Abstract:
A light emitting display for providing a uniform current flow to a set of pixels to enable uniform brightness for the pixels. The pixels are situated in a pixel portion of a panel where the pixels are located at regions defined by a plurality of scan lines and a plurality of data lines. The uniform power is supplied by a set of power lines on each side of the pixel portion. The uniform voltage is maintained between the power lines by a set of power connection lines. The power connection lines connect the end points of two opposing power lines with interior points of the other two power lines at a set of electric junctions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0080625, filed on Oct. 8, 2004, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a light emitting display, and more particularly, to a light emitting display, in which a voltage drop in a power line is uniform, thereby providing a uniform brightness in the pixels. 
     2. Discussion of Related Art 
     Recently, various flat panel displays have been developed to replace a cathode ray tube (CRT) display, because the CRT display is relatively heavy and bulky. Flat panel display types include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panel (PDPs), light emitting display (LEDs), and similar flat panel technologies. 
     Light emitting displays include a plurality of light emitting devices, wherein each light emitting device emits light by electron-hole recombination or a similar process. Light emitting displays are classified into inorganic light emitting displays that include an inorganic emission layer and organic light emitting displays that include an organic emission layer. Light emitting displays have response times that are relatively fast and power consumption that is relatively low. 
       FIG. 1  is a plan view of a conventional light emitting display. A conventional light emitting display includes: a substrate  10 , a pixel portion  20  that includes a plurality of pixels  21  formed adjacent to a region defined by a plurality of scan lines S, a plurality of data lines D and a plurality of pixel power lines VDD, which are formed on the substrate  10 ; a scan driver  30 ; a data driver  40 ; a first power line  50 ; a second pixel power line  52 ; and a pad hub  60 . 
     The scan driver  30  is placed adjacent to one side of the pixel portion  20  and electrically connected to a first set of pads Ps on the pad hub  60  through a scan control signal line  32 . The scan driver  30  generates scan signals in response to a scan control signal transmitted through the scan control line  32  and supplies the scan signals to the scan lines S of the pixel portion  20 . 
     The data driver  40  is electrically connected to the data line D and the second set of pads Pd on the pad hub  60 . The data driver  40  may be mounted as a chip onto the substrate  10 . 
     The second pixel power line  52  is formed on the whole area of the pixel portion  20 . The second pixel power line  52  supplies a second pixel driving voltage from the third set of pads Pvss on the pad hub  60  to each pixel  21 . 
     The first power line  50  is placed adjacent to a top side of the pixel portion  20 . The first power line  50  is commonly connected to the first ends of the first pixel power lines VDD. The first power line  50  receives the first pixel driving voltage from a first power supplying line  48  through a fourth set of pads Pvdd on the pad hub  60  and supplies it to the first pixel power line VDD of each pixel  21 . 
     The respective first ends of the first pixel power lines VDD are commonly connected to the first power line  50 . Each first pixel power line VDD supplies the first pixel driving voltage from the first power line  50  to each pixel  21 . 
     Thus, each pixel  21  is controlled by the scan signal transmitted through the scan line S. Each pixel  21  emits light based on the current supplied from the first pixel power line VDD to the light emitting device in response to the data signal transmitted through the data line D, thereby displaying an image. 
     In the conventional light emitting display, the respective first pixel power lines VDD that are commonly connected to the first power line  50  are different in length, so that line resistance on the first pixel power lines is not uniform. Therefore, the voltage drop (i.e., IR drop) in the first pixel driving voltage supplied to the pixels  21  differs between pixels. That is, the voltage drop of the first pixel power line VDD becomes smaller as the first pixel power line VDD gets closer to the first power line  50 , but becomes larger as it gets far away from the first power line  50 . Hence, in the conventional light emitting display, the voltage drop in the first pixel power line VDD is different according to the position of the pixel  21 , so that the intensity of current supplied to the pixel  21  is not uniform. Rather, the intensity of the current varies with respect to the same data signal according to the positions of the pixel  21 , thereby making the brightness non-uniform. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide a light emitting display, in which the voltage drop in the power lines is uniform to make brightness uniform. The embodiments of the invention include a light emitting display having: a pixel portion including a plurality of pixels defined by a plurality of scan lines and a plurality of data lines; a first power line arranged on a first side of the pixel portion for supplying a driving voltage; a second power line arranged on a second side of the pixel portion for supplying the driving voltage; a third power line arranged on a third side of the pixel portion for supplying the driving voltage; a fourth power line arranged on a fourth side of the pixel portion for supplying the driving voltage; first and second power connection lines to connect the first and second power lines with the third power line through first and second electric junctions; and third and fourth power connection lines to connect the first and second power lines with the fourth power line through third and fourth electric junctions, where each of the electric junctions are interior points on the third or fourth power lines. 
