Abstract:
A driving apparatus for an organic electro-luminescence display device for reducing a deterioration of organic light-emitting diode device in the organic electro-luminescence display device is disclosed. In the driving apparatus, a data supplier supplies a data signal to an anode of an organic light-emitting diode device. A first voltage source generates a first voltage. A second voltage source generates a second voltage higher than said first voltage. A voltage stabilizer stabilizes said second voltage to be supplied to the cathode of the organic light-emitting diode device. First and second switching devices selectively apply said first and second voltages to a cathode of the organic light-emitting diode device.

Description:
This application claims the benefit of Korean Patent Application No. P2004-78087 filed in Korea on Sep. 30, 2004, which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an organic electro-luminescence display (ELD), and more particularly to a driving apparatus for an organic electro-luminescence display device that is adaptive for reducing a deterioration of organic light-emitting diode device in the organic electro-luminescence display device. 
   2. Description of the Related Art 
   Recently, there have been developed various flat panel display devices reduced in weight and bulk that is capable of eliminating disadvantages of a cathode ray tube (CRT). Such flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electro-luminescence (EL) display, etc. device. 
   In such flat panel display devices, the PDP has the most advantage for making a large dimension screen because its structure and manufacturing process are simple, but has a drawback in that it has low light-emission efficiency and large power consumption. The LCD has a difficulty in making a large dimension screen because it is fabricated by a semiconductor process, but has an expanded demand as it is mainly used for a display device of a notebook personal computer. However, the LCD has a drawback in that it has a difficulty in making a large dimension screen and it has large power consumption due to a backlight unit. Also, the LCD has characteristics of a large light loss and a narrow viewing angle due to optical devices such as a polarizing filter, a prism sheet, a diffuser and the like. 
   On the other hand, the EL display device is largely classified into an inorganic EL device and an organic EL device depending upon a material of a light-emitting layer, and is a self-luminous device. When compared with the above-mentioned display devices, the EL display device has advantages of a fast response speed, large light-emission efficiency, a large brightness and a large viewing angle. The organic EL display device can display a picture at approximately 10[V] and a high brightness of ten thousands of [cd/m 2 ]. 
     FIG. 1  is a schematic section view showing a structure of a conventional organic EL display device. 
   In the organic EL display device  1 , as shown in  FIG. 1 , an anode electrode  2  is formed from a transparent electrode pattern on a substrate  1 . On the substrate  1 , a hole carrier layer  3 , a light-emitting layer  4  formed from an organic material, an electron carrier layer  5  and a cathode  6  made from a metal are disposed. 
     FIG. 2  is a circuit diagram of a driving apparatus for the conventional organic EL display device, and  FIG. 3  is a circuit diagram for explaining an operation principle of an organic light-emitting diode device in the organic EL display device shown in  FIG. 2 . Further,  FIG. 4  is a driving waveform diagram of the organic EL display device shown in  FIG. 2 . 
   Referring to  FIG. 2  to  FIG. 4 , the driving apparatus for the conventional organic EL display device includes a data voltage source Vdata connected to an anode of an organic light-emitting diode device  20 , first and second scan voltage sources Vin 1  and Vin 2  connected to a cathode of the organic light-emitting diode device  20 . 
   The data voltage source Vdata supplies a positive voltage to data lines DL 1  to DLm of the organic EL display device while the first and second scan voltage sources Vin 1  and Vin 2  supply a negative voltage and a positive voltage to scan lines SL 1  to SLn of the organic EL display device. 
   Generally, the driving apparatus for the organic EL display device applies the same voltage to the data voltage source Vdata supplying a positive voltage to the data lines DL 1  to DLm and the second scan voltage source Vin 2  supplying a positive voltage to the scan lines SL 1  to SLn. A ground voltage GND is applied to the first scan voltage source Vin 1  supplying a negative voltage to the san lines SL 1  to SLn. 
   Further, the driving apparatus includes switching devices  21  connected between the anode of the organic light-emitting diode device  20  and the data voltage source Vdata, and first and second switching devices  22  and  23  connected between the cathode of the organic light-emitting diode device  20  and the first and second scan voltage sources Vin 1  and Vin 2 , respectively. 
   The first switching devices  22  are sequentially turned on in response to a control signal T 1  to thereby sequentially apply a scanning pulse SCAN having a negative voltage, that is, a forward voltage to the scan lines SL 1  to SLn. A data pulse DATA is synchronized with the scanning pulse SCAN applied to the scan lines SL 1  to SLn to be applied to the data lines DL 1  to DLm as a positive voltage. 
   More specifically, as the first switching device  22  connected to the first scan line SL 1  is turned on in response to the control signal T 1 , the scanning pulse SCAN is applied to the first scan line SL 1  as a negative voltage. At the same time, the data pulse DATA is applied to the data lines DL 1  to DLm as a positive voltage. When a negative voltage is applied to the first scan line SL 1  and a positive voltage is applied to the data lines DL 1  to DLm, the organic light-emitting diode device  20  at the first line is emitted by a forward bias. Thereafter, as the second switching device  23  connected to the first scan line SL 1  is turned on in response to a control signal T 1 , the scanning pulse SCAN is applied to the first scan line SL 1  as a positive voltage. While the control signal T 2  supplying a positive voltage to the first scan line SL 1  and the first control signal T 1  supplying a negative voltage to the second scan line SL 2  being applied, the organic EL display device sequentially emits a light to display a picture. 
