JP2006119206A - Liquid crystal display - Google Patents

Liquid crystal display Download PDF

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JP2006119206A
JP2006119206A JP2004304546A JP2004304546A JP2006119206A JP 2006119206 A JP2006119206 A JP 2006119206A JP 2004304546 A JP2004304546 A JP 2004304546A JP 2004304546 A JP2004304546 A JP 2004304546A JP 2006119206 A JP2006119206 A JP 2006119206A
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Prior art keywords
liquid crystal
light source
signal
dimming
period
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JP2004304546A
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Japanese (ja)
Inventor
Tatsujiro Takamatsu
Kentaro Teranishi
Yoshinori Yasuda
吉範 安田
謙太郎 寺西
竜二郎 高松
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Toshiba Matsushita Display Technology Co Ltd
東芝松下ディスプレイテクノロジー株式会社
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Priority to JP2004304546A priority Critical patent/JP2006119206A/en
Publication of JP2006119206A publication Critical patent/JP2006119206A/en
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02BCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00Energy efficient lighting technologies
    • Y02B20/16Gas discharge lamps, e.g. fluorescent lamps, high intensity discharge lamps [HID] or molecular radiators
    • Y02B20/20High pressure [UHP] or high intensity discharge lamps [HID]
    • Y02B20/202Specially adapted circuits

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display having excellent visual field angle characteristics and display quality. <P>SOLUTION: The liquid crystal display is provided with: a liquid crystal panel 1 wherein a liquid crystal layer 30 held between a pair of substrates contains bend-arranged liquid crystal molecules in a prescribed display state; a panel driving part 60 supplying video signals including a display signal corresponding to a display image and a black signal corresponding to a black image to the liquid crystal panel 1; a backlight 50 having a light source 51 illuminating the liquid crystal panel 1 from its rear surface and controlling light by the ratio of an off-period and an on-period of the light source 51; and a light source driving part 70 outputting a light control signal having a prescribed frequency on the basis of an input signal according to a light controlling level to the light source 51. The frequency of the light control signal is different from the frequency of the video signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device using an OCB (Optically Compensated Bend) technique capable of realizing a wide viewing angle and a high-speed response.

  Liquid crystal display devices are applied to various fields by taking advantage of features such as light weight, thinness, and low power consumption.

  Currently, an OCB type liquid crystal display device has attracted attention as a liquid crystal display device capable of improving the viewing angle and the response speed. The OCB type liquid crystal display device includes a liquid crystal panel configured by holding a liquid crystal layer having liquid crystal molecules arranged in a bend between a pair of substrates, a backlight for illuminating the liquid crystal panel from the back, and the like. This OCB type liquid crystal display device has an improved response speed as compared with the TN type liquid crystal display device, and can further optically self-compensate the influence of birefringence of light passing through the liquid crystal layer depending on the alignment state of the liquid crystal molecules. There is an advantage that the corner is wide.

  When an image is displayed using such an OCB type liquid crystal display device, the birefringence is controlled and combined with a polarizing plate, for example, a black image is displayed by blocking light when a high voltage is applied, and when a low voltage is applied. It is conceivable to display a white screen through light.

  By the way, as described above, in the OCB type liquid crystal display device, the alignment state of the liquid crystal molecules is changed from the splay alignment to the bend alignment in order to display an image. However, when the voltage required to maintain such bend alignment is not applied over a long period, the alignment state of the liquid crystal molecules may reversely transition to the initial splay alignment. In this splay alignment state, image defects such as alignment defects or point defects occur, and satisfactory image display cannot be performed.

  Also, when displaying a moving image, the image may appear blurred due to the influence of the afterimage due to the image of the preceding frame.

  For the purpose of preventing such reverse transition of the alignment state of liquid crystal molecules and blurring of the image, a non-video signal, which is a signal different from the video signal, is written to the pixel electrode for a certain period (this is referred to as black insertion). The liquid crystal display device as described above has been studied (for example, see Patent Document 1). Here, the non-video signal is not uniquely determined. For example, a white image is displayed when a relatively low voltage is applied, and a black image is displayed when a relatively high voltage is applied. In this case, a signal for displaying a black image is used as a non-video signal. By writing this non-video signal within a predetermined period, a relatively high voltage is applied to the pixel electrode, so that the bend orientation can be maintained. Further, by displaying a black image, the afterimage is eliminated, and blurring of the image can be prevented.

  On the other hand, the backlight includes a fluorescent tube as a light source for illuminating the liquid crystal panel. As a required performance for a display monitor or a television, a variable range of brightness adjustment is widely required due to a large change in ambient brightness, for example, a dimming range such as 10 to 100% is required. There is a case.

