Patent Publication Number: US-8525756-B2

Title: Organic light emitting display and driving method thereof to characterize pixel parameter values

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2007-0035011, filed on Apr. 10, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The field relates to an organic light emitting display and a driving method thereof, and more particularly to an organic light emitting display capable of displaying an image with uniform luminance regardless of deterioration of an organic light emitting diode and threshold voltage or mobility of a drive transistor, and a driving method thereof. 
     2. Discussion of Related Technology 
     In recent years, a variety of flat panel displays of reduced weight and volume, when compared to a cathode ray tube have been developed and commercialized. A flat panel display may take the form of a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting display (OLED), etc. 
     Among the flat panel displays, the organic light emitting display uses an organic light emitting diode to display an image, the organic light emitting diode generating light by means of the recombination of electrons and holes. Such an organic light emitting display has advantages in that it has a rapid response time and is also driven with low power consumption. 
       FIG. 1  is a circuit view showing a pixel of a conventional organic light emitting display. 
     Referring to  FIG. 1 , the pixel  4  includes an organic light emitting diode (OLED), data lines (Dm), and a pixel circuit  2  connected to the scan lines (Sn) to control the organic light emitting diode (OLED). 
     An anode electrode of the organic light emitting diode (OLED) is connected to the pixel circuit  2 , and a cathode electrode is connected to the second power source (ELVSS). Such an organic light emitting diode (OLED) generates a predetermined luminance to correspond to an electric current supplied from the pixel circuit  2 . 
     The pixel circuit  2  controls an electric current capacity supplied to the organic light emitting diode (OLED) to correspond to a data signal supplied to the data lines (Dm) when a scan signal is supplied to the scan lines (Sn). For this purpose, the pixel circuit  2  includes a second transistor (M 2 ) connected between the first power source (ELVDD) and the organic light emitting diode (OLED); a first transistor (M 1 ) connected between the second transistor (M 2 ) and the data lines (Dm) and the scan lines (Sn); and a storage capacitor (Cst) connected between a gate electrode and a first electrode of the second transistor (M 2 ). 
     A gate electrode of the first transistor (M 1 ) is connected to the scan lines (Sn), and a first electrode is connected to the data lines (Dm). A second electrode of the first transistor (M 1 ) is connected to one side terminal of the storage capacitor (Cst). Here, the first electrode is either a source electrode or a drain electrode, and the second electrode is the electrode which is different from the first electrode. For example, if the first electrode is a source electrode, the second electrode is a drain electrode. When a scan signal is supplied from the scan lines (Sn), the first transistor (M 1 ) connected to the scan lines (Sn) and the data lines (Dm) is turned on to supply the data signal from the data lines (Dm) to the storage capacitor (Cst). As a result, the storage capacitor (Cst) charges a voltage corresponding to the data signal. 
     The gate electrode of the second transistor (M 2 ) is connected to one terminal of the storage capacitor (Cst), and the first electrode is connected to the other terminal of the storage capacitor (Cst) and to the first power source (ELVDD). The second electrode of the second transistor (M 2 ) is connected to the anode electrode of the organic light emitting diode (OLED). The second transistor (M 2 ) controls the electric current so as to correspond to the voltage stored in the storage capacitor (Cst), the electric current flowing from the first power source (ELVDD) to the second power source (ELVSS) via the organic light emitting diode (OLED). In response, the organic light emitting diode (OLED) generates light according to the amount of electric current supplied from the second transistor (M 2 ). 
     However, an organic light emitting display having a pixel such as that of  FIG. 1  has a disadvantage that it is difficult to display an image having a desired luminance due to the changes in current caused by the deterioration of the organic light emitting diode (OLED). The organic light emitting diode deteriorates with the passage of time, and therefore, the organic light emitting diode generates light of reduced luminance over time despite receiving the same level of a data signal. Also, the conventional organic light emitting display has a problem that it does not display an image having a uniform luminance due to non-uniformity in the threshold voltage and/or mobility of the drive transistors (M 2 ) in each of the pixels  4 . 