     FIG. 5  is a detailed view of the A portion shown in  FIG. 4 . 
   Referring to  FIG. 5 , when the scanning pulse SCAN is switched from a negative voltage into a positive voltage, an overshoot phenomenon caused by the switching emerges from the scanning pulse SCAN. Such an overshoot phenomenon causes a deterioration of the organic light-emitting diode devices  20 . This appears more seriously as a level of the positive voltage applied to the cathode of the organic light-emitting diode device  20  shown in  FIG. 5  goes higher. 
   If the second scan voltage source Vin 2  is supplied with a lower voltage than the data voltage source Vdata so as to reduce the overshoot phenomenon, then a voltage of the data voltage source Vdata supplied to the anode of the organic light-emitting diode device  20  becomes larger than that of the second scan voltage source Vin 2  supplied to the cathode of the organic light-emitting diode  20 . In this case, there is raised a problem in that, as the organic light-emitting diode devices  20  at the selected lines as well as the remaining organic light-emitting diode devices  20  of the organic EL display device are forwardly biased, a light-emission is made while a current flowing in all the organic light-emitting diode devices  20 . 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a driving apparatus for an organic electro-luminescence display device that is adaptive for reducing a deterioration of organic light-emitting diode device in the organic electro-luminescence display device. 
   In order to achieve these and other objects of the invention, a driving apparatus for an organic electro-luminescence display device according to an embodiment of the present invention includes an organic light-emitting diode device; data supplying means for supplying a data signal to an anode of the organic light-emitting diode device; a first voltage source for generating a first voltage; a second voltage source for generating a second voltage higher than said first voltage; voltage stabilizing means for stabilizing said second voltage to be supplied to the cathode of the organic light-emitting diode device; and first and second switching devices for selectively applying said first and second voltages to a cathode of the organic light-emitting diode device. 
   In the driving apparatus, said first voltage is a ground voltage. 
   In the driving apparatus, the voltage stabilizing means is a Zener diode device, and the Zener diode device is connected, in series, between the second voltage source and the cathode of the organic light-emitting diode device. 
   Herein, a breakdown voltage of the Zener diode device is lower than a threshold voltage of the organic light-emitting diode device. 
   A voltage applied to the cathode of the organic light-emitting device is a difference voltage between a voltage supplied from the second voltage source and the breakdown voltage of the Zener diode device. 
   Alternatively, the voltage stabilizing means is a capacitor, and the capacitor is connected, in parallel, between the second voltage source and the cathode of the organic light-emitting diode device. 
   Herein, a voltage applied to the cathode of the organic light-emitting diode device has the same level as a voltage applied to the anode of the organic light-emitting diode device. 
   Otherwise, the voltage stabilizing means includes a Zener diode device and a capacitor; and the Zener diode device is connected, in series, between the second voltage source and the cathode of the organic light-emitting diode device, and the capacitor is connected, in parallel, between the Zener diode device and the cathode of the organic light-emitting diode device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic section view showing a structure of a conventional organic electro-luminescence display device; 
       FIG. 2  is a circuit diagram of a driving apparatus for the conventional organic electro-luminescence display device; 
       FIG. 3  is a circuit diagram for explaining an operation principle of an organic light-emitting diode device in the organic electro-luminescence display device shown in  FIG. 2 ; 
       FIG. 4  is a driving waveform diagram of the organic electro-luminescence display device shown in  FIG. 2 ; 
       FIG. 5  is a detailed view of the A portion shown in  FIG. 4 ; 
       FIG. 6  is a circuit diagram of a driving apparatus for an organic electro-luminescence display device according to a first embodiment of the present invention; 
       FIG. 7  is a circuit diagram for explaining an operation principle of an organic light-emitting diode device in the organic electro-luminescence display device shown in  FIG. 6 ; 
       FIG. 8  is a driving waveform diagram of the organic electro-luminescence display device shown in  FIG. 6 ; 
       FIG. 9  is a detailed view of the B portion shown in  FIG. 8 ; 
       FIG. 10  is a circuit diagram of a driving apparatus for an organic electro-luminescence display device according to a second embodiment of the present invention; 
       FIG. 11  is a circuit diagram for explaining an operation principle of an organic light-emitting diode device in the organic electro-luminescence display device shown in  FIG. 10 ; 
       FIG. 12  is a driving waveform diagram of the organic electro-luminescence display device shown in  FIG. 10 ; 
       FIG. 13  is a detailed view of the C portion shown in  FIG. 12 ; 
       FIG. 14  is a circuit diagram of a driving apparatus for an organic electro-luminescence display device according to a third embodiment of the present invention; and 
       FIG. 15  is a circuit diagram for explaining an operation principle of an organic light-emitting diode device in the organic electro-luminescence display device shown in  FIG. 14 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
   Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to  FIGS. 6 to 14 . 
     FIG. 6  is a circuit diagram of a driving apparatus for an organic electro-luminescence display device according to a first embodiment of the present invention. 
   Referring to  FIG. 6 , the driving apparatus for the organic EL display device according to the first embodiment of the present invention includes a data voltage source Vdata connected to an anode of an organic light-emitting diode device  40 , first and second scan voltage sources Vin 1  and Vin 2  connected to a cathode of the organic light-emitting diode device  40 . 
