Patent Publication Number: US-7710367-B2

Title: Organic light emitting display and method of driving the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0094122, filed on Nov. 17, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an organic light emitting display and a method of driving the same, and more particularly, to an organic light emitting display having improved display quality. 
     2. Discussion of the Background 
     Various thin and lightweight flat panel displays (FPD) have been developed to replace cathode ray tubes (CRT). Such FPDs include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays. 
     Generally, organic light emitting displays display images using organic light emitting diodes (OLED), which generate light by re-combination of electrons and holes. Organic light emitting displays typically have high response speed and low power consumption. 
       FIG. 1  shows a conventional organic light emitting display. 
     Referring to  FIG. 1 , the conventional organic light emitting display includes an image display unit  30  including pixels  40  formed at crossings of scan lines S 1  to Sn and data lines D 1  to Dm, a scan driver  10  for driving the scan lines S 1  to Sn, a data driver  20  for driving the data lines D 1  to Dm, and a timing controller  50  for controlling the scan and data drivers  10  and  20 . 
     The scan driver  10  generates scan signals in response to scan driving control signals SCS from the timing controller  50  and sequentially supplies the scan signals to the scan lines S 1  to Sn. The scan driver  10  also generates emission control signals in response to the scan driving control signals SCS and sequentially supplies the emission control signals to emission control lines E 1  to En. 
     The data driver  20  generates data signals in response to data driving control signals DCS from the timing controller  50  and supplies the data signals to the data lines D 1  to Dm. The data driver  20  supplies the data signals for one horizontal line to the data lines D 1  to Dm every one horizontal period. 
     The timing controller  50  generates the data driving control signals DCS and the scan driving control signals SCS in response to input synchronizing signals. The timing controller  50  supplies the data driving control signals DCS to the data driver  20  and the scan driving control signals SCS to the scan driver  10 . The timing controller  50  re-aligns data Data supplied from the outside and supplies the data Data to the data driver  20 . 
     The image display unit  30  is coupled with a first power source ELVDD and a second power source ELVSS, which are supplied to the pixels  40 . The pixels  40  display images corresponding to the data signals supplied thereto. The emission time of the pixels  40  is controlled by the emission control signals. 
     Here, the emission control signals are sequentially supplied to the first to nth emission control lines E 1  to En together with the scan signals. Therefore, all of the pixels  40  included in the image display unit  30  emit light except for the short time during which the emission control signals are supplied. 
     However, the voltage of the first power source ELVDD may change in accordance with whether the pixels  40  emit light, that is, in accordance with the pattern and brightness of the images displayed by the image display unit  30 . To be specific, the load applied to the first power source ELVDD in one frame varies with whether the pixels  40  emit light. Hence, when a large number of pixels  40  emit light in one frame, a large load is applied to the first power source ELVDD. On the other hand, when a small number of pixels  40  emit light in one frame, a small load is applied to the first power source ELVDD. Therefore, the voltage of the first power source ELVDD may change to correspond to the load. In this case, it may not be possible to display images with uniform brightness. 
     SUMMARY OF THE INVENTION 
     The present invention provides a organic light emitting display capable of improving display quality and a method of driving the same. 
     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. 
     The present invention discloses an organic light emitting display including a scan driver for sequentially supplying scan signals to odd scan lines in an i th  (i is a natural number) frame and for sequentially supplying scan signals to even scan lines in an (i+1) th  frame, a data driver for supplying data signals corresponding to the scan signals supplied to the odd scan lines in the i th  frame and for supplying data signals corresponding to the scan signals supplied to the even scan lines in the (i+1) th  frame, and an image display unit including a plurality of pixels coupled with the scan lines and the data lines. The scan driver supplies emission control signals to odd emission control signal lines so that pixels coupled with the odd scan lines do not emit light in a period where the scan signals are supplied to the odd scan lines and supplies emission control signals to even emission control signal lines so that pixels coupled with the even scan lines do not emit light in a period where the scan signals are supplied to the even scan lines. 
