Abstract:
A display device and a method for driving the same are disclosed. The display device confirms whether display data applied to a display panel are uniformly maintained for a predetermined time. As a result of confirmation, if the display data are uniformly maintained for a predetermined time, pixels of the display panel are made for a predetermined block unit so that screen save modes are performed to sequentially apply screen save mode data to pixels of each block. The screen save modes are completed after there are sequentially performed for all blocks on the display panel. Thus, uniform luminance deviation can be obtained on the display panel of the display device and further picture quality of the display device can be improved.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a display device and a method for driving the same, and more particularly, to a display device and a method for driving the same that can uniformly maintain a degradation deviation of a whole display panel in upper, lower, left, and right directions in a self-luminescent display device. 
   2. Background of the Related Art 
   Generally, a display device has a degradation deviation on a display panel by driving the display panel. Recently, self-luminescent display devices, such as a cathode ray tube (CRT), a field emission display (FED), a plasma display panel (PDP), and an electroluminescence (EL), are used as display devices. Since such self-luminescent display devices have a variable screen in view of a graphic screen, certain pixels of a panel are not continuously maintained in turn-on or turn-off state. 
   However, in a text screen, when the text screen is continuously displayed, some of pixels constituting the text screen can continuously be maintained in turn-on state while other pixels can continuously be maintained in turn-off state. 
   Therefore, a great difference exists between luminance of pixels continuously maintained in turn-on state and luminance of pixels continuously maintained in turn-off state. In other words, the pixels continuously maintained in turn-on state have a short life due to degradation while the pixels continuously maintained in turn-off state relatively have a long life. 
   The pixels having different lives deteriorate picture quality of the display device. 
   To solve such a problem, there is provided a method for prolonging a life of a display panel of a display device by applying an inverse voltage to the display panel. However, this method is made without any noticeable result. 
     FIG. 1  is a diagram showing a display of a general text type. 
   Luminance according to lives of pixels continuously maintained in turn-off state in  FIG. 1  is shown in an upper graph of  FIG. 2 . As shown in  FIG. 2 , it is noted that luminance of pixels continuously maintained in turn-on state according to their operation time is remarkably deteriorated as compared with the pixels continuously maintained in turn-off state. 
   Meanwhile, the pixels continuously maintained in turn-off state have lower luminance than the pixels continuously maintained in turn-on state. Luminance of pixels continuously maintained in turn-off state according to their operation time is shown in a lower graph of  FIG. 2 . 
   In other words, in the pixels continuously maintained in turn-on state, charges continuously move within them. Accordingly, as shown in the lower graph of  FIG. 2 , the pixels continuously maintained in turn-on state have rapidly deteriorated luminance according to life as compared with the pixels continuously maintained in turn-off state. Further, the pixels continuously maintained in turn-on state have a shorter life than the pixels continuously maintained in turn-off state. 
   Consequently, the life difference generates luminance difference between the pixels and deteriorates picture quality of the display device. 
   In other words, if the display device displays a text screen, once the pixels are set up in turn-on or turn-off state, they continuously remain as they are. In this case, luminance difference exists between the turned on pixels and the turned off pixels, thereby remarkably deteriorating picture quality. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to a display device and a method for driving the same that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
   An object of the present invention is to provide a display device and a method for driving the same that can prevent picture quality from being deteriorated. 
   Another object of the present invention is to provide a display device and a method for driving the same that can minimize a degradation deviation between pixels continuously maintained in turn-on state and pixels continuously maintained in turn-off state. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
   To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a display device confirms whether display data applied to a display panel are uniformly maintained for a predetermined time. As a result of confirmation, if the display data are uniformly maintained for a predetermined time, pixels of the display panel are made for a predetermined block unit so that screen save modes are performed to sequentially apply screen save mode data to pixels of each block. The screen save modes are completed after there are sequentially performed for all blocks on the display panel. 
   Preferably, as a result of confirmation, if the display data are changed for a predetermined time, the display data are recognized as active data such as graphic data. Therefore, the display device directly displays the display data on the display panel without performing the screen save modes. 
