JP2011145712A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such problems that a display defect occurs under a specific drive condition or in a specific temperature range and hence the contrast degrades. <P>SOLUTION: An OCB liquid crystal display device displaying an image in a bend alignment state of a liquid crystal is disclosed, which has a voltage applying means for applying a voltage to the liquid crystal sealed inside a liquid crystal panel 132 and displaying the image by varying the applied voltages by the voltage applying means. The liquid crystal display device has a backlight element 131 at the back side of the liquid crystal panel 132, and the backlight element 131 has a strong light intensity at the long wavelength side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device used for a liquid crystal television, a portable OA device, and the like.

  At present, the most commonly used liquid crystal display devices are TN type (twisted nematic type). In recent years, OCB (Optically Compensated Bend) type liquid crystal display devices (sometimes called π cells) have been reported in various ways. This mode has the features of fast response and wide viewing angle. For details of the OCB type liquid crystal display device, please refer to “The Institute of Electrical Communication, IEICE Technical Report EDI98-144, pages 199”.

  Here, a conventional OCB type liquid crystal display device will be briefly described with reference to FIG. FIG. 21 is a schematic cross-sectional view of a conventional OCB-type liquid crystal display device, FIG. 21 (a) is a schematic cross-sectional view of a conventional OCB-type liquid crystal display device when no voltage is applied, and FIG. 21 (b) is the same. It is a schematic sectional drawing of a voltage application state.

  Nematic liquid crystal is injected between the substrates 2 and 3 constituting the OCB type liquid crystal display device 1, and the alignment state of the liquid crystal to which no voltage is applied is called the splay state 4 (FIG. 21 (a)). is there. By applying a relatively large voltage to the liquid crystal layer when the power is turned on, the splay alignment is changed to the bend alignment (FIG. 21 (b)). Displaying using this bend alignment state 5 is a feature of the OCB mode, and is a device that changes the transmittance of the panel by changing the magnitude of the voltage. FIG. 22 shows the voltage-transmittance characteristics of such an OCB type liquid crystal display device. The transmittance decreases with increasing applied voltage.

  The OCB type liquid crystal display device is usually operated within a voltage range in which the liquid crystal inside the liquid crystal panel maintains bend alignment. That is, when the voltage is lower than a specific voltage, the splay alignment state becomes stable, and splay alignment transition occurs. This voltage is defined as a transition voltage VL. When the transition from the bend alignment to the splay alignment occurs, the white level display transmittance rapidly decreases as shown in FIG. 22 (applied voltage <VL). FIG. 22 is a graph showing voltage-transmittance characteristics of the OCB type liquid crystal display device. At this time, there is a problem that the appearance varies greatly depending on the observation angle. Further, this transition is an irreversible change, and the pixel once having the splay alignment is left as a display defect (such as a bright spot) on the liquid crystal display device, thereby preventing its normal display operation.

  In addition, a TN liquid crystal display device or the like may be provided with a sharpening circuit for making a display image clear. A sharpening circuit is a circuit that drives a liquid crystal display device by applying a differential wave to a rectangular wave of a voltage between liquid crystal substrates.

  Patent Document 1 proposes a liquid crystal display device that uses a parallel rubbing-processed liquid crystal display device (substantially equivalent to an OCB type liquid crystal display device) and the phase difference of the retardation plate and the liquid crystal layer satisfies a predetermined relationship. ing. This relationship is characterized in that the phase difference is (M + 1) λ / 2 at the first voltage and Mλ / 2 at the second voltage. Here, M is an integer, and λ is a visible light wavelength.

  The liquid crystal display device requires external illumination light because the liquid crystal itself does not emit light. The irradiation light source of this external irradiation light is defined as a backlight element. A cold-cathode tube, which is one of the currently popular backlight elements, is mainly composed of a fluorescent lamp, a light guide plate, a diffusion plate, a prism sheet, and a polarization conversion element.

JP 7-49509 A

  However, the OCB type liquid crystal display device has a problem that a display defect occurs in a specific driving condition and a specific temperature range, and a problem that a contrast is lowered.

  That is, the liquid crystal display device according to the embodiment of the present invention has voltage application means for applying a voltage to the liquid crystal sealed in the liquid crystal panel, and performs display by changing the voltage applied by the voltage application means. The liquid crystal display device is an OCB type liquid crystal display device that performs display in a bend alignment state, and has a backlight element on the back side of the liquid crystal panel, and the backlight element has a high light intensity on the long wavelength side.

  Further, the liquid crystal display device according to the embodiment of the present invention has voltage application means for applying a voltage to the liquid crystal sealed in the liquid crystal panel, and performs display by changing the voltage applied by the voltage application means. An OCB-type liquid crystal display device that displays a liquid crystal in a bend alignment state, comprising: a voltage applying unit that applies a voltage to the liquid crystal; and a color display unit that performs a plurality of types of color display. The gamma characteristic is different in at least one color display.

  In addition, the liquid crystal display device according to the embodiment of the present invention has voltage applying means for applying a voltage to the liquid crystal sealed in the liquid crystal panel, and the voltage applied by the voltage applying means is changed to change the liquid crystal. An OCB type liquid crystal display device that performs display by adjusting the amount of refraction, and applies a voltage for performing display with the largest phase difference and liquid crystal when the voltage for performing display with the smallest amount of transmitted light is applied. In this case, the difference in phase difference of the liquid crystal is smaller than λ / 2.

According to the present invention, the OCB type liquid crystal display device can overcome the problem that display defects occur in a specific driving condition, a specific temperature range, and the problem that contrast decreases.

1 is a perspective view showing a part of an OCB type liquid crystal display device according to Embodiment 1 of the present invention. Block diagram when a sharpening circuit and a voltage limiting circuit are installed in the OCB type liquid crystal display device according to the first embodiment Conceptual diagram of voltage waveforms when a sharpening circuit and a voltage limiting circuit are installed in the OCB type liquid crystal display device according to the first embodiment Conceptual diagram of a system for setting a white level display voltage value optimum for the temperature environment in the OCB type liquid crystal display device according to the second embodiment of the present invention The figure which shows the graph which shows the gamma correction curve of the display input signal-source voltage in the OCB type liquid crystal display device which concerns on Embodiment 3 of this invention FIG. 6 is a block diagram showing a specific configuration of a drive circuit unit of a liquid crystal display device according to Embodiment 3. Circuit diagram showing specific configuration of gradation drive voltage generation circuit The figure which shows the graph which shows the characteristic of the voltage-transmittance of the black level display voltage value vicinity of the OCB type liquid crystal display device which concerns on Embodiment 4 of this invention The figure which shows the relationship between the applied voltage and the transmittance | permeability in the OCB type liquid crystal display device which concerns on Embodiment 5 of this invention The figure which shows the graph which shows the voltage-transmittance characteristic in the case of emphasizing color purity in Embodiment 5 The figure which shows the graph which shows the neutral voltage-transmittance characteristic in emphasis on contrast and color purity in Embodiment 5. FIG. 10 is a graph showing voltage-transmittance characteristics in the simulation of the OCB liquid crystal display device according to the fifth embodiment. FIG. 6 is a graph showing voltage-transmittance characteristics in the OCB type liquid crystal display device according to the sixth embodiment. FIG. 10 is a graph showing voltage-transmittance characteristics in the OCB-type liquid crystal display device according to the seventh embodiment. Schematic diagram for explaining the black writing method FIG. 16 is a schematic diagram showing a configuration of a liquid crystal display device according to Embodiment 9 of the present invention, FIG. 16 (a) is a schematic diagram showing a configuration of a conventional TN type liquid crystal display device, and FIG. FIG. 16 (c) is a schematic diagram showing another configuration of the OCB type liquid crystal display device of the present invention. The figure which shows the graph which shows the light emission characteristic of the conventional backlight element The figure which shows the graph which shows the light emission characteristic of the backlight element which strengthened the red light emission intensity in Embodiment 11 of this invention Schematic for explaining the principle of sequential lighting system R-OCB liquid crystal display device schematic cross-sectional view FIG. 21 (a) is a schematic cross-sectional view of a conventional OCB type liquid crystal display device, FIG. 21 (a) is a schematic cross-sectional view of a conventional OCB type liquid crystal display device with no voltage applied, and FIG. Schematic cross section The figure which shows the graph which shows the voltage-transmittance characteristic of the OCB type liquid crystal display device Conceptual diagram of the voltage waveform when a sharpening circuit (without voltage adjustment circuit) is installed in a conventional OCB type liquid crystal display device FIG. 24 is a diagram illustrating a method for setting a white display voltage in a liquid crystal display device in a birefringence mode, and FIG. FIG. 24 (b) is a graph showing a case where the white display voltage is not adjusted to the peak of the birefringence amount.

