Patent Publication Number: US-2015062191-A1

Title: Method of driving a light-source and display apparatus for performing the method

Description:
This application claims priority from and the benefit of Korean Patent Application No. 10-2013-0106392, filed on Sep. 5, 2013, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field 
     Exemplary embodiments of the present invention relate to a method of driving a light-source for improving display quality and a display apparatus performing the method. 
     2. Discussion of the Background 
     Generally, a liquid crystal display (LCD) apparatus includes an LCD panel displaying images using a light transmittance of a liquid crystal and a backlight unit disposed under the LCD panel and providing light to the LCD panel. 
     The LCD panel may include an array substrate, a color filter substrate and a liquid crystal layer. The array substrate may include a plurality of pixel electrodes and a plurality of thin-film transistors (TFTs) electrically connected to the pixel electrodes. The color filter substrate generally faces the array substrate and may have a common electrode and a plurality of color filters. The liquid crystal layer may be interposed between the array substrate and the color filter substrate. When an electric field generated between the pixel electrode and the common electrode is applied to the liquid crystal layer, the arrangement of liquid crystal molecules of the liquid crystal layer is altered to change the optical transmissivity of the liquid crystal layer, such that an image is displayed on the LCD panel. The LCD panel displays a white image of a high luminance when an optical transmittance is increased to maximum, and the LCD panel displays a black image of a low luminance when the optical transmittance is decreased to minimum. 
     In order to decrease power consumption of the backlight unit, a luminance of light generated from the backlight unit may be adjusted based on a grayscale of an image displayed on the LCD panel. When an image data signal is provided to the LCD panel, a luminance control signal adjusted by the image data signal is provided to the backlight unit. However, a response time of the LCD panel responding to the image data signal is delayed when compared to a response time of the backlight unit responding to the luminance control signal. Thus, a blinking is observed because of the response time difference between the LCD panel and the backlight unit. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention provide a method of driving a light-source for improving a display quality of a repetitive image. 
     Exemplary embodiments of the present invention provide a display apparatus performing the method. 
     Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. 
     An exemplary embodiment of the present invention discloses a method of driving a light-source that provides a display panel displaying a picture during at least one frame period with light. The method includes determining a dimming-level configured to control a luminance of the light based on image data, determining whether the dimming-level of a current picture corresponds to a repetition dimming mode based on the dimming-level of a first previous picture, the first previous picture being displayed on the display panel prior to the current picture, and determining the dimming-level of the current picture to a fixed dimming-level in the repetition dimming mode. 
     An exemplary embodiment of the present invention also discloses a display apparatus. The display apparatus includes a display panel configured to display a picture during at least one frame period, a data driving part configured to drive the display panel utilizing image data, a light-source part configured to provide the display panel with light and a light-source driving part configured to determine a dimming-level controlling a luminance of the light based on the image data, determine whether the dimming-level of a current picture corresponds to a repetition dimming mode based on the dimming-level of a first previous picture, and determine the dimming-level of the current picture to a fixed dimming-level in the repetition dimming mode, the first previous picture being displayed on the display panel prior to the current picture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a block diagram illustrating a display apparatus according to an exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating the light-source driving part of  FIG. 1 . 
         FIG. 3  is a block diagram illustrating the timing control part of  FIG. 1 . 
         FIGS. 4A ,  4 B, and  4 C are diagrams illustrating an operation of the repetition determining part of  FIG. 2 . 
         FIG. 5  is a flowchart illustrating the method of driving a light-source part shown in  FIG. 1 . 
         FIG. 6  is a diagram illustrating the method of driving the light-source part shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements. 
     It will be understood that when an element or layer is referred to as being “on” or “connected to” another element or layer, it can be directly on or directly connected to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on” or “directly connected to” another element or layer, there are no intervening elements or layers present. It will be understood that for the purposes of this disclosure, “at least one of X, Y, and Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ). 
       FIG. 1  is a block diagram illustrating a display apparatus according to an exemplary embodiment. 
     Referring to  FIG. 1 , the display apparatus may include a light-source part  100 , a light-source driving part  200 , a timing control part  300 , a display panel  400 , a data driving part  500 , and a gate driving part  600 . 
