KR20060001694A - Liquid crystal display device and method for driving the same - Google Patents

Abstract

A liquid crystal display device and a driving method thereof according to the present invention provide a best contrast ratio by appropriately allocating limited power for each screen area, and comprising: a liquid crystal panel for displaying an image; A plurality of lamps supplying light to the liquid crystal panel; Analyze the video signal to generate a signal that emphasizes the luminance with individual weights for each area of the screen, apply an image signal to the liquid crystal panel through a data driver, and apply a scan signal to the liquid crystal panel through a gate driver. A controller; And an inverter for individually driving the lamps within a maximum power range according to the signal of the timing controller.

LED, Power Limit, Contrast Ratio (C / R), Video Analysis, Dimming Ratio

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND METHOD FOR DRIVING THE SAME}

1 is an exemplary view showing an example in which the lamps are arranged in a general direct type.

2A is a block diagram illustrating a process of driving a lamp by an input image;

FIG. 2B is an exemplary diagram showing a relationship between dimming ratio and power of FIG. 2A; FIG.

3 is a view showing a liquid crystal display device according to the present invention;

4A is a block diagram showing driving of a liquid crystal display device according to the present invention;

Figure 4b is a diagram showing the relationship between dimming ratio and power in the present invention.

5 is an exemplary view illustrating an example in which dimming ratios are adjusted for each screen area according to the present invention.

*** Description of the symbols for the main parts of the drawings ***

101: liquid crystal panel 120: data driver

122: data line 130: gate driver

132: gate line 140: timing control unit

142: image analyzer 144: signal generator

147: inverter 149: lamp

DCS: Dimming Control Signal DATA: Data

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display and a driving method thereof, and more particularly, to a liquid crystal display and a driving method thereof to realize high image quality with limited power by differentially distributing power according to luminance of each screen area. .

In today's information society, display is more important as a visual information transmission medium. In order to occupy a major position in the future, display needs to satisfy requirements such as low power consumption, thinning, light weight, and high quality.

The display itself has a cathode ray tube (CRT), an electroluminescent diode (EL), a light emitting diode (LED), a vacuum fluorescence display (VFD), an electric field It can be divided into emission type such as Field Emission Display (FED), Plasma Display Panel (PDP), and non-emission type such as Liquid Crystal Display (LCD). .

A liquid crystal display device displays an image by using optical anisotropy of liquid crystal. Plasma display panels or electric fields are not only small in view of conventional CRTs, but also smaller than CRT tubes having the same average power consumption. Along with the emission display, it is recently attracting attention as a next generation display device.

In general, a liquid crystal display device is a flat panel display device in which a data signal according to image information is individually supplied to pixels arranged in a matrix form, and a desired image can be displayed by adjusting light transmittance of the pixels. to be.

The liquid crystal display device is bonded so that a thin film transistor array board and a color filter board facing each other have a predetermined cell-gap, and are bonded to the bonded cell-gap. Supply liquid to a liquid crystal panel manufactured by filling a liquid crystal layer, a driving unit for supplying various control signals, image information, and driving voltages to the liquid crystal panel, and a liquid crystal panel having a non-luminescent property. And a backlight unit for expressing image information.

In the thin film transistor array substrate, a plurality of gate lines arranged horizontally and a plurality of data lines arranged vertically intersect with each other, and pixels are defined in a plurality of regions that are divided and partitioned. The pixel includes a switching element electrically connected to the gate line and the data line, and a pixel electrode to which a voltage of image information applied from the data line is applied.

The color filter substrate is arranged with red, blue and green color filters displaying a color image by combining the light supplied from the backlight unit. Prevent light leakage. A common electrode is formed on the front surface of the color filter substrate, by applying a constant electric field to the liquid crystal layer by a voltage difference between the common voltage applied to the common electrode and the voltage of the image information applied to the pixel electrode of the thin film transistor array substrate. , To adjust the transmittance of light.

The driving unit is provided outside the liquid crystal panel, and the driving unit is electrically connected to the outer region of the liquid crystal panel to supply various signals to the liquid crystal panel. The driver includes a timing controller, a gate driver, and a data driver. The timing controller is configured to receive external data including image information and a control signal to supply the gate driver and the data driver in accordance with the timing, and the gate driver is configured to receive a control signal from the timing controller and the gate line. A scan signal is applied to the data lines, and the data driver receives control signals and image information from the timing controller to apply image information to the data lines.

