Patent Publication Number: US-2015077414-A1

Title: Display device and driving method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional application based on pending application Ser. No. 12/929,802, filed Feb. 16, 2011, the entire contents of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments relate to a display device and a driving method thereof. More particularly, embodiments relate to an organic light emitting diode (OLED) display and a driving method thereof. 
     2. Description of the Related Art 
     A display device includes a display panel formed of a plurality of pixels arranged in a matrix format. A display panel may include a plurality of scan lines formed in a row direction and a plurality of data lines formed in a column line. The plurality of scan lines and the plurality of data lines are arranged to cross each other. Each of the plurality of pixels is driven by a scan signal and a data signal transmitted from respectively corresponding scan and data lines. 
     The display device is classified into a passive matrix (PM) light emitting display device and an active matrix (AM) light emitting display device depending on the method of driving the pixels. In view of resolution, contrast, and response time, the trend is towards the AM display devices in which respective unit pixels are selectively turned on or off. 
     The display device is used as a display unit for a personal computer, a portable phone, a PDA, and other mobile information devices, or as a monitor for various kinds of information systems. A liquid crystal panel-based LCD, an organic light emitting diode (OLED) display, a plasma panel-based PDP, etc., are well known. Various kinds of emissive display devices, which have lower weight and volume than CRTs, have been recently developed. Particularly, organic light emitting diode (OLED) displays have come to the forefront, due to their excellent emissive efficiency, luminance, and viewing angle, and short response time. 
     Each pixel of the OLED display includes an OLED and a driving transistor for driving the OLED. However, the current flowing in the OLED is changed due to changes in the threshold voltage of the driving transistor. In order to solve this problem, the threshold voltage of the driving transistor is calculated to compensate a data voltage with the calculated threshold voltage. However, the threshold voltage cannot be accurately calculated, resulting in inconsistent luminance of the OLED. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     Embodiments are therefore directed to a display device and driving method thereof, which substantially overcome one or more of the problems due to the limitations and disadvantages of the related art. 
     It is therefore a feature of an embodiment to provide a display device that can constantly maintain luminance of an organic light emitting diode, and a driving method thereof. 
     A display device according to an exemplary embodiment includes a display unit and a data driver. The display unit includes a plurality of scan lines to which a plurality of scan signals are transmitted, a plurality of data lines to which a plurality of compensation data signals are transmitted, a plurality of light emitting signal lines to which a plurality of light emitting signals are transmitted, and a plurality of pixels respectively connected to the plurality of scan lines, the plurality of data lines, and the plurality of light emitting signal lines. The data driver generates a data voltage corresponding to an image data signal, and converting the data voltage to the compensation data signal. The data driver includes a compensator configured to generate an additive voltage by adding a predetermined first power source voltage to the data voltage, receive a feedback voltage corresponding to a threshold voltage of a driving transistor of each pixel according to a compensation control signal generated by synchronization with the scan signal, and generate a difference between the additive voltage and the feedback voltage as the compensation data signal. 
     The compensator may include an additive voltage generator configured to generate the additive voltage by adding the data voltage and the first power source voltage, a compensation data voltage generator configured to generate the compensation data signal by performing subtraction between the additive voltage and the feedback voltage, a first switch transmitting the feedback voltage to the compensation data voltage generator according to the compensation control signal; and a second switch transmitting the compensation data signal to the pixel according to a load signal that instructs transmission of the compensation data signal to the plurality of data lines. The compensation data voltage generator may include a non-inversion terminal receiving the additive voltage, an inversion terminal receiving the feedback voltage, and an output terminal connected to the data line. 
     Each of the plurality of pixels may includes a switch transistor having a source terminal connected to the data line and a gate line connected to the scan line, a driving transistor having a source terminal receiving the first power source voltage and a gate terminal connected to a drain terminal of the switching transistor, a capacitor having a first end connected to the source terminal of the driving transistor and a second end connected between the gate terminals of the driving transistor, a light emission control transistor having a gate terminal connected to the light emitting signal line and a source terminal connected to the drain of the driving transistor, an organic light emitting diode (OLED) having an anode connected to the drain terminal of the light emission control transistor and a cathode receiving a second power source voltage, and a threshold voltage compensation transistor having a gate terminal receiving the compensation control signal, a drain terminal connected to the drain terminal of the driving transistor, and a source terminal connected to the source terminal of the switching transistor. 