As a method of changing the light quantity of the fluorescent tube, a burst light control method or the like is known. In this burst dimming method, the oscillation operation of the inverter circuit is forcibly turned on / off, and the dimming is performed by changing the ratio between the on period and the off period (referred to as “duty ratio”). (For example, refer to Patent Document 2).
JP 2003-309784 A JP 2002-359097 A

  In the OCB type liquid crystal display device, when adopting a fixed frequency PWM method that changes the ratio of the ON period and OFF period of the dimming pulse according to the level of the dimming signal when dimming the backlight, black insertion of the liquid crystal panel And the backlight off period interfere with each other to generate periods with different average luminance. As a result, it is easy for a viewer to visually recognize the display screen such that a black belt is present, and there is a possibility that the display quality is deteriorated.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a liquid crystal display device excellent in viewing angle characteristics and display quality.

A liquid crystal display device according to a first aspect of the present invention provides:
A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates;
An optical compensation element that optically compensates for retardation of the liquid crystal layer containing bend-aligned liquid crystal molecules in a predetermined display state in which a voltage is applied to the liquid crystal layer;
Panel driving means for supplying a display signal corresponding to a display image and a video signal including a black signal corresponding to a black image to the liquid crystal panel;
A light source that illuminates the liquid crystal panel from the back, and a backlight that can be dimmed according to a ratio between an off period and an on period of the light source;
Light source driving means for outputting a dimming signal having a predetermined frequency based on an input signal corresponding to the dimming level to the light source;
With
The frequency of the dimming signal is different from the frequency of the video signal.

A liquid crystal display device according to a second aspect of the present invention provides:
A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates;
An optical compensation element that optically compensates for retardation of the liquid crystal layer containing bend-aligned liquid crystal molecules in a predetermined display state in which a voltage is applied to the liquid crystal layer;
Panel driving means for supplying a display signal corresponding to a display image and a video signal including a black signal corresponding to a black image to the liquid crystal panel;
A plurality of light sources that illuminate the liquid crystal panel from the back, and a backlight that can be dimmed according to a ratio between an off period and an on period of the light source;
Light source driving means for outputting a dimming signal having a predetermined frequency based on an input signal corresponding to the dimming level to the light source;
With
The light source driving means supplies a first dimming signal to the first light source and supplies a second dimming signal out of phase with the first dimming signal to the second light source. Features.

  According to the present invention, a liquid crystal display device excellent in viewing angle characteristics and display quality can be provided.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a liquid crystal display device using an OCB (Optically Compensated Bend) mode method will be described as an example of the liquid crystal display device.

  As shown in FIG. 1, the OCB type liquid crystal display device includes a liquid crystal panel 1 having a liquid crystal layer 30 sandwiched between a pair of substrates, that is, an array substrate 10 and a counter substrate 20, and the liquid crystal panel 1 on the back surface. A backlight 50 for illuminating from is provided. The liquid crystal panel 1 is, for example, a transmission type, and is configured to be able to transmit backlight light from the backlight 50 arranged on the array substrate 10 side to the counter substrate 20 side. Further, the liquid crystal panel 1 includes an effective display unit 2 that substantially displays an image. The effective display unit 2 is composed of display pixels PX arranged in a matrix.

  The array substrate 10 is formed using an insulating substrate 11 having optical transparency such as glass. The array substrate 10 includes a switch element 12, a pixel electrode 13, an alignment film 14 and the like on one main surface of an insulating substrate 11. The switch element 12 is disposed in each display pixel PX, and includes a TFT (Thin Film Transistor), a MIM (Metal Insulated Metal), or the like. The pixel electrode 13 is disposed in each display pixel PX and is electrically connected to the switch element 12. The pixel electrode 13 is formed of a light-transmitting conductive member such as ITO (Indium Tin Oxide). The alignment film 14 is disposed so as to cover the entire main surface of the insulating substrate 11, and is formed of a light transmissive material.

  The counter substrate 20 is formed using an insulating substrate 21 having optical transparency such as glass. The counter substrate 20 includes a counter electrode 22 and an alignment film 23 on one main surface of an insulating substrate 21. The counter electrode 22 is disposed in common in all the display pixels in the effective display portion 2 and is formed of a conductive member having optical transparency such as ITO. The alignment film 23 is disposed so as to cover the entire main surface of the insulating substrate 21 and is made of a light-transmitting material.

  In the color display type liquid crystal display device, the liquid crystal panel 1 includes display pixels of a plurality of colors, for example, red (R), green (G), and blue (B) color pixels. That is, the red pixel includes a red color filter that transmits red wavelength light, the green pixel includes a green color filter that transmits green wavelength light, and the blue pixel includes a blue color filter that transmits blue wavelength light. Yes. These color filters are arranged on the main surface of the array substrate 10 or the counter substrate 20.

