Patent Publication Number: US-2007109254-A1

Title: Liquid crystal display and method of driving the same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
      This application claims priority from Korean Patent Application No. 10-2005-0110137, filed on Nov. 17, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      Apparatuses and methods consistent with the present invention relate to a liquid crystal display (LCD) and a method of driving the LCD in which color mixing is reduced.  
      2. Related Art  
      A related art LCD displays images by respectively supplying voltages to pixels according to input image signals to control light transmittance of the pixels, and are used in laptop computers, desktop computers, LCD televisions, and mobile telecommunication terminals. An LCD is a light receiving display device, which cannot emit light by itself but receives light from an external source to form an image. Thus, LCDs require a backlight unit, radiating light and a driving unit to drive the liquid crystal panel.  
      Referring to  FIG. 1 , a related art LCD includes a liquid crystal panel  10 , a backlight unit  35  supplying light to the liquid crystal panel  10 , and a driving unit driving the liquid crystal panel  10 . The liquid crystal panel  10  includes m x n liquid crystal pixels arranged in a matrix, in which m data lines D 1  through D m  and n gate lines G 1  through G n  intersect each other, and thin film transistors (TFT) are formed at the intersections of the data lines D 1  through D m  and the gate lines G 1  through G n . The driving unit includes a data driver  15  supplying data signals to the data lines D 1  through D m , a gate driver  20  supplying scan signals to the gate lines G 1  through G n  timing controller  25  controlling the data driver  15  and the gate driver  20  with a synchronization signal, and an inverter  30  driving the backlight unit  35 .  
      The TFTs of the liquid crystal pixels respond to the scan signals supplied by the gate lines G 1l  through G 1l  and are switched according to the data signals supplied by the data lines D 1l  through D m .  
      The timing controller  25  generates control signals to control the gate driver  20  and the data driver  15  using vertical/horizontal synchronization signals. The data driver  15  responds to the control signals of the timing controller  25  to convert digital image signals into analog data signals and supplies the analog data signals to the data lines D 1l  through D m . The gate driver  20  responds to the control signals of the timing controller  25  and sequentially supplies scan pulses to the gate lines G 1l  through G n  to select a horizontal line of the liquid crystal panel to which the data signals are supplied. The inverter  30  supplies a backlight unit driving voltage to the backlight unit  35 , which emits a light beam corresponding to the backlight unit driving voltage to the liquid crystal panel  10 .  
      Related art LCDs can be TFT-LCDs using TFTs as switching devices. Color can be realized in a space-dividing mode in which one of red light (R), green light (G), and blue light (B) is displayed in each pixel to form a color image, or in a time-dividing mode in which all of the pixels display R, G and B in a temporal sequence. In the time-dividing mode, the LCD includes light sources for R, G, and B respectively, and the light sources emit light sequentially. More specifically, all of the pixels are scanned according to the operation of the gate driver and the data driver and then the red light source is turned on. Then, after the red light source is turned off, all of the pixels are scanned again and the green light source is turned on. Finally, after the green light source is turned off, all of the pixels are scanned and the blue light source is turned on. In the space-dividing mode, R, G and B color filters are mounted in regions corresponding to the pixel electrodes to display color. Accordingly, the lighting time of each color light sources is shorter in the time-dividing mode than in the space-dividing mode for a given frame frequency.  
      To display a moving image, the responding speed and the operating speed of the liquid crystals of an LCD must be equal to or greater than the frame frequency of the moving image. Also, the frame frequency may be increased to realize a higher resolution mobile image with greater precision. When the reaction speed and the operating speed of the liquid crystals are low, the time allotted for the liquid crystals to be arranged in the LCD is insufficient, and thus the image is crushed or diffused. Since it is difficult to improve the responding speed and the operating speed of the liquid crystals, it is also difficult to increase the frame frequency.  
       FIG. 2  is a timing diagram of a related art process in which data is supplied from a data driver and liquid crystals are arranged according to the data, marked for lines of a liquid crystal panel with respect to time and how a color beam corresponding to the data is supplied after the liquid crystals are arranged.  