     The light-source part  100  provides the display panel  400  with light. The light-source part  100  may be of a direct-illumination type or an edge-illumination type. If the light-source part  100  is a direct-illumination type, it may include at least one light-source that generates the light and is disposed under the display panel  400 . However, if the light-source part  100  is an edge-illumination type, it may include a light guide plate (LGP) that guides the light toward the display panel  400  and at least one light-source that is disposed at an edge of the LGP. In addition, the light-source part may include at least one light-emitting block that is individually driven in a local dimming mode. 
     The light-source driving part  200  provides the light-source part  100  with a driving signal LDS. The light-source driving part  200  generates a dimming-level signal to control a luminance of the light which is applied to the display panel  400 , based on image data D. The light-source driving part  200  may correct the dimming-level through temporal and spatial low pass filers to generate corrected dimming-level signal DMc. The light-source driving part  200  generates a driving signal LDS utilizing the corrected dimming-level signal DMc to drive the light-source part  100 , providing the light-source part  100  with the driving signal LDS. In addition, the light-source driving part  200  may provide the timing control part  300  with the corrected dimming-level signal DMc. 
     The light-source driving part  200  is configured to determine whether a picture displayed on the display panel  400  is a repetitive picture. A repetitive picture is a picture that is repeated according to a period. When the picture is the repetitive picture, the light-source driving part  200  drives the light-source part  100  using a fixed dimming-level. Thus, when the display panel  400  displays the repetitive picture, the light-source part  100  generates a light of fixed luminance corresponding to the fixed dimming-level. Therefore, display degradation, such as a crawling, a blinking, etc., occurring by a response-time difference between the display panel  400  and the light-source part  100  may be reduced. 
     The timing control part  300  may control the driving timing of the display apparatus. For example, the timing control part  300  may generate a data control signal DCS configured to control the data driving part  500  and a gate control signal GCS configured to control the gate driving part  600 . 
     In addition, the timing control part  300  may receive the corrected dimming-level signal DMc from the light-source driving part  200  and correct the image data D based on the corrected dimming-level DMc to provide the data driving part  500  with corrected image data Dc. 
     The display panel  400  may include a plurality of gate lines GL1 to GLm, a plurality of data lines DL1 to DLn and a plurality of pixels P. The gate lines GL1 to GLm may extend in a first direction D1. The data lines DL1 to DLn may extend in a second direction D2, crossing the first direction D1. Each of the pixels P includes a switching element TR, which is electrically connected to a gate line and a data line, and a liquid crystal capacitor CLC, which is connected to the switching element TR. 
     The data driving part  500  may be electrically connected to end portions of the data lines DL1 to DLn. The data driving part  500  converts the corrected image data Dc received from the timing control part  300  to a grayscale voltage and provides the data lines DL1 to DLn with the grayscale voltages based on the data control signal DCS. 
     The gate driving part  600  may be electrically connected to end portions of the gate lines GL1 to GLm. The gate driving part  600  generates a plurality of gate signals utilizing the gate control signal GCS received from the timing control part  300  and gate-on and gate-off voltages received from a voltage generating part (not shown). The gate driving part  600  sequentially provides the gate lines GL1 to GLm with gate signals. 
       FIG. 2  is a block diagram illustrating a light-source driving part shown in  FIG. 1 .  FIG. 3  is a block diagram illustrating a timing control part shown in  FIG. 1 . 
     Referring to  FIGS. 1 ,  2 , and  3 , the light-source driving part  200  may include a dimming-level determining part  210 , a repetition determining part  220 , a dimming-level correcting part  230  and a driving signal generating part  240 . 
     The dimming-level determining part  210  calculates a representative grayscale of a current frame utilizing a histogram based on the image data D of the current frame. The dimming-level determining part  210  determines a dimming-level DM of the light-source part  100  utilizing the representative grayscale. 
     The repetition determining part  200  determines whether the dimming-level DM of a current picture received from the dimming-level determining part  210  is a dimming-level of a repetition dimming mode which is repeated by a period. When the dimming-level DM of the current picture corresponds to the repetition dimming mode, the repetition determining part  200  determines the dimming-level of the current picture as a fixed dimming-level. A method of driving the repetition determining part  200  will be explained referring to  FIGS. 4A to 4C . 
