Abstract:
Systems for emitting light incorporating pixel structures of organic light-emitting diodes (OLEDs) are provided. A representative system comprises: a first sub-pixel area including a first OLED; and a second sub-pixel area including a second OLED and a second control circuit, wherein said second control circuit includes electronic components for controlling said first and second OLEDs.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to organic light-emitting diodes (OLEDs).  
         [0003]     2. Description of the Related Art  
         [0004]     An organic light-emitting diode (OLED) display is a flat display capable of emitting a light in which an organic compound is employed as a lighting material. An OLED display may provide advantages of compactness, slightness, a wide viewing angle, a high contrast, and a high response speed, among others.  
         [0005]     Referring to  FIG. 1 , a sub-pixel of a conventional OLED display is schematically depicted. The OLED display comprises a plurality of pixels, each comprising a plurality of sub-pixel areas  11 . A power line  12 , a data line  13  and a scan line  14  are shown. The sub-pixel area  11  includes a light-emitting area  15  and a non-light-emitting area  16 .  
         [0006]     The light-emitting area  15  comprises an OLED formed with an organic compound film through which electrical energy (provided by the power line) is transformed into light energy. he non-light-emitting area  16  has a control circuit (not shown) for controlling the OLED in the light-emitting area  15 .  
         [0007]     The control circuit typically comprises diodes, transistors, capacitors and other electronic components. Since the non-light-emitting area  16  does not emit any light, it is desired to have a smaller area thereof. The ratio of the area of the light-emitting area  15  to the area of the sub-pixel area  11  is called the “aperture ratio.” Thus, a higher aperture ratio corresponds to higher luminance.  
         [0008]     Referring to  FIG. 2A , a prior pixel structure of a typical full-color OLED display is schematically depicted. In the full-color OLED display, each pixel comprises a red sub-pixel area  17 , a green sub-pixel area  18  and a blue sub-pixel area  19 . In the red sub-pixel area  17 , a light-emitting area  20  has an R-OLED and a non-light-emitting area  21  has a control circuit for the R-OLED. In the green and blue sub-pixel areas  18 ,  19 , similar structures as that set forth in the red sub-pixel area  17  are provided.  
         [0009]     By virtue of the control circuits of the sub-pixel areas  17 ,  18 ,  19 , the luminance of the OLEDs may be controlled to achieve full color image display. Since light emission efficiency of the presently available red, green, and blue OLEDs is not identical and since the light-emitting areas corresponding thereto are generally the same, the OLED of poorer light emission efficiency has to be supplied with larger electric energy so as to have the same luminance as that of the other OLEDs.  
         [0010]     Referring to  FIG. 2B , another prior pixel structure of a typical full-color OLED display is schematically depicted. In this full-color OLED display, each pixel comprises a red sub-pixel area  22 , a green sub-pixel area  23 , a blue sub-pixel area  24  and a white sub-pixel area  25 . In the white sub-pixel area  25 , a light-emitting area  26  has a W-OLED and a non-light-emitting area  27  has a control circuit for the W-OLED.  
         [0011]     In  FIG. 2A , if a white image is desired to be displayed, illumination from red, green, and blue sub-pixels  17 ,  18 , and  19  should be combined. However, in  FIG. 2B , if a white image is desired to be displayed, only the white sub-pixel  25  is required to emit that is, the red, green, and blue sub-pixels  22 ,  23 , and  24  need not emit. Therefore, the RGBW OLED display of  FIG. 2B  typically requires less power consumption than the RGB OLED display of  FIG. 2A  when a white image is displayed. However, since the control circuits in the non-light-emitting areas must accommodate a fixed area, the RGBW OLED display of  FIG. 2B  suffers from having smaller light-emitting area, that is, a lower aperture ratio than the aperture ratio of the RGB OLED display of  FIG. 2A .  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention provides systems for emitting light. An embodiment of such a system comprises a pixel structure of an organic light-emitting diode (OLED). The pixel structure comprises: a first sub-pixel area including a first OLED; and a second sub-pixel area including a second OLED and a second control circuit, wherein said second control circuit includes electronic components for controlling said first and second OLEDs.  