  Embodiments of the present invention will be described below with reference to the drawings.

  (Embodiment 1) FIG. 1 is a perspective view showing a part of an OCB type liquid crystal display device according to Embodiment 1 of the present invention.

  In the OCB type liquid crystal display device 20, a liquid crystal layer 13 including liquid crystal molecules 12 is inserted between substrates 10 and 11 arranged in parallel to each other to form a liquid crystal panel. Although not shown, transparent electrodes for applying an electric field to the liquid crystal layer 13 and alignment films for regulating the alignment of liquid crystal molecules are formed on the surfaces of the substrates 10 and 11 facing each other. . Further, TFT elements are formed on the substrate 10 (or the substrate 11) to constitute an active matrix substrate.

  The alignment film is subjected to an alignment treatment so that the alignment directions in the substrate plane are in the same direction, that is, parallel alignment. The liquid crystal molecules 12 gradually rise as the distance from the surfaces of the substrates 10 and 11 increases, and the liquid crystal molecules 13 have a bend alignment in which the tilt angle of the liquid crystal molecules is 90 degrees at the approximate center in the thickness direction. Further, on the outside of the substrates 10 and 11, polarizing plates 15 and 16 and optical compensation plates 17 and 18 are arranged, and the two polarizing plates 15 and 16 are arranged such that the polarization axes are orthogonal or parallel to each other, The polarization axis and the orientation direction of the liquid crystal molecules are arranged at an angle of 45 degrees. Then, using the difference in refractive index anisotropy of the liquid crystal layer between the on state where a high voltage is applied and the off state where a low voltage is applied, the polarization state is changed through the polarizing plate and the optical compensator. The transmittance is controlled and displayed.

  The relationship between the transmittance and the applied voltage of the OCB type liquid crystal display device according to the first embodiment showed characteristics as shown in FIG. 22 as in the conventional technique. Here, in order to display the white level, a voltage of approximately VL is applied, and in order to display the black level, a voltage at which the luminance is substantially minimized is used. Here, the white level is a case where the luminance of each pixel is maximized, and the black level is a case where the luminance of each pixel is minimized. In order to actually display black, it is distinguished in terms of notation that all the RGB pixels are set to the black level.

  As described in the prior art, when the white level display voltage value is lower than the transition voltage VL in the OCB type liquid crystal display device, splay alignment occurs and display defects such as bright spots occur. This is because the amount of birefringence received from each of the polarized light passes through the splay-aligned liquid crystal and the bend-aligned liquid crystal.

  As described in the prior art, the sharpening circuit is a circuit that makes the display image clearer by putting a differential wave on the rectangular wave of the voltage between the substrates. Therefore, the sharpening circuit is provided in the OCB type liquid crystal display device. When combined, the display image can be clear. FIG. 23 shows a conceptual diagram thereof. In this example, a black and white band is provided in the vertical direction. The video signal alone is a rectangular wave, but by passing through a sharpening circuit here, the differential waveform is superimposed and a peak voltage is further applied in a short time when the voltage changes. As a result, the edge of the video is emphasized, and a sharp display is obtained.

  However, when the OCB type liquid crystal display device was displayed using a sharpening circuit, there was a problem that display defects due to splay alignment occurred. The cause is that the inter-substrate voltage falls below the transition voltage VL as a result of superimposing the differential wave height ΔVw on the white level display voltage value set to the transition voltage VL, and the orientation from bend to splay This is because metastasis occurred.

  Therefore, in this embodiment, a voltage limiting circuit (limiter circuit) 23 that is a voltage limiting means is installed as a mechanism that can set the lower limit value of the inter-substrate voltage (defined as a limit voltage) in the conventional sharpening circuit. . The conceptual diagram is shown in FIG. 2 (a) and 2 (b) are block diagrams when the sharpening circuit 22 and the voltage limiting circuit 23 are installed in the OCB type liquid crystal display device according to the first embodiment.

  By this mechanism, if the inter-substrate voltage to be applied is lower than the transition voltage VL, the limit voltage is set to VL and the inter-substrate voltage VL is applied between the substrates.

  This limit voltage was set to a constant value so as not to fluctuate when adjusting the display voltage value by a mechanism as shown in FIG. 2 (b).

  In FIG. 2B, 31 is a black level voltage generating circuit for generating a black level display voltage VB, and 32 is a white level voltage generating circuit for generating a white level display voltage VW. In the black level voltage generation circuit 31 and the white level voltage generation circuit 32, the black level display voltage VB is fixed or adjustable to a desired value by a control signal from a control circuit (not shown), and the white level display voltage VW is Fixed or adjustable to the desired value. Reference numeral 36 denotes a gradation voltage generation circuit (note that gradation control will be described in detail in a third embodiment described later). Reference numeral 25 denotes a limiter voltage generation circuit for limiting voltage adjusting means for adjusting the limit voltage of the voltage limiting circuit 23. The limiter voltage generating circuit 25 is connected to the voltage limiting circuit 23, and a voltage is applied to the voltage limiting circuit 23 by the limiter voltage generating circuit 25 to set a limit voltage.

  Actually, the limiter circuit 23 was installed in the sharpening circuit 22, the limit voltage was set to VL, and the OCB type liquid crystal display device was driven with the voltage waveform as shown in FIG. FIG. 3 is a conceptual diagram of voltage waveforms when a sharpening circuit and a voltage limiting circuit are installed in the OCB type liquid crystal display device according to the first embodiment.

  Here, the difference from the conventional sharpening circuit is that the differential wave height ΔVW at the time of white level display is removed by a voltage limiting circuit (limiter). In this way, in the OCB type liquid crystal display device in which the edge of the image is emphasized by the sharpening circuit and a sharp display is obtained, the occurrence of display defects due to the alignment transition from the bend alignment to the splay alignment is suppressed. Can do.

  As will be described in the second embodiment to be described later, by incorporating a mechanism for adjusting the limit voltage in the device, a slight white level display voltage value fluctuation (for example, a change in operating temperature or a variation in the liquid crystal panel) can be obtained. Correspondingly, it is possible to cope with a slight variation in the white level display voltage value.

   (Embodiment 2) In this embodiment, display defects accompanying the change in orientation from bend to spray are not generated within the entire temperature range in which the OCB type liquid crystal display device is used.

The inventors of the present application have found that the transition voltage VL at which the orientation transition from the bend to the splay (that is, the transition from the normal display orientation state to the non-display orientation state) occurs is temperature-dependent. Table 1 shows the relationship between transition voltage and temperature. The transition voltage was 2.5V at room temperature, but the transition voltage increased from around 0 ° C and reached 3V at -20 ° C.