  The array substrate 10 and the counter substrate 20 having the above-described configuration are arranged in a state where a predetermined gap is maintained with a spacer (not shown), and are bonded together by a sealing material. The liquid crystal layer 30 is sealed in the gap between the array substrate 10 and the counter substrate 20. The liquid crystal molecules 31 included in the liquid crystal layer 30 can be selected from materials having positive dielectric anisotropy and optically positive uniaxiality.

  Such an OCB type liquid crystal display device optically compensates for the retardation of the liquid crystal layer 30 including the liquid crystal molecules 31 bend-aligned as shown in FIG. 1 in a predetermined display state in which a voltage is applied to the liquid crystal layer 30. An optical compensation element 40 is provided. The optical compensation element 40 is arranged on one main surface of the liquid crystal panel 1, that is, the outer surface on the array substrate 10 side, and on the other main surface of the liquid crystal panel 1, that is, the outer surface on the counter substrate 20 side. Second compensation element 40B.

  For example, as illustrated in FIG. 2, the first compensation element 40A includes a polarizing plate 41A and a plurality of optical elements 42A and 43A having a function as a retardation plate. Similarly, the second compensation element 40B includes a polarizing plate 41B and a plurality of optical elements 42B and 43B that function as retardation plates. The optical elements 42A and 42B mainly function as retardation plates having retardation (phase difference) in the thickness direction. The optical elements 43A and 43B mainly function as retardation plates having retardation (phase difference) in the in-plane direction.

  As shown in FIG. 3, the alignment films 14 and 23 have been subjected to parallel alignment processing (that is, have been rubbed in the direction indicated by the arrow A in the figure). Thereby, the orthogonal projection (liquid crystal alignment direction) of the optical axis of the liquid crystal molecules 31 is parallel to the arrow A in the figure. In a state where an image can be displayed, that is, in a state where a predetermined bias is applied, the liquid crystal molecules 31 are arranged in the cross section of the liquid crystal layer 30 defined by the arrow A as shown in FIG. A bend arrangement between 20 and 20.

  At this time, the polarizing plate 41A is arranged so that its transmission axis faces the direction indicated by the arrow B in the drawing. Further, the polarizing plate 41B is arranged so that the transmission axis thereof faces the direction indicated by the arrow C in the drawing. That is, the transmission axes of the polarizing plates 41A and 41B form an angle of 45 ° with respect to the liquid crystal alignment direction A, and are orthogonal to each other. Thus, the arrangement in which the transmission axes of the polarizing plates are orthogonal to each other is called crossed Nicol, and the birefringence amount (retardation amount) of the object between the pair of polarizing plates is effectively 0 or an integral multiple of the wavelength. Light is not transmitted and a black image is displayed. Conversely, if the birefringence amount (retardation amount) of the object between the pair of polarizing plates is effectively λ / 2 with respect to the incident light having the wavelength λ, the light is transmitted and a white image (or color image) is displayed. Is done.

  The optical elements 43A and 43B compensate for the influence of retardation remaining in the liquid crystal layer 30 when the screen is observed from the front direction in a specific voltage application state (for example, a state where a high voltage is applied to display a black image). . The optical elements 42A and 42B compensate for the influence of retardation of the liquid crystal layer 30 when the screen is observed from an oblique direction in a specific voltage application state (for example, a state where a high voltage is applied to display a black image). . As a result, viewing angle characteristics and display quality can be improved in the OCB type liquid crystal display device.

  As shown in FIG. 4, the liquid crystal display device provides a panel drive unit 60 that functions as a panel drive unit that supplies a video signal to the liquid crystal panel 1 configured as described above, and a light control signal to the backlight 50. A light source driving unit (FPGA) 70 that functions as a light source driving means for outputting is provided.

  That is, the panel drive unit 60 is electrically connected to the liquid crystal panel 1 via a flexible printed circuit board or the like. The panel driving unit 60 outputs a display signal corresponding to a display image and a video signal including a black signal corresponding to a black image used for black insertion, other control signals, and the like based on the input video data. To supply.

  The backlight 50 includes a plurality of light sources 51 (a, b, c...) As shown in FIG. As these light sources 51 (a, b, c...), A fluorescent tube such as a straight tubular cold cathode tube extending in the longitudinal direction (scanning line Y direction) of the liquid crystal panel 1 is used, and is orthogonal to the longitudinal direction. They are arranged side by side in the direction (signal line X direction). The backlight 50 employs a burst dimming method, and dimming is possible by changing the ratio (duty ratio) between the off period and the on period of each light source 51 (a, b, c...). To do. Each light source 51 (a, b, c...) Is driven based on a PWM (pulse-width modulation) type dimming signal.