         [0013]     In another embodiment of such a system, the pixel structure of an organic light-emitting diode (OLED) comprises a blue sub-pixel area including a blue OLED, and a white sub-pixel area including a white OLED and a second control circuit. The second control circuit includes electronic components for controlling the blue and white OLEDs. The blue sub-pixel area can include no electronic components. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The invention will become more fully understood from the detailed description given below for illustration only. The embodiments described are not limitative of the present invention. In the drawings:  
         [0015]      FIG. 1  illustrates schematically a prior sub-pixel structure of organic light-emitting diode (OLED) display;  
         [0016]      FIG. 2A  illustrates schematically a prior pixel structure of a full-color organic light-emitting diode (OLED) display;  
         [0017]      FIG. 2B  illustrates schematically another prior pixel structure of a full-color organic light-emitting diode (OLED) display;  
         [0018]      FIG. 3  illustrates schematically a pixel structure of a first of embodiment an OLED display;  
         [0019]      FIG. 4  illustrates schematically an embodiment of a control circuit for a pixel structure of an OLED display;  
         [0020]      FIG. 5  illustrates schematically a pixel structure of a second embodiment of an OLED display;  
         [0021]      FIG. 6  illustrates schematically the control circuit for pixel structure of the OLED display of  FIG. 5 ;  
         [0022]      FIG. 7  illustrates schematically a third embodiment of a pixel structure of OLED display.  
         [0023]      FIG. 8  illustrates schematically an embodiment of a display device; and  
         [0024]      FIG. 9  illustrates schematically an embodiment of an electronic device. 
     
    
     DETAILED DESCRIPTION  
       [0025]     Referring to  FIG. 3 , a first embodiment of a pixel structure of an organic light-emitting diode (OLED) display-is depicted schematically. The pixel structure  3  of the OLED display comprises: a first sub-pixel area  31  and a second sub-pixel area  32 . The first sub-pixel area  31  includes a first OLED  33 , but does not include a control circuit. The second sub-pixel area  32  includes a second OLED  34  and a control circuit  35 . The control circuit  35  includes a first control circuit portion  35   a , and a second control circuit portion  35   b . The first control circuit portion  35   a  includes electronic components for controlling the first OLED  33 , and the second control circuit portion  35   b  includes electronic components for controlling the second OLED  34 .  
         [0026]     In this embodiment, the light emission efficiency of the first OLED  33  can be lower than that of the second OLED  34 . For example, the first OLED  33  can be a blue OLED and the second OLED  34  can be a red, green or white OLED. Since the first control circuit portion  35   a  for controlling the first OLED  33  is disposed in the second sub-pixel area  32 , but not in the first sub-pixel area  31 , the area of the first OLED  33  may be increased as compared to that used in the prior art. This potentially enables brightness and lifetime of the first OLED  33  resident in the first sub-pixel area  31  to be improved.  
         [0027]     Referring to  FIG. 4 , a first embodiment of a control circuit  35  for the pixel  3  of the OLED display is depicted schematically. As mentioned above, both of the control circuit portions  35   a  and  35   b  are disposed in the second sub-pixel area  32 . The first control circuit portion  35   a  comprises a first switch transistor  41 , a first capacitor  43 , and a first driving transistor  45  that are used for controlling the first OLED  33 . The second control circuit portion  35   b  comprises a second switch transistor  42 , a second capacitor  44 , and a second driving transistor  46 , that which are used for controlling the second OLED  34 .  
         [0028]     When a signal Vscan 1  on a scan line is transmitted to the gate of the first switch transistor  41 , a signal Vdata 1  on a data line is taken and stored in the first capacitor  43  through the first switch transistor  41  and turns on the first driving transistor  45 . The first driving transistor  45  is connected to a power line having a voltage level of Vdd 1  and the first OLED  33 , and thereby provides a driving current to the first OLED  33 . The first OLED  33  is also connected to a voltage level Vss 1  and receives the driving current. Once the driving current is being received, electric energy provided by the power line is transformed into light energy. With regard to the transistors mentioned above, amorphous Si (a-Si) thin film transistors (TFTs), high temperature poly-silicon TFTs, low temperature poly-silicon TFTs and single crystal silicon TFTs may be used. The first switch transistor  41 , the first capacitor  43  and the first driving transistor  45  are disposed in the second sub-pixel area  32  to increase the area of the first OLED  33  as compared to that in the prior art. Therefore, brightness and lifetime of the OLED  33  in the first sub-pixel area  31  are can be improved.  
         [0029]     Referring to  FIG. 5 , a second embodiment of a pixel structure of an OLED display is depicted. The pixel structure  5  of the OLED display comprises a first sub-pixel area  51  and a second sub-pixel area  52 . The first sub-pixel area  51  comprises a first OLED  53  and a first control circuit  55  having electronic components for controlling the first OLED  53 . The second sub-pixel area  52  comprises a second OLED  54  and a second control circuit  56 . The second control circuit  56  includes at least one electronic component for controlling the first OLED  53  and at least one electronic component for controlling the second OLED  54 . For example, the second control circuit  56  disposed in the second sub-pixel area  52  comprises a first control circuit portion  56   a  for controlling the first OLED  53  and a second control circuit portion  56   b  for controlling the second OLED  54 . In this embodiment, the light emission efficiency of the first OLED  53  can be lower than that of the second OLED  54 . For example, the first OLED  53  can be a blue OLED and the second OLED  54  can be a red, green or white OLED. At least one of the electronic components for controlling the first OLED  53  is disposed in the second sub-pixel area  52 . Thus, the area of the first OLED  53  can be increased compared to the conventional OLED. Therefore, brightness and lifetime of the first OLED  53  can be improved.  