  When the OCB type liquid crystal display device was actually driven, no display defect occurred at room temperature, but a display defect due to orientation transition from bend to splay occurred at low temperature. This is because the transition voltage VL increases due to the temperature drop and exceeds the white level display voltage value. In order not to cause display defects within the operating temperature range, it is necessary to drive with a voltage equal to or higher than the transition voltage VL at each operating temperature.

  (Embodiment 2-1) In Embodiment 2-1, the white level display voltage value is set to a substantially constant value equal to or higher than the transition voltage VL in the entire temperature range. In this embodiment, the operating temperature range is set to −20 ° C. or higher. In consideration of the case where it is used for in-vehicle monitors, etc., the lower limit of the operating temperature is -20 ° C.

  At this time, assuming that the maximum value of the transition voltage VL at each temperature is VLmax, VLmax = 3.0V in the present embodiment. The transition voltage VLmax depends on the pretilt, and what determines the pretilt is a liquid crystal material or an alignment film. In the present embodiment, ZL1-2293 (trade name, manufactured by Merck & Co., Inc.) was used as the liquid crystal material, and AL-1052 (trade name, JSR) was used as the alignment film.

  The liquid crystal display device configured in this way is driven with a minimum drive voltage of 3.0 V, and is driven with a voltage of 3.0 V or higher at all operating temperatures (-20 to 80 ° C.). The generation of display defects due to the orientation transition to can be suppressed.

  In addition, voltage adjustment means for adjusting the white level display voltage value corresponding to the operating temperature (details will be described in the embodiment 2-2 described later) is not required, so that the cost of the device can be kept low. . However, since the white level display voltage value is set higher than necessary even at room temperature, there is a problem that the brightness is lowered. However, this problem can be solved by the embodiment 2-2 described later.

   (Embodiment 2-2) In Embodiment 2-2, the minimum voltage value of the voltage to drive the white level display voltage value at each use temperature of the OCB type liquid crystal display device is not always lower than the VL of each temperature. As a means for determination, the following voltage determination mechanism was installed.

  That is, the white level display voltage value is automatically set so as not to always fall below the VL of each temperature by the voltage determination mechanism as shown in FIG.

  The liquid crystal display device 21 is provided with a read-only internal storage device ROM to store the temperature characteristic data shown in Table 1 above.

  A thermistor S is built in a position where the external temperature of the liquid crystal display device 21 can be detected (for example, near the surface of the liquid crystal display element), and the external use temperature is detected by the thermistor S. This mechanism for detecting the external temperature is called temperature detection means.

  The temperature characteristic data and the external use temperature are collated by the determination unit 22, and a white level display voltage value that does not fall below VL is always determined at the temperature at which the apparatus is used. Based on the determination, the white level display voltage value is optimized corresponding to the external use temperature.

  This configuration increases the cost of the liquid crystal display device, but the white level display voltage value at room temperature is not set higher than necessary, so the optimum white level display voltage according to the temperature is not set. Since the value can be obtained, the liquid crystal display device can display a bright display without impairing the brightness. Further, since the liquid crystal display device has some temperature distribution, there may be some difference between the detected temperature and the temperature in the liquid crystal display device. For this reason, a configuration with a margin of 0.1 V may be practically used.

  Further, in this embodiment, a configuration in which the operation guarantee temperature is set to −20 ° C. has been considered. However, for example, when the operating temperature of the outside air temperature is temporarily lowered and the operating temperature is −20 ° C. or lower, a display defect due to splay alignment transition occurs. In consideration of such a situation, a restoring means for restoring a display defect once generated to a normal display state may be provided. As a specific example, a mechanism is conceivable in which a waveform similar to a transition waveform for transition from a splay alignment to a bend alignment applied at power-on can be arbitrarily applied.

  (Embodiment 2-3) In the present embodiment, a liquid crystal display device is provided with a mechanism for a user to adjust the white level display voltage value to an optimum value for each temperature. When the operating temperature was lowered and splay alignment occurred, the user manually handled the white level display voltage value to increase it.

  However, in this embodiment, since splay alignment once occurs, it is necessary to separately provide means and a switch for applying a transition waveform for transition from splay alignment to bend alignment as restoring means.

  In this way, the user can adjust the optimum white level display voltage value for each use temperature.

  (Embodiment 3) In the present embodiment, low contrast and gradation inversion display are suppressed by a black level voltage adjustment mechanism for adjusting a black level display voltage value.

  As shown in FIG. 22, the voltage-transmittance characteristics of the OCB type liquid crystal display device have the following characteristics. As the voltage applied to the liquid crystal layer (> VL) increases, the transmittance decreases monotonously and shows a minimum value (the voltage at that time is VH), and then the transmittance increases monotonously as the voltage increases further. Go. Here, a characteristic of the OCB type liquid crystal display device is that the transmittance has a minimum value. This is in contrast to a conventional element (for example, a TN liquid crystal display device) in which the transmittance simply decreases with increasing voltage.

  It is ideal to perform black level display using this minimum voltage. At this time, the best contrast is obtained. In addition, when driving with a voltage higher than the minimum value, a phenomenon occurs in which the transmittance increases conversely with the increase in voltage. This is called tone reversal and causes a problem in displaying.

  In order to obtain high contrast in the OCB type liquid crystal display device and to suppress gradation inversion display, it is particularly important to adjust the black level display voltage value to the minimum value VH by this black level voltage adjustment mechanism.

  The voltage adjustment method used in the conventional TN liquid crystal display device is a voltage adjustment method in which the amplitude between the source voltage and the counter substrate, that is, the amplitude of the inter-substrate voltage is constant. That is, not only the black level display voltage value but also the white level display voltage value has been changed simultaneously.

  When this method is applied to an OCB type liquid crystal display device and the black level display voltage value is adjusted, if the white level display voltage value falls below the transition voltage VL, the alignment transition occurs from the bend alignment to the splay alignment. There was a problem that a defect occurred. Further, when the white level display voltage value becomes too high, there is a problem that the brightness is lowered. In the OCB type liquid crystal display device, the white level display voltage value is limited to the transition voltage VL or higher, and is desirably fixed at this voltage.

  Therefore, in order to suppress the deterioration of the display quality, a mechanism for adjusting the black level display voltage value with the white level display voltage value fixed is incorporated in the present embodiment. With this mechanism, high contrast was obtained by adjusting the black level display voltage value as well as suppressing display defects and brightness reduction.

  FIG. 5 shows a conceptual diagram thereof. When the display element was shipped, the voltage was adjusted so that the black level display voltage value would be optimal for the liquid crystal panel. During this adjustment, the white level display voltage value was not changed. Specifically, a gamma correction mechanism for display input signal-source voltage as shown in FIG. 5 was introduced. As a specific implementation method, a resistance division and gamma table as shown in FIG. FIG. 7 shows an example in which the image signal is 4 bits (16 gradations), but the present invention is not limited to this. In addition, the present invention is effective even when the image signal is 8 bits (256 gradations).

  In the present embodiment, the optimum gamma correction is performed at the same time as the adjustment of the black level display voltage value. Here, each gamma correction curve has a similar shape, and the shape of the curve from the white level display voltage value to the black level display voltage value is constant. With this mechanism, high contrast and correct gradation display change were obtained. The liquid crystal display device may be provided with an adjustment mechanism that allows the user to adjust the black level display voltage value.

  Next, with reference to FIG. 6 and FIG. 7, a specific configuration and operation of the third embodiment will be described. FIG. 6 is a block diagram showing a specific configuration of the drive circuit section of the liquid crystal display device according to the third embodiment, and FIG. 7 is a circuit diagram showing a specific configuration of the grayscale drive voltage generation circuit. For convenience of explanation, the image signal is a digital signal, and the gradation data has a 4-bit (D1 to D4) configuration and will be described as a liquid crystal display device that performs 16 gradation display.