   The data voltage source Vdata supplies a positive voltage to data lines DL 1  to DLm connected to the anode of the organic light-emitting diode device while the first and second scan voltage sources Vin 1  and Vin 2  supply a negative voltage and a positive voltage to scan lines SL 1  to SLn connected to the cathode of the organic light-emitting diode device  40 . 
   Further, the driving apparatus includes data switching devices  41  connected between the anode of the organic light-emitting diode device  40  and the data voltage source Vdata, first and second switching devices  42  and  43  connected between the cathode of the organic light-emitting diode device  40  and the first and second scan voltage sources Vin 1  and Vin 2 , respectively, and a capacitor C connected, in parallel, between the second scan voltage source Vin 2  and the second switching device  43 . 
   The capacitor C charges a voltage applied from the anode of the organic light-emitting diode device  40  to the cathode thereof at a fast time when a scanning pulse SCAN applied to the scan lines SL 1  to SLn is switched from a negative polarity into a positive polarity, thereby stabilizing a voltage of the output terminal to reduce an overshoot phenomenon. 
     FIG. 7  is a circuit diagram for explaining an operation principle of an organic light-emitting diode device in the organic electro-luminescence display device shown in  FIG. 6 , and  FIG. 8  is a driving waveform diagram of the organic electro-luminescence display device shown in  FIG. 6 . Further,  FIG. 9  is a detailed view of the B portion shown in  FIG. 8 . 
   Referring to  FIG. 7  to  FIG. 9 , the first switching devices  42  are sequentially turned on in response to a control signal T 1  to thereby sequentially apply a scanning pulse SCAN having a negative voltage, that is, a forward voltage to the scan lines SL 1  to SLn. A data pulse DATA is synchronized with the scanning pulse SCAN applied to the scan lines SL 1  to SLn to be applied to the data lines DL 1  to DLm as a positive voltage. 
   More specifically, as the first switching device  42  connected to the first scan line SL 1  is turned on in response to the control signal T 1 , the scanning pulse SCAN is applied to the first scan line SL 1  as a negative voltage. The data pulse DATA is synchronized with the scanning pulse SCAN to be applied to the data lines DL 1  to DLm as a positive voltage. When a negative voltage is applied to the first scan line SL 1  and a positive voltage is applied to the data lines DL 1  to DLm′, the organic light-emitting diode device  40  at the first line flows a current to make a light emission by a forward bias. Thereafter, as the second switching device  43  connected to the first scan line SL 1  is turned on in response to a control signal T 2 , the scanning pulse SCAN is applied to the first scan line SL 1  as a positive voltage. While the control signal T 2  supplying a positive voltage to the first scan line SL 1  and the first control signal T 1  supplying a negative voltage to the second scan line SL 2  being applied, the organic EL display device sequentially emits a light to display a picture. 
   When the scanning pulse SCAN applied to the scan lines SL 1  to SLn is switched from a negative voltage into a positive voltage, an overshoot caused by the switching emerges from the scanning pulse SCAN. 
   Such an overshoot appearing at the scan lines SL 1  to SLn can be reduced by the capacitor C connected, in parallel, between the second scan voltage source Vin 2  and the second switching device  43 . 
   The capacitor C charges a voltage applied from the anode of the organic light-emitting diode device  40  to the cathode thereof at a fast time when a scanning pulse SCAN applied to the scan lines SL 1  to SLn is switched from a negative polarity into a positive polarity, thereby stabilizing a voltage of the output terminal to reduce an overshoot phenomenon. 
     FIG. 10  is a circuit diagram of a driving apparatus for an organic electro-luminescence display device according to a second embodiment of the present invention. 
   The driving apparatus for the organic EL display device according to the second embodiment of the present invention as shown in  FIG. 10  has the same elements as that according to the first embodiment of the present invention shown in  FIG. 6  except that the capacitor C connected, in parallel, between the second voltage source Vin 2  and the second switching device  43  is replaced by a Zener diode device  45  connected, in series, between the second voltage source Vin 2  and the second switching device  43 . 
   The Zener diode device  45  plays a role to limit a voltage of a second scan voltage source Vin 2  applied to a cathode of an organic light-emitting device  40  into a constant voltage, thereby reducing an overshoot phenomenon. 
     FIG. 11  is a circuit diagram for explaining an operation principle of an organic light-emitting diode device in the organic electro-luminescence display device shown in  FIG. 10 , and  FIG. 12  is a driving waveform diagram of the organic electro-luminescence display device shown in  FIG. 10 . 
   Referring to  FIG. 11  and  FIG. 12 , first switching devices  42  are sequentially turned on in response to a control signal T 1  to thereby sequentially apply a scanning pulse SCAN having a negative voltage, that is, a forward voltage to scan lines SL 1  to SLn. A data pulse DATA is synchronized with the scanning pulse SCAN applied to the scan lines SL 1  to SLn to be applied to the data lines DL 1  to DLm as a positive voltage. 
   When the scanning pulse SCAN applied to the scan lines SL 1  to SLn is switched from a negative voltage into a positive voltage, an overshoot caused by the switching emerges from the scanning pulse SCAN. 
   Such an overshoot appearing at the scan lines SL 1  to SLn can be reduced by the Zener diode device  45  connected, in series, between the second scan voltage source Vin 2  and the second switching device  43 . 
   The Zener diode device  45  acts as a constant voltage source for limiting a voltage of the second scan voltage source Vin 2  applied to the cathode of the organic light-emitting diode device  40  into a constant voltage. 
   In other words, when the scanning pulse SCAN is switched from a negative voltage into a positive voltage, a positive voltage Vhigh applied to the scan lines SL 1  to SLn results in a difference between a positive voltage supplied from the second voltage source Vin 2  and a breakdown voltage Vz of the Zener diode device  45 . 
   This can be expressed by the following equation:
 
