or all of the driving circuit may be formed integrally with the display portion (liquid crystal panel), or the driving circuit and the display portion 104 are formed separately and electrically connected via a flexible substrate or the like. May be.

  8A to 8C are schematic diagrams showing voltages (data signals) applied to the pixel electrodes 116. FIG. In the present embodiment, the controller 100 divides one frame period into first and second periods, and independently controls the voltage applied to the pixel electrode 116 in the first and second periods. One frame period is the inverse ratio of the number of screen rewrites per second, and in the case of a general liquid crystal display device, one frame period is 16.7 ms (1 second / 60 frames).

As described above, white browning occurs when the transmittance when viewed from an oblique direction is higher than the transmittance when viewed from the front, and this phenomenon occurs when the applied voltage is low. On the other hand, as shown in FIGS. 8A to 8C, if the first voltage h ₁ is applied in the first period and the second voltage h ₂ is applied in the second period, The substantial luminance is intermediate between the luminance in the first period and the luminance in the second period. Therefore, the voltage range in which white breakage occurs is narrowed by individually controlling the applied voltage in the first period and the second period, and the same effect as the HT method described above can be obtained. Hereinafter, a method of obtaining the same effect as the HT method by dividing one frame period into a plurality of periods and individually controlling the applied voltage for each period will be referred to as a time-division HT method.

  8A to 8C, the voltage applied to the pixel electrode is a positive voltage. However, in an actual liquid crystal display device, for example, the polarity of the applied voltage is reversed every frame in order to prevent image sticking. ing. Therefore, also in this embodiment, as shown in FIGS. 9A to 9C, the polarity of the applied voltage (data signal) is inverted every frame.

  FIG. 10 is a flowchart illustrating a driving method of the liquid crystal display device according to the first embodiment.

When the controller unit 100 inputs an image signal in step S11, the controller unit 100 proceeds to step S12, and determines the applied voltage h1 in the _first period according to the image signal. Basically, the applied voltage h ₁ in the first period may be a voltage when the image signal is DA (digital-analog) converted by the data driver 102. Next, the controller unit 100 proceeds to _one of steps S13, S14, and S15 according to the voltage value of the applied voltage h1 in the _first period, and determines the applied voltage h2 in the _second period.

That is, when the applied voltage h ₁ in the first period is less than 2.5V (h ₁ <2.5V), the process proceeds from step S12 to step S13, and the applied voltage h ₂ in the second period is set to 0V ( h ₂ = 0V). The voltage applied to the first period is a voltage applied h ₂ of the second period and 0V when less than 2.5V is because does not occur discolor in this voltage range.

When the applied voltage h _{1 in} the first period is 2.5 V or more and 5 V or less (2.5 V ≦ h ₁ ≦ 5 V), the process proceeds from step S12 to step S14, and the applied voltage h _{2 in} the second period. Is determined according to the applied voltage h ₁ in the first period. At this time, the relationship between the applied voltage h ₁ in the first period and the applied voltage h _{2 in} the second period is obtained by a preliminary experiment shown below, and is set in the controller unit 100 in advance.

That is, in the preliminary experiment, as shown in FIG. 11, the light receiving elements (PMTs) 145 a and 145 b are arranged on the front surface of the liquid crystal panel 140 and in an oblique direction (in this example, upward 60 ° direction). Then, a constant voltage with a period from 2.5V to 5V is applied as the first voltage _{h 1} in the first period to the liquid crystal panel 140, from 0V in the second period to the first voltage _{h 1} Is applied to obtain a voltage with the smallest difference in luminance measured by the light receiving elements 145a and 145b. Thereafter, the applied voltage h1 in the _first period is changed, and the voltage in the second period in which the difference in luminance measured by the light receiving elements 145a and 145b is minimized is obtained. In this way, the second applied voltage h ₂ that minimizes the difference in luminance measured by the light receiving elements 145a and 145b for each applied voltage h ₁ in the first period is obtained, and the first applied voltage h ₁ and A relationship with the second applied voltage h ₂ is set in the controller unit 100.

Note that the optimum value of the applied voltage h2 in the _second period differs depending on the structure of the liquid crystal panel (size, cell gap, domain regulating structure, resolution, type of liquid crystal, etc.), so preliminary experiments were performed for each panel structure. , it is necessary to set the relation between the applied voltage h ₁ of the first period to the controller 100 according to the result and the applied voltage h ₂ of the second period.