  In FIG. 6, 31 is a black level voltage generating circuit for generating a black level display voltage VB, and 32 is a white level voltage generating circuit for generating a white level display voltage VW. The black level voltage generation circuit 31 and the white level voltage generation circuit 32 are composed of variable resistors, and the black level display voltage VB can be fixed or adjusted to a desired value by a control signal from the control circuit 33. The level display voltage VW is fixed or adjustable to a desired value.

  Reference numeral 36 denotes a gradation voltage generation circuit. The gradation voltage generation circuit 37, the black level voltage generation circuit 31, and the white level voltage generation circuit 32 constitute a gradation voltage generation circuit 37.

  The gradation voltage generation circuit 36 generates 16 gradation voltages V1 to V16 between the black level display voltage VB and the white level display voltage VW. Here, the minimum voltage V1 is the white level display voltage VW, and the maximum voltage V16 is the black level display voltage VB. Note that the gradation voltage generation circuit 36 has a function of performing γ correction based on γ correction data from the control circuit 33 as described later.

  A temperature sensor 34 is connected to the control circuit 33. The temperature sensor 34 detects a use environment temperature of the liquid crystal display device, and the control circuit 33 adjusts the value of the variable resistance of the white level voltage generation circuit 32 in accordance with the detected temperature from the temperature sensor 34. Thereby, the optimum white level display voltage VW corresponding to the temperature change is automatically set. The control circuit 33 is connected to manual adjustment knobs 35a, 35b, and 35c. The manual adjustment knob 35a is a switch for adjusting the white level display voltage VW, the manual adjustment knob 35b is a switch for adjusting the black level display voltage VB, and the manual adjustment knob 35c is a switch for γ correction. When the user operates these manual adjustment knobs 35a and 35b, the white level display voltage VW and the black level display voltage VB can be finely adjusted individually to obtain image quality according to the user's preference. Can do. Further, when the user operates the manual adjustment knob 35c, a gradation having desired γ characteristics can be obtained.

  Next, a specific configuration of the gradation voltage generation circuit 36 will be described with reference to FIG. Three variable resistors r1, r2, and r3 connected in series are interposed between the high voltage black level display voltage VB and the low voltage white level display voltage VW. The variable resistors r1, r2, and r3 are configured to be supplied with γ correction data from the control circuit 33 and adjusted to a resistance value corresponding to the γ correction data. The connection point P1 between the terminal for the black level display voltage VB and the variable resistor r1 is connected to the common line L5 via the individual connection run L1, and the switch SW1 is interposed in the individual connection run L1. The connection point P2 between the variable resistor r1 and the variable resistor r2 is connected to the common line L5 via the individual connection run L2, and the switch SW2 is interposed in the individual connection run L2. The connection point P3 between the variable resistor r2 and the variable resistor r3 is connected to the common line L5 via the individual connection run L3, and the switch SW3 is interposed in the individual connection run L3. The connection point P4 between the variable resistor 3 and the terminal for the white level display voltage VW is connected to the common line L5 via the individual connection run L4, and the switch SW4 is interposed in the individual connection run L4. Yes. These switches SW1 to SW4 are configured such that the switching mode changes in accordance with the logic level of each bit data D1 to D4 of the digital image signal. For example, when [D1, D2, D3, D4] = [0, 0.0, 0], all the switches SW1 to SW4 are OFF, and the white level display voltage VW (= first gradation voltage V1) is applied to the common line L5. Is output. Similarly, the switching modes of the switches SW1 to SW4 change corresponding to the logic levels of D1 to D4, and V2 to V16 (= black level display voltage VB) are generated. In this way, a gradation signal voltage corresponding to the gradation of the digital image signal is generated.

  When the γ characteristic is changed, if the manual adjustment knob 35c is operated, the resistance values of the variable resistors r1 to r3 change accordingly, and thereby the voltage levels of V2 to V15 change. If the manual adjustment knobs 35a and 35b are operated in advance, the voltage levels of V1 and V2 can be set to desired values. Therefore, the desired gradation can be obtained by operating these manual adjustment knobs 35a, 35b, and 35c.

  The following voltage can be set by the drive circuit having the above configuration.

  (1) As in the third embodiment, it is possible to independently adjust the black level display voltage value and the white level display voltage value, which is a voltage value for displaying the white level. Then, it is possible to set the voltage so that the white level display voltage value, which is a voltage value for displaying the white level when adjusting the black level display voltage value, does not fluctuate. Accordingly, at the time of voltage adjustment, the white level display voltage value does not fall below the transition voltage VL, and there is no problem that alignment transition occurs from bend alignment to splay alignment and display defects occur.

  (2) The black level display voltage value can be set for each color (RGB) as in the fourth embodiment described later.

  (3) As in Embodiment 5 described later, it is possible to set the white level display voltage value for each color (RGB).

  Although the voltage can be set as described above, the voltage can be set either at the time of manufacturing the liquid crystal display device or after the manufacturing. When the liquid crystal display device is manufactured, it is possible to obtain a liquid crystal display device in which the contrast is reduced and the gradation inversion display is suppressed by including the step of adjusting the black level display voltage value as described above.

  In the above-described method, the black level display voltage value is adjusted by the user at the time of shipment. Further, a mechanism for automatically detecting this voltage correction may be provided. This can be realized by providing a voltage fluctuation mechanism for gradually changing the voltage and a light quantity detection mechanism for detecting the light quantity. Specific examples are shown below.

  An element for detecting the amount of transmitted light, such as a photodiode (PD), is mounted on the liquid crystal display device to detect the display brightness. The voltage applied to the liquid crystal is increased or decreased by a voltage fluctuation mechanism, and the voltage value is fed back in the direction of decreasing brightness detected by a PD. A voltage having a minimum luminance is detected.

  When the voltage value for displaying the black level is the black level display voltage value as in the above configuration, the black level voltage adjusting means for adjusting the black level display voltage value, more specifically, the white level display voltage value By providing a mechanism for adjusting the black level display voltage value while fixing the image, it becomes possible to always maintain a high contrast display.

  (Embodiment 4) This embodiment is characterized in that a black level display voltage value is set for each color.

  Through detailed examinations by the inventors of the present application, it has been clarified through experiments that the OCB type liquid crystal element has a transmitted light wavelength dependency in voltage-transmittance characteristics. FIG. 8 (a) is a graph showing the relationship between the transmittance and the applied voltage in the vicinity of the black level display of the OCB type liquid crystal display device used in the present embodiment. In the vicinity of the black level display voltage value, there was a characteristic of VH (blue) (= 6.0 V) <VH (green), VH (red) (= 6.5 V) as shown in FIG.

  As described above, in the OCB type liquid crystal display device, the voltage VH at which the transmittance becomes a minimum value is different for each color because the phase difference amount of the liquid crystal layer is not zero when performing black level display, This is because the amount of phase difference of the liquid crystal display device as a whole is set to zero by canceling out the amount of phase difference of the phase difference plate arranged on the liquid crystal display. That is, the liquid crystal layer has a phase difference, and the voltage VH at which the transmittance becomes a minimum value varies depending on the wavelength dependency of the phase difference amount. This is not a problem limited to the OCB type liquid crystal display device. This is a problem peculiar to a liquid crystal display device having a mode for controlling the amount of birefringence and a retardation plate.

  On the other hand, such wavelength dependence hardly appears in the conventional TN liquid crystal display device. The reason is that the TN mode is a mode that controls the transmission of light by the optical rotation of the liquid crystal inside the substrate, and is designed so that the wavelength dependence of the transmitted light is reduced by controlling the thickness d of the liquid crystal layer. is there.

  In OCB type liquid crystal display devices, when RGB (red, green, blue) display is set with the same black level display voltage value as used in conventional TN type liquid crystal display devices, black is slightly colored and contrast is increased. There was a problem with the drop. For example, when set at 6.5 V, there are problems that blue light leaks slightly and gradation inversion in blue occurs.

