Patent Publication Number: US-8976104-B2

Title: Display device and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2009-0110605, filed on Nov. 17, 2009, in the Korean Intellectual Property Office, which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a display device and driving method thereof, which improve image quality. 
     2. Discussion of Related Art 
     Generally, a liquid crystal display (LCD) comprises a liquid crystal panel and backlight assembly. The backlight assembly is positioned under the liquid crystal panel and provides light to the liquid crystal panel. The liquid crystal panel displays an image by adjusting the transmittance of the light provided from the backlight assembly. 
     The backlight assembly comprises a light source to generate light. The light source can be a cold cathode fluorescent lamp (CCFL), a fat fluorescent lamp (FFL), a light emitting diode (LED), etc. 
     The LED is made in a type of a chip and has a comparatively long life, fast turn-on time, and low electric consumption. For these reasons, the LED is increasingly adopted and used as the light source of the back light assembly. 
     The backlight assembly can be classified into an edge lit type and a direct lit type according to the position of the light source. The direct lit type backlight assembly has a plurality of light sources arranged under the liquid crystal panel, and the light sources directly illuminate the liquid crystal panel. The edge lit type backlight assembly has at least one light source arranged at the side of a light guide plate, and the light source indirectly illuminates the light crystal panel through the light guide plate. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment of the display device comprises a optical member, a plurality of light sources to illuminate the optical member, a representative determining part to determine representative values of image blocks based on image signals applied to the image blocks, wherein the image blocks are arranged in a matrix and correspond to portions of a display panel, a representative integration part to determine integrated representative values based on the representative values of the image blocks in one of a row and a column direction of the matrix, and a light control part to control the plurality of light sources based on the integrated representative values. 
     The display device may further comprise at least one of a prism or a lens sheet on the optical member. The display may further comprise a boundary compensation part to determine boundary representative values based on the integrated representative values of at least one neighboring image block. 
     The plurality of light sources may be arranged at a side or facing opposite sides of the optical member and may be light emitting diodes. 
     The integrated representative values may be determined by applying weight values to the representative values, wherein the weight values are relative values depending on an illumination distribution of the optical member and are represented as lower values at bright portions and higher values at the dark portions 
     The representative values determined by the representative determining part may be representative image signals determined based on the image signals or representative light intensities determined after the image signals are converted into light intensities. 
     An exemplary embodiment of the driving method comprises determining representative values of image blocks based on image signals applied to the image blocks, wherein the image blocks are arranged in a matrix and correspond to portions of a display panel, determining integrated representative values based on the representative values of the image blocks in one of a row and a column direction of the matrix, and controlling a first plurality of light sources based on the integrated representative values, wherein the first plurality of light sources illuminate an optical member. 
     The plurality of light sources may be arranged at a side or facing opposite sides of the optical member and may be light emitting diodes. 
     The integrated representative values may be determined by applying weight values to the representative values, wherein the weight values are relative values depending on an illumination distribution of the optical member and are represented as lower values at bright portions and higher values at the dark portions 
     The driving method further comprises determining boundary representative values based on the integrated representative values of at least one neighboring image block and controlling a second plurality of light sources based on the boundary representative values. 
     The driving method further comprises determining boundary representative values based on the integrated representative values of at least one neighboring image block and compensating the image signals corresponding to the integrated representative values and the boundary representative values. 
     The representative values determined by the representative determining part may be representative image signals determined based on the image signals or representative light intensities determined after the image signals are converted into light intensities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings briefly described below illustrate exemplary embodiments of the present invention and, together with the description, serve to explain the principles of the present invention. 
         FIG. 1  is an exploded perspective of one embodiment of the display device. 
         FIG. 2  is a block diagram to functionally describe the display device of  FIG. 1 . 
         FIG. 3  and  FIG. 4  are image blocks arranged in a matrix and light emitting blocks arranged at a side thereof. 
         FIG. 5  is a conceptual graph to represent luminance of the light emitting blocks in order to display an image of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
     According to an exemplary embodiment of the present invention, a local dimming driving method improves a contrast ratio of an image, by which the intensities of the light sources can be controlled based on image signals applied to the liquid crystal panel. 