     A driving method according to another exemplary embodiment is provided to a display device including a plurality of scan lines to which a plurality of scan signals are transmitted, a plurality of data lines to which a plurality of compensation data signals are transmitted, a plurality of light emitting signal lines to which a plurality of light emitting signals are transmitted, and a plurality of pixels respectively connected to the plurality of scan lines, the plurality of data lines, and the plurality of light emitting signal lines. The driving method includes generating a data voltage corresponding to an image data signal, generating an additive voltage by adding a predetermined power source voltage to the data voltage, receiving a feedback voltage corresponding to a threshold voltage of a driving transistor of each of the plurality of pixels according to a compensation control signal generated by synchronization with the scan signal, and generating a difference between the additive voltage and the feedback voltage and transmitting the difference as a compensation data signal to the plurality of data lines. The feedback voltage may equal a difference between the power source voltage and the threshold voltage of the driving transistor. 
     A display device according to another exemplary embodiment includes a display unit and a data driver. The display unit includes a plurality of scan lines to which a plurality of scan signals are transmitted, a plurality of data lines to which a plurality of compensation data signals are transmitted, a plurality of light emitting signal lines to which a plurality of light emitting signals are transmitted, and a plurality of pixels respectively connected to the plurality of scan lines, the plurality of data lines, and the plurality of light emitting signal lines. The data driver is configured to generate a data voltage corresponding to an image data signal and converts the data voltage to the compensation data signal. The data driver includes a compensator configured to detect a feedback voltage corresponding to the degree of deterioration of the pixel according to a compensation control signal generated from the scan signal with a predetermined phase delay and to compensate the data voltage by calculating the variation amount of the feedback voltage. 
     Each of the plurality of pixels may include a switching transistor having a source terminal connected to the data line and a gate terminal connected to the scan line, a driving transistor having a source terminal receiving a first power source voltage and a gate terminal connected to a drain terminal of the switching transistor, a capacitor having a first end connected to the source terminal of the driving transistor and a second end connected between the gate terminal of the driving transistor, a light emission control transistor having a gate terminal connected to the light emitting signal line and a source terminal connected to the drain terminal of the driving transistor; an organic light emitting diode (OLED) having an anode connected to the drain terminal of the light emission control transistor and a cathode receiving a second power source voltage, and a threshold voltage compensation transistor having a gate terminal receiving the compensation control signal, a drain terminal connected to the drain terminal of the driving transistor, and a source terminal connected to the source terminal of the switching transistor. 
     The compensator may include a deterioration detector detecting a voltage at both ends of the organic light emitting diode as the feedback voltage according to the compensation control signal, and a compensation data voltage generator configured to calculate the variation amount of the feedback voltage and generate the compensation data signal by compensating the data voltage by the amount of the calculated feedback voltage. 
     The compensator may further include a switch transmitting the compensation data signal to the pixel according to a load signal that instructs transmission of the compensation data signal to the plurality of data lines. The deterioration detector may include an analog digital converter transmitting the feedback voltage to the compensation data voltage generator, and a switch transmitting the feedback voltage to the analog digital converter according to the compensation control signal. 
     A driving method according to another exemplary embodiment is a provided to a display device including a plurality of scan lines to which a plurality of scan signals are transmitted, a plurality of data lines to which a plurality of compensation data signals are transmitted, a plurality of light emitting signal lines to which a plurality of light emitting signals are transmitted, and a plurality of pixels respectively connected to the plurality of scan lines, the plurality of data lines, and the plurality of light emitting signal lines. The driving method includes generating a data voltage corresponding to an image data signal, detecting a feedback voltage corresponding to the degree of deterioration of the pixel according to a compensation control signal generated from the scan signal with a predetermined phase delay, and compensating the data voltage by calculating the variation amount of the feedback voltage. 
     Detecting the feedback voltage may include applying the data voltage to each of the plurality of pixels, transmitting a current corresponding to the data voltage to an organic light emitting diode according to the light emission control signal, and generating a voltage at both ends of the organic light emitting diode with the feedback voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which: 
         FIG. 1  illustrates a display device according to an exemplary embodiment. 
         FIG. 2  illustrates an equivalent circuit diagram of a compensator and a pixel according to a first exemplary embodiment. 
         FIG. 3  illustrates a waveform diagram of a driving method of the display device according to the first exemplary embodiment. 
         FIG. 4  illustrates an equivalent circuit diagram of a compensator and a pixel according to a second exemplary embodiment. 
         FIG. 5  illustrates a waveform diagram of a driving method of a display device according to the second exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Korean Patent Application No. 10-2010-0015379, filed on Feb. 19, 2010, in the Korean Intellectual Property Office, and entitled: “Display Device and Driving Method Thereof,” is incorporated by reference herein in its entirety. 