     SUMMARY OF CERTAIN INVENTIVE ASPECTS 
     One aspect is an organic light emitting display, including a plurality of pixels, each arranged near intersections of data lines, scan lines, power lines, and light emitting control lines. The display also includes a scan driver configured to supply a scan signal to the scan lines and to supply a light emitting control signal to the light emitting control lines, a control line driver configured to supply a control signal to a plurality of control lines, a data driver configured to generate a data signal for the data lines, and a sensing unit configured to sense information about at least one of an organic light emitting diode, a voltage of a drive transistor, and mobility of the drive transistor for one or more of the pixels. The display also includes a switching unit configured to connect one of the sensing unit and the first power source with the power lines and to connect one of the sensing unit and the data driver with the data lines, a control block configured to store the sensed information, and a timing controller configured to generate the second data based on the sensed information and a first data received from another circuit. 
     Another aspect is a method of driving an organic light emitting display. The method includes generating a first voltage while supplying an electric current to a drive transistor and an organic light emitting diode, converting the first voltage into a first digital value and storing the first digital value in a memory, generating a second voltage while supplying an electric current to the organic light emitting diode via the data lines, converting the second voltage into a second digital value and storing the second digital value in the memory, and converting a first data supplied from another circuit to a second data based on the first digital value and the second digital value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of certain inventive embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a circuit view showing pixels of a conventional organic light emitting display. 
         FIG. 2  is a block diagram showing an organic light emitting display according to one embodiment. 
         FIG. 3  is a circuit diagram showing one embodiment of the pixels of  FIG. 2 . 
         FIG. 4  is a block diagram showing a switching unit, a sensing unit and a control block shown in  FIG. 2 . 
         FIG. 5  is a block diagram showing an embodiment of the data driver shown in  FIG. 2 . 
         FIG. 6   a  and  FIG. 6   b  are waveform views showing a method for driving an organic light emitting display according to one embodiment. 
         FIG. 7  is a block diagram showing a configuration where a data driver, a timing controller, a control block, a sensing unit, a switching unit and pixels are connected to each other. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS 
     Hereinafter, certain embodiments will be described with reference to the accompanying drawings. Here, when one element is connected to another element, one element may be not only directly connected to another element but also indirectly connected to another element via a third element. Further, irrelative elements may be omitted for clarity. Also, like reference numerals generally refer to like elements throughout. 
       FIG. 2  is a diagram showing an organic light emitting display according to one embodiment. 
     Referring to  FIG. 2 , an organic light emitting display includes pixels  140  connected to scan lines (S 1  to Sn), light emitting control lines (E 1  to En) and data lines (D 1  to Dm); a scan driver  110  for driving the scan lines (S 1  to Sn) and the light emitting control lines (E 1  to En); a control line driver  160  for driving control lines (CL 1  to CLn); a data driver  120  for driving the data lines (D 1  to Dm); and a timing controller  150  for controlling the scan driver  110 , the data driver  120 , and the control line driver  160 . 
     Also, the organic light emitting display according to one embodiment of the present invention further includes a sensing unit  180  for extracting the information about the deterioration of the organic light emitting diode and the threshold voltage/mobility of the drive transistor, the organic light emitting diode and the drive transistor being included in each of the pixels  140 ; a switching unit  170  for selectively connecting the sensing unit  180  and the data driver  120  to the data lines (D 1  to Dm) and selectively connecting the sensing unit  180  and the first power source (ELVDD) to the power lines (V 1  to Vm); and a control block  190  for storing the information sensed in the sensing unit  180 . 
     The pixel unit  130  includes pixels  140  arranged near intersecting points of the scan lines (S 1  to Sn), the light emitting control lines (E 1  to En), the power lines (V 1  to Vm), and the data lines (D 1  to Dm). The pixels  140  charge a voltage according to the data signal and supply an electric current corresponding to the charged voltage to the organic light emitting diode, thereby generating light having a desired luminance. 
     The scan driver  110  supplies a scan signal to the scan lines (S 1  to Sn) according to the control of the timing controller  150 . Also, the scan driver  110  supplies a light emitting control signal to the light emitting control lines (E 1  to En) according to the timing controller  150 . 
     The control line driver  160  supplies a control signal to the control lines (CL 1  to CLn) according to the control of the timing controller  150 . 
     The data driver  120  supplies a data signal to the data lines (D 1  to Dm) according to the control of the timing controller  150 . 