     In another embodiment, a light emitting display includes: a pixel portion including a plurality of pixels to emit light, where each pixel receives a current corresponding to a data signal that is transmitted through a data line and where each pixel is controlled by a scan signal transmitted through a scan line from a pixel power line; a first power line arranged on a first side of the pixel portion through which an external driving voltage is supplied; a second power line arranged on a second side of the pixel portion through which the external driving voltage is supplied; a third power line to supply the driving voltage to a first end of the pixel power line; a fourth power line to supply the driving voltage to a second end of the pixel power line; a first power connection line having a first end electrically connected to the first power line and a second end electrically connected between a first end and a middle of the third power line; a second power connection line having a first end electrically connected to the second power line and a second end electrically connected between a second end and the middle of the third power line; a third power connection line having a first end electrically connected to the first power line, and a second end electrically connected between a first end and a middle of the fourth power line; and a fourth power connection line having a first end electrically connected to the second power line and a second end electrically connected between a second end and the middle of the fourth power line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a conventional light emitting display. 
         FIG. 2  is a plan view of a light emitting display according to a first embodiment of the present invention. 
         FIG. 3  is a plan view of a light emitting display according to a second embodiment of the present invention. 
         FIG. 4  shows current distribution of the light emitting display of  FIG. 3  according to the position of the pixels. 
         FIG. 5  is a graph illustrating the intensity of current supplied to each pixel connected to the scan line of  FIGS. 2 and 3 . 
         FIG. 6  is a plan view of a light emitting display according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a plan view of a light emitting display according to a first embodiment of the present invention. A light emitting display according to the first embodiment of the present invention includes a pixel portion  120  placed on a substrate  110  and having a plurality of pixels  121  defined by a plurality of data lines D, a plurality of scan lines S, and a plurality of first pixel power lines VDD; first through fourth power lines  150 ,  152 ,  154  and  156 ; and first through fourth power connection lines  153 ,  155 ,  157  and  159 . Further, the light emitting display according to an embodiment of the present invention includes a scan driver  130 , a data driver  140 , a second pixel power line  170  and a pad hub  160 . 
     The scan driver  130  is placed adjacent to one side of the pixel portion  120  and is electrically connected to a first set of pads Ps on the pad hub  160 . The scan driver  130  generates scan signals according to scan control signal lines extended from the first set of pads Ps and supplies the scan signals to the scan lines S of the pixel portion  120  in sequence. 
     The data driver  140  is electrically connected to the data line D and second set of pads on the pad hub  160 . The data driver  140  can be directly formed on the substrate  110  or embedded as a chip onto the substrate  110 . The chip type data driver can be embedded on the substrate  110  by a chip on glass method, a wire bonding method, a flip chip method, a beam lead bonding method, or similar technique. The data driver  140  receives a data control signal and a data signal from the second set of pads Pd and supplies the data signal to the data lines D based on the data control signal. 
     The first power line  150  is arranged in parallel on a first side (right side) of the pixel portion  120 . The first power line  150  has a first end electrically connected to a third set of pads Pvdd 1  on the pad hub  160 . Further, the first power line  150  receives the first pixel driving voltage from the third set of pads Pvdd 1  and supplies it to both the third power line  154  via the first power connection line  153  and the fourth power line  156  via the third power connection line  157 . 
     The second power line  152  is arranged in parallel with a second side (left side) of the pixel portion  120 . The second power line  152  has a first end electrically connected to a fourth set of pads Pvdd 2  on the pad hub  160 . Further, the second power line  152  receives the first pixel driving voltage from the fourth set of pads Pvdd 2  and supplies it to both the third power line  154  via the second power connection line  155  and the fourth power line  156  via the fourth power connection line  159 . 
     The third power line  154  is arranged in parallel with a top side of the pixel portion  120 . The third power line  154  has a first end electrically connected to a first end (top end) of each first pixel power line VDD. Further, the third power line  154  supplies the first pixel driving voltage from the first and second power connection lines  153  and  155  to the first end of each pixel power line VDD. 
     The fourth power line  156  is arranged in parallel with a bottom side of the pixel portion  120 . The fourth power line  156  has a first end electrically connected to a second end (bottom end) of each first pixel power line VDD. Further, the fourth power line  156  supplies the first pixel driving voltage from the third and fourth power connection lines  157  and  159  to the second end of each pixel power line VDD. 