   Preferably, to uniformly maintain picture quality of the display device, the screen save mode data having a predetermined type to be directly applied to the display panel if the display data are not changed for a predetermined time are in advance stored in a memory of the display device. 
   Preferably, to perform the screen save modes, the pixels can be made for one block unit among a block consisting of a plurality of pixel columns, a block consisting of plurality of pixel rows, and N×M (N, M is a positive integer) pixel block. At this time, screen save mode data designated as turn-on or turn-off are simultaneously applied to all pixels within the same block. 
   Preferably, to perform the screen save mode, the pixels are divided into one of the column block, the row block, and the N×M block, and an inverse value of the display data is periodically applied to the pixels within each block. 
   Preferably, as the screen save mode data, certain graphic data can be provided to the display panel at a certain time period to uniformly maintain the degradation state of the whole pixels. 
   It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 

   
     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 application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
       FIG.1  is a diagram showing a display of a general text type, 
       FIG. 2  is a graph showing lives of pixels in the related art; 
       FIG. 3  is a block diagram showing a configuration of a display device according to the present invention; 
       FIGS. 4A and 4B  are diagrams showing a screen save mode that turns on pixels for a column block unit; 
       FIGS. 5A and 5B  are diagrams showing a screen save mode that turns on pixels for a row block unit; 
       FIGS. 6A and 6B  are diagrams showing a screen save mode that turns on pixels for N×M block unit; 
       FIG. 7  is a graph showing lives of pixels according to the present invention; 
       FIGS. 8A and 8B  are diagrams showing a screen save mode using inverse data; and 
       FIG. 9  is a flow chart showing a step of compensating degradation of a display device according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
   Pixels of a display device may partially be degraded in view of characteristic of the display device. It is necessary to uniformly compensate display quality of whole pixels so as to uniformly maintain display quality of the partially degraded display device. 
     FIG. 3  is a block diagram showing a configuration of a display device according to the present invention. 
   Referring to  FIG. 3 , the display device of the present invention includes a display panel  10  having a plurality of pixels arranged in a column and row unit, a pixel column driving unit  20  for driving the pixels in column, a pixel row driving unit  30  for driving the pixels in row, and a control unit  40  for driving the pixel column driving unit  20  and the pixel row driving unit  30  using a control signal. 
   The control unit  40  divides the pixels into a predetermined block unit by driving the pixel column driving unit  20  and the pixel row driving unit  30  using the control signal. The control unit  40  performs screen save modes of the display panel for the predetermined block unit. 
   Meanwhile, a reference numeral  50  which is not described denotes a memory that stores various types of the screen save modes. 
   The predetermined block for the screen save modes may be one of a column block consisting of at least one pixel column, a row block consisting of at least one pixel row, and N×M pixel block consisting of N×M (N, M is positive integer number) pixels. 
   The screen save modes may turn on or off all pixels within each block. 
   In  FIG. 3 , the control unit  40  confirms whether display data applied to the display panel  10  are uniformly maintained for a predetermined time. If the display data are uniformly maintained for a predetermined time, the control unit  40  divides the display panel  10  into at least one block. The screen save modes are then performed. In other words, the display data and the screen save mode data are sequentially applied from the memory  50  to the one block of the display panel  10  under the control of the control unit  40 . 
   Meanwhile, if the display data are changed to other data during the screen save modes, the control unit  40  releases the screen save modes and displays the display data only on the display panel  10 . 
   If the display data are continuously variable data without being uniformly maintained for a predetermined time, the control unit  40  continuously displays the display data on the display panel  10  without performing the screen save modes. 
   Inverse data of the display data may be used as the screen save mode data. 
   First Embodiment 
     FIGS. 4A and 4B  are diagrams showing screen save modes that turn on pixels of a display device for a column block unit. 
   In  FIGS. 4A and 4B , a plurality of columns are regarded as one block unit and pixels are turned on for a block unit, so that the screen save modes are performed. 
     FIG. 4A  shows a first column block  100   a  of the screen save modes implemented for the column block unit, and  FIG. 4B  shows the last column block  100   d  of the screen save modes implemented for the column block unit. 