  That is, the light source driving unit 70 sets the ratio between the on period and the off period of the pulse signal having a predetermined frequency based on the input signal (input PWM signal) corresponding to the dimming level, and each light source 51 (a, b , C...), A dimming signal (output PWM signal) having a predetermined frequency set is output. That is, the light source driving unit 70 is configured to be able to output a plurality of types of dimming signals in which the frequency, phase, duty ratio, etc. are individually set based on one input signal (that is, provided with a plurality of light sources). The backlight is configured so that it can be driven in multiple phases).

  For example, as illustrated in FIG. 5, the light source driving unit 70 counts the ON period and the OFF period of the input signal based on the reference clock. The light source driving unit 70 recognizes the frequency of the input signal and the duty ratio based on the on period and the off period. In the example shown in FIG. 5, both the on period and the off period of the input signal correspond to 12 clocks. The frequency of the input signal corresponds to 24 clocks and the duty ratio is 50%.

  The light source driving unit 70 generates a plurality of types of dimming signals in which the ratio between the on period and the off period is determined based on the input signal, and determines the phase difference between the dimming signals. In the example illustrated in FIG. 5, the light source driving unit 70 generates three types of dimming signals having the same frequency and the same duty ratio as the input signal, and at least one dimming signal has an on period. Determine the phase difference. That is, the first dimming signal is a signal having a duty ratio of 50% synchronized with the input signal. The second dimming signal is a signal having a phase shift of 120 ° (that is, 8 clocks) with respect to the first dimming signal and a duty ratio of 50%. The third dimming signal is a signal having a phase shift of 120 ° (that is, 8 clocks) with respect to the second dimming signal and a duty ratio of 50%.

  And the light source drive part 70 outputs the produced | generated multiple types of light control signal to a corresponding light source.

  In order to light each light source 51 (a, b, c...) Of the backlight 50, it is necessary to apply a high-voltage AC voltage. For this reason, the light source 51 (a, b, c...) Is a high voltage capable of turning on the light source 51 (a, b, c...) With a low DC voltage (that is, dimming signal) output from the light source driving unit 70. Is turned on / off (i.e., turned on / off) by an output signal output through a lighting device such as a DC / AC inverter 71 that converts the current into an AC voltage.

  By the way, when the black insertion of the liquid crystal panel 1 overlaps with the off period of the backlight 50, a black belt is easily visually recognized on the display screen, and there is a possibility that the display quality is deteriorated. This phenomenon will be described based on the following comparative example.

(Comparative example)
The liquid crystal display device according to the comparative example has a specification as shown in FIG. That is, the liquid crystal panel 1 adopts the OCB mode as described above, and the black insertion rate is 11%. Here, the black insertion rate corresponds to a ratio of a period during which a black signal is supplied to the liquid crystal panel 1 in one frame period (one vertical scanning period). The frequency of the video signal supplied to the liquid crystal panel 1 by the panel driving unit 60 is 60 Hz, which is the same as the black insertion frequency. It is assumed that this video signal is synchronized with the dimming signal output from the light source driving unit 70 based on the synchronization signal input to the panel driving unit 60 and the light source driving unit 70.

  For example, as shown in FIG. 7, the black insertion rate of 11% corresponds to a case where a black image is written in 1/540 sec (one scene) obtained by dividing one frame period, that is, 1/60 sec into nine. As shown in FIG. 8, when the effective display portion 2 of the liquid crystal panel 1 is divided into 18 areas extending in the longitudinal direction, the black insertion rate of 11% is 2 within one display screen (one scene). This means displaying a black image in the area. Then, as shown in FIG. 8, the black image scans the entire area of the effective display unit 2 in 1/60 sec.

  The backlight 50 includes six light sources 51 (a, b, c, d, e, f), and each light source mainly includes three areas of the effective display section 2 divided into 18 as shown in FIG. It shall be illuminated. That is, the light source 51a mainly illuminates the first to third areas R1 to R3 of the effective display unit 2. Similarly, the light source 51b mainly illuminates the fourth to sixth areas R4 to R6 of the effective display unit 2. The light source 51c mainly illuminates the seventh to ninth areas R7 to R9 of the effective display unit 2. The light source 51d mainly illuminates the tenth to twelfth areas R10 to R12 of the effective display unit 2. The light source 51e mainly illuminates the thirteenth to fifteenth areas R13 to R15 of the effective display unit 2. The light source 51f mainly illuminates the sixteenth to eighteenth areas R16 to R18 of the effective display unit 2.