In step S12, the voltage applied _{h 1} of the first period is greater than 5V _(h 1> 5V) when the processing proceeds to step S15, the voltage applied to the voltage applied _{h 2} of the second period the first period h ₁ (h ₂ = h ₁ ). The applied voltage h ₁ of the first period is a voltage applied h ₂ of the second period the same as the applied voltage h ₁ of the first period when it exceeds 5V is that discolor occurs in this voltage range This is because, in addition to this, in order to ensure higher luminance, it is better to apply a high voltage also in the second period.

After such determining the applied voltage h ₂ of the applied voltage h ₁ and second period of the first period, the process proceeds to step S16. Then, the controller unit 100, a reference power supply circuit unit 101 controls the data driver 102 and gate driver 103, to each pixel of the display unit 104, a first applied voltage _{h 1} is applied to the first period, applying a second applied voltage h ₂ in the second period.

FIG. 12 is a diagram illustrating a TV characteristic according to the driving method of the present embodiment, with the applied voltage in the first period on the horizontal axis and the transmittance on the vertical axis. Here, the TV characteristic in the case where the applied voltage h ₁ in the first period and the applied voltage h _{2 in} the second period are always the same (that is, the conventional example) is indicated by a one-dot chain line as a reference characteristic (Ref). ing. Further, the TV characteristic when viewed from the front according to the driving method (example) of the present embodiment is indicated by a solid line, and the TV characteristic when viewed from an oblique direction (up to 60 °) is indicated by a broken line. .

  As shown in FIG. 12, in this embodiment, the difference between the transmittance when viewed from the front when the applied voltage is low (3.5 V or less) and the transmittance when viewed from an oblique direction is small, and white brown It turns out that injury is suppressed.

  By the way, in the MVA liquid crystal display device having the structure shown in FIGS. 5 and 6, when a voltage is applied between the pixel electrode 116 and the counter electrode 123, liquid crystal molecules in a region near the slit 116 a or the protrusion 124 are predetermined. There is a slight time difference until the liquid crystal molecules in the region away from the slit 116a or the protrusion 124 are aligned in a predetermined direction after being aligned in the direction of. On the other hand, in this embodiment, since one frame is divided into first and second periods and the applied voltage in each period is individually controlled, the pixel is driven at a speed twice that of a conventional liquid crystal display device. Will be. When the driving speed is high and there is a difference in reaction speed between the liquid crystal molecules in the vicinity of the slit 116a or the protrusion 124 and the liquid crystal molecules in the area away from the slit 116a or the protrusion 124, T in one pixel. It can be regarded as having a plurality of regions having different threshold values of -V characteristics. Therefore, it is considered that the white brown reduction effect according to the present embodiment includes the effect of the above-described HT method.

In the above-described first embodiment, the length of the first period and the length of the second period are the same, but the length of the first period and the length of the second period may be different. . Further, in the first embodiment described above are the same or lower voltages than the voltage applied h ₁ of the applied voltage h ₂ of the second period the first period, the first to the second period the applied voltage h ₁ is applied, even if the first applied voltage h ₁ equal to or or lower also the second applied voltage h ₂ is applied to the first period, it is possible to obtain the same effect.

(Second Embodiment)
In the first embodiment, as described above, it is necessary to perform a preliminary experiment to determine the optimum value of the applied voltage in the second period for each structure of the liquid crystal panel. In the second embodiment and the third embodiment, the effect of suppressing white-browning was examined by determining the applied voltage in the second period on a constant basis without conducting a preliminary experiment.

In FIG. 13A, the horizontal axis represents the applied voltage h1 in the _first period, and the vertical axis represents the applied voltage h2 in the _second period. FIG. Note that this embodiment is different from the first embodiment in that the method for determining the applied voltage h2 in the _second period is different, and the basic structure of the liquid crystal panel and the drive circuit is the same as that of the first embodiment. Therefore, the description thereof is omitted here.

As shown in FIG. 13A, in the first driving method (hereinafter referred to as Example 1), when the applied voltage h1 in the _first period is less than 2.5V, the applied voltage in the second period. the h ₂ is set to 0V. In addition, when the applied voltage h ₁ in the first period is 2.5 V or more and 5.0 V or less, the second applied voltage h ₂ is changed from 0.1 V to 5 V according to the applied voltage h ₁ in the first period. Is linearly changed. Furthermore, when the applied voltage h1 in the _first period exceeds 5V, the applied voltage h2 in the _second period is the same as the applied voltage h1 in the _first period.

FIG. 13B shows the second driving method according to the second embodiment, with the horizontal axis representing the applied voltage h ₁ in the first period and the vertical axis representing the applied voltage h ₂ in the second period. FIG.