     In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
     Throughout this specification and the claims that follow, when it is described that an element is “coupled” to another element, the element may be “directly coupled” to the other element or “electrically coupled” to the other element through a third element. In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
       FIG. 1  illustrates a display device according to an exemplary embodiment. Referring to  FIG. 1 , a display device according may include a display unit  100 , a scan driver  200 , a data driver  300 , a light emission driver  400 , and a controller  500 . 
     The display unit  100  includes a plurality of signal lines S 1 -Sn, D 1 -Dm, and E 1 -En, and a plurality of pixels PX connected to the signal lines and arranged in a matrix format. The signal lines S 1 -Sn, D 1 -Dm, and E 1 -En include a plurality of scan lines S 1 -Sn transmitting scan signals SS 1 -SSn, a plurality of data lines D 1 -Dm transmitting a compensation data voltage Vdata_c, and a plurality of light emitting signal lines E 1 -En transmitting light emitting signals EM 1 -EMn. The scan lines S 1 -Sn and the light emitting signal lines E 1 -En extend substantially in a row direction and substantially parallel with each other, and the data lines D 1 -Dm extend substantially in a column direction and substantially parallel with each other. 
     The scan driver  200  is connected to the signal lines S 1 -Sn of the display unit  100 , and sequentially applies the scan signals SS 1 -SSn to the scan lines S 1 -Sn according to a scan control signal CONT 1 . The plurality of scan signals SS 1 -SSn are formed of a combination of a scan ON voltage Von turning on a switching transistor M 2  of each pixel PX ( FIG. 2 ) and a scan OFF voltage turning off the switching transistor M 2 . If the switching transistor M 2  is formed as a p-channel field effect transistor, the scan ON voltage is a low voltage and the scan OFF voltage is a high voltage. 
     The data driver  300  is connected to the data lines D 1 -Dm of the display unit  100 , generates a data voltage Vdata corresponding to image data signals DR, DG, and DB input from the controller  500  according to a data control signal CONT 2 , converts the data voltage Vdata to a compensation data voltage Vdata_c compensated for a threshold voltage Vth of a driving transistor M 1  of each pixel PX, and applies the compensation data voltage Vdata_c to the data lines D 1 -Dm. 
     The data driver  300  includes a compensator  310  that generates the compensation data voltage Vdata_c in accordance with a feedback voltage Vfb. The feedback voltage Vfb is determined by a voltage between an anode and a cathode of the organic light emitting diode OLED when a current I OLED  flows thereto, and increases with an increasing deterioration degree of the organic light emitting diode OLED. The feedback voltage Vfb is used to compensate the data voltage Vdata. 
     The light emission driver  400  is connected to the light emitting signal lines E 1 -En of the display unit  100 , and sequentially applies the plurality of light emitting signals EM 1 -EMn to the light emitting signal lines E 1 -En according to a light emission control signal CONT 3 . The plurality of light emitting signals EM 1 -EMn are formed of a combination of a gate ON voltage Von turning on a light emission control transistor M 3  of each pixel PX and a gate OFF voltage turning off the light emission control transistor M 3 . If the light emission control transistor M 3  is formed as a p-channel field effect transistor, the gate ON voltage Von and the gate OFF voltage Voff are respectively a low voltage and a high voltage. 
     The controller  500  receives an input signal IS, a horizontal synchronization signal Hsync, a vertical synchronization signal Vsync, and a main clock signal MCLK from an external source to generate the image data signals DR, DG, and DB, the scan control signal CONT 1 , the data control signal CONT 2 , and the light emission control signal CONT 3 . The scan control signal CONT 1  includes a scan start signal STV that instructs the start of scanning and at least one clock signal controlling the scan start signal STV and an output cycle of the gate ON voltage. The scan control signal CONT 1  may further include an output enable signal OE that limits the duration of the gate ON voltage Von. The data control signal CONT 2  includes a horizontal synchronization start signal STH that informs the start of transmission of the image data signals DR, DG, and DB of pixels PX in one row to the data driver  300 , and a load signal LOAD that instructs application of a compensation data voltage Vdata_c to the data lines D 1 -Dm. 
     The light emission control signal CONT 3  includes a synchronization signal that instructs the start of scanning of the gate ON voltage Von with respect to the light emitting signal lines E 1 -En and at least one clock signal that controls an output of the gate ON voltage Von. The light emission control signal CONT 3  may further include a signal that limits the duration of the gate ON voltage Von. 
