JP2007155819A - Liquid crystal display device and dimmer driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand a dimming range using a blinking backlight in a liquid crystal display device using black insertion driving. <P>SOLUTION: In the liquid crystal display device 1 of the invention, the driving control section 7 of a control section 10 controls the black insertion driving of the liquid crystal display panel 3 via a gate driver 5 and a source driver 6, and a PWM control section 9 controls the operation of the backlight 2 via an inverter 4 according to control of the driving control section. At this time, the PWM control section 9 uses PWM dimming, and when dimming for reducing luminance further from a limit duty ratio of a pulse signal in the backlight 2, a dimming system is switched and the dimming range (luminance) is expanded. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  A method of changing the brightness of a liquid crystal display panel in a liquid crystal display device is generally used as a PWM dimming method for a backlight. In this PWM dimming method, dimming is performed by changing the duty ratio of a pulse signal that emits light from a plurality of CCFLs (cold cathode tubes) constituting a backlight, and voltage adjustment that changes the tube current of the cold cathode tubes. A wide dimming range can be obtained compared to light or current dimming methods.

  In recent years, blinking backlights have been devised for the purpose of improving the visibility of moving images of liquid crystals by applying the principle of PWM dimming. This is to perform impulse-type display driving by turning on / off the backlight in synchronization with driving of the liquid crystal, and may be used alone or in combination with a black insertion driving type liquid crystal display element.

  In the latter case, it is mainly used in combination with an OCB type liquid crystal display element, and it is possible to achieve both good video visibility and high contrast.

  OCB type liquid crystal display elements are often used in combination with an active matrix substrate having TFT transistors and the like. This OCB type liquid crystal display element can respond at high speed and can be written twice in one frame period. A technique for making use of this characteristic and writing a black display period separately from a display signal in one frame is disclosed (for example, Patent Document 1 and Patent Document 2). This is called black insertion driving.

  When the blinking backlight is used to improve the moving image visibility of the liquid crystal display element, the duty ratio of the pulse signal for emitting the backlight in the dimming signal 100% is reduced to some extent in order to obtain good moving image visibility. It is necessary to keep it. For this reason, the blinking backlight has a problem that the dimming range becomes narrower than usual. For example, when the duty ratio of a pulse signal for obtaining good video visibility is 50%, when a backlight having an original dimming range (luminance) of 10% to 100% is used as a blinking backlight, The light control range (luminance) is 20% to 100%.

Further, when combined with a black insertion drive type liquid crystal display element, the dimming range is further limited due to restrictions on the timing of black insertion and the emission timing of the blinking backlight.
Japanese Patent Application No. 2000-214827 Japanese Patent Application No. 2002-107695

  As described above, when the blinking backlight and the black insertion drive type liquid crystal display element are combined, the dimming range is restricted due to the restrictions on the timing of black insertion and the emission timing of the blinking backlight. There was a problem that became narrow.

  An object of the present invention is to provide a liquid crystal display device and a dimming drive method capable of expanding a dimming range using a blinking backlight in a liquid crystal display device using a black insertion drive type liquid crystal display element. is there.

  According to the present invention, there is provided a dimming drive method for a liquid crystal display device in which a black insertion drive type liquid crystal display element and a blinking backlight are combined, wherein the phase of the black insertion drive and the backlight emission is adjusted. There is provided a dimming drive method characterized by performing transmission luminance adjustment.

  Further, according to the present invention, in a liquid crystal display device combining a black insertion drive type liquid crystal display element and a blinking backlight, the transmission luminance is adjusted by adjusting the phase of the black insertion drive and the backlight emission. The liquid crystal display device is characterized in that the light is adjusted.

  The liquid crystal display device of the present invention combines a blinking backlight and a black insertion drive type liquid crystal display element, and when the backlight reaches the minimum value of the duty ratio of the pulse signal, the liquid crystal black insertion drive and the backlight intermittently By adjusting the driving phase and matching a part of the light emission period of the backlight with the response part and the black insertion part of the liquid crystal, the amount of transmitted light can be reduced and the light control range can be expanded.

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

  FIG. 1 shows a configuration of a liquid crystal display device of the present invention. The liquid crystal display device 1 has a transmissive liquid crystal display panel 3 with a backlight 2 disposed on the back surface. The liquid crystal display panel 3 has a plurality of gate lines and a plurality of source lines (not shown), and is connected to the gate driver 5 and the source driver 6, respectively. The control unit 10 includes a drive control unit 7 that controls driving of the liquid crystal display panel 3, an opposing control unit 8, and a PWM control unit 9 that controls the backlight 2 via the inverter 4.

  The backlight 2 uses a direct type backlight having a plurality of CCFLs (cold cathode fluorescent lamps) as a blinking backlight.

  The liquid crystal display panel 3 uses an OCB type liquid crystal display element having excellent response characteristics as a black insertion drive type liquid crystal display element.