     The switching unit  170  selectively connects the sensing unit  180  and the first power source (ELVDD) to the power lines (V 1  to Vm). When the sensing unit  180  is connected to the power lines (V 1  to Vm) by the switching unit  170 , information about deterioration of the organic light emitting diode and threshold voltage of the drive transistor are extracted. When the power lines (V 1  to Vm) are connected to the first power source (ELVDD) by the switching unit  170 , light is generated in the pixel  140 , wherein the light corresponds to the data signal. 
     Also, the switching unit  170  selectively connects the sensing unit  180  and the data driver  120  to the data lines (D 1  to Dm). When the sensing unit  180  is connected to the data lines (D 1  to Dm) by the switching unit  170 , information about deterioration of the organic light emitting diode in the pixel  140  is extracted. When the data lines (D 1  to Dm) are connected to the data driver  120  by the switching unit  170 , a data signal is supplied to the data lines (D 1  to Dm). For this purpose, the switching unit  170  includes at least two switching elements installed in each of the channels. 
     The sensing unit  180  extracts the information about deterioration of the organic light emitting diode and threshold voltage/mobility of the drive transistor from the pixels  140  via the power lines (V 1  to Vm). Furthermore, the sensing unit  180  extracts the information about deterioration of the organic light emitting diode from the pixels  140  via the data lines (D 1  to Dm). For this purpose, the sensing unit  180  includes an electric current source unit in each of channels. 
     The control block  190  stores the information about deterioration and the threshold voltage and/or mobility of the drive transistor supplied from the sensing unit  180 . For this purpose, the control block  190  includes a memory; and a controller for transmitting the information stored in the memory to the timing controller  150 . 
     The timing controller  150  controls the data driver  120 , the scan driver  110  and the control line driver  160 . Also, the timing controller  150  converts a bit value of a first data (Data 1 ) received from another circuit according to the information supplied from the control block  190  to generate a second data (Data 2 ). Here, the first data (Data 1 ) is set to i bits (i is an integer), and the second data (Data 2 ) is set to j bits (j is an integer greater than i). 
     The second data (Data 2 ) stored in the timing controller  150  is supplied to the data driver  120 . The data driver  120  uses the second data (Data 2 ) to generate a data signal and supplies the generated data signal to the pixels  140 . 
       FIG. 3  is a diagram showing one embodiment of the pixels shown in  FIG. 2 . In  FIG. 3 , the pixel shown is connected to an m th  data line (Dm) and an n th  scan line (Sn). 
     Referring to  FIG. 3 , the pixel  140  includes an organic light emitting diode (OLED) and a pixel circuit  142  for supplying an electric current to the organic light emitting diode (OLED). 
     The anode electrode of the organic light emitting diode (OLED) is connected to the pixel circuit  142 , and the cathode electrode is connected to the second power source (ELVSS). Such an organic light emitting diode (OLED) generates light having a predetermined luminance to correspond to the electric current supplied from the pixel circuit  142 . 
     The pixel circuit  142  controls the capacity of an electric current flowing in the organic light emitting diode (OLED) to correspond to the voltage stored in the storage capacitor (Cst). The pixel circuit  142  supplies the information about threshold voltage and/or mobility of the drive transistor and deterioration of the organic light emitting diode (OLED) to the sensing unit  180  when the third transistor (M 3 ) and the fourth transistor (M 4 ) are turned on. Further, the pixel circuit  142  supplies the information about deterioration of the organic light emitting diode (OLED) to the sensing unit  180  when the first transistor (M 1 ) and the fourth transistor (M 4 ) are turned on. For this purpose, the pixel circuit  142  includes four transistors (M 1  to M 4 ) and a storage capacitor (Cst). 
     gate electrode of the first transistor (M 1 ) is connected to the scan line (Sn), and a first electrode is connected to the data line (Dm). A second electrode of the first transistor (M 1 ) is connected to a first terminal of the storage capacitor (Cst). The first transistor (M 1 ) is turned on when a scan signal is supplied to the scan line (Sn). 
     The gate electrode of the second transistor (M 2 ) is connected to a first terminal of the storage capacitor (Cst), and a first electrode is connected to a second terminal and to power line (Vm) of the storage capacitor (Cst). The second transistor (M 2 ) supplies electric current to the organic light emitting diode (OLED), the electric current corresponding to a voltage value stored in the storage capacitor (Cst), when the power line (Vm) is connected to the first power source (ELVDD). Accordingly, the organic light emitting diode (OLED) generates light corresponding to an electric current supplied from the second transistor (M 2 ). 