     The present invention also discloses a method of driving an organic light emitting display including supplying scan signals to odd scan lines in an i th  (i is a natural number) frame, not emitting light from pixels coupled with the odd scan lines in a period where the scan signals are supplied to the odd scan lines, supplying scan signals to even scan lines in an (i+1) th  frame, and not emitting light from pixels coupled with the even scan lines in a period where the scan signals are supplied to the even scan lines. 
     The present invention also discloses a method of driving an organic light emitting display including emitting light from first pixels in a period where scan signals are supplied in a first frame, and emitting light from second pixels in a period where scan signals are supplied in a second frame. The first pixels and the second pixels are exclusive of each other. 
     It is to be understood that both the foregoing general description and the following detailed description 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 specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  shows a conventional organic light emitting display. 
         FIG. 2  shows an organic light emitting display according to a first exemplary embodiment of the present invention. 
         FIG.3  shows an organic light emitting display according to a second exemplary embodiment of the present invention. 
         FIG. 4  shows an exemplary pixel structure for the pixels of  FIG. 2 . 
         FIG. 5A  and  FIG. 5B  show waveforms for describing a method of driving an organic light emitting display according to an exemplary embodiment of the present invention. 
         FIG. 6A  and  FIG. 6B  show emission regions by the driving waveforms of  FIG. 5A  and  FIG. 5B . 
         FIG. 7A  and  FIG. 7B  show waveforms for describing a method of driving an organic light emitting display according to an exemplary embodiment of the present invention. 
         FIG. 8A  and  FIG. 8B  show emission regions by the driving waveforms of  FIG. 7A  and  FIG. 7B . 
         FIG. 9  shows an organic light emitting display according to a third exemplary embodiment of the present invention. 
         FIG. 10  shows another exemplary pixel structure for the pixel of  FIG. 2 . 
         FIG. 11  shows driving waveforms that may be supplied to the pixel of  FIG. 10 . 
     
    
    
     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. 
       FIG. 2  shows an organic light emitting display according to a first exemplary embodiment of the present invention. Referring to  FIG. 2 , the organic light emitting display includes an image display unit  130  having pixels  140  arranged at crossings between scan lines S 1  to Sn and data lines D 1  to Dm, a scan driver  110  for driving the scan lines S 1  to Sn, a data driver  120  for driving the data lines D 1  to Dm, and a timing controller  150  for controlling the scan and data drivers  110  and  120 . 
     The scan driver  10  generates scan signals in response to scan driving control signals SCS from the timing controller  150  and supplies the scan signals to the scan lines. Here, the scan driver  110  may sequentially supply the scan signals to the odd scan lines S 1 , S 3 , S 5 , . . . in an i th  (i is a natural number) frame, as shown in  FIG. 5A , and to the even scan lines S 2 , S 4 , S 6 , . . . in an (i+1) th  frame, as shown in  FIG. 5B . The scan driver  110  also supplies emission control signals EMI to odd emission control signal lines E 1 , E 3 , E 5 , . . . in the i th  frame and to even emission control signal lines E 2 , E 4 , E 6 , . . . in the (i+1) th  frame. 
     The data driver  120  generates the data signals in response to data driving control signals DSC from the timing controller  150  and supplies the data signals to the data lines D 1  to Dm. Here, the data driver  120  supplies the data signals for the pixels  140  of the odd horizontal lines in the i th  frame and supplies the data signals for the pixels  140  of the even horizontal lines in the (i+1) th  frame. Here, the pixels  140  of the odd horizontal lines are coupled with the odd scan lines S 1 , S 3 , S 5 , . . . and the odd emission control signal lines E 1 , E 3 , E 5 , . . . , and the pixels  140  of the even horizontal lines are coupled with the even scan lines S 2 , S 4 , S 6 , . . . and the even emission control signal lines E 2 , E 4 , E 6 ,. 