       FIG. 2  illustrates an equivalent circuit diagram of a compensator  310   a  and the pixel PX according to a first exemplary embodiment. Referring to  FIG. 2 , the compensator  310   a  may include an additive voltage generator  312 , a compensation data voltage generator  314 , and switches SW 1  and SW 2 . The pixel PX includes an organic light emitting diode OLED, a driving transistor M 1 , a capacitor Cst, the switching transistor M 2 , a light emission control transistor M 3 , and a threshold voltage compensation transistor M 4 . 
     The additive voltage Va is the sum of the data voltage Vdata and a predetermined power source voltage VDD. The compensator receives a feedback voltage Vfb corresponding to the threshold voltage Vth of the driving transistor M 1  of each pixel PX according to a compensation control signal CCS_ 1 , and generates a compensation data voltage Vdata_c corresponding to a voltage difference between the additive voltage Va and the feedback voltage Vfb. The data control signal CONT 2  according to the first exemplary embodiment includes the compensation control signal CCS_ 1  for compensation of the threshold voltage Vth of the driving transistor M 1  of each pixel PX. The compensation control signal CCS_ 1  includes a low-level pulse signal generated in synchronization with a low-level pulse of the scan signal. 
     While the compensator  310 a illustrated in  FIG. 2  includes one subtractor AD connected to the data line D 1  for ease of explanation, multiple subtractors AD may be provided and respectively connected to the plurality of data lines D 1 -Dm. Each of the subtractors AD may sequentially receive a feedback voltage Vfb from the plurality of pixels PX respectively connected to the plurality of data lines D 1 -Dm. In addition, the pixel PX of  FIG. 2  is an example of a pixel connected to the scan line S 1  and the data line D 1 . 
     The additive voltage generator  312  receives the data voltage Vdata corresponding to the image data signals DR, DG, and DB, and adds the data voltage Vdata and the power source voltage VDD to generate the additive voltage Va. 
     The compensation data voltage generator  314  includes the subtractor AD. The subtractor AD receives the additive voltage Va through a non-inversion terminal (+) and receives the feedback voltage Vfb through an inversion terminal (−). The subtractor AD generates a compensation data voltage Vdata_c corresponding to a difference between the additive voltage Va and the feedback voltage Vfb. 
     The switch SW 1  includes a first end connected to the inversion terminal (−) of the subtractor AD and a second end connected to a source terminal of the switching transistor M 2  of the pixel PX. The switch SW 1  is turned on/off according to the compensation control signal CCS_ 1 . The switch SW 2  includes a first end connected to an output terminal of the subtractor AD and a second end connected to the source terminal of the switching transistor M 2  of the pixel PX. The switch SW 2  is turned on/off according to the load signal LOAD. 
     For example, the switch SW 1  is turned on when the compensation control signal CCS_ 1  is low and turned off when the compensation control signal CCS_ 1  is high. In addition, the switch SW 2  is turned on when the load signal LOAD is low and turned off when the load signal LOAD is high. 
     The driving transistor M 1  of the pixel PX includes a source terminal receiving the power source voltage VDD and a drain terminal connected to a source terminal of the light emitting transistor M 3 . The switching transistor M 2  includes a gate terminal receiving the scan signal SS 1 , a drain terminal connected to the source terminal of the driving transistor M 1 , and a source terminal connected to the data line D 1 . The capacitor Cst is connected between the source terminal and the gate terminal of the driving transistor M 1 . The capacitor Cst charges a data voltage applied to the gate terminal of the driving transistor M 1  and maintains the charge of the data voltage when the switching transistor M 2  is turned off. 
     The light emission control transistor M 3  of the pixel PX includes a gate terminal receiving a light emitting signal EM 1  and a drain terminal connected to an anode of the organic light emitting diode OLED. The light emission control transistor M 3  is selectively turned on according to the light emitting signal EM 1  to supply a current I OLED  flowing in the driving transistor M 1  to the organic light emitting diode OLED. 
     The threshold voltage compensation transistor M 4  of the pixel PX includes a gate terminal receiving the compensation control signal CCS_ 1 , a drain terminal connected to the drain terminal of the driving transistor M 1 , and a source terminal connected to the source terminal of the switching transistor M 2 . The threshold voltage compensation transistor M 4  is selectively turned on by the compensation control signal CCS_ 1  to transmit the feedback voltage Vfb at the drain terminal of the driving transistor M 1  to the compensator  310   a  when the driving transistor M 1  is diode-connected. That is, the feedback voltage Vfb corresponds to a voltage difference between the power source voltage VDD and the threshold voltage Vth of the driving transistor M 1 . 