     According to the present exemplary embodiment, when the dimming-level DM of the current picture corresponds to a normal dimming mode, the light-source part  100  is driven based on the dimming-level DM. In this case, the dimming-level DM is determined from the dimming-level determining part  210  to generate the light of the luminance corresponding to the dimming-level DM. Alternatively, when the dimming-level DM of the current picture corresponds to the repetition dimming mode, the light-source part  100  is driven based on the fixed dimming-level DM determined from the repetition determining part  200  to generate the light of the luminance corresponding to the fixed dimming-level DM. 
     The dimming-level correcting part  230  corrects the dimming-level received from the dimming-level determining part  210  or the repetition determining part  220  through the temporal and the spatial low pass filers and outputs corrected dimming-level signal DMc. 
     The driving signal generating part  240  generates the driving signal LDS utilizing the corrected dimming-level DMc to drive the light-source part  100 , and provides the light-source part  100  with the driving signal LDS. 
     The timing control part  300  may include a pixel correcting part  310 . The pixel correcting part  310  corrects the image data D based on the corrected dimming-level signal DMc received from the light-source driving part  200  to generate corrected image data Dc. For example, when the corrected dimming-level DMc has a high level corresponding to a high luminance, the image data D are corrected as corrected image data Dc which have a grayscale level lower than a grayscale level of the image data. However, when the corrected dimming-level DMc has a low level corresponding to a low luminance, the image data D are corrected as corrected image data Dc which have the grayscale level higher than the grayscale level of the image data. Thus, electric power consumption for driving the display panel  400  may be decreased. 
       FIGS. 4A ,  4 B and  4 C are conceptual diagrams illustrating an operation of a repetition determining part shown in  FIG. 2 . 
     Referring to  FIGS. 1 ,  2 ,  4 A,  4 B and  4 C, a method of determining a repetition dimming mode will be explained hereinafter. 
     A current picture ‘C’ corresponds to the image data that is currently received. A first previous picture ‘B’ is displayed on the display panel  400  prior to the current picture ‘C’. A second previous picture ‘A’ is displayed on the display panel  400  prior to the first previous picture ‘B’. The picture A, B or C may include at least one frame image which is displayed on the display panel  400  during one frame. 
     As shown in  FIG. 4A , the dimming-level determining part  210  determines the dimming-level of the light-source part  100  corresponding to the current picture C as a first dimming-level ‘a’, determines the dimming-level of the light-source part  100  corresponding to the first previous picture B as a second dimming-level ‘b’, and determines the dimming-level of the light-source part  100  corresponding to the second previous picture A as the first dimming-level ‘a’. 
     When the repetition determining part  220  receives the first dimming-level ‘a’ of the current picture C, the repetition determining part  220  compares the first dimming-level ‘a’ of the current picture C with the second dimming-level ‘b’ of the first previous picture B and determines whether the current picture C is different from the first previous picture B. 
     For example, when the second dimming-level ‘b’ of the first previous picture B is more than a first reference value REF1 or less than a second reference value REF2, the repetition determining part  220  determines that the current picture C is different from the first previous picture B. When the current picture C is different from the first previous picture B, the repetition determining part  220  stores the first dimming-level ‘a’ of the current picture C, the second dimming-level ‘b’ of the first previous picture B and the first dimming-level ‘a’ of the second previous picture A. The first reference value REF1 (a+BRDR) may be a first allowable value BRDR added to the first dimming-level ‘a’ of the current picture C. The second reference value REF2 (a-BRDR) may be the first allowable value BRDR subtracted from the first dimming-level ‘a’ of the current picture C. The first allowable value BRDR is a parameter that may be stored at a register. 
     However, when the second dimming-level ‘b’ of the first previous picture B is less than the first reference value REF1 or more than the second reference value REF2, the repetition determining part  220  determines that the current picture C is not a repetitive picture. Thus, the current picture C may be displayed based on the first dimming-level ‘a’ which is determined from the dimming-level determining part  210 . 
     The repetition determining part  220  then compares the first dimming-level ‘a’ of the current picture C with the first dimming-level ‘a’ of the second previous picture A to determine a repetition dimming mode. 