  Therefore, in this embodiment, in order to obtain a good contrast, the black level display voltage values of the R, G, and B pixels are set to the voltage values VH (R), VH (G), and VH at which the transmittance is minimized. Set to (B).

  Specifically, the black level display voltage value is set for each of R, G, and B using the configuration described in the third embodiment (FIGS. 6 and 7). As shown in FIG. 8 (b), 37R, 37G, and 37B are gradation voltage generation circuits for gradation control for each of R, G, and B, respectively, and the gradation voltage generation circuits 37R, 37G, and 37B Is connected to the control circuit 33. Then, the control circuit 33 can set the black level display voltage values of the R, G, and B pixels to voltage values VH (R), VH (G), and VH (B) at which the transmittance is minimized. it can.

  In this example shown in FIG. 8, the R and G pixels are set to display a black level at a voltage of 6.5 V, and the B is set to display a black level at a voltage of 6.0 V.

  Here, since the white level display voltage value is determined by the transition voltage for transition from bend alignment to splay alignment, it is assumed that there is no RGB wavelength dependency. Since this method provides maximum brightness, maximum contrast is achieved.

  The voltage setting can be performed either at the time of manufacturing the liquid crystal display device or after the manufacturing. At the time of manufacturing the liquid crystal display device, by having a black level adjustment step for adjusting to a different black level display voltage value in at least one color display of the plurality of types of color display, low contrast and gradation inversion display are suppressed. A liquid crystal display device can be obtained.

  Here, using the specific mechanism described in the third embodiment, the black level display voltage value may be adjusted while the white level voltage value is fixed. Here, this mechanism may be a mechanism for adjusting R, G, and B separately.

  Further, as described above, in this embodiment, the R and G pixels are set to display black level at a voltage of 6.5 V, and the B is set to display black level at a voltage of 6.0 V. did. Here, the black level display voltage value is adjusted independently for each of R, G, and B, but an adjustment mechanism having the following black level adjusting means may be used. That is, among the black level display voltage values for each color display, when setting the black level display voltage value corresponding to B, a one-system voltage adjustment mechanism that links the black level display voltage values corresponding to R and G is used. You can also. Also, the following two voltage adjustment mechanisms can be used. That is, it is possible to use two systems of adjustment mechanisms in which the system for adjusting the black level display voltage values of R and G in conjunction with the system for adjusting the black level display voltage value of B are independent.

  (Embodiment 5) In Embodiment 4, the wavelength dependence of transmitted light near the black level display voltage value is taken into account, but in this embodiment, the color reproducibility near the white level display voltage value is improved. I let you. FIG. 9 shows the relationship between the applied voltage and the transmittance in the OCB type liquid crystal display device of this embodiment.

  In the present embodiment, color display is performed using a color filter having a plurality of types of color pixels. Further, instead of the color filter, a backlight element based on the sequential color illumination method described in Embodiment 13 described later can be used.

  As shown in FIG. 9, there is a problem that the overall blue transmittance is high and the transmittance decreases in the order of green and red. This is a problem specific to a mode in which display is performed by controlling the birefringence amount of the liquid crystal layer. This is because the phase difference amount of the liquid crystal layer has wavelength dependence. The amount of retardation that the liquid crystal layer has is generally represented by 2πΔnd / λ. Here, Δn is the amount of birefringence of the liquid crystal layer, d is the thickness of the liquid crystal layer, λ is the wavelength, and π is the circumference. This phase difference is a function of the wavelength λ, which is a cause of wavelength dependence. Since the blue wavelength is shorter than the other light, the amount of phase difference received by the blue light is increased.

  If the splay alignment transition does not occur here, the characteristic should be as shown in FIG. This is a result obtained by optical simulation. Thus, blue has a peak of transmittance at a relatively high voltage, and red has a peak at a relatively low voltage. The voltage value at which the transmittance reaches a peak for each color is defined as a white peak voltage value, and the white peak voltage values for RGB are expressed as VRwp, VGwp, and VBwp. The transmittance IR, IG, IB of each color at this peak was almost the same result.

Therefore, in order to drive the liquid crystal display device with the maximum brightness, it is ideal to perform display using this peak. However, in the present embodiment, since the white peak voltage values are all VL or less, a drive voltage less than VL cannot be used. Therefore, it is necessary to perform display using a voltage equal to or higher than the transition voltage VL as the white level display voltage value.

  When each pixel of RGB is driven with the same white level display voltage value, the blue transmittance becomes higher than the red and green transmittances as described above, and there is a problem that the white display becomes bluish. It was. When compared with the vicinity of the black display, human vision is very sensitive to the color change near the white display. Therefore, adjustment of color reproducibility in the vicinity of the white level display voltage value is very important.

  However, this method has a feature that a high contrast can be obtained because the brightness is relatively high.

  (Embodiment 5-1) In order to solve the problem that the white display becomes bluish, in the present invention, the white level display voltage value is changed in each pixel. As shown in FIGS. 10 and 11, the white level display voltage value in each color was changed. At this time, there is a relationship of VRw ≦ VGw <VBw, which is characterized in that the white level display voltage value in the blue transmitting pixel is high. In particular, the inventors of the present application have found that it is very important to adjust the light intensity of blue because the hue during white display is easily affected by the intensity of blue.

  In particular, FIG. 10 shows the case where the white level display voltage value is set so that the transmittance of each color is constant, and reliable color reproducibility can be realized and high color purity can be realized. However, there is a problem that brightness and contrast are lowered.

  FIG. 11 shows a neutral condition, which is a technique that achieves both realistic color purity and brightness. With either method, a significantly higher color reproducibility can be realized as compared with the case where each pixel is driven with the same white level display voltage value.

  (Embodiment 6) In Embodiment 5, the white peak voltage values VRwp, VGwp, and VBwp of each color are lower than the transition voltage VL.

  Therefore, in the present embodiment, the white peak voltage value of each color is made equal to or higher than the transition voltage VL by increasing the thickness d of the liquid crystal layer. In the present embodiment, the thickness d of the liquid crystal layer is increased to 10 μm while keeping the liquid crystal material. As a result, high brightness and high contrast were realized.

  As a result of increasing the thickness d of the liquid crystal layer to 10 μm, the white peak voltage value of the transmittance of each color exceeded the transition voltage VL as shown in FIG. This is due to the following two reasons.

  That is, one reason is that the transition voltage VL is determined by the liquid crystal material used in the OCB type liquid crystal display device and does not depend on the thickness of the liquid crystal layer. The present inventors found this fact through experiments.

  The second reason is that the transmittance peak with respect to the applied voltage is shifted to the high voltage side as the thickness d of the liquid crystal layer is increased. This is because the retardation Δnd received by the transmitted light from the liquid crystal increases as the thickness d of the liquid crystal layer increases, and the absolute value of the phase difference amount 2πΔnd / λ of the liquid crystal layer increases from the above-described equation.

  At this time, as shown in FIG. 13, the voltage for obtaining the maximum transmittance is different for each color. Therefore, it is necessary to change the white level display voltage value for each.

  In the present embodiment, the white level display voltage values VRw, VGw, and VBw for each color pixel are set to the white peak voltage values VRwp, VGwp, and VBwp for each color. That is, VRw (= VRwp) <VGwp (= VGwp) <VBwp (= VBwp) is set. As a result, high brightness and high contrast were realized. At this time, since the drive voltage was larger than the transition voltage VL, display defects due to splay alignment transition did not occur.

  However, this method has a problem that the driving voltage becomes very large. When the liquid crystal layer was realized with a thickness of 5 μm as in the fifth embodiment, the drive voltage was about 6V. However, when the thickness of the liquid crystal layer is 10 μm in the present embodiment, the driving voltage is required to be about twice, resulting in a driving voltage of 12V. For this reason, a normal TFT active matrix substrate could not be used.