     The first power connection line  153  has a “U”-shape and is electrically connected to the middle of the right portion of the third power line  154 . The first power connection line  153  has a first end electrically connected to the top end of the first power line  150  and a second end electrically connected to the third power line  154 . The second end of the first power connection line  153  is electrically connected to a region between the middle and the first end of the third power line  154  at a first electric junction. The distance from this first electric junction to the middle of the third power line  154  is equal to the distance from the first electric junction to the first end of the third power line  154 . The first power connection line  153  supplies the first pixel driving voltage from the first power line  150  to the right portion of the third power line  154 . 
     The second power connection line  155  has a “U”-shape and is electrically connected to the middle of the left portion of the third power line  154 . The second power connection line  155  has a first end electrically connected to the top end of the second power line  152  and a second end electrically connected to the third power line  154  at a second electric junction. The distance from this second electric junction to the middle of the third power line  154  is equal to the distance from the electric junction to the second end of the third power line  154 . The second power connection line  155  supplies the first pixel driving voltage from the second power line  152  to the left portion of the third power line  154 . 
     The third power connection line  157  is electrically connected to the middle of the right portion of the fourth power line  156 . The third power connection line  157  has a first end electrically connected to the bottom end of the first power line  150  and a second end electrically connected to the fourth power line  156  at a third electric junction. The distance from this third electric junction to the middle of the fourth power line  156  is equal to the distance from the third electric junction to the first end of the fourth power line  156 . 
     The width and the length of the third power connection line  157  are designed to equalize the first pixel driving voltage supplied from the first power connection line  153  to the first electric junction on the third power line  154  with the first pixel driving voltage supplied from the third power connection line  157  to the third electric junction on the fourth power line  156 . The third power connection line  157  can be narrower than the first power line  150 . The third power connection line  157  drops and supplies the first pixel driving voltage from the first power line  150  to the right portion of the fourth power line  156  at the third electric junction. 
     The fourth power connection line  159  is electrically connected to the middle of the left portion of the fourth power line  156 . The fourth power connection line  159  has a first end electrically connected to the bottom end of the second power line  152  and a second end electrically connected to the fourth power line  156  at a fourth electric junction. The distance from the fourth electric junction between the fourth power connection line  159  and the fourth power line  156  to the middle of the fourth power line  156  is equal to the distance from the fourth electric junction to the second end of the fourth power line  156 . 
     The width and the length of the fourth power connection line  159  are designed to equalize the first pixel driving voltage supplied from the second power connection line  155  to the second electric junction with the first pixel driving voltage supplied from the fourth power connection line  159  to the fourth electric junction. The third and fourth power connection lines  157  and  159  are different in line resistance from the first and second power connection lines  153  and  155 . The fourth power connection line  159  can be narrower than the second power line  152 . The fourth power connection line  159  drops and supplies the first pixel driving voltage from the second power line  152  to the left portion of the fourth power line  156 , i.e., through the fourth electric junction. 
     The second pixel power line  170  is formed on the whole area of the pixel portion  120 . The second pixel power line  170  supplies a second pixel driving voltage from a fifth set of pads Pvss on the pad hub  160  to each pixel  121 . The second pixel power line  170  is arranged in parallel with and separately from the scan line S of the pixel portion  120 . 
     Each first pixel power line VDD has its first end electrically connected to the third power line  154  and its second end electrically connected to the fourth power line  156 . Each first pixel power line VDD supplies the first pixel driving voltage from the third and fourth power lines  154  and  156  to each pixel  121 . The first pixel driving voltages supplied to the first and second ends of each first pixel power line VDD are made uniform by the first through fourth power connection lines  153 ,  155 ,  157  and  159 . 
     Each pixel  121  is controlled by the scan signal transmitted to the scan line S, and emits light based on current supplied to the light emitting device from the first pixel power line VDD, thereby displaying an image. Each pixel  121  includes a pixel circuit that outputs the current from the first pixel power line VDD in correspondence to the data signal transmitted to the data line D in response to the scan signal supplied from at least one scan line S. The pixel circuit includes at least one transistor and at least one capacitor. 
       FIG. 3  is a plan view of a light emitting display according to a second embodiment of the present invention. A light emitting display according to the second embodiment of the present invention has the same configuration as that of the first embodiment except the third and fourth power connection lines  157  and  159 . 
     The third power connection line  157  has a curved “S” shape and is electrically connected to the middle of the right portion of the fourth power line  156 . The third power connection line  157  has a first end electrically connected to the bottom end of the first power line  150  and a second end electrically connected to the fourth power line  156 . The second end of the third power connection line  157  is electrically connected to a region between the middle and the first end of the fourth power line  156  at a third electric junction. The distance from the third electric junction to the middle of the fourth power line  156  is equal to the distance from the third electric junction to the first end of the fourth power line  156 . 