      The time required to turn on the liquid crystals according to data signals is referred to as a rising time τ, a rising section is S, and a section in which the liquid crystals stay on is U. The time required to turn all of the liquid crystals off is referred to as a falling time. A falling section is T. The backlight unit supplies light in the section U in which the liquid crystals are on. This process is repeated sequentially for R, G, and B.  
       FIG. 3  is a timing diagram of scan pulses supplied sequentially to first through nth gate lines G 1l  through Gn according to a related art synchronization signal V sync . When scanning is completed by supplying all the scan pulses, the backlight unit corresponding to the gate lines is turned on and supply light to the liquid crystal panel.  
       FIG. 4  is a timing diagram illustrates the data recording time for R, G, and B and the corresponding backlight unit driving time in a related art liquid crystal panel including backlight unit formed of eight line blocks. A red data signal is sequentially supplied to a first line through a last line of the liquid crystal panel and scanning is performed according to data signals transmitted through each of the gate lines. At t=t 3 , a red beam is radiated from a first line block of the backlight unit in response to the red data signal and pulse scanning, and at t=t 4 , a red beam is radiated from a second line block of the backlight unit. In the same manner, the red beam is radiated sequentially from the third through eighth line blocks. Then a green data signal is supplied, and a green beam is radiated sequentially from the first through eighth line blocks. Next, a blue data signal is supplied, and a blue beam is radiated sequentially from the first through eighth line blocks. In addition, from t=t 3  to t=t 7 , the blue beam and the red beam are both radiated to the liquid crystal panel at substantially the same time. There are also periods when the red beam and the green beam or the green beam and the blue beam are radiated to the liquid crystal panel at substantially the same time.  
      As described above with respect to the related art, data color displayed in some portions of a screen may be different from the colors of light sources turned on in other portions of a screen, and ideally, interference should not occur. However, since light is radiated in every direction to obtain uniformity, neighboring color beams affect liquid crystals meant to be displaying other colors and thus cause color mixing, thereby deteriorating color characteristics.  
     SUMMARY OF THE INVENTION  
      The present invention provides an LCD and a method of driving the LCD in which color mixing is prevented by alternately supplying data signals to separate panel regions.  
      According to an aspect of the present invention, there is provided an LCD comprising: a liquid crystal panel divided into a plurality of panel regions having data lines and gate lines arranged two-dimensionally; gate drivers that correspond to the panel regions, are independently driven, and alternately supply gate signals to the corresponding panel regions; a data driver supplying data signals to the data lines; and a backlight unit radiating light to the liquid crystal panel.  
      The panel regions may be symmetric about the horizontal center of the liquid crystal panel.  
      The gate drivers respectively may adopt a shift register mode.  
      The panel regions may comprise a first panel region and a second panel region separated in a vertical direction along the data lines of the liquid crystal panel and the gate drivers may comprise a first gate driver and a second gate driver.  
      The first gate driver sequentially may supply the gate signals to lower gate lines through upper gate lines of the first panel region and the second gate driver may sequentially supply gate signals to lower gate lines through upper gate lines of the second panel region.  
      The first gate driver sequentially may supply gate signals to upper gate lines through the lower gate lines of the first panel region and the second gate driver may sequentially supply gate signals to lower gate lines through upper gate lines of the second panel region.  
      The LCD further may comprise: an inverter driving the backlight unit; and a timing controller controlling the data driver using a horizontal synchronization signal, the gate drivers using a vertical synchronization signal, and the inverter.  
      According to another aspect, there is provided an LCD comprising: a liquid crystal panel divided into a plurality of panel regions having data lines and gate lines arranged two-dimensionally; a gate driver alternately supplying gate signals to the panel regions; a data driver supplying data signals to data lines; and a backlight unit radiating light to the liquid crystal panel.  
      The gate driver may adopt a decoding mode.  
      According to another aspect of the present invention, there is provided a method of driving an LCD comprising: dividing a liquid crystal panel into a plurality of panel regions having data lines and gate lines; driving the panel regions alternately; and radiating light from light sources of a backlight unit corresponding to the lines for which scanning is completed.  