  In the present embodiment, this is realized by using an MIM type high voltage type active matrix substrate. At the same time, there is a problem that the power consumption becomes very large, but a liquid crystal display device in which display defects due to splay alignment transition do not occur can be obtained.

  This embodiment is a technique for realizing very high display quality. However, it is necessary to increase the drive voltage. On the other hand, the fifth embodiment is a method realized by using a normal active matrix substrate.

  (Seventh Embodiment) In the sixth embodiment, by increasing the thickness of the liquid crystal layer, it is possible to perform display using the white peak voltage value that maximizes the transmittance as the white level display voltage value.

  In the present embodiment, a white display with a well-balanced color when the black writing method is used is realized. The black writing method is a driving method that adds black writing for screen blanking in addition to rewriting display data within one frame, and realizes display that does not cause display defects due to splay alignment transition even at display voltages below the transition voltage VL. it can. This will be specifically described with reference to FIG. FIG. 15 is a schematic diagram for explaining the black writing method.

  When the applied voltage becomes VL or less, the splay alignment state becomes stable, and an alignment transition from bend alignment to splay alignment occurs. When this transition from the bend alignment to the splay alignment occurs, a display defect occurs and the transmittance decreases. However, the transmittance decreases even below VL as shown by the alternate long and short dash line in FIG. The black writing method is a method for suppressing this. For example, as shown in FIG. 15 (b), in addition to rewriting display data in one field of 16.7ms, by performing black writing of about 1ms, it is possible to suppress a decrease in transmittance even below VL, Brightness can be improved. Refer to IDW'99 Proceedings of the Sixth International Display Workships P.37-40 for details on the black writing method.

  In this embodiment, when the black writing method is used, the relationship between the transmittance and the applied voltage is as shown in FIG. Here, when the white peak voltage values VRw, VGw, and VBw for red transmission, green transmission, and blue transmission are set to be the same as the white peak voltage value VRwp for red transmission, white is displayed in red, and further green transmission and blue There was a display problem due to the gradation reversal of transmission. In addition, when the white peak voltage values VRw, VGw, and VBw for red transmission, green transmission, and blue transmission are set to the same for the white peak voltage value VBwp for blue transmission, tone inversion does not occur, but white is displayed in blue. Problem has occurred.

  In the present embodiment, the white level display voltage values VRw, VGw, VBw for each color pixel are set to the white peak voltage values VRwp, VGwp, VBwp for each color. That is, VRw (= VRwp) <VGwp (= VGwp) <VBwp (= VBwp) is set. As a result, a white display with a well-balanced color was realized. Further, display problems due to gradation inversion did not occur.

  This embodiment has the advantage that the brightness can be maximized while maintaining the color balance.

  (Embodiment 8) In the embodiment, white display with a well-balanced color is realized by setting the white level display voltage value to be the same for each color pixel in the black writing method. In the present embodiment, in the black writing method, the color balance during white display is realized by varying the black writing time for screen blanking for each color pixel. We have found that the brightness can be controlled by controlling the black writing time. Furthermore, it was discovered that the color balance during white display can be adjusted by changing this for each color pixel display.

  Specifically, a projection type liquid crystal display device that performs display by combining three OCB type liquid crystal display devices of red transmission, green transmission, and blue transmission was used. First, the white level display voltage value was set to a constant value such as VRw = VGw = VBw = VBwp. Here, IR ′, IG ′, and IB are used for the transmittance of each color pixel in the white level display voltage value. When the black writing time for each color pixel is tb (red), tb (green), tb (blue), that is, tb (blue) = tb (red) x (IB / IR ') tb (green) = It was set as tb (red) x (IG '/ IR'). By setting the black writing time for each color pixel in this way, the amount of transmitted light from each color pixel becomes substantially equal, and a white level display with a balanced color is realized.

  Here, the white level display voltage value is assumed to be constant for each color pixel, but each white level display voltage value is not necessarily constant. The relationship between the black writing times in the respective color pixels is tb (blue)> tb (green) ≧ tb (red), which is important for adjusting the color balance when performing white display.

  (Embodiment 9) Embodiment 9 will be described with reference to FIG. In this embodiment, high contrast and high purity of color are realized by setting the effective pixel area of each color pixel constituting the liquid crystal display device for each color. Here, the effective pixel area is an area of pixels that actually contribute to display in each color pixel.

  In a conventional TN liquid crystal display device or the like, the transmittance is almost independent of wavelength, so each color pixel has an equal area. That is, as shown in FIG. 16 (a), the areas of the R, G, and B constituting the color filter 90 and the black matrix 90M and the TFT section 93 and the display section 94 constituting the TFT element 92 are different for each color pixel. The configuration was equal. In practice, the TFT element 92 and the like are formed on a substrate, but the substrate and the backlight are not shown.

  On the other hand, in the OCB type liquid crystal display device, as shown in the fifth embodiment, there is a relationship of IB (blue intensity)> IG (green intensity)> IR (red intensity), and the white level display voltage value is When the same driving is performed, the display becomes bluish. Further, when the white level display voltage value is set with the transmittance of each color constant, the contrast is lowered.

  Therefore, in the present embodiment, in the OCB liquid crystal display device, the effective pixel area of each color pixel is set to (IB / IG) times for the green pixels and (IB / IR) times for the red pixels, based on the area of the blue pixels. .

  That is, the inventors of the present application change the areas of the color filter 95, the black matrix 95M, and the TFT portions 97 and the display portions 98 of the TFT element 96 for each color pixel as shown in FIG. 16 (b). Realized by that.

  More specifically, on the basis of the area of the display unit 98B constituting the blue pixel, the area of the display unit 98G constituting the green pixel is (IB / IG) times the area of the display unit 98R constituting the red pixel. Was (IB / IR) times. Similarly, the color filters 95G and 95R and the TFT units 97G and 97R are set to (IB / IG) times and (IB / IR) times, respectively, based on the color filter 95B and the TFT unit 97B.

  With such a configuration, light from a backlight element (not shown) can have almost the same transmittance for each color (R, G, B) even at the same white level display voltage value. High purity and high contrast.

  (Embodiment 10) In the embodiment 9, high purity and high contrast of color are realized by designing the effective pixel area of each pixel to be different for each color pixel.

  In this embodiment, the transmittance of each color pixel is controlled by making the transmittance of each color pixel of the color filter different to adjust the color balance during white display. At this time, the effective pixel area of each color pixel is the same. Specifically, the transmittance of the color filter corresponding to each color pixel is set to (IB / IG) times for the green pixel and (IB / IR) times for the red pixel, based on the transmittance of the blue pixel. With this configuration, substantially the same transmittance was obtained for each color pixel even at the same white level display voltage value, and high purity and high contrast of the color were realized.

  Such a configuration is a method capable of adjusting the color balance of white display while using the conventional TFT element, color filter, and black matrix structure having a constant effective pixel area.

The thickness of the liquid crystal layer for at least one of the plurality of color pixels may be different from the thickness of the liquid crystal layer for the other color pixels. Specifically, as shown in FIG. 16 (c), the thickness of the liquid crystal layer 85 is changed by changing the thickness of the color filters 80R, 80G, and 80B for each of R, G, and B. The liquid crystal layer 85b and the liquid crystal layer 85c are configured. As a result, when a voltage is applied to each of the liquid crystal layers 85a, 85b, and 85c, the birefringence received from the liquid crystal layers 85a, 85b, and 85c can be made equal for each of the 80R, 80G, and 80B color filters 80R, 80G, and 80B. The transmittance of 80B can be made the same. Therefore, adjustment of the color balance of white display can be realized.
(Eleventh Embodiment) As described in the fifth embodiment, the OCB type liquid crystal display device has a problem that a white display is displayed in a bluish color.