     The gate electrode of the third transistor (M 3 ) is connected to the light emitting control line (En), and a first electrode is connected to a second electrode of the second transistor (M 2 ). A second electrode of the third transistor (M 3 ) is connected to the organic light emitting diode (OLED). The third transistor (M 3 ) is turned off when a light emitting control signal is supplied to the light emitting control line (En), and turned on when the light emitting control signal is not supplied to the light emitting control line (En). 
     The gate electrode of the fourth transistor (M 4 ) is connected to the control line (CLn), and a first electrode is connected to the second electrode of the third transistor (M 3 ). Also, a second electrode of the fourth transistor (M 4 ) is connected to the gate electrode of the second transistor (M 2 ). The fourth transistor (M 4 ) is turned on when the first control signal is supplied. 
     The storage capacitor (Cst) is connected between the gate electrode and the first electrode of the second transistor (M 2 ). The storage capacitor (Cst) is charged a voltage corresponding to the data signal. 
       FIG. 4  is a block diagram showing a switching unit, a sensing unit and a control block shown in  FIG. 2 . In  FIG. 4 , the switching unit, the sensing unit, and the control block are connected to an m th  power line (Vm) and an m th  data line (Dm). 
     Referring to  FIG. 4 , each of the channels of the switching unit  170  includes four switching elements (SW 1  to SW 4 ). Each of the channels of the sensing unit  180  includes an electric current source unit  181  and an analog-digital converter (ADC)  182 . One ADC may be shared by one or all of a plurality of channels. The control block  190  includes a memory  191  and a controller  192 . 
     The first switching element (SW 1 ) is between the power line (Vm) and the first power source line (ELVDD). The first switching element (SW 1 ) is maintained in a turned-on state during a period when the light having a luminance corresponding to the data signal is generated in the pixel  140 . 
     The second switching element (SW 2 ) is between the electric current source unit  181  and the power line (Vm). The second switching element (SW 2 ) is turned on when the information about the deterioration of the organic light emitting diode (OLED) and the threshold voltage and/or mobility of the second transistor (M 2 ) are sensed. 
     The third switching element (SW 3 ) is between the electric current source unit  181  and the data line (Dm). The third switching element (SW 3 ) is turned on when the information about the deterioration of the organic light emitting diode (OLED) is sensed. 
     The fourth switching element (SW 4 ) is between the data driver  120  and the data line (Dm). The fourth switching element (SW 4 ) is turned on when the data signal is supplied to the data line (Dm). 
     The electric current source unit  181  senses the information about deterioration of the organic light emitting diode and threshold voltage and/or mobility of the drive transistor while supplying a constant electric current to the power line (Vm) and the data line (Dm). The electric current source unit  181  generates a voltage, and supplies the generated voltage to the ADC  182 . 
     The constant electric current supplied from the electric current source unit  181  to the power line (Vm) is supplied to the second power source (ELVSS) via the second transistor (M 2 ), the third transistor (M 3 ) and the organic light emitting diode (OLED) of the pixel  140 . The electric current source unit  181  extracts a first voltage corresponding to the information about threshold voltage and/or mobility of the second transistor (M 2 ) and deterioration of the organic light emitting diode (OLED), and supplies the extracted first voltage to the ADC  182 . 
     The constant electric current supplied from the electric current source unit  181  to the data line (Dm) is supplied to the second power source (ELVSS) via the first transistor (M 1 ), the fourth transistor (M 4 ), and the organic light emitting diode (OLED) of the pixel  140 . At this time, the electric current source unit  181  extracts a second voltage corresponding to the information about deterioration of the organic light emitting diode (OLED), and supplies the extracted second voltage to the ADC  182 . 
     The resistance of the organic light emitting diode (OLED) increases as the organic light emitting diode (OLED) deteriorates. Accordingly, when the constant electric current is supplied, the voltage at the organic light emitting diode (OLED) changes according to the deterioration of the organic light emitting diode (OLED). In this case, a level of the deterioration of the organic light emitting diode (OLED) may be determined by sensing the voltage at the organic light emitting diode (OLED) while applying the constant electric current. Also, if the constant electric current is supplied via the second transistor (M 2 ), a voltage is applied to the gate electrode of the second transistor (M 2 ). Here, the threshold voltage and/or mobility of the second transistor (M 2 ) may be determined by applying the voltage to the gate electrode of the second transistor (M 2 ) since the voltage applied to the gate electrode of the second transistor (M 2 ) is determined by the threshold voltage and/or mobility of the second transistor (M 2 ). 