   As shown in  FIGS. 4A and 4B , the screen save mode is sequentially applied to each of the column blocks  100   a – 100   d , and the corresponding columns within the currently chosen column block ( 100   a  in  FIG. 4A and 100   d  in  FIG. 4B ) are turned on while columns corresponding to the other column blocks ( 100   b  and  100   c ) are turned off, except for pixels that are displaying display data. These steps are repeated until the screen save modes of all column blocks  100   a – 100   d  are completed. 
   The control unit  40  confirms whether the display data applied to the display panel  10  are uniformly maintained for a predetermined time. If the display data are uniformly maintained for a predetermined time, the control unit  40  divides the pixels of the display panel  10  into at least one pixel column block  100   a – 100   d . Then, the screen save modes are sequentially performed on the pixel column blocks  100   a – 100   d.    
   The screen save modes mean that pixels corresponding to each pixel column block are simultaneously driven in the same type. When the screen save modes are performed, the same type may be made in such a manner that all pixels within each block are turned on or off. 
   Meanwhile, if the display data are changed during the screen save modes, the control unit  40  releases the screen save modes and displays the display data only on the display panel  10 . 
   Second Embodiment 
     FIGS. 5A and 5B  are diagrams showing screen save modes that turn on pixels for a row block unit. 
   In  FIGS. 5A and 5B , a plurality of rows are regarded as one block unit and pixels are turned on for a block unit, so that the screen save modes are performed. 
     FIG. 5A  show a first row block  200   a  of the screen save modes implemented for the row block unit, and  FIG. 5B  shows the last row block  200   d  of the screen save modes implemented for the row block unit. 
   As shown in  FIGS. 5A and 5B , the screen save mode is sequentially applied to each of the row blocks  200   a – 200   d , and the corresponding columns within the currently chosen row block ( 200   a ,  FIG. 5A and 200   d  in  FIG. 5B ) are turned on while rows corresponding to the other row blocks ( 200   b  and  200   c ) are turned off, except for pixels that are displaying display data. These steps are repeated until the screen save modes of all row blocks  200   a – 200   d  are completed. 
   The control unit  40  confirms whether the display data applied to the display panel  10  are uniformly maintained for a predetermined time. If the display data are uniformly maintained for a predetermined time, the control unit  40  divides the pixels of the display panel  10  into at least one pixel row block  200   a – 200   d . Then, the screen save modes are sequentially performed on the pixel row blocks  200   a – 200   d  by the control unit  40 . 
   The screen save modes mean that pixels corresponding to each pixel row block are simultaneously driven in the same type. 
   Meanwhile, if the display data are changed during the screen save modes, the control unit  40  releases the screen save modes and displays the display data only on the display panel  10 . 
   The screen save modes for the row block unit are useful for display devices that perform display for a character unit. In this case, a user can manipulate the display device for the screen save mode for the row block unit without reducing viewing sensitivity when viewing a screen displayed in the display device. 
   Third Embodiment 
     FIGS. 6A and 6B  are diagrams showing screen save modes that turn on pixels for N1×M1 block unit. 
     FIG. 6A  show a first N1×M1 pixel block  300   a  of the screen save modes implemented for a certain pixel block unit, and  FIG. 6B  shows the last N1×M1 pixel block  300   h  of the screen save modes implemented for the certain pixel block unit. 
   Pixels of the currently chosen N1×M1 pixel block ( 300   a  in  FIG. 5A and 300   h  in  FIG. 6B ) are turned on while pixels of the other N×M pixel blocks  300   b – 300   g  are turned off, except for pixels that are displaying display data. These steps are repeated until the screen save modes of all N1×M1 pixel blocks  300   a – 300   h  are completed. 
   The control unit  40  confirms whether the display data applied to the display panel  10  are uniformly maintained for a predetermined time. If the display data are uniformly maintained for a predetermined time, the control unit  40  divides the pixels of the display panel  10  into at least one N1×M1 (N1 and M1 are positive integers) pixel row block  300   a – 300   h . The screen save mode is then sequentially performed on the N1×M1 pixel blocks  300   a – 300   h.    