      The driving the panel regions may comprise: supplying data signals to the data lines with a data driver; supplying alternately scan signals to the gate lines of the respective panel regions using a gate driver; and controlling the data driver with a horizontal synchronization signal and controlling the gate drivers with a vertical synchronization signal.  
      The panel regions may comprise a first panel region and a second panel region separated in a vertical direction along the data lines of the liquid crystal panel and the gate drivers may comprise a first gate driver and a second gate driver, and the supplying of the scan signals to the gate lines may comprise: sequentially supplying gate signals to lower gate lines through upper gate lines of the first panel region with the first gate driver; and sequentially supplying gate signals to upper gate lines through lower gate lines of the second panel region with the second gate driver.  
      The panel regions may comprise a first panel region and a second panel region separated in a vertical direction along the data lines of the liquid crystal panel and the gate drivers may comprise a first gate driver and a second gate driver, and the supplying of the scan signals to the gate lines may comprise: sequentially supplying gate signals to upper gate lines through lower gate lines of the first panel region with the first gate driver; and sequentially supplying gate signals to lower gate lines through upper gate lines of the second panel region with the second gate driver.  
      The driving the panel regions may comprise: supplying data signals to the data lines with a data driver; supplying scan signals to the gate lines of the respective panel regions with respective gate drivers corresponding to the panel regions; and controlling the data driver with a horizontal synchronization signal and controlling the gate drivers with a vertical synchronization signal.  
      The method of driving the LCD, may further comprise: dividing the liquid crystal panel into a first panel region and a second panel region along a direction perpendicular to the data lines; and alternately supplying gate signals to the first and second panel regions, while sequentially supplying the gates signals to upper gate lines through the lower gate lines of the first panel region and to upper gate lines through lower gate lines of the second panel region. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The above and other aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a schematic view of a related art LCD;  
       FIG. 2  is a timing diagram illustrating the driving scheme of the related art LCD of  FIG. 1 ;  
       FIG. 3  is a timing diagram of scan pulses supplied to gate lines of the related art LCD of  FIG. 1  according to a synchronization signal;  1341   FIG. 4  is a timing diagram illustrating data transmission time, liquid crystal reaction time, and light radiation time of gate lines in the related art LCD of  FIG. 1 ;  
       FIG. 5  illustrates an LCD according to an exemplary embodiment of the present invention;  
       FIG. 6  is a timing diagram of scan pulses supplied to gate lines of the LCD of  FIG. 5  according to a horizontal synchronization signal of the exemplary embodiment;  
       FIG. 7  illustrates the LCD of the exemplary embodiment of  FIG. 5  having eight gate lines;  
       FIG. 8  is a timing diagram illustrating data transmission time, liquid crystal reaction time, and light radiation time of gate lines in the LCD of the exemplary embodiment of  FIG. 5 ;  
       FIG. 9  illustrates an LCD according to another exemplary embodiment of the present invention; and  
       FIG. 10  is a flowchart illustrating the operation of an LCD according to an exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION  
      The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.  
      Referring to  FIG. 5 , a liquid crystal display (LCD) according to an exemplary embodiment of the present invention includes a liquid crystal panel  100  which is divided into a plurality of panel regions and a backlight unit  110  that is divided into a plurality of backlight regions corresponding to the panel regions and supplies light.  
      The backlight regions face the corresponding panel regions, and the backlight unit  110  may be a direct type light emitting backlight or an edge type light emitting backlight. The liquid crystal panel  100  further includes a data driver  121  supplying data signals to the liquid crystal panel  100  and gate drivers  131 ,  132  which correspond to the panel regions and supply scan signals to the panel regions.  
      In an exemplary embodiment of the present invention, the liquid crystal panel  100  may include a first panel region  101  and a second panel region  102 . The backlight unit  110  is divided into a first backlight region  111  facing the first panel region  101  and a second backlight region  112  facing the second panel region  102 .  