       FIG. 1  is an exploded perspective of an exemplary embodiment of the display device.  FIG. 2  is a block diagram to functionally describe the display device of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the display device comprises a display unit  100 , a backlight assembly  200  and a controller board  300 . The display unit  100  comprises a display panel  110  and a panel driving part  120 . 
     The display panel  110  includes a first substrate  112 , a second substrate  114  facing the first substrate, and a liquid crystal layer  116  interposed between the first and second substrates  112  and  114 . The first substrate  112  may include a plurality of pixels to adjust a transmittance of light provided from the backlight assembly and display an image. Each pixel can include a switching element TR connected to a gate line GL and a data line DL. Each pixel can further include a liquid crystal capacitor CLC and a storage capacitor CST respectively connected to the switching element TR. 
     The panel driving part  120  includes a data printed circuit board  122 , a data driving circuit film  124  connecting between the data printed circuit board  122  and the display panel  110 , and a gate driving circuit film  126  connected to the display panel  110 . The data driving circuit film  124  is connected to the data lines of the first substrate  112  and the gate driving circuit film  126  is connected to the gate lines of the first substrate  112 . The data and gate driving circuit films  124  and  126  may comprise driving chips outputting driving signals to drive the display panel  110  in response to control signals supplied from the data printed circuit board  122 . 
     The backlight assembly  200  may comprise a light source  210 , a light source driving part  220 , a light guide plate  230 , a prism sheet  245 , and a container  240 . The backlight assembly  200  is disposed under the display panel  110  and provides the display panel  110  with light. 
     The backlight assembly  200  is an edge lit type that the plurality of light sources may be arranged at a side or facing opposite sides of the light guide plate  230 . 
     The light source  210  may be a point light source, such as a light emitting diode (LED). The light source  210  is integrated on a driving board  214 . The driving board  214  may include control lines (not shown) to control the light source  210  and power supply lines (not shown) to supply power to the light source  210 . The light source  210  may be a white LED to emit white light or RGB LEDs to emit red, green or blue light, respectively. 
     The light source  210  can include a plurality of light emitting blocks B and each of light emitting blocks B includes at least one LED. Each LED may be controlled independently. The light emitting blocks B can provide image blocks of the display panel  110  with light independently of each other. By the independent control of the light emitting blocks B a local dimming may be achieved wherein the image blocks may display different light intensities independently even in a case where the display panel  110  receives the same image signals or display the same light intensities even in a case where the display panel  110  receives different image signals with respect to the image blocks. 
     The light source driving part  220  determines duty ratios of the light emitting blocks B using integrated representative values which correspond to the light emitting blocks B and are output from the controller board  300 . The light source driving part  220  generates driving signals of light sources based on the duty ratios. The light source driving part  220  provides the light emitting blocks B with the driving signals of light sources and controls the light emitting blocks B, respectively. 
     A light guide plate  230  is an optical member which guides light emitted from the light sources  210 . The light sources  210  are arranged at a side or sides of the optical member to a bottom surface of the display panel  110 . A prism sheet  245  is an optical member which refracts and collimates light emitted from the light guide plate  230 . 
     The container  240  can accommodate the display panel  100 , the light sources  210 , the light guide plate  230  and so on. The container  240  includes a bottom plate  242  and side plates  244  connected to the bottom plate  242 . 
     One or more additional optical sheets (not shown) can be further inserted between the display panel  110  and the light guide plate  230  as an optical member in order to promote light characteristics. For example, an exemplary optical sheets can a diffuse sheet to promote light uniformity. 
     The controller board  300  is electrically connected to the display panel  100  and the backlight assembly  200  and controls the display panel  100  and the backlight assembly  200 . The controller board  300  includes a controller unit  310 , a first connector  340 , a second connector  350  and a third connector  360 . 
     The first connector  340  is connected to an external device (not shown). The first connector  340  carriers image signals IS and control signals CS to the controller unit  310 . The image signals IS and control signals CS are transmitted from the external device. The second connector  350  is electrically connected to the display panel  100  and carries the image signals IS to the display panel  100 . The third connector  360  is electrically connected to the light source driving part  220  of the backlight assembly  200 . 
     The controller unit  310  comprises a representative determining part  311 , a representative integration part  312 , a boundary compensation part  313  and a pixel compensation part  315 . 