     The timing controller  150  generates the data driving control signals DCS and the scan driving control signals SCS in response to input synchronizing signals and supplies the data driving control signals DCS to the data driver  120  and the scan driving control signals SCS to the scan driver  110 . The timing controller  150  re-aligns input data Data to supply the data Data to the data driver  120 . 
     The image display unit  130  includes the plurality of pixels  140  coupled with the scan lines S and the data lines D. The pixels  140  may be commonly coupled with a second power source ELVSS. 
     The pixels  140  of the odd horizontal lines are coupled with first power source lines ELVDD 1 , and the pixels  140  of the even horizontal lines are coupled with second power source lines ELVDD 2 . Here, the first power source lines ELVDD 1  are coupled with a first power source ELVDDo, and the second power source lines ELVDD 2  are coupled with a third power source ELVDDe. The first power source ELVDDo and the third power source ELVDDe may output substantially the same voltage. When the pixels  140  of the odd and even horizontal lines are coupled with power sources ELVDDo and ELVDDe, respectively, since currents do not flow through the power sources of the horizontal lines to which the data signals are not applied, voltages of the power sources do not change. When the voltages of the corresponding power sources change when light is emitted after supplying data signals, since the voltages corresponding to the data signals stored in the pixels also change by the amount of change in the voltages of the power sources due to coupling of storage capacitors, it may be possible to prevent non-uniform images due to change in the power source voltages. 
     Also, the number of pixels  140  coupled with the first or third power source ELVDDo or ELVDDe may be half the number of pixels coupled with the power source ELVDD of  FIG. 1 . Hence, the load value that changes in accordance with whether the pixels  140  emit light may be minimized. Accordingly, it is possible to reduce the amount of change in the voltages of the first and third power sources ELVDDo and ELVDDe as compared with conventional art. 
     Alternatively, as  FIG. 3  shows, according to an exemplary embodiment of the present invention, the first and second power source lines ELVDD 1  and ELVDD 2  may each be coupled with two adjacent pixels  140 . In this case, it is possible to reduce the number of first and second power source lines ELVDD 1  and ELVDD 2 . 
       FIG. 4  is a circuit diagram showing an example of a pixel structure that may be used for the pixels of  FIG. 2  and  FIG. 3 . Here, various pixel structures including the emission control signal lines E may be used for the pixels  140 . 
     Referring to  FIG. 4 , a pixel  140  includes an organic light emitting diode (OLED) and a pixel circuit  142 . The pixel circuit  142  is coupled with a data line D, a scan line S, and an emission control signal line E to control the OLED. 
     The OLED&#39;s anode is coupled with the pixel circuit  142 , and its cathode is coupled with the second power source ELVSS. The OLED generates light corresponding to the current supplied from the pixel circuit  142 . 
     The pixel circuit  142  includes a first transistor M 1 , a second transistor M 2 , a third transistor M 3 , and a storage capacitor C. The first transistor M 1  is turned on when a scan signal is supplied to the first scan line S 1 . When the first transistor M 1  is turned on, the data signal supplied to the first data line D 1  is supplied to an electrode of the storage capacitor C, which charges a voltage corresponding to the data signal. 
     The second transistor M 2  supplies a current, corresponding to the voltage charged in the storage capacitor C, to the third transistor M 3 . The gate terminal of the third transistor M 3  is coupled with the first emission control signal line E 1 , and the first terminal of the third transistor M 3  is coupled with the second terminal of the second transistor M 2 . Here, when the first terminal of the third transistor M 3  is a source terminal, the second terminal of the third transistor M 3  is set as a drain terminal, and vice versa. The third transistor M 3  is turned on when the emission control signal EMI is not supplied to the first emission control signal line E 1 , and it is turned off when the emission control signal EMI is supplied to the first emission control signal line E 1 . When the third transistor M 3  is turned on, the current supplied from the second transistor M 2  is supplied to the OLED to generate light of predetermined brightness. 