  This problem is not limited to the OCB type liquid crystal display device. The phenomenon of being displayed in bluish color is because the phase difference amount of the liquid crystal layer has a wavelength dependence, and the phase difference amount becomes large with blue light, that is, light with a short wavelength. If the product of the birefringence amount Δn of the liquid crystal layer and the thickness d of the liquid crystal layer is Δnd, Δnd / λ is an amount proportional to the phase difference. Here, λ is a wavelength.

  Therefore, the phase difference amount 2πΔnd / λ of the liquid crystal layer depends on the wavelength of light, and the phase difference amount becomes larger as the light has a shorter wavelength. Here, π is the circumference ratio. For this reason, the amount of light modulation received by the liquid crystal generally increases as the light has a shorter wavelength. Therefore, in the mode in which the display is performed by controlling the birefringence amount of the liquid crystal layer, the problem of being displayed in bluish when white display is common.

  Therefore, in order to solve the above problem, in this embodiment, the chromaticity distribution of light emission of the backlight element is optimized. This will be described with reference to FIGS. FIG. 17 is a graph showing the light emission characteristics of a conventional backlight element. FIG. 18 is a graph showing the light emission characteristics of the backlight element in which the red light emission intensity is increased in the eleventh embodiment.

  A conventional backlight element has a light emission dispersion characteristic as shown in FIG. In the present embodiment, as shown in FIG. 18, the emission intensity of red is improved. As a result, it was possible to maintain the color balance when the entire liquid crystal element displayed white.

  In the present embodiment, since the birefringence amount is not adjusted, there is a problem that the black color reproducibility is deteriorated. At this time, the black chromaticity coordinates were reddish, but in applications other than video equipment that requires extremely high color purity reproducibility (for example, for OA equipment), there was almost no problem. It was. This is because the human eye sense is sensitive to white color change but not so sensitive to black color change. Note that, as in this embodiment, the method of changing the characteristics of the backlight element is a method that can be realized relatively easily.

  Further, in this embodiment, the configuration in which the color balance can be maintained by optimizing the chromaticity distribution of the light emission of the backlight element is described, but in addition, the color balance may be maintained by a polarizing plate. it can. Furthermore, in addition to using a polarizing plate, for example, coloring means, specifically, a prism sheet may be provided. Further, the backlight element may be provided with scattering means having coloring properties, specifically, a diffusing plate or scattering dots provided on a light guide plate constituting the backlight element.

  Specific examples will be described below.

  (Embodiment 11-1) According to this study, in order to define the light intensity for displaying red, it is only necessary to measure the intensity of light near 610 nm, and for displaying blue, 430 nm What is necessary is just to measure the nearby light. In this embodiment, the red light intensity of the backlight element is increased, and in order to quantify this, it is effective to take the ratio with reference to the blue light intensity.

  As shown in FIG. 17, the conventional backlight element has a ratio of light intensity (luminance) of 610 nm ± 10 nm and light intensity (luminance) of 430 nm ± 10 nm of 1.78.

  In order to see the effect of this embodiment, the light intensity of the wavelength corresponding to the red display color and the light intensity of the wavelength corresponding to the blue display color among the emission wavelengths of the backlight element are more than doubled when compared in luminance. Had to be. In chromaticity coordinates, x had to be greater than 0.32. This criterion was applied when the OCB type liquid crystal display device was used for OA equipment that requires relatively high color purity reproducibility. When an OCB type liquid crystal display device is used for video equipment that requires extremely high color purity reproducibility, it is desirable that x of chromaticity coordinates is 0.36 or more. If the chromaticity coordinate x was 0.4 or more, the color purity reproducibility was almost completely achieved.

  (Twelfth Embodiment) In the eleventh embodiment, the inventors of the present invention maintain a color balance when displaying white using a backlight element having a higher emission intensity in the wavelength range near red than in the past. I was able to.

  However, in this case, the black at the time of black display becomes reddish, which is a problem when the OCB type liquid crystal display device is used for video equipment. This is because video equipment requires extremely high color purity.

  Therefore, in the present embodiment, in order to cope with the above problem, high color purity during black display is realized while maintaining the color balance during white display. Specifically, a black display with high color purity was realized by using a polarizing plate that has a blue light transmittance higher than that of other green and red light during black display.

  The polarizing plate has no wavelength dependency when transmitting (white display) with respect to light passing therethrough, and by controlling the wavelength dependency of the absorption rate of the absorber for leakage light during absorption (black display). It is possible to have wavelength dependence. This makes it possible to achieve high color purity during black display while maintaining the color balance during white display.

  (Embodiment 13) In this embodiment, color adjustment is realized at the time of black display and white display when a sequential color illumination method using a backlight element that displays a plurality of types of colors is used as a color display means. did.

  As shown in Fig. 19 (a), the sequential color illumination method divides one field period into three fields, R, G, and B, and writes a specific color image and a specific color in each field period. As shown in FIG. 19 (b), a specific configuration is such that a sequential color illumination type backlight element 131 is provided on the back side (downward in the drawing) side of the liquid crystal panel 132. The red light emitting element 131R, the green light emitting element 131G, and the blue light emitting element 131B are arranged on the side of the backlight element 131. The sequential color illumination method does not require a color filter as compared with the color filter method, and therefore exhibits bright display performance.

  Also in the sequential color illumination system, gradation inversion and low contrast can be suppressed by applying to the fourth embodiment and adjusting the black level voltage value for each color pixel.

  Further, the sequential color illumination method is applied to the sixth embodiment, and in the white display, the color balance is adjusted by controlling the pulse time and the pulse height of the backlight element that emits light for each color display. Here, as shown in FIG. 19 (a), the emission pulse times of the red, green and blue display backlight elements are tl (red), tl (green), tl (blue), and the emission pulse height is Il. (Red), Il (green), and Il (blue). By setting tl (blue) <tl (green) ≤ tl (red) and Il (blue) <Il (green) ≤ Il (red), a color-balanced white display is realized. I was able to. At this time, the white level display voltage value is constant for each color display.

  (Other Matters) Although the first to thirteenth embodiments have been described above, the present invention is not limited to the OCB type liquid crystal display device. Any mode in which display is performed by controlling the amount of birefringence of the liquid crystal is effective.

  Further, the present invention is similarly effective in a liquid crystal display device in which the birefringence of the liquid crystal layer when displaying a black level is not 0 and a liquid crystal display device using a retardation plate in which the phase difference is not 0.

  For example, the present invention is also effective in an R-OCB type liquid crystal display device having a contrast of 10 or more as shown in FIG. As shown in FIG. 20, the R-OCB type liquid crystal display device has a laminated structure of a diffusion plate 40, a polarizing plate 41, a retardation plate 42, a glass substrate 43, a liquid crystal 44, a reflective electrode 45, and a glass substrate 46 from the top. The liquid crystal 44 on the glass substrate 46 is vertically aligned by using an alignment film (not shown) formed on the reflective electrode 45 of a vertical alignment type. Such an R-OCB type liquid crystal display device has a high viewing angle, high-speed response, and high luminance performance. For details of the R-OCB type liquid crystal display device, refer to SID 96 DIGEST p618-621.

  Further, the ASV (Advanced Super Buoy) mode rubbed in the parallel direction can be applied to the third to thirteenth embodiments.

  Further, in the mode in which the display is performed by controlling the phase difference amount, there is a problem that the contrast is reduced when the black level is displayed, the gradation is inverted, and when the white level is displayed, the display is bluish. This is a problem particularly in a display element having a high contrast. For display elements having a contrast of 200 or more, the color adjustment of the present invention is essential, and it is desirable that the display elements of 100 or more also include the color adjusting means of the present invention. Further, the present invention is not so problematic for OA display that displays a personal computer screen or the like, but is particularly necessary for a display device that displays video such as a TV that generally displays a natural image.