     The representative determining part  311  determines representative values of image blocks based on image signals IS applied to image blocks, wherein the image blocks corresponding to portions of a display panel  100  are arranged in a matrix. The representative values may be representative image signals determined based on the image signals corresponding to the image blocks or representative light intensities determined after the image signals are converted into light intensities. 
     The representative integration part  312  integrates the representative values of the image blocks in row or column directions of the matrix and determines integrated representative values. The integrated representative values may be determined by applying weight values to the representative values, wherein the weight values are relative values depending on an illumination distribution of the optical member and are represented as lower values at bright portions and higher values at the dark portions. 
     The boundary compensation part  313  determines boundary representative values based on the integrated representative values of at least one neighboring image block. The boundary compensation part  313  provides the pixel compensation part  315  with the boundary representative values and transmits the integrated representative values to the light source driving part  220 . 
     The pixel compensation part  315  compensates the image signals IS corresponding to the integrated representative values and the boundary representative values. For example, when an entire image displayed darkens by backlight dimming, the image signals IS to display a bright figure can be compensated to offset the effect of the backlight dimming so that the bright figure is displayed with substantially the same light intensity, regardless of the backlight dimming. In addition, the image signals IS corresponding to the boundary representative values can be compensated to reduce differences in light intensities caused by the light emitting blocks that are driven based on the integrated representative values. 
       FIG. 3  and  FIG. 4  show image blocks arranged in a matrix and light emitting blocks arranged at a side thereof. 
     Image blocks G are conceptual portions of the display panel  110 , arranged in a 2-dimension matrix. The image blocks G have weight values according to an illumination distribution in the image blocks G. The illumination distribution in the image blocks G corresponds to the arrangement of the light emitting blocks B. The weight values may be relatively small values at the image blocks G close to the light source  210  and relatively big values at the image blocks G far from the light source  210 . If the light sources are arranged at a side of the optical member, the image blocks close to the side of the optical member have relatively small weight values and the image blocks far from the side have relatively large weight values. If the light sources are arranged at facing opposite sides of the optical member, the image blocks close to the sides of the optical member have relatively small weight values and the image blocks of center portions far from the sides have relatively large weight values. 
     An illumination intensity distribution of the image blocks G can be varied according to the types or arrangement of an optical member(s). Thus, the Weight values are determined through the actual estimation of illumination intensity distribution. 
     For example, a first integrate representative value corresponding to a first light emitting block B 1  can be determined by the weighted average of the representative values of the image blocks G 1  arranged corresponding to the first light emitting block B 1 . Second to m-th integrate representative values corresponding to second to m-th light emitting blocks B 2  to Bm can be similarly determined by the weighted average. 
     Referring to  FIG. 4 , when three circle figures having the same image signal are displayed at different rows among columns (1), (2) and (3) of the image blocks G, the light emitting blocks would be driven in the same illumination if the integrated representative values were not determined by applying weight values to the representative values of the image blocks G having the three circle figures. However the edge lit type backlight assembly  200  can have a non-uniform illumination distribution at different locations of a light output so that images having different illuminations can be displayed even if the same image signals are applied to a liquid crystal display. 
     To make an illumination distribution substantially uniform when the same image signals are applied to a liquid crystal display, the light emitting blocks of the backlight assembly  200  can be operated to illuminate different light intensities, based on the weight values and the representative values of the image blocks G. 
     For example, in  FIG. 4 , the weight values are assigned to the rows A-H of the image blocks G. Image blocks corresponding to a first circle figure of the column (1) are assigned the weight values of 0.77˜0.88, image blocks corresponding to a second circle figure of the column (2) are assigned in 0.87˜0.91 and image blocks corresponding to a third circle figure of the column (3) are assigned in 0.98˜1. Thus, although the applied image signals are the same in corresponding image blocks, the integrated representative values can be determined as different values in an order of (3)&gt;(2)&gt;(1). 
       FIG. 5  is a conceptual graph to represent luminance of the light emitting blocks in order to display an image of  FIG. 4 . 
     After the integrated representative values are determined, the light emitting blocks are driven to illuminate different light intensities as shown in  FIG. 5  by the weight values corresponding to image blocks, respectively. 
     According to exemplary embodiments of the present invention, the light emitting blocks can be driven independently based on an illumination distribution of the backlight assembly and image signals.