       FIG. 5A  and  FIG. 5B  show driving waveforms that may be supplied to the pixels of  FIG. 4 . 
     Referring to  FIG. 5A , scan signals are sequentially supplied to the odd scan lines S 1 , S 3 , S 5 , . . . in the i th  frame. At this time, data signals corresponding to the scan signals supplied to the odd scan lines S 1 , S 3 , S 5 , . . . are supplied to the data lines D. Further, the emission control signals EMI are supplied to the odd emission control signal lines Eo. 
     Then, predetermined light is generated only by the pixels  140  of the even horizontal lines in the i th  frame. That is, the pixels  140  of the even horizontal lines generate light in response to the voltages charged in an (i−1) th  frame (emission period: on) in a period where the voltages corresponding to the data signals are charged in the pixels  140  of the odd horizontal lines (non-emission period: off). Hence, the image display unit  130  generates light in the i th  frame as shown in  FIG. 6A . 
     Referring to  FIG. 5B , scan signals are sequentially supplied to the even scan lines S 2 , S 4 , S 6 , . . . in the (i+1) th  frame. At this time, data signals corresponding to the scan signals supplied to the even scan lines S 2 , S 4 , S 6 , . . . are supplied to the data lines D. Further, the emission control signals EMI are supplied to the even emission control signal lines Ee. 
     Then, predetermined light is generated only by the pixels  140  of the odd horizontal lines in the (i+1) th  frame. That is, the pixels  140  of the odd horizontal lines generate light in response to the voltages charged in the i th  frame in a period where the voltages corresponding to the data signals are charged in the pixels  140  of the even horizontal lines. Hence, the display unit  130  generates light in the (i+1) th  frame as shown in  FIG. 6B . 
     That is, according to an exemplary embodiment of the present invention, the pixels of the even horizontal lines emit light in the i th  frame, and the pixels of the odd horizontal lines emit light in the (i+1) th  frame. Accordingly, the change in the load of the first and third power sources ELVDDo and ELVDDe may be decreased so that it is possible to more uniformly display images of desired brightness. According to an exemplary embodiment of the present invention, since the power sources coupled with the pixels  140  to supply predetermined currents to the OLEDs include the first power source ELVDDo and the third power source ELVDDe, it is possible to reduce the amount of change in voltages. 
     Alternatively, predetermined spare time may be generated after supplying the scan signals in the i th  and (i+1) th  frames. According to an exemplary embodiment of the present invention, all pixels may emit light in the spare time, which will be described in detail below with references to  FIG. 7A  and  FIG. 7B . 
     Referring to  FIG. 7A , scan signals are sequentially supplied to the odd scan lines S 1 , S 3 , S 5 , . . . in the i th  frame. While scanning the odd scan lines, the emission control signals EMI are supplied to the odd emission control signal lines Eo. However, once all odd scan lines have been scanned, the emission control signals EMI are no longer supplied to the odd emission control signal lines Eo. Accordingly, as shown in  FIG. 8A , predetermined light is generated by the pixels of the even horizontal lines while scanning the odd scan lines, and then predetermined light is generated by all pixels after all odd scan lines have been scanned. 
     Referring to  FIG. 7B , scan signals are sequentially supplied to the even scan lines S 2 , S 4 , S 6 , . . . in the (i+1) th  frame. While scanning the even scan lines, the emission control signals EMI are supplied to the even emission control signal lines Ee. However, once all even scan lines have been scanned, the emission control signals EMI are no longer supplied to the even emission control signal lines Ee. Accordingly, as shown in  FIG. 8B , predetermined light is generated by the pixels of the odd horizontal lines while scanning the even scan lines, and then predetermined light is generated by all pixels after all even scan lines have been scanned. 