  The light source driving unit 70 outputs one type of dimming signal having the same phase, the same frequency, and the same duty ratio to all the light sources 51 (a, b, c, d, e, f) based on the input signal. Output. Here, the frequency of the output dimming signal is n times (n is an integer) the frequency of the video signal (black insertion), and is 60 Hz (n = 1). The duty ratio of the dimming signal is 33% (that is, 1/3 of one cycle of the dimming signal is an on period and 2/3 is an off period). That is, as shown in FIG. 7, all the light sources 51 (a, b, c, d, e, f) are turned on in 1/3 of 1/60 sec and turned off in 2/3. .

  Thus, in the comparative example in which the frequency of the video signal (black insertion) and the frequency of the dimming signal are the same, as shown in FIG. 7, in any frame (every 1/60 sec), A black image is displayed in a predetermined area of the effective display portion 2, that is, in a range from the first area R1 to the sixth area R6.

  For this reason, the average luminance, that is, the lighting time for two frames in each area, that is, 1/30 sec (18 scenes), is 4 in the range from the first area R1 to the sixth area R6, whereas the seventh area R7. And 6 in the range from the 18th area R18. Therefore, the luminance in a part of the display screen is extremely small, and it is easy to visually recognize that there is one black belt in such an area. That is, it is easy to visually recognize as if a black belt is fixedly displayed at a predetermined position on the display screen.

  Further, when the frequency of the dimming signal is n times the frequency of the video signal (black insertion), it is easy to visually recognize as if n black bands are fixedly displayed at a predetermined position on the display screen.

Example 1
The liquid crystal display device according to Example 1 is configured with specifications as shown in FIG. That is, the liquid crystal panel 1 and the backlight 50 are configured similarly to the comparative example.

  The light source driving unit 70 outputs one type of dimming signal having the same phase, the same frequency, and the same duty ratio to all the light sources 51 (a, b, c, d, e, f) based on the input signal. Output. Here, the frequency of the output dimming signal is 90 Hz, unlike n times the frequency of the video signal (black insertion). The duty ratio of the dimming signal is 33%.

  As described above, in Example 1 having a configuration in which the frequency of the dimming signal is different from n times the frequency of the video signal (black insertion), as shown in FIG. Every 1/90 sec). That is, in the first frame, after the black image is displayed in the first area R1 and the second area R2, the black image is displayed in the third area R3 and the fourth area R4. In the subsequent second frame, the black image is displayed in the 15th area R15 and the 16th area R16, after the black image is displayed in the 13th area R13 and the 14th area R14. In the subsequent third frame, after black images are displayed in the seventh area R7 and the eighth area R8, black images are displayed in the ninth area R9 and the tenth area R10. The display position of the black image moves periodically with these three frames as one unit (the following fourth frame is the same as the first frame).

  For this reason, the average luminance, that is, the lighting time for 3 frames in each area, that is, 1/30 sec (18 scenes), is 5 or more, and the extremely low luminance area disappears. That is, the black belt is displayed in 6 of the 18 scenes, but moves within the display screen at a high speed (30 Hz), so that the decrease in luminance is averaged over all areas. Therefore, the black belt is hardly visually recognized in the display screen, and the display quality is improved.

  When the frequency of the dimming signal is set to be approximately (n + 1/2) times the frequency of the video signal, where n is an integer, the black band moves the fastest. For this reason, the decrease in luminance is further averaged in the display lower surface, and the display quality is further improved.

(Example 2)
The liquid crystal display device according to Example 2 has a specification as shown in FIG. That is, the liquid crystal panel 1 and the backlight 50 are configured similarly to the comparative example.

  The light source driving unit 70 has three types of adjustments having the same frequency, the same duty ratio, and different phases for all the light sources 51 (a, b, c, d, e, f) based on the input signal. Outputs an optical signal. Here, the light source driving unit 70 outputs the same first dimming signal to the light sources 51a and 51b, and outputs the same second dimming signal to the light sources 51c and 51d. The same third dimming signal is output to 51f. The frequency of these first to third dimming signals is 60 Hz (n = 1) corresponding to n times the frequency of the video signal (black insertion). The duty ratio of these first to third dimming signals is 33%. Further, these first to third dimming signals are out of phase with each other. The amount of phase shift between these dimming signals is set so that at least one light source is turned on within one frame period. Here, since three types of dimming signals are output, the phase between the dimming signals may be shifted by 120 °. Thereby, the period (light-out time) when the plurality of light sources are simultaneously turned off can be shortened, and the period interfering with black insertion can be dispersed in time.

  As described above, in the second embodiment in which the frequency of the dimming signal is the same as the frequency of the video signal (black insertion), each light source 51 (a, b, c, d, e, f) of the backlight 50 is provided. It is driven by three kinds of first to third dimming signals each having a phase difference. That is, the light sources 51a and 51b are lit in the first 1/3 period within one frame period based on the first dimming signal, and the light sources 51c and 51d are based on the second dimming signal for one frame period. The light sources 51e and 51f are lit during the 1/3 period following the light sources 51c and 51d within the 1 frame period based on the third dimming signal. .