         [0030]     Referring to  FIG. 6 , the control circuits for the pixel  5  of the OLED display are depicted in greater detail. The first control circuit  55  comprises a first switch transistor  61 . The second control circuit  56  comprises a first control circuit portion  56   a  including a first capacitor  63  and a first driving transistor  65 , and a second control circuit portion  56   b  including a second switch transistor  62 , a second capacitor  64  and a second driving transistor  66 . The first control circuit  55  and the first control circuit portion  56   a  are used for controlling the first OLED  53 . The second control circuit portion  56   b  is used for controlling the second OLED  54 .  
         [0031]     Referring to  FIG. 7 , a third embodiment of a pixel structure of an OLED display is depicted. The pixel structure  7  of the OLED display comprises an R sub-pixel area  71 , a G sub-pixel area  72 , a B sub-pixel area  73 , and a W sub-pixel area  74 . The R sub-pixel area  71  includes an R-OLED  711  and a control circuit  712 . The G sub-pixel area  72  includes a G-OLED  721  and a control circuit  722 . The B sub-pixel area  73  includes a B-OLED  731  and a control circuit  732 . The W sub-pixel area  74  includes a W-OLED  741  and a control circuit  742 .  
         [0032]     According to this embodiment, the control circuit  712  includes all the electronic components, including a switch transistor, a driving transistor and a capacitor, for controlling the R-OLED  711 . The control circuit  722  includes all the electronic components, including a switch transistor, a driving transistor and a capacitor, for controlling the G-OLED  721 . However, the control circuit  732  only includes a portion of the electronic components for controlling the B-OLED  731 . The other electronic components for controlling the B-OLED  731  are disposed in the W sub-pixel area  74 . For example, as shown in  FIG. 7 , only one transistor for controlling the B-OLED  731  is disposed in the B sub-pixel area  73 , while a transistor and a capacitor for controlling the B-OLED  731  are disposed in the W sub-pixel area  74 . Thus, the W sub-pixel area  74  includes the control circuit  742  for controlling both the B-OLED  731  and the W-OLED  741 .  
         [0033]     Thus, the control circuit  732  disposed in the B sub-pixel area  73  accomodates the smallest area, and the control circuit  742  disposed in the W sub-pixel area  74  accomodates the largest area, among the four color sub-pixel areas. Generally, white OLED has the highest light emitting efficiency, and blue the lowest light emitting efficiency among the four color OLED materials. Therefore, by re-arrangment of the electronic components for controlling the B-OLED, e.g. disposing the electronic components for controlling the B-OLED in the white sub-pixel area, the B-OLED area is increased and the W-OLED area is decreased. Thus, the total light emitting efficiency of the B-OLED in the B sub-pixel area and the total light emitting efficiency of the W-OLED in the W sub-pixel area can be optimally adjusted.  
         [0034]      FIG. 8  shows an embodiment of a system implemented as a display device  80 . Display device  80  comprises a display panel  81  incorporating a pixel structure, such as the pixel structure  7  as shown in  FIG. 7 . The display panel  81  can be coupled to a controller  82 . The controller  82  can comprise source and gate driving circuits (not shown), controlling the display panel  81  for operation of the display device  80 .  
         [0035]      FIG. 9  is a schematic diagram illustrating an embodiment of a system implemented as an electronic device  90 . Electronic device  90  incorporates a display device, such as the display device  80  shown in  FIG. 8 . An input  91  is coupled to the controller  82  of the display device  80 . The input  91  can include a processor or the like to input image data to the controller  82  to render an image. The electronic device  90  may be a portable device such as a PDA, notebook computer, tablet computer, cellular phone, or a display monitor device, or a non-portable device such as a desktop computer, for example.  
         [0036]     In conclusion, some embodiment of the present invention dispose the electrical components for controlling B-OLEDs to W sub-pixel areas. Thus, the area of a B-OLED, which has low light emitting efficiency, can be increased. Therefore, the total light emitting efficiency of the B-OLED in the B sub-pixel area can be increased.  
         [0037]     While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts herein.