       FIG. 9  shows an organic light emitting display according to another exemplary embodiment of the present invention. Referring to  FIG. 9 , the pixels  140  may be coupled with one first power source ELVDD. Specifically, the pixels  140  of the odd horizontal lines are coupled with the first power source lines ELVDD 1 , and the pixels  140  of the even horizontal lines are coupled with the second power source lines ELVDD 2 . The first and second power source lines ELVDD 1  and ELVDD 2  are coupled with the first power source ELVDD. 
     As shown in  FIG. 5A  and  FIG. 5B , as well as  FIG. 7A  and  FIG. 7B , the pixels  140  of the odd horizontal lines and the pixels  140  of the even horizontal lines are alternately driven. Hence, the change in the load applied to the first power source ELVDD may be minimized so that it is possible to improve display quality. 
     According to another exemplary embodiment of the present invention, all pixels  140  may be coupled with the first power source lines ELVDD 1 , which are coupled with the first power source ELVDD. Even when all pixels  140  are coupled with the first power source ELVDD, since the pixels  140  of the odd horizontal lines and the pixels  140  of the even horizontal lines are alternately driven, it may be possible to decrease the change in the load applied to the first power source ELVDD, thereby improving display quality. 
     As noted above, various pixel structures may be used for the pixels  140  of  FIG. 2  and  FIG. 3 . 
       FIG. 10  is a circuit diagram showing another example of a pixel structure that may be used for the pixels  140 . 
     Referring to  FIG. 10 , the pixels  140  include an OLED and a pixel circuit  142 . The pixel circuit  142  is coupled with a data line Dm, a scan line Sn, and an emission control signal line En to control the OLED. 
     The OLED&#39;s anode is coupled with the pixel circuit  142 , and its cathode is couples with a second power source ELVSS. The OLED generates light corresponding to the current supplied from the pixel circuit  142 . 
     The pixel circuit  142  includes first and sixth transistors M 1  and M 6  coupled between a first power source ELVDD and the data line Dm, a third transistor M 3  coupled with the OLED and the emission control signal line En, a second transistor M 2  coupled between the third transistor M 3  and a first node N 1 , a fifth transistor M 5  having a first terminal and gate terminal coupled with the first node N 1  and a second terminal coupled with the gate terminal of the second transistor M 2 , and a fourth transistor M 4  coupled between the gate terminal and the second terminal of the second transistor M 2 . 
     The first terminal of the first transistor M 1  is coupled with the data line Dm, and the second terminal of the first transistor M 1  is coupled with the first node N 1 . The gate terminal of the first transistor M 1  is coupled with the scan line Sn. The first transistor M 1  is turned on when the scan signal is supplied to the scan line Sn to supply an initialization signal and the data signal from the data line Dm to the first node N 1 . 
     The first terminal of the second transistor M 2  is coupled with the first node N 1 , and the gate terminal of the second transistor M 2  is coupled with the storage capacitor C. The second terminal of the second transistor M 2  is coupled with the first terminal of the third transistor M 3 . The second transistor M 2  supplies the current corresponding to the voltage charged in the storage capacitor C to the OLED. 
     The first terminal of the third transistor M 3  is coupled with the second terminal of the second transistor M 2 , and the gate terminal of the third transistor M 3  is coupled with the emission control signal line En. The second terminal of the third transistor M 3  is coupled with the OLED. The third transistor M 3  is turned on when the emission control signal EMI is not supplied to the emission control signal line En to transmit the current supplied from the second transistor M 2  to the OLED. 
     The second terminal of the fourth transistor M 4  is coupled with the gate terminal of the second transistor M 2 , and the first terminal of the fourth transistor M 4  is coupled with the second terminal of the second transistor M 2 . The gate terminal of the fourth transistor M 4  is coupled with the scan line Sn. The fourth transistor M 4  is turned on when the scan signal is supplied to the scan line Sn so that electric current flows through the second transistor M 2 . Therefore, the second transistor M 2  may operate as a diode. 