  At this time, as shown in FIG. 10, the area where the black image is displayed is different for each scene (every 1/540 sec). At this time, since the timing of black insertion and the timing of turning on the light source overlap, the black image moves in the entire area.

  For this reason, the average brightness of 2 frames in each area, that is, 1/30 sec (18 scenes), that is, the lighting time is all constant 4, and the overall brightness decreases, but the black band is high-speed (30 Hz) in the display screen. Therefore, the decrease in luminance is averaged over the entire area. Therefore, the black belt is hardly visually recognized in the display screen, and the display quality is improved.

(Example 3)
The liquid crystal display device according to the third embodiment is basically configured with the same specifications as in the second embodiment as shown in FIG. In the third embodiment, since the three types of dimming signals output from the light source driving unit 70 to the light source 51 (a, b, c, d, e, f) are different from those in the second embodiment, the light source is turned on. Timing is different.

  That is, the light sources 51c and 51d are lit in the first 1/3 period within one frame period based on the first dimming signal, and the light sources 51e and 51f are based on the second dimming signal for one frame period. The light sources 51a and 51b are lit in the 1/3 period following the light sources 51c and 51d in one frame period based on the third dimming signal. .

  At this time, as shown in FIG. 11, the timing of black insertion and the timing of turning off the light source overlap. For this reason, the average luminance, that is, the lighting time of 2 frames in each area, that is, 1/30 sec (18 scenes), that is, the lighting time is all constant 6, and the overall luminance is high, and the black belt may move within the display screen. Absent. Therefore, the brightness of the entire display screen is made uniform, and the brightness can be increased, and the display quality is further improved.

Example 4
The liquid crystal display device according to Example 4 has a specification as shown in FIG. That is, the liquid crystal panel 1 and the backlight 50 are configured similarly to the comparative example.

  The light source driving unit 70 has three types of adjustments having the same frequency, the same duty ratio, and different phases for all the light sources 51 (a, b, c, d, e, f) based on the input signal. Outputs an optical signal. Here, the light source driving unit 70 outputs the same first dimming signal to the light sources 51a and 51b, and outputs the same second dimming signal to the light sources 51c and 51d. The same third dimming signal is output to 51f. The frequency of these first to third dimming signals is 90 Hz, unlike n times the frequency of the video signal (black insertion). The duty ratio of these first to third dimming signals is 33%. Further, these first to third dimming signals are out of phase with each other. Here, the phase between the dimming signals is shifted by 120 °.

  As described above, in Example 4 having a configuration in which the frequency of the dimming signal is different from the frequency n times that of the video signal (black insertion), each light source 51 (a, b, c, d, e, f) of the backlight 50 is used. ) Are driven by three types of first to third dimming signals each having a phase difference. That is, the light sources 51a and 51b are lit in the first 1/3 period within one frame period based on the first dimming signal, and the light sources 51c and 51d are based on the second dimming signal for one frame period. The light sources 51e and 51f are lit during the 1/3 period following the light sources 51c and 51d within the 1 frame period based on the third dimming signal. .

  At this time, as shown in FIG. 12, the area where the black image is displayed is different for each scene (every 1/540 sec). At this time, the timing of black insertion and the timing of turning on the light source partially overlap. That is, in the first frame, the black image is displayed in the first area R1 and the second area R2, the black image is displayed in the third area R3 and the fourth area R4, and then the seventh area. Black images are displayed in R7 and the eighth area R8. In the subsequent second frame, no black image is displayed in the entire area. In the subsequent third frame, the black image is displayed in the 15th area R15 and the 16th area R16 after the black image is displayed in the 11th area R11 and the 12th area R12. The display position of the black image moves periodically with these three frames as one unit (the following fourth frame is the same as the first frame).

  For this reason, the average luminance, that is, the lighting time for 3 frames in each area, that is, 1/30 sec (18 scenes), is 5 or more, and the extremely low luminance area disappears. That is, the black belt is displayed in 6 of the 18 scenes, but moves within the display screen at a high speed (30 Hz), so that the decrease in luminance is averaged over all areas. Therefore, the black belt is hardly visually recognized in the display screen, and the display quality is improved.

(Example 5)
The liquid crystal display device according to Example 5 has a specification as shown in FIG. That is, the liquid crystal panel 1 and the backlight 50 are configured similarly to the comparative example.