     The width and the length of the third power connection line  157  are designed to equalize the first pixel driving voltage supplied from the first power connection line  153  to the first electric junction of the third power line  154  with the first pixel driving voltage supplied from the third power connection line  157  to the third electric junction of the fourth power line  156 . The third power connection line  157  can be narrower than the first power line  150 . The third power connection line  157  drops and supplies the first pixel driving voltage from the first power line  150  to the right portion of the fourth power line  156 , i.e., to the third electric junction. 
     The fourth power connection line  159  has a curved “S” shape and is electrically connected to the middle of the left portion of the fourth power line  156 . The fourth power connection line  159  has a first end electrically connected to the bottom end of the second power line  152  and a second end electrically connected to the fourth power line  156 . The second end of the fourth power connection line  159  is electrically connected to a region between the middle and the second end of the fourth power line  156  at the fourth electric junction. The distance from the fourth electric junction to the middle of the fourth power line  156  is equal to the distance from the fourth electric junction to the second end of the fourth power line  156 . 
     The width and the length of the fourth power connection line  159  are designed to equalize the first pixel driving voltage supplied from the second power connection line  155  to the second electric junction of the third power line  154  with the first pixel driving voltage supplied from the fourth power connection line  159  to the fourth electric junction. The third and fourth power connection lines  157  and  159  have different line resistances from the first and second power connection lines  153  and  155 . The fourth power connection line  159  can be narrower than the second power line  152 . The fourth power connection line  159  drops and supplies the first pixel driving voltage from the second power line  152  to the left portion of the fourth power line  156 , i.e., to the fourth electric junction. 
       FIG. 4  shows distribution of the current supplied to the pixel portion  120  shown in  FIG. 3 . The light emitting display according to the second embodiment of the present invention employs the third and fourth power connection lines  157  and  159  to provide a uniform first pixel driving voltage to be supplied to the third and fourth power lines  154  and  156 , so that the uniformity of the current supplied to the pixel portion  120  is improved. Even though the current distribution illustrated in  FIG. 4  is somewhat non-uniform because of the voltage drop in the first and second power lines  150  and  152  adjacent to the pixel portion  120  and the voltage drop in the first pixel power line VDD, the distribution flowing in the whole pixel portion  120  is generally symmetrically uniform with respect to horizontal and vertical directions. The current distribution of the pixel portion  120  provided in the light emitting display according to the first embodiment is also similar to that shown in  FIG. 4 . 
       FIG. 5  is a graph illustrating the intensity of current supplied to each pixel  121  connected to the 1 st  through n th  scan lines shown in  FIG. 3 . The currents are symmetrically supplied to the respective pixels  121  connected to the 1 st  through n th  scan lines. The current flowing in the pixel portion  120  is uniform regardless of the side of the scan line, such as the top side corresponding to the 1 st  scan line of the pixel portion  120  and the bottom side corresponding to the n th  scan line of the pixel portion  120 , because the first pixel driving voltage supplied to the first and second end of the first pixel power lines VDD is made uniform by the third and fourth power connection lines  157  and  159 . 
     In the light emitting display according to the first and second embodiments of the present invention, the voltage drop of the first pixel driving voltage supplied to the third and fourth power lines  154  and  156  is made uniform by the third and fourth power connection lines  157  and  159 , so that the current supplied from the first pixel power line VDD to the pixels  121  is uniform. In the light emitting display according to the first and second embodiments of the present invention, the uniform current flows in the whole pixel portion  120 , so that the brightness is also uniform, thereby improving picture quality. 
       FIG. 6  is a plan view of a light emitting display according to a third embodiment of the present invention. The light emitting display according to the third embodiment of the present invention has the same configuration as those of the first and second embodiments except for the configuration of the data driver  140  supplying the data signal to the data line D of the pixel portion  120 . 
     In the light emitting display according to the third embodiment of the present invention, the data driver  140  is embedded on a flexible printed circuit (FPC)  180  connected to the substrate  110 . Thus, the data driver  140  is electrically connected with the data line D of the pixel portion  120  through the pad hub of the substrate  110 , thereby supplying the data signal. In another embodiment, the data driver  140  may be embedded in a chip on board mounted on a printed circuit board, a chip on film directly mounted on a film or on a film type connector that is generally used for a tape carrier package, as well as, mounted on the flexible printed circuit  180 . 
     As described above, the present invention provides a light emitting display, in which pixel driving voltages respectively applied to opposite ends of a pixel power line are made uniform and thus the currents supplied to the respective pixels are made uniform. The uniform current flows in the whole pixel portion, so that the brightness is uniform, thereby improving picture quality. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.