     The gate terminal and first terminal of the fifth transistor M 5  are coupled with the first node N 1 , and the second terminal of the fifth transistor M 5  is coupled with the gate terminal of the second transistor M 2 . That is, electric current flows through the fifth transistor M 5  so that the fifth transistor M 5  operates as a diode to supply an initializing voltage from the data line Dm to the gate terminal of the second transistor M 2 . 
     The second terminal of the sixth transistor M 6  is coupled with the first node N 1 , and the first terminal of the sixth transistor M 6  is coupled with the first power source ELVDD. The gate terminal of the sixth transistor M 6  is coupled with the emission control signal line En. The sixth transistor M 6  is turned on when the emission control signal EMI is not supplied to the emission control signal line En to electrically connect the first power source ELVDD and the first node N 1  to each other. 
     The operation of the pixel circuit  142  of  FIG. 10  will be described in detail with reference to  FIG. 11 . First, the scan signal is supplied to the scan line Sn, and an initializing voltage Vi is supplied to the data line Dm. At this time, the emission control signal EMI is supplied to the emission control signal line En so that the third and sixth transistors M 3  and M 6  are turned off. 
     When the scan signal is supplied to the nth scan line Sn, the first and fourth transistors M 1  and M 4  are turned on. When the first transistor M 1  is turned on, the initializing voltage Vi is supplied to the first node N 1  from the data line Dm. When the initializing voltage Vi is supplied to the first node N 1 , the fifth transistor M 5 , through which electric current flows to operate as a diode, is turned on so that the initializing voltage Vi is supplied to the gate terminal of the second transistor M 2 . 
     Here, the initializing voltage Vi is less than the voltage of the data signal. Specifically, as  FIG. 11  shows, the initializing voltage Vi is less than the lowest data signal that the data driver  120  supplies. Therefore, when the initializing voltage Vi is supplied to the first node N 1 , the voltage of the gate terminal of the second transistor M 2  is reduced to the initializing voltage Vi. Then, the second transistor M 2  may be turned on regardless of the voltage of the data signal applied to the first node N 1 . 
     After supplying the initializing voltage Vi to the gate terminal of the second transistor M 2 , a data signal DS, which corresponds to a predetermined gray scale, is supplied to the data line Dm. The data signal DS is supplied to the first node N 1  via the first transistor M 1 . At this time, since the gate terminal of the second transistor M 2  is initialized by the initializing voltage Vi, the second transistor M 2  is turned on. When the second transistor M 2  is turned on, the data signal DS applied to the first node N 1  is supplied to one side of the storage capacitor C via the second and fourth transistors M 2  and M 4 . At this time, the data signal DS, whose voltage is reduced by the voltage corresponding to the threshold voltage Vth of the second transistor M 2 , is supplied to one side of the storage capacitor C, and a voltage corresponding to the data signal DS, as reduced by the threshold voltage Vth of the second transistor M 2 , is charged in the storage capacitor C. 
     The emission control signal EMI (the odd or even emission control signal) supplied to the nth emission control signal line En is turned off so that the fourth and sixth transistors M 4  and M 6  may be turned on. When the fourth and sixth transistors M 4  and M 6  are turned on, the current corresponding to the voltage charged in the storage capacitor C is supplied to the OLED via the second transistor M 2  and the third transistor M 3  so that light corresponding to the data signal DS may be generated by the OLED. 
     As described above, with an organic light emitting display according to exemplary embodiments of the present invention, and a method of driving the same, some pixels emit light in the i th  (i is a natural number) frame and the other pixels emit light in the (i+1) th  frame. When the pixels alternately emit light in the ith and i+1th frames, it is possible to prevent images from being non-uniform in accordance with changes in the first power source and to minimize the amount of change in the load (the voltage) of the first power source ELVDD. Also, according to embodiments of the present invention, the power source for supplying predetermined currents to the OLEDs may be divided into two power sources. Hence, the number of pixels coupled with the divided power sources may be decreased so that it is possible to decrease the amount of change in voltage of the divided power sources, thereby improving display quality. 
     It will be apparent to those skilled in the art that various modifications and variation 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.