  The light source driving unit 70 has three types of adjustments having the same frequency, the same duty ratio, and different phases for all the light sources 51 (a, b, c, d, e, f) based on the input signal. Outputs an optical signal. Here, the light source driving unit 70 outputs the same first dimming signal to the light sources 51a and 51d, outputs the same second dimming signal to the light sources 51b and 51e, and further, the light source 51c and The same third dimming signal is output to 51f. The frequency of these first to third dimming signals is 90 Hz, unlike n times the frequency of the video signal (black insertion). The duty ratio of these first to third dimming signals is 33%. Further, these first to third dimming signals are out of phase with each other. Here, the phase between the dimming signals is shifted by 120 °.

  Thus, in the fifth embodiment having a configuration in which the frequency of the dimming signal is different from the frequency n times that of the video signal (black insertion), each light source 51 (a, b, c, d, e, f) of the backlight 50 is used. ) Are driven by three types of first to third dimming signals each having a phase difference. That is, the light sources 51a and 51d are turned on in the first 1/3 period in one frame period based on the first dimming signal, and the light sources 51b and 51e are in one frame period based on the second dimming signal. The light sources 51c and 51f are turned on in the 1/3 period following the light sources 51b and 51e in the 1 frame period based on the third dimming signal. .

  At this time, as shown in FIG. 13, the area where the black image is displayed is different for each scene (every 1/540 sec). At this time, the timing of black insertion and the timing of turning on the light source partially overlap. That is, in the first frame, the black image is displayed in the third area R3 after the black image is displayed in the first area R1 and the second area R2, and then the fifth area R5 and the sixth area R6. After the black image is displayed, the black image is further displayed in the ninth area R9. In the subsequent second frame, no black image is displayed in the entire area. In the subsequent third frame, the black image is displayed in the tenth area R10, the black image is displayed in the thirteenth area R13 and the fourteenth area R14, and then the black image is displayed in the sixteenth area. Thereafter, a black image is further displayed in the seventeenth area R17 and the eighteenth area R18. The display position of the black image moves periodically with these three frames as one unit (the following fourth frame is the same as the first frame).

  For this reason, the average luminance, that is, the lighting time for 3 frames in each area, that is, 1/30 sec (18 scenes), is 5 or more, and the extremely low luminance area disappears. That is, the black belt is displayed in 8 of the 18 scenes, but moves within the display screen at a high speed (30 Hz), so that the decrease in luminance is averaged over all areas. Therefore, the black belt is hardly visually recognized in the display screen, and the display quality is improved.

  As described above, according to this embodiment, in the OCB type liquid crystal display device capable of improving the viewing angle and the response speed, by performing so-called black insertion for writing a black image in a predetermined period within one frame, This prevents reverse transition of the alignment state of liquid crystal molecules and blurring of images. On the other hand, a wide light control range is realized by a backlight employing a burst light control method.

  When the liquid crystal panel having such a configuration and the backlight are combined, (1) the frequency of the dimming signal supplied to the light source of the backlight is different from n times the frequency of the video signal when n is an integer. (2) The first dimming signal is supplied to the first light source that constitutes the backlight, and the second dimming signal that is out of phase with the first dimming signal is supplied to the second light source. At least one of these means is adopted. This prevents a decrease in average luminance caused by the overlap of the black insertion timing of the liquid crystal panel and the backlight extinguishing period. Therefore, the black belt is hardly visually recognized in the display screen, and the display quality can be improved.

  Further, when n is increased, n black bands are simultaneously displayed in the display screen, and the positions where black images are displayed can be dispersed. According to the simulation by the inventors, when the frequency of the video signal (black insertion) is 60 Hz, the frequency of the dimming signal is 510 Hz (video signal frequency × (8 + 1/2)). The eight black belts moved at 30 Hz, and the visibility of the black belts decreased.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the gist of the invention in the stage of implementation. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

FIG. 1 is a cross-sectional view schematically showing a configuration of an OCB type liquid crystal display device as an embodiment of the present invention. FIG. 2 is a diagram schematically showing a configuration of an optical compensation element applied to the OCB type liquid crystal display device. FIG. 3 is a diagram showing the relationship between the optical axis direction and the liquid crystal alignment direction of each optical member constituting the optical compensation element shown in FIG. FIG. 4 is a diagram schematically showing a configuration for driving the liquid crystal display panel and the backlight. FIG. 5 is a diagram illustrating an example of a method of generating a plurality of types of dimming signals based on input signals from the light source driving unit illustrated in FIG. FIG. 6 is a diagram for explaining the specifications of the liquid crystal display devices according to the comparative example and Examples 1 to 5. FIG. 7 is a diagram for explaining the black insertion timing and the light source lighting timing in the liquid crystal display device of the comparative example. FIG. 8 is a diagram for explaining the relationship between the light source constituting the backlight and the area of the effective display portion illuminated by each light source in the comparative example and Examples 1 to 5. FIG. 9 is a diagram for explaining black insertion timing and light source lighting timing in the liquid crystal display device according to the first embodiment. FIG. 10 is a diagram for explaining black insertion timing and light source lighting timing in the liquid crystal display device according to the second embodiment. FIG. 11 is a diagram for explaining black insertion timing and light source lighting timing in the liquid crystal display device according to the third embodiment. FIG. 12 is a diagram for explaining black insertion timing and light source lighting timing in the liquid crystal display device according to the fourth embodiment. FIG. 13 is a diagram for explaining black insertion timing and light source lighting timing in the liquid crystal display device according to the fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel 2 ... Effective display part 10 ... Array substrate 20 ... Opposite substrate 30 ... Liquid crystal layer 31 ... Liquid crystal molecule 40 ... Optical compensation element 50 ... Backlight 51 (a, b, c, d, e, f) ... Light source 60 ... Panel drive unit 70 ... Light source drive unit