      The first panel region  101  includes m x n liquid crystals arranged in a matrix, m data lines D 1l , through Dim and n gate lines G 1l  through G 1n  cross each other in the first panel region  101 , and thin film transistors are formed at the intersections of the data lines D 1l , through D 1m  and the gate lines G 1l  through G 1n . The second panel region  102  includes m x n liquid crystals arranged in a matrix, m data lines D 2l  through D 2m  and n gate lines G 2l  through G 2n  cross each other in the second panel region  102 , and thin film transistors are formed at the intersections of the data lines D 2l  through D 2 m and the gate lines G 2l  through G 2n .  
      In the present exemplary embodiment, the liquid crystal panel  100  is divided into a plurality of panel regions along the data lines in a vertical direction.  FIG. 5  shows an example being divided into two panel regions, but the exemplary embodiment is not limited thereto. The number of backlight regions of the backlight unit  110  corresponds to the number of the panel regions of the liquid crystal panel  100 , and the backlight regions of the backlight unit  110  respectively radiate light onto the panel regions of the liquid crystal panel. The backlight unit  110  is driven in response to a vertical synchronization signal from a timing controller  140 . The backlight unit  110  includes a plurality of light sources radiating light beams of different colors, and the liquid crystal panel  100  and the backlight unit  110  are sequentially driven according to each color.  
      The LCD further includes the data driver  121  supplying data signals to the data lines of the first panel region  101  and the second panel region  102 , a first gate driver  131  supplying scan signals to the gate lines of the first panel region  101 , and a second gate driver  132  supplying scan signals to the gate lines of the second panel region  102 .  
      The data driver  121  and the first and second gate drivers  131  and  132  are controlled by the timing controller  140 . The timing controller  140  controls the first and second gate drivers  131  and  132  using a vertical synchronization signal and controls the data driver  121  using a horizontal synchronization signal. The backlight unit  110  is driven by an inverter  145 , and the inverter  145  is controlled by the timing controller  140 . In the present exemplary embodiment, gate signals are alternately supplied to a plurality of panel regions. In particular, the timing controller  140  alternately drives the first and second gate drivers  131  and  132  to supply gate signals to the gate lines of the first panel region  101  and gate signals to the gate lines of the second panel region  102 . More specifically, a gate signal is supplied to a first gate line G 1l  of the first panel region  101 , and then a gate signal is supplied to a first gate line G 2l  of the second panel region  102 . Then, a gate signal is supplied to a second gate line G 12  of the first panel region  101  and then a gate signal is supplied to a second gate line G 22  of the second panel region  102 . Thus, gate signals are alternately supplied to the first panel region  101  and the second panel region  102 .  
      The first and second gate drivers  131  and  132  supply gate signals to the corresponding panel regions  101  and  102  in a shift register mode. In the shift register mode, gate signals are sequentially transmitted according to the order of the gate lines. The data driver  121  supplies data signals to the first and second panel regions  101  and  102 .  
      When gate signals are supplied to the first and second panel regions  101  and  102 , the gate signals can be alternately supplied symmetrically about the horizontal center of the liquid crystal panel  100 . For example but not by way of limitation, as illustrated in  FIG. 6 , gate signals are sequentially supplied to lower gate lines through upper gate lines of the first panel region  101  and gate signals are sequentially supplied to upper gate lines through lower gate lines of the second panel region  102 . Also, gate signals may be sequentially supplied to upper gate lines through lower gate lines of the first panel region  101  and from lower gate lines through upper gate lines of the second panel region  102 .  
      Specifically, in an exemplary embodiment of the present invention, as illustrated in  FIG. 7 , the liquid crystal panel  100  is divided into the first and second panel regions  101  and  102  and includes eight gate lines, and the backlight unit  110  includes light source lines corresponding to the gate lines of the liquid crystal panel  100 . The transmission time of the data signals and gate signals for each line and the supply time of each color beam is described below.  