 V high= Vin 2 −|Vz|   (1)
 
   Accordingly, when the scanning pulse SCAN is switched from a negative voltage into a positive voltage, the positive voltage Vhigh applied to the cathode of the organic light-emitting diode device  40  has a lower voltage than the prior art, thereby reducing an overshoot phenomenon. At this time, the breakdown voltage Vz of the Zener diode device  45  must be smaller than a threshold voltage Vth of the organic light-emitting diode device  40 . 
   If the breakdown voltage Vz of the Zener diode  45  is larger than or equal to the threshold voltage Vth of the organic light-emitting diode device  40 , then a difference between a voltage from the data voltage source Vdata connected to the anode of the organic light-emitting diode device  40  and a positive voltage Vhigh applied to the cathode of the organic light-emitting diode device  40  becomes larger then the threshold voltage Vth of the organic light-emitting diode device  40  when the second switching device  43  is turned on. Thus, a forward bias is applied to the organic light-emitting diode device  40  and a current flow in the organic light-emitting diode device by a voltage applied to the organic light emitting diode device  40 , thereby allowing the organic light-emitting diode device  40  to make a light emission. 
   For this reason, the breakdown of the Zener diode device  45  must be lower than the threshold voltage Vth of the organic light-emitting diode device  40 . 
   This can be expressed by the following equation:
 
|Vz|&lt;Vth  (2)
 