Claims (7)

  1. A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates;
    An optical compensation element that optically compensates for retardation of the liquid crystal layer containing bend-aligned liquid crystal molecules in a predetermined display state in which a voltage is applied to the liquid crystal layer;
    Panel driving means for supplying a display signal corresponding to a display image and a video signal including a black signal corresponding to a black image to the liquid crystal panel;
    A light source that illuminates the liquid crystal panel from the back, and a backlight that can be dimmed according to a ratio between an off period and an on period of the light source;
    Light source driving means for outputting a dimming signal having a predetermined frequency based on an input signal corresponding to the dimming level to the light source;
    With
    The frequency of the dimming signal is different from n times the frequency of the video signal, where n is an integer.
  2.   2. The liquid crystal display device according to claim 1, wherein the frequency of the dimming signal is substantially (n + 1/2) times the frequency of the video signal.
  3. A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates;
    An optical compensation element that optically compensates for retardation of the liquid crystal layer containing bend-aligned liquid crystal molecules in a predetermined display state in which a voltage is applied to the liquid crystal layer;
    Panel driving means for supplying a display signal corresponding to a display image and a video signal including a black signal corresponding to a black image to the liquid crystal panel;
    A plurality of light sources that illuminate the liquid crystal panel from the back, and a backlight that can be dimmed according to a ratio between an off period and an on period of the light source;
    Light source driving means for outputting a dimming signal having a predetermined frequency based on an input signal corresponding to the dimming level to the light source;
    With
    The light source driving means supplies a first dimming signal to the first light source and supplies a second dimming signal out of phase with the first dimming signal to the second light source. A characteristic liquid crystal display device.
  4. A liquid crystal panel configured by holding a liquid crystal layer between a pair of substrates;
    An optical compensation element that optically compensates for retardation of the liquid crystal layer containing bend-aligned liquid crystal molecules in a predetermined display state in which a voltage is applied to the liquid crystal layer;
    Panel driving means for supplying a display signal corresponding to a display image and a video signal including a black signal corresponding to a black image to the liquid crystal panel;
    A plurality of light sources that illuminate the liquid crystal panel from the back, and a backlight that can be dimmed according to a ratio between an off period and an on period of the light source;
    Light source driving means for outputting a dimming signal having a predetermined frequency based on an input signal corresponding to the dimming level to the light source;
    With
    The frequency of the dimming signal is different from the frequency of the video signal,
    The light source driving means supplies a first dimming signal to the first light source and a second dimming signal out of phase with the first dimming signal to the second light source. A liquid crystal display device characterized by the above.
  5.   5. The light source driving unit according to claim 1, wherein the light source driving unit counts the input signal based on a reference clock and determines a ratio between an off period and an on period of the dimming signal. Liquid crystal display device.
  6.   The said light source drive means counts the said input signal based on a reference | standard clock, The phase difference of the said 1st dimming signal and the said 2nd dimming signal is determined, The Claim 3 or 4 characterized by the above-mentioned. Liquid crystal display device.
  7.   5. The liquid crystal display device according to claim 1, wherein the light source driving unit outputs the dimming signal in synchronization with the input signal or the video signal. 6.
JP2004304546A 2004-10-19 2004-10-19 Liquid crystal display Pending JP2006119206A (en)

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WO2007144989A1 (en) * 2006-06-16 2007-12-21 Sharp Kabushiki Kaisha Display device and television receiver
WO2007144988A1 (en) * 2006-06-16 2007-12-21 Sharp Kabushiki Kaisha Display device and television receiver
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WO2007144989A1 (en) * 2006-06-16 2007-12-21 Sharp Kabushiki Kaisha Display device and television receiver
WO2007144988A1 (en) * 2006-06-16 2007-12-21 Sharp Kabushiki Kaisha Display device and television receiver
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