The backlight unit supplies light to the liquid crystal layer that does not emit light by itself. The backlight unit may include a lamp that emits light, optical members that condense and diffuse the light of the lamp and evenly supply the front surface of the liquid crystal panel, and an inverter for controlling on / off of the lamp and adjusting the amount of light. It consists of

The backlight unit is divided into an edge type and a direct type according to the position of the lamp. The edge type arranges the lamp on the side of the backlight unit to supply light to the front of the liquid crystal panel with a small number of lamps. A plurality of light emitting diodes may be disposed on the rear surface of the liquid crystal panel to realize bright brightness. Such lamps typically include cold cathod electrode fluorescent lamps (CCFL) or external electrode fluorescent lamps (EEFL).

1 is an exemplary view showing an example in which lamps are arranged in a general direct type.                         

Referring to FIG. 1, the plurality of lamps 20 are arranged side by side at a predetermined distance between the optical sheet 11 and the reflecting plate 12 and correspond to the front surface of the liquid crystal panel. Light emitted from the lamps 20 to the front surface is irradiated to the liquid crystal panel through the optical sheet 11, and light emitted to the rear surface is reflected by the reflector plate 12 to the liquid crystal panel through the optical sheet 11. Is investigated.

High voltage is required to drive the lamps 20. Since such high voltage is not sufficient for the voltage generated in the liquid crystal display, an inverter is provided to generate a voltage suitable for driving the lamp 20. The inverter receives an DC voltage to form an AC voltage capable of driving the lamp 20, and transforms the AC voltage to form a high voltage. That is, it basically includes an oscillator for generating an AC voltage and a transformer for boosting. Since the light amount of the lamp 20 directly affects the brightness of the image displayed on the liquid crystal panel, the amount of tube current supplied from the inverter to the lamp 20 is controlled to control the light amount of the lamp 20. By doing so, it is possible to emphasize the brightness of the image. As described above, the method of adjusting the magnitude of the tube current supplied to the lamp 20 is possible by controlling the on / off time of the switch electrically connecting the inverter and the lamp 20. That is, as the inverter cuts off or connects the switch within the maximum cycle time that can supply the tube 20 per frame to the lamp 20, the time for actually supplying the tube current is adjusted. As such, the value of the actual tube current supply time with respect to the cycle time during which the inverter can supply the tube current to the lamp 20 in each frame is a dimming duty. The inverter may control the amount of light emitted from the lamp 20 by controlling the dimming ratio. In other words, if the dimming ratio is determined according to the power to be supplied to the lamp 20 in the liquid crystal display, and the tube current is supplied, the lamp 20 can be driven with the desired power.

Recently, a method of analyzing the image to be displayed every frame and adjusting the amount of light of the lamp 20 according to the luminance of the image has been widely used. In order to control the amount of light of the lamp 20, the section of the tube current supplied from the inverter to the lamp 20 may be adjusted. That is, when the tube current is supplied for a long time, the reaction in the lamp 20 occurs more strongly, and a large amount of light is emitted. However, when the tube current is supplied for a short time, only a small amount of light is emitted from the lamp 20. When the image to be displayed on the screen has a high brightness on average, the supply of the tube current to the lamp 20 is increased, and when the image has a low brightness, the supply of the tube current to the lamp 20 is reduced. This driving will be described with reference to FIG.

FIG. 2A is a block diagram illustrating a process of driving a lamp by an input image, and FIG. 2B is an exemplary diagram illustrating a relationship between dimming ratio and power of FIG. 2A.

Referring to the drawings, first, an LCD analyzes an image of data input from an external source. In particular, by analyzing the luminance signal of the image to be displayed, it determines the amount of light to be emitted from the lamp to represent the image, and thereby determine the power to be supplied to the lamp. Next, the dimming duty for supplying input power to the lamp is determined. Power is the product of the product of voltage and current. Therefore, by adjusting the supply time of the tube current supplied to the lamp by the dimming ratio, it is possible to adjust the input power. As described above, when the input power is determined and thus the dimming ratio is determined, the inverter is driven according to the dimming ratio to adjust the amount of light in the lamp. 2B, the dimming ratio is set to a substantially constant minimum value. When the dimming ratio is too low, it is possible to shorten the life of the lamp, and in Fig. 2b the dimming ratio is determined between 40% and 100%. Therefore, when the dimming ratio is 40%, the minimum input power is supplied, and when the dimming ratio is 100%, the maximum input power is supplied to the lamp.