     For example, when the first dimming-level ‘a’ of the second previous picture A is less than a third reference value REF3 or more than a fourth reference value REF4, the current picture C is determined as the repetitive picture. The third reference value REF3 (a+BRSR) may be a second allowable BRSR value added to the first dimming-level ‘a’ of the current picture C. The fourth reference value REF4 (a−BRSR) may be the second allowable value BRSR subtracted from the first dimming-level ‘a’ of the current picture C. The second allowable value BRSR a parameter that may be stored at the register. 
     However, when the first dimming-level ‘a’ of the second previous picture A is more than the third reference value REF3 or less than the fourth reference value REF4, the repetition determining part  220  determines that the current picture C is not the repetitive picture. Thus, the current picture C may be displayed based on the first dimming-level ‘a’ which is determined from the dimming-level determining part  210 . 
     As shown in  FIG. 4C , when the dimming-level is repeated as a first repetition pattern (a→b→a), a first flag may be set, when the dimming-level is repeated as a second repetition pattern (a→b→a→b), a second flag may be set and when the dimming-level is repeated as a third repetition pattern (a→b→a→b→a), a third flag may be set. The repetition pattern of the repetition dimming mode may be selected by a selection parameter which is stored at the register. For example, when the selection parameter stored at the register is the first flag, the repetition determining part  220  determines the repetition dimming mode if the dimming-levels received from the dimming-level determining part  210  are repeated as the first repetition pattern (a→b→a). 
     When the repetition dimming mode is determined, the repetition determining part  220  determines the dimming-level of the current picture C based on the fixed dimming-level, which is unrelated to the dimming-level received from the dimming-level determining part  210 . The fixed dimming-level may be set as one of the dimming-levels of the current picture and the first previous picture. For example, the fixed dimming-level may be set as a maximum or a minimum of the first dimming-level ‘a’ of the current picture C and the second dimming-level ‘b’ of the first previous picture B. The fixed dimming-level may also correspond to a level parameter stored at the register. For example, when the level parameter is ‘1’, the fixed dimming-level may be the first dimming-level ‘a’ which is the maximum of the first dimming-level of the current picture and the second dimming-level of the first previous picture. When the level parameter is ‘0’, the fixed dimming-level may be the second dimming-level which is the minimum of the first dimming-level of the current picture and the second dimming-level of the first previous picture. 
     When the repetition dimming mode is determined, the light-source part  100  is driven by the fixed dimming-level so that the light having fixed luminance corresponding to the fixed dimming-level is provided to the display panel  400  during a repetition dimming period. During the repetition dimming period, the repetition picture is displayed on the display panel  400 . In this manner, a display deterioration occurring by a response-time difference between the display panel  400  and the light-source part  100  may be prevented. 
       FIG. 5  is a flowchart illustrating the method of driving a light-source part shown in  FIG. 1 .  FIG. 6  is a diagram illustrating the method of driving a light-source part shown in  FIG. 5 . 
     Referring to  FIGS. 1 ,  2 ,  5  and  6 , the repetition determining part  220  receives a first dimming-level ‘a’ of a current picture K (step S 110 ). 
     The repetition determining part  220  compares a second dimming-level ‘b’ of the first previous picture K−1 with first and second reference values REF1 and REF2, respectively (step S 120 ). The first reference value REF1 (a+BRDR) is set as a first allowable value BRDR added to the first dimming-level ‘a’ of the current picture K. The second reference value REF2 (a-BRDR) is set as the first allowable value BRDR subtracted from the first dimming-level ‘a’ of the current picture K. The first allowable value BRDR is a parameter which is stored at a register. 
     If the dimming-level of the previous picture K−1 is less than the first reference value REF1 or more than the second reference value REF2, the repetition determining part  220  determines that the current picture K is not changed. Thus, the current picture K is driven with a luminance corresponding to a normal dimming mode (step S 170 ). 
     However, if the second dimming-level ‘b’ of the first previous picture K−1 is more than the first reference value REF1 or less than the second reference value REF2, the repetition determining part  220  determines that the current picture K is changed and then the repetition determining part  220  stores the first dimming-level ‘a’ of the current picture K, the second dimming-level ‘b’ of the first previous picture K−1 and the first dimming-level ‘a’ of the second previous picture K−2 (step S 130 ). 