     The electric current value of the constant electric current supplied to the pixel  140  is experimentally determined so that the information about the threshold voltage and/or mobility of the second transistor (M 2 ) and the deterioration of the organic light emitting diode (OLED) can be extracted from the electric current source unit  181 . For example, the constant electric current may be set to an electric current value that will be supplied to the organic light emitting diode (OLED) when the pixel  140  is allowed to emit the light with the highest luminance. 
     The ADC  182  converts the first voltage supplied to the electric current source unit  181  into a first digital value, and converts the second voltage into a second digital value. 
     The memory  191  stores the first digital value and the second digital value supplied to the ADC  182 . The memory  191  stores the information about the threshold voltage and/or mobility of the second transistor (M 2 ) and the deterioration of the organic light emitting diode (OLED) of each of the pixels  140  in the pixel unit  130 . For this purpose, the memory  191  may be a frame memory. 
     The controller  192  supplies the first digital value and the second digital value to the timing controller  150 , wherein the first digital value and the second digital value are extracted from the pixel  140  to which a first data (Data 1 ) will be supplied, the first data (Data 1 ) being received from the current timing controller  150 . 
     The timing controller  150  receives a first data (Data 1 ) and receives the first digital value and the second digital value from the controller  192 . After the timing controller  150  receives the first digital value and the second digital value, it converts a bit value of the first data (Data 1 ) to generate a second data (Data 2 ), thereby displaying an image having a uniform luminance. 
     For example, the timing controller  150  generates a second data (Data 2 ) with reference to the second digital value since the value of the first data (Data 1 ) is increased as the organic light emitting diode (OLED) deteriorates. Accordingly, the second data (Data 2 ) reflects the information about the deterioration of the organic light emitting diode (OLED) and therefore the timing controller  150  prevents the emitted light from having a lower luminance from being generated as the organic light emitting diode (OLED) is deteriorates. Also, the timing controller  150  generates a second data (Data 2 ) to compensate for threshold voltage and/or mobility variation of the second transistor (M 2 ) based on the first digital value. Accordingly, with the timing controller  150  an image may be displayed, which has a uniform luminance regardless of the threshold voltage and/or mobility of the second transistor (M 2 ). Here, the information about the threshold voltage and/or mobility of the second transistor (M 2 ) may be obtained using the second digital value and the first digital value. 
     The first digital value and the second digital value supplied from the ADC  182  may be supplied to the controller  192 . The controller  192  may use the first digital value and the second digital value to generate a new first digital value including only the information about the threshold voltage and/or mobility of the second transistor (M 2 ). The controller  192  stores the second digital value supplied from the ADC  182 ; and the newly generated first digital value in the memory  191 . In this case, the second digital value stored in the memory  191  includes the information about the deterioration of the organic light emitting diode (OLED), and the first digital value includes the information about the threshold voltage and/or mobility of the second transistor (M 2 ), and therefore extracting the information about the threshold voltage and/or mobility of the second transistor (M 2 ) from the timing controller  150  may be omitted. 
     The data driver  120  uses the second data (Data) to generate a data signal and supplies the generated data signal to the pixel  140 . 
       FIG. 5  is a diagram showing one embodiment of a data driver. 
     Referring to  FIG. 5 , the data driver includes a shift register unit  121 , a sampling latch unit  122 , a holding latch unit  123 , a signal generation unit  124 , and a buffer unit  125 . 
     The shift register unit  121  receives a source start pulse (SSP) and a source shift clock (SSC) from the timing controller  150 . The shift register unit  121  receiving the source shift clock (SSC) and the source start pulse (SSP) sequentially generates the sampling signals while shifting the source start pulse (SSP) during each period of the source shift clock (SSC). For this purpose, the shift register unit  121  includes m shift registers ( 121   l  to  121   m ). In some embodiments, m is greater than 9. 