     FIG. 13  is a detailed view of the C area shown in  FIG. 12 . 
   Referring to  FIG. 13 , a positive voltage applied to the scan lines SL 1  to SLn becomes a difference between the voltage supplied from the second scan voltage source Vin 2  and the breakdown voltage Vz of the Zener diode  45 , which lowers a magnitude of the positive voltage applied to the cathode of the organic light-emitting diode device  40 , thereby reducing an overshoot phenomenon. 
     FIG. 14  is a circuit diagram of a driving apparatus for an organic electro-luminescence display device according to a third embodiment of the present invention, and  FIG. 15  is a circuit diagram for explaining an operation principle of an organic light-emitting diode device in the organic electro-luminescence display device shown in  FIG. 14 . 
   The driving apparatus for the organic EL display device according to the third embodiment of the present invention as shown in  FIG. 14  has the same elements as that according to the first embodiment of the present invention shown in  FIG. 6  except that it includes a Zener diode device  45  connected, in series, between the second voltage source Vin 2  and the second switching device  43 , and a capacitor C connected, in parallel, between the second scan voltage source Vin 2  and the Zener diode device  45 . 
   The Zener diode device  45  plays a role to limit a voltage of a second scan voltage source Vin 2  applied to a cathode of an organic light-emitting device  40  into a constant voltage, thereby reducing an overshoot phenomenon. 
   Further, the capacitor C charges a voltage applied from the anode of the organic light-emitting diode device  40  to the cathode thereof at a fast time when a scanning pulse SCAN applied to the scan lines SL 1  to SLn is switched from a negative polarity into a positive polarity, thereby stabilizing a voltage of the output terminal to reduce an overshoot phenomenon. 
   Referring to  FIG. 15 , when the scanning pulse SCAN applied to the scan lines SL 1  to SLn is switched from a negative voltage into a positive voltage, an overshoot caused by the switching emerges from the scanning pulse SCAN. 
   Such an overshoot appearing at the scan lines SL 1  to SLn can be reduced by the Zener diode device  45  connected, in series, between the second scan voltage source Vin 2  and the second switching device  43 . Also, the overshoot can be more reduced by the capacitor C connected, in parallel, between the second voltage source Vin 2  and the Zener diode device  45 . 
   The Zener diode device  45  acts as a constant voltage source for limiting a voltage of the second scan voltage source Vin 2  applied to the cathode of the organic light-emitting diode device  40  into a constant voltage. 
   In other words, when the scanning pulse SCAN is switched from a negative voltage into a positive voltage, a positive voltage Vhigh applied to the scan lines SL 1  to SLn results in a difference between a positive voltage supplied from the second voltage source Vin 2  and a breakdown voltage Vz of the Zener diode device  45 . 
   This can be expressed by the following equation:
 
 V high= Vin 2 −|Vz|   (3)
 
   Accordingly, when the scanning pulse SCAN is switched from a negative voltage into a positive voltage, the positive voltage Vhigh applied to the cathode of the organic light-emitting diode device  40  has a lower voltage than the prior art, thereby reducing an overshoot phenomenon. 
   As mentioned above, the breakdown voltage Vz of the Zener diode device  45  must be lower than a threshold voltage Vth of the organic light-emitting diode device  40 . 
   This can be expressed by the following equation:
 
 |Vz|&lt;Vth   (4)
 
   Further, the capacitor C charges a voltage applied from the anode of the organic light-emitting diode device  40  at a fast time when a scanning pulse SCAN applied to the scan lines SL 1  to SLn is switched from a negative polarity into a positive polarity, thereby stabilizing a voltage of the output terminal to reduce an overshoot phenomenon. 
   As described above, the driving apparatus for the organic EL display device according to the embodiments of the present invention includes any one of the Zener diode device connected, in series, between the second scan voltage source and the second switching device and the capacitor connected, in parallel, between the second scan voltage source and the Zener diode device. 
   Accordingly, the capacitor charges a voltage applied from the anode of the organic light-emitting diode device to the cathode thereof at a fast time, thereby stabilizing a voltage of the output terminal to reduce an overshoot phenomenon. Furthermore, the Zener diode device allows a positive voltage supplied to the cathode of the organic light-emitting diode device to have a lower voltage than the prior art when the scanning pulse is switched from a negative voltage into a positive voltage, thereby reducing an overshoot phenomenon. As a result, it becomes possible to reduce a deterioration of organic light-emitting diode device. 
   Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.