Cold cathode fluorescent lamps used in the lamp is provided with an inverter individually, the drive is independently controlled by the inverter. However, since the dimming ratio of the cold cathode fluorescent lamp is determined according to the average brightness of the image and the lamp is driven, it is difficult to control the partial luminance of the image in detail. In addition, since the external electrode fluorescent lamp is controlled by one inverter, partial luminance control on the entire screen is more difficult than the cold cathode fluorescent lamp. Therefore, when all the screens are displayed at a bright brightness or when the average brightness is high but a part of the screen is displayed at low brightness, all the lamps need to be driven with a high amount of light. In this case, more power consumption is required.

In addition, when a bright screen is displayed, a sufficient visual effect may be provided without supplying the maximum power to the lamp. Therefore, the power consumption increases more than necessary in a bright screen of more than halftone.

Accordingly, the present invention was devised to solve the above-described problems, and an object of the present invention is to reduce the power consumption and to control the luminance of the entire screen for each region, thereby maintaining the same image quality. An apparatus and a driving method thereof are provided.

A liquid crystal display device and a driving method thereof for achieving the object of the present invention as described above comprises a liquid crystal panel for displaying an image; A plurality of lamps supplying light to the liquid crystal panel; Analyze the video signal to generate a signal that emphasizes the luminance with individual weights for each area of the screen, apply an image signal to the liquid crystal panel through a data driver, and apply a scan signal to the liquid crystal panel through a gate driver. A controller; And an inverter for individually driving the lamps within a maximum power range according to the signal of the timing controller.

3 is a view showing a liquid crystal display device according to the present invention.

The liquid crystal panel 101 is manufactured by bonding the first and second substrates facing each other to maintain a constant cell gap, and filling the cell gap with liquid crystal to form a liquid crystal layer. A plurality of data lines 122 are arranged in the vertical direction on the first substrate, and a plurality of gate lines 132 are arranged in the horizontal direction, and the data lines 122 and the gate lines 132 cross each other. Form a plurality of regions. This area is defined as a pixel (not shown). The pixel is electrically connected to the gate line 132 and the data line 122.

The data driver 120 is electrically connected to the liquid crystal panel 101 through the data lines 122, and the gate driver 130 is electrically connected to the liquid crystal panel 101 through the gate lines 132. Is connected.

When data DATA is applied from an external source such as a graphics card, the timing controller 140 generates various control signals for driving the liquid crystal display device by using the data DATA. In addition, the timing controller 140 applies control signals and an image signal to the data driver 120, and applies control signals to the gate driver 130. In addition, the timing controller 140 includes an image analyzer 142 and a signal generator 144 added in the present invention.

In general, the image information is composed of a luminance signal and a color difference signal. When the luminance signal is detected and analyzed, the luminance distribution of the screen can be known. Data DATA supplied from a graphics card or the like includes image information, a control signal, and a driving voltage. The image analyzer 142 primarily analyzes the luminance signal detected from the image information and calculates an average luminance of the image. In this way, the first dimming ratio is determined according to the calculated average luminance. Then, the luminance signal is analyzed secondarily, the luminance of each region of the image is inspected, and a dimming ratio is finally added by individually adding a dimming ratio according to the luminance of each region. The signal generator 144 outputs a dimming control signal DCS to the inverter 147 according to the second dimming ratio determined by the image analyzer 142.

The inverter 147 individually drives the lamps 149 according to the dimming control signal DCS applied from the timing controller 140 to emit different amounts of light corresponding to the image for each region. However, the backlight unit to which the cold cathode fluorescent lamp (CCFL) is applied to the lamp 149 has a limitation in brightness control for each region of the image, so that the light emitting diode (LED) is applied to the lamp. By applying the above, precise luminance control can be performed for each area of the liquid crystal panel. In general, since light emitting diodes (LEDs) are provided to correspond to each pixel, luminance control may be performed for each unit pixel or several pixels.

Therefore, in order to maximize the effect of luminance control for each region of the image which is a feature of the present invention, it is most preferable to apply the light emitting diode as a lamp.

Referring to the driving of the liquid crystal display as described above in detail as follows.

Figure 4a is a block diagram showing the driving of the liquid crystal display according to the present invention, Figure 4b is a diagram showing the relationship between dimming ratio and power in the present invention.

Referring to the drawings, first, in analyzing image information of data DATA, first and second image analysis are performed. In the first image analysis, the luminance of the image information is detected to obtain an average luminance in an image of one frame unit. Through the first image analysis, input power to be supplied to the entire image is determined. The input power supplied to drive the lamp is limited to less than the maximum power, in order to reduce the unnecessary consumption of power in the screen of high brightness. As such, when the input power to be supplied to the lamp is determined by the first image analysis, the first dimming ratio of the tube current for supplying the input power to the lamp is determined. The inverter controlling the driving of the lamp may adjust the input power by adjusting the supply time of the tube current supplied to the lamp.