   At this time, the screen save modes mean that pixels corresponding to each N1×M1 pixel block are simultaneously driven in the same type. 
   Meanwhile, if the display data are changed during the screen save modes, the control unit  40  releases the screen save mode and displays the display data only on the display panel  10 . 
   When the screen save modes are performed, the same type may be made in such a manner that all pixels within each block are turned on or off. 
     FIG. 7  is a graph showing lives of pixels according to the present invention. 
   In  FIG. 7 , a graph at an upper portion shows lives of the pixels of the display device when the screen save modes are performed on the display device for the pixel block unit while a graph at a lower portion shows lives of pixels when the pixels of the display device are continuously turned on without performing the screen save modes. 
   As shown in  FIG. 7 , in the screen save modes of the present invention, it is noted that luminance difference according to a life reduced by half between the pixels continuously maintained in turn-on state and the pixels continuously maintained in turn-off state is not great. Accordingly, it is noted that picture quality of the display device can be improved. 
     FIG. 8A  is a diagram showing a screen when the display device is in a general display state while  FIG. 8B  is a diagram showing a screen when turned on pixels and turned off pixels are inversed on the screen. 
   In  FIGS. 8A and 8B , the control unit  40  confirms whether the display data applied to the display panel  10  are uniformly maintained for a predetermined time. If the display data are uniformly maintained for a predetermined time, the control unit  40  divides the pixels of the display panel  10  into at least one pixel block  400 . Then, the control unit  40  sequentially applies the screen save mode data to the at least one pixel block  400 . 
   The screen save mode data are inverse data of data corresponding to each pixel block of the display data. 
   Meanwhile, the block for the screen save modes may be one of a column block consisting of at least one pixel column, a row block consisting of at least one pixel row, and a pixel block consisting of N×M(N1 and M1 are positive integers) pixels. 
   The screen save mode data are to turn off the pixels turned on according to the display data among the pixels belonging to each pixel block and at the same time to turn on the pixels turned off according to the display data among the pixels belonging to each pixel block. 
   As described above, when the pixel data of the current screen and their inverse data are provided to the screen of the display device, graphs on lives of the pixels of the display device are equal to the graph at the upper portion of  FIG. 7 . Accordingly, the display panel of the display device has improved picture quality. 
     FIG. 9  is a flow chart showing steps of compensating degradation deviation of the display device according to the present invention. 
   If data are displayed on the display panel of the display device (S 1 ), the control unit  40  of the display device confirms whether the display data are uniformly maintained for a predetermined time (T sec.) without any change (S 2 ). If the display data are continuously changed, the display device continuously performs the display step under the control of the control unit  40 . Meanwhile, if it is determined that the display data are continuously displayed on the screen for a predetermined time, the display device is subject to the screen save modes according to the present invention under the control of the control unit  40 . 
   The screen save modes may be implemented in various types. These various types are previously divided and then stored in the memory of the display device. Also, the types of the screen save modes are previously designated by a user or manufacturer. The display device performs the screen save modes of the previously designated types as above. As an example, the first screen save mode is implemented for a column block unit, the second screen save mode is implemented for a row block unit, and the third screen save mode is implemented for a pixel block unit (S 4 ). 
   Meanwhile, it is confirmed whether the display data are changed during the screen save modes (S 5 ). If the display data are changed, the screen save modes are directly ended by the control unit  40  and the display device displays the display data on the screen (S 6 ). 
   As aforementioned, the driving method of the display device according to the present invention has the following advantages. 
   First, turn-on state and turn-off state of a plurality of the pixels to which the same data are successively applied for a predetermined time are switched so that the pixels can uniformly be turned on over the whole screen. 
   Furthermore, by periodically applying inverse data of current video data to the whole pixels constituting the screen, luminance deviation can uniformly be maintained at a small range between the pixels over the whole screen of the display panel. As a result, it is possible to improve picture quality of the screen. 
   The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.