     The sampling latch unit  122  sequentially stores the second data (Data 2 ) in response to the sampling signal sequentially supplied from the shift register unit  121 . For this purpose, the sampling latch unit  122  includes the m number of sampling latch  122   l  to  122   m  so as to store the m number of the second data (Data 2 ). 
     The holding latch unit  123  receives a source output enable (SOE) signal from the timing controller  150 . The holding latch unit  123  receiving the source output enable (SOE) signal receives a second data (Data 2 ) from the sampling latch unit  122  and stores the received second data (Data 2 ). The holding latch unit  123  supplies the second data (Data 2 ) stored therein to the signal generation unit  124 . For this purpose, the holding latch unit  123  includes the m number of holding latches  123   l  to  123   m.    
     The signal generation unit  124  receives second data (Data 2 ) from the holding latch unit  123 , and generates the m number of data signals according to the received second data (Data 2 ). For this purpose, the signal generation unit  124  includes the m number of digital-analog converters (hereinafter, referred to as a “DAC”)  124   l  to  124   m . That is, the signal generation unit  124  uses the DACs ( 124   l  to  124   m ), arranged in each channel to generate the m number of data signals and supplies the generated data signals to the buffer unit  125 . 
     The buffer unit  125  supplies the m number of the data signals supplied from the signal generation unit  124  to each of the m number of the data lines (D 1  to Dm). For this purpose, the buffer unit  125  includes the m number of buffers ( 125   l  to  125   m ). 
       FIG. 6   a  and  FIG. 6   b  are diagrams showing a driving waveform supplied to the pixel and the switching unit. 
       FIG. 6   a  show a waveform view for sensing information about the threshold voltage and/or mobility of the second transistor (M 2 ) and the deterioration of the organic light emitting diode (OLED) in the pixels  140 . The second switching element (SW 2 ) and the third switching element (SW 3 ) are maintained in a turned-on state. 
     An operation of the organic light emitting display will be described in more detail with reference to  FIG. 6   a  and  FIG. 7 . First, when a control signal is supplied to the control line (CL 1   n ), the fourth transistor (M 4 ) is turned on. Also, the third transistor (M 3 ) is turned on since a light emitting control signal is not supplied to the light emitting control line (En). 
     When the fourth transistor (M 4 ) and third transistor (M 3 ) are turned on, the second transistor (M 2 ) is connected in a diode configuration. As a result, an electric current is supplied from the electric current source unit  181  to the second power source (ELVSS) through the second transistor (M 2 ), the third transistor (M 3 ), and the organic light emitting diode (OLED). As a result, a first voltage is generated according to the electric current flowing in the electric current source unit  181 . For example, the first voltage is the result of a combination of the threshold and/or mobility of the second transistor (M 2 ) and the resistance of the organic light emitting diode (OLED), showing the deterioration thereof. As described above, the first voltage applied to the electric current source unit  181  is converted into a first digital value in the ADC  182 , and the converted first digital value is then supplied to the memory  191 . 
     To characterize the organic light emitting diode (OLED) without the second transistor (M 2 ) the third transistor (M 3 ) is turned off when the light emitting control signal is supplied to the light emitting control line (En), and the first transistor (M 1 ) is also turned on when the scan signal is supplied to the scan line (Sn). 
     When the first transistor (M 1 ) is turned on, the constant electric current supplied from the electric current source unit  181  is supplied to the second power source (ELVSS) through the first transistor (M 1 ), the fourth transistor (M 4 ), and the organic light emitting diode (OLED). As a result, a second voltage is generated according to the constant electric current flowing in the electric current source unit  181  applied to the organic light emitting diode (OLED). The second voltage applied to the electric current source unit  181  is converted into a second digital value in the ADC  182 , and the converted second digital value is supplied to the memory  191 . 
     The first digital value and the second digital value corresponding to each of all the pixels  140  are stored in the memory  191  through the aforementioned procedures. The procedure of sensing the information about the threshold voltage and/or mobility of the second transistor (M 2 ) and the deterioration of the organic light emitting diode (OLED) may be carried out, for example, whenever power is supplied to the organic light emitting display. 
     The first digital value and the second digital value generated in the ADC  182  may be supplied to the controller  192 . In this case, the controller  192  converts the first digital value so that it can have the information about the threshold voltage and/or mobility of the second transistor (M 2 ), and then stores the converted first digital value in the memory  191 . 