     After the first, second, and third dimming levels are stored, the first dimming-level ‘a’ of the current picture K is compared with the first dimming-level ‘a’ of the second previous picture K−2 (step S 140 ). 
     For example, the first dimming-level ‘a’ of the second previous picture K−2 is less than the third reference value REF3 or more than the fourth reference value REF4, the repetition determining part  220  determines that the current picture K is repeated (step S 140 ). The third reference value REF3 is set as a second allowable BRSR value added to the first dimming-level ‘a’ of the current picture K. The fourth reference value REF4 is set as the second allowable value BRSR subtracted from the first dimming-level ‘a’ of the current picture K. The second allowable value BRSR a parameter which is stored at the register. 
     However, if the dimming-level of the second previous picture K−2 is more than the third reference value REF3 or less than the fourth reference value REF4, the repetition determining part  220  determines that the current picture K is not the repetitive picture. If this is the case, the current picture K may be driven with the luminance corresponding to the normal dimming mode (step S 170 ). 
     When the repetition determining part  220  determines that the current picture K is repeated (step S 140 ), the repetition determining part  220  determines a repetition pattern based on the selection parameter stored at the register (step S 150 ). 
     When the selection parameter is the first flag corresponding to the first repetition pattern (a→b→a), the repetition determining part  220  may drive from the current picture K as the repetition dimming mode (step S 160 ). However, when the selection parameter is the second flag corresponding to the second repetition pattern (a→b→a→b), the repetition determining part  220  may drive from a first next picture K+1 as the repetition dimming mode, and when the selection parameter is the third flag corresponding to the third repetition pattern (a→b→a→b→a), the repetition determining part  220  may drive from a second next picture K+2 as the repetition dimming mode. 
     In the repetition dimming mode, the repetition determining part  220  determines the dimming-level of the current picture K to be the fixed dimming-level which corresponds to the level parameter stored at the register. 
     For example, referring to  FIG. 6 , when the level parameter is ‘0’, the fixed dimming-level may be the first dimming-level ‘a’ which is the minimum of the first dimming-level ‘a’ of the current picture K and the second dimming-level ‘b’ of the first previous picture K−1. Thus, the dimming-level of the current picture K determines the fixed dimming-level ‘b’. 
     As shown in  FIG. 6 , the second and first previous picture K−2 and K−1 are being driven in the repetition dimming mode, and thus, the second and first previous picture K−2 and K−1 respectively have the first and second dimming-levels ‘a’ and ‘b’ determined from the dimming-level determining part  210 . The current picture K is being driven in the repetition dimming mode, and thus, the current picture K has the second dimming-level b that is the fixed dimming-level determined from the repetition determining part  220 . Thus, the light-source part  100  is driven with the second dimming-level b that is the fixed dimming-level during the repetition dimming period wherein the dimming-level is repeated as the repetition pattern (a→b→a). 
     After the repetition dimming period, a third dimming-level ‘i’ of a current picture Q is received, the repetition determining part  220  compares the third dimming-level ‘i’ of the current picture Q with the first dimming-level ‘a’ of a previous picture Q−1 (step S 120 ). The third dimming-level ‘i’ of the current picture Q is more than the second reference value REF2 so that the repetition determining part  220  determines that the current picture Q is not the repetitive picture. Thus, the current picture Q is driven with the luminance corresponding to the normal dimming mode (step S 170 ). 
     Therefore, the dimming-level of the current picture Q is held to the third dimming-level ‘i’ determined from the dimming-level determining part  210 . Thus, the light-source part  100  provides the display panel  400  with the light of the luminance corresponding to the third dimming-level ‘i’ during a period during which the current picture Q is displayed on the display panel  400 . 
     According to the exemplary embodiments of the present invention, the light-source part provides the display panel with the light of the fixed luminance corresponding to the fixed dimming-level during a period during which the repetitive picture is displayed on the display panel, so that the display degradation, such as crawling, blinking, etc, occurring by a response-time difference between the display panel and the light-source part may be prevented. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of the present invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific exemplary embodiments disclosed, and that modifications to the disclosed exemplary embodiments, as well as other exemplary embodiments, are intended to be included within the scope of the appended claims. The present invention is defined by the following claims, with equivalents of the claims to be included therein.