  Further, the liquid crystal display device of the present invention has a phase difference between the liquid crystal when a voltage for performing display with the smallest amount of transmitted light and a phase difference with liquid crystal when applied with a voltage for performing display with the largest amount of transmitted light. By adopting a configuration in which the difference is smaller than λ / 2, a liquid crystal display device with stable gradation and good contrast can be obtained. This will be described with reference to FIG.

  FIG. 24 is a graph (voltage-transmittance characteristics) showing a method for setting a white display voltage in a liquid crystal display device in a birefringence mode, and FIG. 24 (a) shows the white display voltage adjusted to the peak of the birefringence amount. FIG. 24B is a graph showing the case where the white display voltage is not matched with the peak of the birefringence amount.

  As shown in FIG. 24 (a), in a conventional birefringence mode liquid crystal display device, the white display voltage Va16 is aligned with the peak (phase difference λ / 2) position of the birefringence amount to obtain Ia16 (expressed in 16 gradations). Means the maximum gradation). A solid line indicates a liquid crystal display device having a normal liquid crystal layer thickness, and a broken line indicates a liquid crystal display device having a liquid crystal layer when it becomes narrow due to variations.

  When the thickness of the liquid crystal layer becomes narrower, the broken line shifts to the left (on the paper surface) with respect to the solid line, so that Ia16 decreases to Ia′16. In that case, Ia15, which is one gradation lower than Ia16, also decreases to Ia′15. Here, when Ia16-Ia15 (normal gradation difference) and Ia'16-Ia'15 (gradation difference in the case of variation) are compared, a large difference in gradation difference occurs between them.

  However, as shown in FIG. 24 (b), in the liquid crystal display device of the present invention, the white display voltage Vb16 is not aligned with the peak position of the birefringence amount (smaller than the phase difference λ / 2), and the position shifted from the peak position. Ib16 was determined according to the above.

  With this configuration, Ib16-Ib15 (normal gradation difference) and Ib'16-Ib'15 (gradation when there are variations) even if the liquid crystal layer varies and the peak shifts as shown by the broken line. When comparing (difference), there is no significant difference between the two. This is achieved by using the slow position of the voltage-transmittance curve. Therefore, it is possible to obtain a liquid crystal display device that can cope with variations in the liquid crystal layer, has stable gradation, and has excellent display performance.

  Further, as described above, the first to thirteenth embodiments have been described, but by appropriately combining the respective liquid crystal display devices, liquid crystal display devices that combine the characteristics of the individual embodiments can be manufactured. .

  According to the configuration of the present invention, the problems of the present invention can be sufficiently achieved. In other words, according to the present invention, the OCB type liquid crystal display device can overcome the problem that a display defect occurs in a specific driving condition, a specific temperature range, and a problem that the contrast is lowered.

  1 ... Liquid crystal display device, 2 ... 3 ... Substrate, 4 ... Spray state, 5 Bend alignment state, 10 ... 11 ... Substrate, 12 ... Liquid crystal molecule, 13 ... Liquid crystal layer, 15/16 ... Polarizing plate, 17/18 ... Optical Compensation plate, 20 ... Liquid crystal display device, 21 ... Liquid crystal display device, 22 ... Sharpening circuit, 23 ... Voltage limiting circuit, 25 ... Limiter voltage generation circuit, 31 ... Black level voltage generation circuit, 32 ... White level voltage generation circuit, 33 ... Control circuit, 34 ... Temperature sensor, 35a, 35b, 35c ... Manual adjustment knob, 36 ... Gradation voltage generation circuit, 37 ... Gradation voltage generation circuit, 40 ... Diffusion plate, 41 ... Polarizing plate, 42 ... Phase difference Plate, 43 ... Glass substrate, 44 ... Liquid crystal, 45 ... Reflective electrode, 46 ... Glass substrate, 85/90/95 ... Color filter, 82/92/96 ... TFT element, 80M / 90M / 95M ... Black matrix, 132 ... Liquid crystal panel, 131 ... Back light element, 131R ... Red light emitting element, 131G ... Green light emitting element, 131B ... Blue light emitting element, V1 ... Minimum voltage, r1, r2, r3 ... Variable Resistance, P1, P2, P3, P4 ... Connection point, L1, L2, L3, L4, L5 ... Individual connection run, L5 ... Common line, SW1, SW2, SW3, SW4 ... Switch, VB ... Black level display voltage, VW ... white level display voltage.

Claims (19)

  An OCB type liquid crystal having voltage applying means for applying a voltage to the liquid crystal sealed in the liquid crystal panel, displaying by changing the voltage applied by the voltage applying means, and displaying the liquid crystal in a bend alignment state. A display device, comprising a backlight element on the back side of the liquid crystal panel, the backlight element having a high light intensity on the long wavelength side.   2. The liquid crystal display device according to claim 1, wherein the luminance in the vicinity of 610 nm of the emission wavelength of the backlight element is twice or more than the luminance in the vicinity of 430 nm.   2. The liquid crystal display device according to claim 1, wherein a luminance in the vicinity of 610 nm of the light emission wavelength of the backlight element is 1.78 times or more than a luminance in the vicinity of 430 nm.   The liquid crystal display device according to claim 1, wherein x is 0.32 or more in the xy chromaticity coordinates of light emission of the backlight element.   The liquid crystal display device according to claim 1, wherein x is 0.36 or more in the xy chromaticity coordinates of light emission of the backlight element.   The liquid crystal display device according to claim 1, wherein x is 0.40 or more in the xy chromaticity coordinates of light emission of the backlight element.   The liquid crystal display device according to claim 1, wherein the color balance of the phosphor constituting the backlight element is adjusted.   The liquid crystal display device according to claim 1, wherein the backlight element has coloring means.   The liquid crystal display device according to claim 8, wherein the coloring means is a prism sheet.   The liquid crystal display device according to claim 8, wherein the backlight element has scattering means having coloring properties.   The liquid crystal display device according to claim 10, wherein the scattering means is a diffusion plate.   The liquid crystal display device according to claim 10, wherein the scattering means is a scattering dot provided on a light guide plate constituting the backlight element.   The liquid crystal display device according to claim 8, wherein the coloring means is a polarization conversion element. An OCB type liquid crystal having voltage applying means for applying a voltage to the liquid crystal sealed in the liquid crystal panel, displaying by changing the voltage applied by the voltage applying means, and displaying the liquid crystal in a bend alignment state. A display device,
A liquid crystal display device comprising voltage applying means for applying a voltage to the liquid crystal and color display means for performing a plurality of types of color display, wherein in the plurality of types of color display, at least one type of color display has different gamma characteristics.   The liquid crystal display device according to claim 14, wherein display is performed using a black writing method. An OCB type liquid crystal display having voltage applying means for applying a voltage to the liquid crystal sealed in the liquid crystal panel, and changing the voltage applied by the voltage applying means to adjust the amount of birefringence of the liquid crystal for display. A device,
Liquid crystal display in which the difference between the phase difference of the liquid crystal when a voltage for performing display with the smallest amount of transmitted light and the voltage for performing display with the largest amount of transmitted light is less than λ / 2 apparatus.   The liquid crystal panel has a pair of substrates, and has a configuration in which the pretilt direction of the liquid crystal in contact with the pair of substrates is substantially parallel aligned so that the positional relationship is plane-symmetric with respect to the center plane between the substrates. Item 17. A liquid crystal display device according to item 16.   The liquid crystal display device according to claim 1, wherein the contrast value is 100 or more.   The liquid crystal display device according to claim 1, wherein the contrast value is 10 or more.

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