       FIG. 6   b  shows a waveform view for carrying out a normal display operation. During a normal display period, the scan driver  110  sequentially supplies a scan signal to the scan lines (S 1  to Sn), and sequentially supplies a light emitting control signal to the light emitting control lines (E 1  to En). The first switching element (SW 1 ) and the fourth switching element (SW 4 ) are maintained in a turned-on state during the normal display period. Also, the fourth transistor (M 4 ) is maintained in a turned-off state during the normal display period. 
     An operation of the organic light emitting display will be described in more detail with reference to  FIG. 6   b  and  FIG. 7 . First, a first data (Data 1 ) is supplied to the timing controller  150 . The controller  192  supplies a first digital value and a second digital value to the timing controller  150 , the first digital value and the second digital value being extracted from the pixel  140  connected with the data line (Dm) and the scan line (Sn), as described above. 
     The timing controller  150  receiving the first digital value and the second digital value converts the first data (Data 1 ) to generate a second data (Data 2 ). The second data (Data 2 ) is set to compensate for the deterioration of the organic light emitting diode (OLED) and the threshold voltage and/or mobility of the second transistor (M 2 ). 
     For example, a “00001110” may be the first data (Data 1 ). The timing controller  150  may generate “000011110” as the second data (Data 2 ) to compensate for the deterioration of the organic light emitting diode (OLED) and/or a shift in the threshold voltage and/or mobility of the second transistor (M 2 ). 
     The second data (Data 2 ) generated in the timing controller  150  is supplied to a DAC  124   m  via a sampling latch  122   m  and a holding latch  123   m . The DAC  124   m  then uses the second data (Data 2 ) to generate a data signal and supplies the generated data signal to the data line (Dm) via a buffer  125   m.    
     Because the first transistor (M 1 ) is turned on if the scan signal is supplied to the scan line (Sn), the data signal supplied to the data line (Dm) is supplied to the gate electrode of the second transistor (M 2 ). The storage capacitor (Cst) is charged with a voltage corresponding to a difference between the first power source (ELVDD) and the data signal supplied to the power line (Vm). 
     Meanwhile, because the scan signal is supplied to the scan line (Sn) and the light emitting control signal is supplied to the light emitting control line (En) at the same time, unnecessary electric current is not supplied to the organic light emitting diode (OLED) during a period when the voltage corresponding to the data signal is charged in the storage capacitor (Cst). 
     Then, the first transistor (M 1 ) is turned off when the supply of the scan signal is suspended, and the third transistor (M 3 ) is turned on when the supply of the light emitting control signal is suspended. The second transistor (M 2 ) controls the electric current to correspond to the voltage charged in the storage capacitor (Cst), the electric current flowing from the first power source (ELVDD) to the second power source (ELVSS) through the second transistor (M 2 ), the third transistor (M 3 ) and the organic light emitting diode (OLED). Then, the organic light emitting diode (OLED) generates light having a luminance corresponding to the supplied electric current. The electric current supplied to the organic light emitting diode (OLED) is set to compensate for the deterioration of the organic light emitting diode (OLED) and the threshold voltage and/or mobility of the second transistor (M 2 ), and therefore the electric current may be used to uniformly display an image having a desired luminance. 
     The pixel  140  as shown in  FIG. 3  is provided with PMOS transistors, but the present invention is not limited thereto. The pixels  140  in  FIG. 3  may be configured with NMOS transistors. In this case, polarity of a driving waveform of the NMOS transistors is set to a polarity that is opposite to the polarity of the PNMOS transistors, as is well known in the art. 
     As described above, the organic light emitting display and the driving method thereof stores information about the threshold voltage and/or mobility of the drive transistor and the deterioration of the organic light emitting diode in a memory. The organic light emitting display generates a second data to compensate for the deterioration of the organic light emitting diode and the threshold voltage and/or mobility of the drive transistor using the information stored in the memory, and supplies the generated second data signal to the pixels. As a result, the organic light emitting display displays an image having a uniform luminance regardless of the deterioration of the organic light emitting diode and the threshold voltage and/or mobility of the drive transistor. 
     The description herein discloses certain example embodiments for the purpose of illustrations only, and the invention is not intended to be limited to these embodiments, so it should be understood that other equivalents and modifications could be made.