As described above, after the first dimming ratio is determined, the luminance of each region of the image is analyzed by the second image analysis. That is, the luminance distribution for each region of the image to be displayed on the screen is analyzed, not the average luminance of the entire image in the first image analysis. As such, when the luminance distribution for each region of the image is analyzed, the same luminance may appear in a pattern having a constant area. You may be able to lower or increase the brightness of this pattern to further emphasize the image. The second image analysis is a step for emphasizing the image for each region.

In the second image analysis, the luminance distribution for each region of the image is analyzed as described above, and the available extra power is used except for the input power determined to be supplied to represent the average luminance of the image in the first image analysis. Thus, it is appropriately distributed for each area. That is, subtracting the input power determined in the first image analysis process from the maximum power yields extra available power, and the available power is allocated to drive a lamp corresponding to an area to emphasize luminance for each image area. As described above, after determining the dimming ratio weight for each region using the extra available power, the second dimming ratio is finally determined in addition to the first dimming ratio. The second dimming ratio is information for actually driving the plurality of lamps.

Referring to FIG. 4B, the relationship between the first dimming ratio, the second dimming ratio, and the input power is shown. In the process of determining the first dimming ratio, the first dimming ratio is in the range of 40% to 70%. Is determined. While the range of 40% to 70% is given by way of example, it is important to note that the first dimming ratio is not set to 100%, and a minimum dimming ratio is also set to prevent lamp life shortening. Next, up to 100% may be determined in the second dimming ratio determined by adding a dimming ratio weight for each region. The region for driving the lamp with the second dimming ratio of 100% is the region displayed at the highest luminance. On the other hand, the input power cannot be supplied more than the set maximum power, and the size of the minimum power increases because an area in which the input power is additionally supplied to enhance the luminance for each area of the image is generated.

5 is an exemplary view illustrating an example in which the dimming ratio is adjusted for each screen area according to the present invention.

Referring to Fig. 5, the entire screen is divided into areas A to D. First, the first dimming ratio was determined through the first image analysis, and 40% of the dimming ratio was allocated to the A to D regions. This is commonly determined according to the average luminance, and in the second image analysis, the dimming ratio weight is determined for each region. If region A represents the highest luminance, B, C represents the intermediate luminance, and D represents the lowest luminance, the second image analysis process adds a dimming ratio of 60% to region A, and B By adding a dimming ratio of 30% to the C region, the lamps are driven by different dimming ratios in each region of the screen, thereby showing different luminance. In FIG. 5, the entire screen is divided into four parts for convenience of description, but when applying a lamp such as a light emitting diode provided to correspond to the pixels individually, the entire screen is divided into a large number of areas to individually control luminance. You can do it.

As described above, the image finally displayed on the screen through the first and second image analysis may clearly show the brightness of each region of the image while using the limited maximum power. Thus, the contrast ratio of the image is improved.

As described above, the liquid crystal display according to the present invention can improve the contrast ratio of the image by individually driving the lamps by differently setting the weight of the luminance for each region of the image while using a limited maximum power.

Claims (7)

A liquid crystal panel for displaying an image; A plurality of lamps supplying light to the liquid crystal panel; Analyze the video signal to generate a signal that emphasizes the luminance with individual weights for each area of the screen, apply an image signal to the liquid crystal panel through a data driver, and apply a scan signal to the liquid crystal panel through a gate driver. Control unit; And an inverter for individually driving the lamps within a maximum power range according to a signal of the timing controller. The liquid crystal display device according to claim 1, wherein the lamp is a cold cathod electrode fluorescent lamp (CCFL). The liquid crystal display of claim 1, wherein the lamp is a light emitting diode. The image analysis unit of claim 1, wherein the timing controller analyzes the luminance signal of the image signal to determine a dimming ratio obtained by adding a weight to each region to the average luminance of the entire screen, and the dimming ratio determined by the image analyzer. And a signal generator for outputting a control signal to the inverter. Analyzing an image signal to determine an average luminance of the image, determining power to drive lamps according to the average luminance, determining a dimming ratio according to the power, and analyzing luminance for each region of the image Determining a dimming ratio weight according to the allocated power available, and determining a final dimming ratio by adding a dimming ratio weight to the dimming ratio; And individually driving lamps according to the final dimming ratio. 6. The method of claim 5, wherein the available power is power other than the input power from a maximum power set to be used to drive the lamps. 6. The method of claim 5, wherein the sum of power supplied to the driving of the lamps by the final dimming ratio is equal to or less than a preset maximum power.

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