  The drive control unit 7 of the control unit 10 outputs control signals for the backlight 2 and the liquid crystal display panel 3, and the PWM control unit 9 synchronizes the pulse signal duty ratio and on / off timing (phase). Control.

  FIG. 2 shows the concept of operation when PWM dimming is performed in the liquid crystal display device 1. Here, the duty ratio of the pulse signal of the backlight 2 when the dimming signal is 100% is 40%, and the minimum value of the duty ratio of the pulse signal of the single backlight 2 is 10%. (Luminance) is narrowed to 25% to 100%.

  That is, with respect to the operation of the backlight 2 shown in FIG. 2C, the liquid crystal display panel 3 has the liquid crystal transmittance shown in FIG. 2B, and as a result, as shown in FIG. It becomes the transmitted light intensity (luminance) of the liquid crystal display panel 3.

  Therefore, in the dimming driving method of the present invention, the response portion of the liquid crystal display panel 3 is shifted by relatively shifting the lighting timing of the backlight 2 in the state of the limit duty ratio (here, 10%) of the pulse signal of the backlight 2. Light up in a form that includes

  FIG. 3 shows the concept of the light control method of the present invention.

  As a result, even if the duty ratio of the pulse signal of the backlight 2 is the same, the final transmitted light intensity (luminance) is suppressed by the liquid crystal transmittance of the liquid crystal display panel 3, so that the transmission luminance can be reduced. . Further, the transmission luminance can be varied by changing the timing relationship between the lighting timing of the backlight 2 and the signal writing to the liquid crystal display panel 3, that is, the phase in several stages. Therefore, dimming is possible by this method.

  That is, with respect to the operation of the backlight 2 shown in FIG. 3C, the liquid crystal display panel 3 has the liquid crystal transmittance shown in FIG. 3B, and as a result, as shown in FIG. It becomes the transmitted light intensity (luminance) of the liquid crystal display panel 3.

  However, in this method, since the backlight 2 is turned on during the black display period, a decrease in contrast occurs.

  Therefore, in the present invention, PWM dimming is used up to the limit duty ratio of the pulse signal of the backlight 2, and the dimming method of the present invention is employed when the brightness is lowered by further dimming from the limit duty ratio of the pulse signal. Switch. In this way, in most of the dimming, the contrast is not changed in most cases, and the contrast is allowed to be lowered only in the case of extremely low luminance, thereby achieving both the dimming range (luminance) and the image quality.

  That is, the drive control unit 7 of the control unit 10 shown in FIG. 1 controls the black insertion drive of the liquid crystal display panel 3 via the gate driver 5 and the source driver 6, and PWM control is performed according to the control of the drive control unit 7. The unit 9 controls the operation of the backlight 2 through the inverter 4. At this time, the PWM control unit 9 uses the PWM dimming shown in FIG. 2 as described above, and performs the dimming to further reduce the luminance from the limit duty ratio (10%) of the pulse signal in the backlight 2, as shown in FIG. The dimming range (luminance) is expanded by switching to the dimming method shown in FIG. As a result, the luminance can be adjusted in the range of 0% to 100%, usually 3% to 100%.

  As described above, according to the embodiment of the present invention, the dimming range can be further expanded from the limit of PWM dimming in the liquid crystal display element that combines black insertion driving and blinking backlight.

1 is a block diagram schematically showing a circuit configuration of a liquid crystal display device. The figure which shows the operation | movement concept when performing PWM light control in a liquid crystal display device. The figure which shows the concept of the light control system of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 2 ... Back light, 3 ... Liquid crystal display panel, 4 ... Inverter, 5 ... Gate driver, 6 ... Source driver, 7 ... Drive control part, 8 ... Opposition control part, 9 ... PWM control part, 10 ... control unit.

Claims (4)

  A dimming drive method for a liquid crystal display device combining a black insertion drive type liquid crystal display element and a blinking backlight, wherein transmission luminance adjustment is performed by adjusting a phase of the black insertion drive and the backlight emission. A dimming drive method characterized by the above.   In a liquid crystal display device in which a black insertion drive type liquid crystal display element and a blinking backlight are combined, the light intensity is adjusted by adjusting the transmission luminance by adjusting the phase of the black insertion drive and the backlight emission. Liquid crystal display device.   In a liquid crystal display device combining a black insertion drive type liquid crystal display element and a blinking backlight using a plurality of light sources, PWM dimming of the backlight is performed according to a dimming signal, and the PWM dimming becomes a limit A liquid crystal display device characterized in that, when a low-brightness dimming signal is input, the dimming is switched to dimming for adjusting transmission luminance by adjusting the phase of black insertion driving and the backlight emission.   4. The liquid crystal display device according to claim 1, wherein the black insertion drive type liquid crystal display element is an OCB type liquid crystal display element.

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