As shown in FIG. 13B, in the second driving method (hereinafter referred to as Example 2), when the applied voltage h1 in the _first period is less than 2.5V, the applied voltage in the second period. the h ₂ is set to 0V. Further, when the applied voltage h ₁ in the first period is 2.5 V or more and 4.0 V or less, the second applied voltage h ₂ is a straight line from 1 V to 4 V depending on the applied voltage h ₁ in the first period. Change. Further, when the applied voltage h ₁ of the first period is greater than 4V, and the voltage applied h ₂ of the second period the same as the applied voltage h ₁ of the first period.

FIG. 14A is a diagram showing a TV characteristic (solid line) when viewed from the front of the screen according to the first embodiment and a TV characteristic (broken line) from an oblique direction. FIG. 14B is a diagram showing a TV characteristic (solid line) when viewed from the front of the screen according to the second embodiment and a TV characteristic from the oblique direction (broken line). 14A and 14B, when the applied voltage h2 in the _second period is always the same as the applied voltage h1 in the _first period (Ref: conventional example), the TV characteristics are as follows. It is indicated by a dashed line.

  14 (a) and 14 (b), also in the driving method of the second embodiment (Example 1 and Example 2), the transmittance when viewed from the front when the applied voltage is low and the oblique viewing direction. It can be seen that the difference from the transmittance at the time is smaller than that of the conventional example and is not as high as that of the first embodiment, but the browning is suppressed as compared with the conventional example.

  Further, from the comparison between FIGS. 14A and 14B, it can be seen that the driving method of the second embodiment has a greater effect of suppressing the browning than the driving method of the first embodiment. This is considered to be because the effect of the HT method by time division is halved because the start method in the second period is low in the driving method of Example 1 and below the voltage at which the liquid crystal operates. In the driving method of the second embodiment, the start voltage in the second period is set to a relatively high voltage, and thus it is considered that the effect of the HT method by time division is sufficiently exhibited.

  As described above, although the effect of improving the browning is greatly changed by changing the voltage in the second period with respect to the first period, the second applied voltage in a certain interval is linearly changed as in the present embodiment. It was confirmed that even when changed to, white-browning can be improved compared to the conventional case.

(Third embodiment)
In the second embodiment, the effect of improving white-browning when the second applied voltage in a certain interval is linearly changed was examined. In the third embodiment, the second applied voltage is applied over the entire range. We investigated the effect of improving the white-brownness when linearly changing.

FIG. 15 is a diagram illustrating a driving method of the liquid crystal display device according to the third embodiment, in which the horizontal axis represents the applied voltage h ₁ in the first period and the vertical axis represents the applied voltage h ₂ in the second period. is there.

Here, as shown in FIG. 15, a comparative example is a case where the applied voltage in the second period is always 0V. Further, the case where the applied voltage h ₂ in the _second period is 0.5 times the applied voltage h ₁ in the first period is referred to as Example 3, and the applied voltage h ₂ in the _second period is the same as that in the first period. The case where the applied voltage h ₁ was 0.7 times was set as Example 4, and the effects of suppressing the browning of these Comparative Examples, Example 3 and Example 4 were examined.

In FIG. 16, the applied voltage h ₁ in the first period is taken on the horizontal axis, and the transmittance is taken on the vertical axis, and the liquid crystal panel is driven according to the third embodiment (h ₂ = 0.5 h ₁ ). It is a figure which shows TV characteristic (solid line) when it sees, and TV characteristic (dashed line) when it sees from the diagonal direction (upper 60 degrees). In FIG. 17, the applied voltage h ₁ in the first period is taken on the horizontal axis, and the transmittance is taken on the vertical axis, and the liquid crystal panel is driven according to Example 4 (h ₂ = 0.7 h ₁ ). It is a figure which shows TV characteristic (solid line) when it sees from the front direction (solid line) and TV characteristic (dashed line) when it sees from the diagonal direction (upper 60 degrees). Further, in FIG. 18, the horizontal axis represents the applied voltage h ₁ in the first period, the vertical axis represents the transmittance, and the liquid crystal panel was driven according to the comparative example (h ₂ = 0) as viewed from the front. It is a figure which shows TV characteristic (solid line) and TV characteristic (dashed line) when it sees from diagonal direction (upper 60 degrees) sometimes. 16, 17, and 18, when the applied voltage h ₁ in the first period and the applied voltage h _{2 in} the second period are the same (conventional example: Ref) when viewed from the front. The TV characteristics and the TV characteristics when viewed from an oblique direction are indicated by a one-dot chain line.

As can be seen from FIG. 16, in Example 3 (h ₂ = 0.5h ₁ ), the difference between the transmittance when viewed from the front when the applied voltage is low and the transmittance when viewed from the oblique direction is small. It was confirmed that white brown can be prevented.