      Referring to  FIG. 8 , data signals and gate signals regarding a red beam (R) are supplied and light is radiated from a light source line of the backlight unit  110  corresponding to the scanned line. Since the first panel region  101  and the second panel region  102  are alternately scanned, light is also alternately radiated from the backlight regions  111  and  112  of the backlight unit  110 . Thus, only one color beam is radiated during one time period to substantially prevent color mixing. More specifically, only a blue beam is radiated from t 1 -t 3 , and only a red beam is radiated from t 3 -t 8 . In  FIG. 8 , the starting time of the liquid crystal reaction and the light beam radiation time for the first panel region  101  and the second panel region  102  should be marked differently, but since the time difference is small, they are indicated as substantially the same.  
      Referring to  FIG. 9 , an LCD according to another exemplary embodiment of the present invention includes a gate driver  135  adopting a decoding mode to supply gate signals to a first panel region  101  and a second panel region  102 . The rest of the structure of the LCD in  FIG. 9  is substantially the same as the structure of the LCD of  FIG. 5 , and thus its description will not be repeated. In the drawings, like reference numerals denote like elements.  
      The gate driver  135  alternately supplies data signals to the first panel region  101  and the second panel region  102  according to the decoding mode, in which signal transmission lines for supplying data signals are selected by the gate driver  135 . By alternately supplying data signals to data lines of each panel region, as illustrated in  FIG. 8 , different color beams are not substantially simultaneously radiated to the liquid crystal panel  100 , thus substantially preventing color mixing.  
      A driving method of the LCDs of  FIGS. 5 and 9  is described below.  
      Referring to  FIG. 10 , in the driving method of an LCD according to an exemplary embodiment of the present invention, the liquid crystal panel  100  having the data lines D 1l  through D 1m  and D 2l  through D 2 m and the gate lines G 1l , through G 1n  and G 2l  through G 2 n is divided into a plurality of panel regions in a vertical direction, along the data lines D 1l  through D 1m  and D 2l  through D 2m  (S 10 ). The panel regions may respectively have the substantially same area and the substantially same shape. The timing controller  140  controls the data driver  121  using a horizontal synchronization signal and the gate drivers  131  and  132  (or  135 ) using a vertical synchronization signal, and controls the inverter  145 .  
      At about this time, the backlight unit  110  radiates light to the liquid crystal panel  100 , and the timing controller  140  drives the panel regions alternately (S 20 ). The LCD  100  may include more gate drivers than panel regions (not shown) and controls the gate drivers  131  and  132  (or  135 ) to alternately supply gate signals to the first and second panel region  101  and  102 . The gate drivers operate in the shift register mode. Also, the gate drivers  131  and  132  (or  135 ) operating in the decoding mode may alternately transmit gate signals to the panel regions  101  and  102 . The gate signals may be transmitted to the panel regions  101  and  102  symmetrically about the horizontal center of the liquid crystal panel  100 .  
      For example but not by way of limitation, gate signals can be sequentially transmitted to lower gate lines through upper gate lines of the first panel region  101 , and gate signals can be sequentially transmitted to upper gate lines through lower gate lines of the second panel region  102 . When the gate signals are sequentially transmitted to the upper gate lines through the lower gate lines in the first panel region  101 , the gate signals are sequentially transmitted to the lower gate lines through the upper gate lines in the second panel region  102 .  
      The backlight unit is divided into the backlight regions corresponding to the panel regions (S 30 ). The backlight regions radiate light according to the scanning of the panel regions corresponding to the backlight regions (S 40 ).  
      By transmitting gate signals to the separate panel regions  101  and  102  and radiating light beams from the backlight regions so as not to radiate light beams of different color onto the liquid panel, image quality deterioration due to color mixing can be substantially prevented.  
      As described above, the LCD according to the exemplary embodiments can substantially prevent color mixing in a simple way, and thus may have improved image quality. Moreover, according to the exemplary embodiments, there is basically no need to change the structure of a related art liquid crystal panel. Instead, the liquid crystal panel is divided into a plurality of panel regions which are driven separately. Thus, color mixing can be substantially prevented without substantial additional costs.  
      Furthermore, in the driving method of the LCD according to the exemplary embodiments, gate signals are alternately transmitted to the panel regions to substantially reduce the emission time of the backlight regions of the backlight unit that illuminate different color beams from the data input to the screen, thus minimizing color mixing of the image.  
      While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.