In addition, as can be seen from FIG. 17, Example 4 (h ₂ = 0.7 h ₁ ) has an effect of suppressing browning as compared with the conventional example, but the effect is smaller than that of Example 3.

On the other hand, as shown in FIG. 18, in the comparative example in which the applied voltage h2 in the _second period is always 0V, the effect of preventing the browning is hardly recognized.

In the present embodiment, since the lower than the voltage applied even when the applied voltage h ₁ of the first period is higher the applied voltage h ₂ of the second period the first period, the first and second Although the brightness at the time of white display is lower than that of the first embodiment, there is an advantage that the circuit configuration is simplified as compared with the first and second embodiments.

  As described above, in the present invention, one frame period is divided into the first and second periods, and the applied voltage in the second period is controlled according to the applied voltage in the first period. It is possible to suppress a phenomenon that becomes whitish when viewed from an oblique direction (white brown). The present invention can obtain a greater effect when combined with a liquid crystal panel having a high response speed. The inventors of the present application use an MVA type liquid crystal panel, heat the panel temperature to 45 ° C. in order to increase the response speed of the liquid crystal, and drive by the method shown in the first to third embodiments, The improvement effect of white tea was investigated. As a result, in any case, it was confirmed that the effect of improving the white-brown color was even greater than when it was driven at room temperature. In the case of a liquid crystal display device using a backlight for high brightness, the temperature of the panel generally tends to be high. Therefore, by applying the driving method of the present invention to a liquid crystal display device using a backlight for high brightness. In addition, the effect of reducing the browning can be further increased, and a high-brightness liquid crystal display device with excellent display performance can be realized.

  In each of the first to third embodiments, the case where the present invention is applied to an MVA liquid crystal display device has been described. However, not only the MVA liquid crystal display device but also a VA (Vertical Alignment) liquid crystal display. This also occurs in devices and TN liquid crystal display devices. The present invention can also be applied to these liquid crystal display devices.

  In the first to third embodiments, the case where the present invention is applied to a transmissive liquid crystal display device has been described. However, the present invention may be applied to a reflective liquid crystal display device or a transflective liquid crystal display device.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

  (Supplementary Note 1) In a driving method of a liquid crystal display device that displays an image by controlling a voltage applied to a liquid crystal for each pixel, one frame period is divided into a first period and a second period, and the first and second periods A method for driving a liquid crystal display device, characterized in that the voltage applied during the period is individually controlled.

  (Additional remark 2) The applied voltage of the said 1st period is determined according to an image signal, The applied voltage of the said 2nd period is determined according to the applied voltage of the 1st period. A driving method of the liquid crystal display device described.

  (Supplementary Note 3) The range of the applied voltage in the first period is divided into the first, second, and third ranges from the lowest voltage, and when the applied voltage in the first period is in the first range The applied voltage in the second period is 0 V, and when the applied voltage in the first period is in the third range, the applied voltage in the second period is the same as the applied voltage in the first period, and 2. The liquid crystal display device according to appendix 1, wherein when the applied voltage in the first period is in the second range, the applied voltage in the second period is changed according to the applied voltage in the first period. Driving method.

  (Supplementary note 4) The supplementary note 1 is characterized in that the second applied voltage is set such that the difference between the transmittance when the screen is viewed from the front and the transmittance when the screen is viewed from the oblique direction is minimized. A method for driving a liquid crystal display device according to claim 1.

  (Supplementary note 5) The method for driving a liquid crystal display device according to supplementary note 1, wherein the first period and the second period have the same length.

  (Supplementary note 6) The method for driving a liquid crystal display device according to supplementary note 1, wherein the lengths of the first period and the second period are different.

  (Supplementary note 7) The method for driving a liquid crystal display device according to supplementary note 1, wherein an applied voltage in the second period is set to n times the first applied voltage (where 0 <n <1). .

  (Supplementary note 8) The method for driving a liquid crystal display device according to supplementary note 1, wherein dielectric anisotropy of the liquid crystal is negative.

  (Supplementary Note 9) The liquid crystal display device is any of an MVA (Multi-domain Vertical Alignment) liquid crystal display device, a VA (Vertical Alignment) liquid crystal display device, and a TN (Twisted Nematic) liquid crystal display device. The driving method of the liquid crystal display device according to appendix 1.

1A and 1B are schematic cross-sectional views showing the basic structure of an MVA liquid crystal display device. FIG. 2 is a schematic cross-sectional view showing a liquid crystal display device in which a slit is provided in an electrode as a domain regulating structure. FIG. 3 shows a simulation result of TV characteristics when the screen of a conventional MVA type liquid crystal display device is viewed from the front and TV characteristics when viewed from an oblique direction (upward 60 ° direction). FIG. FIG. 4 is a diagram showing a TV characteristic when viewed from the front of two areas (first area and second area) in one pixel and a TV characteristic when viewed from an oblique direction. is there FIG. 5 is a plan view showing a pixel portion of a liquid crystal display device to which the driving method of the present invention is applied. FIG. 6 is a schematic cross-sectional view showing a pixel portion of a liquid crystal display device to which the driving method of the present invention is applied. FIG. 7 is a block diagram showing a driving circuit of the liquid crystal display device according to the first embodiment of the present invention. FIGS. 8A to 8C are schematic diagrams (part 1) showing a voltage (data signal) applied to the pixel electrode. FIGS. 9A to 9C are schematic diagrams (part 2) showing a voltage (data signal) applied to the pixel electrode. FIG. 10 is a flowchart illustrating a driving method of the liquid crystal display device according to the first embodiment. FIG. 11 is a schematic diagram showing a preliminary experiment for determining the relationship between the applied voltage h ₁ in the first period and the applied voltage h _{2 in} the second period in the first embodiment. FIG. 12 is a diagram illustrating a TV characteristic according to the driving method of the first embodiment. FIG. 13A is a diagram illustrating a driving method according to Example 1 of the second embodiment, and FIG. 13B is a diagram illustrating a driving method according to Example 2 of the second embodiment. FIG. 14A is a diagram showing a TV characteristic when viewed from the front of the screen according to Example 1 of the second embodiment and a TV characteristic from an oblique direction, and FIG. FIG. 10 is a diagram showing a TV characteristic when viewed from the front of the screen according to Example 2 of the second embodiment and a TV characteristic from an oblique direction. FIG. 15 is a diagram illustrating a driving method of the liquid crystal display device according to the third embodiment. 16 takes an applied voltage h ₁ of the first period on the horizontal axis and the transmittance on the vertical axis, when viewed from the front when driving the liquid crystal panel according to Example 3 of the third embodiment It is a figure which shows TV characteristic when it sees from the TV characteristic and the diagonal direction (upper 60 degrees). FIG. 17 is a diagram illustrating a TV characteristic when viewed from the front when the liquid crystal panel is driven according to Example 4 of the third embodiment and a TV characteristic when viewed from an oblique direction (up to 60 °). It is. FIG. 18 is a diagram illustrating a TV characteristic when viewed from the front when the liquid crystal panel is driven according to a comparative example of the third embodiment and a TV characteristic when viewed from an oblique direction (up to 60 °). is there.

Explanation of symbols

10, 20 ... substrate,
11, 116 ... pixel electrodes,
11a, 22a, 116a ... slit,
12, 23, 124 ... projections,
13, 24, 118, 128 ... alignment film,
22 ... Counter electrode,
30, 130 ... liquid crystal layer,
30a ... Liquid crystal molecules,
40, 140 ... Liquid crystal panel,
100 ... Controller part,
101: Reference power supply circuit section,
102: Data driver,
103 ... Gate driver,
104 ... display part,
111 ... Gate bus line,
113 ... Data bus line,
115 ... TFT,
141a, 141b ... polarizing plates,
145a, 145b... Light receiving elements.

Claims (2)

In a driving method of a liquid crystal display device that displays an image by controlling a voltage applied to a liquid crystal for each pixel,
One frame period is divided into first and second periods;
Individually controlling the applied voltage in the first and second periods;
The control of the applied voltage in the first period determines the applied voltage in the first period according to an image signal,
The control of the applied voltage in the second period is as follows:
The range of applied voltage in the first period is divided into first, second, and third ranges from the lowest voltage, and the second range has front transmittance when the screen is viewed from an oblique direction. Is a voltage range higher than the transmittance when viewed from
When the applied voltage in the first period is in the first range, the applied voltage in the second period is 0 V, and when the applied voltage in the first period is in the third range, the applied voltage in the second period The applied voltage is the same as the applied voltage in the first period, and when the applied voltage in the first period is in the second range, the applied voltage in the second period is transmitted when the screen is viewed from the front. A driving method of a liquid crystal display device, characterized in that the difference between the transmittance and the transmittance when viewed from an oblique direction is minimized .   The liquid crystal display device is any one of an MVA (Multi-domain Vertical Alignment) liquid crystal display device, a VA (Vertical Alignment) liquid crystal display device, and a TN (Twisted Nematic) liquid crystal display device. 2. A method for driving a liquid crystal display device according to 1.

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