     The organic light emitting diode OLED of the pixel PX includes a cathode receiving the power source voltage VDD. The intensity of light emitted from the organic light emitting diode OLED varies depending upon the current I OLED  supplied from the driving transistor M 1  through the light emission control transistor M 3  so as to display an image. 
     The organic light emitting diode OLED may emit light of one of primary colors. The primary colors may be three primary colors, e.g., red, green, and blue, and a desired color may be expressed by a spatial or temporal sum of the three primary colors. Some of the organic light emitting elements OLED may emit white light to increase luminance. Alternatively, the organic light emitting elements OLED at all of the pixels PX may emit white light. In this case, some of the pixels PX may further include a color filter (not shown) for converting the white light output from the organic light emitting element OLED into any one of the primary colors. 
     The driving transistor M 1 , the switching transistor M 2 , the light emission control transistor M 3 , and the threshold voltage compensation transistor M 4  are illustrated in  FIG. 2  as all being p-channel field effect transistors (FET). However, at least one of the driving transistor M 1 , the switching transistor M 2 , the light emission control transistor M 3 , and the threshold voltage compensation transistor M 4  may be an n-channel FET. In addition, interconnections between the driving transistor M 1 , the switching transistor M 2 , the light emission control transistor M 3 , the threshold voltage compensation transistor M 4 , the capacitor Cst, and the organic light emitting diode OLED may be changed. The pixel PX shown in  FIG. 2  is merely an example, and pixels having a different structure may be used instead. 
       FIG. 3  illustrates a waveform diagram of a driving method of the display device according to the first exemplary embodiment. Referring to  FIG. 3 , the image data signals DR, DG, and DB are transmitted, and the data driver  300  generates the data voltage Vdata corresponding to the image data signals DR, DG, and DB. 
     The additive voltage generator  312  generates the additive voltage Va by adding the power source voltage VDD to the data voltage Vdata. The additive voltage Va is transmitted to the non-inversion terminal (+) of the subtractor AD. In this state, when the scan signal SS 1  becomes low at a time point P 1 , the compensation control signal CCS_ 1  becomes low. Then, the switching transistor M 2  is turned on by the scan signal SS 1  and the threshold voltage compensation transistor M 4  is turned on by the compensation control signal CCS_ 1 . Thus, the gate terminal and the drain terminal of the driving transistor M 1  are connected. Accordingly, a feedback voltage Vfb is generated at the drain terminal of the driving transistor M 1 . In this case, the feedback voltage Vfb corresponds to a voltage obtained by subtracting the threshold voltage Vth of the driving transistor M 1  from the power source voltage VDD. Since the switch SW 1  is in the turn-on state by the compensation control signal CCS_ 1 , the feedback voltage Vfb is transmitted to the inversion terminal (−) of the subtractor AD. The subtractor AD subtracts the feedback voltage Vfb from the additive voltage Va to output the compensation data voltage Vdata_c. The compensation data voltage Vdata_c is obtained as given in Equation 1. 
         V data —   c=Va−Vfb =( VDD+V data)−( VDD−V th)= V data+ V th   (Equation 1)
 
     That is, the compensation data voltage Vdata_c equals the sum of the data voltage Vdata and the threshold voltage Vth of the driving transistor M 1 . At a time point P 2 , the load signal LOAD becomes low and then the switch SW 2  is turned on. Since the switching transistor M 2  is turned-on, the compensation data voltage Vdata_c is transmitted to the gate terminal of the driving transistor M 1  through the switching transistor M 2 . Here, the current I OLED  flowing in the driving transistor M 1  is defined as given in Equation 2. 
         I   OLED   =k *( Vgs−V th) 2    (Equation 2)
 
     Here, Vgs denotes a voltage difference between the voltage at the gate terminal and the voltage at the source terminal of the driving transistor M 1 , and equals (Vdata+Vth)−VDD when Equation 1 is used, and k is a constant. When this value is applied to Equation 2, the current I OLED  flowing in the driving transistor M 1  is as given in Equation 3. 
         I   OLED   =k *( V data− VDD ) 2    (Equation 3)
 
     This means that the current I OLED  flowing in the driving transistor M 1  is not influenced by the threshold voltage Vth. Accordingly, variation of the intensity of the current I OLED  flowing to the driving transistor M 1  due to the threshold voltage Vth can be prevented. That is, luminance of the organic light emitting diode OLED may be constantly maintained by offsetting the threshold voltage Vth of the driving transistor M 1  according to the first exemplary embodiment. 
       FIG. 4  illustrates an equivalent circuit diagram of a compensator  310   b  and the pixel PX according to a second exemplary embodiment of the present invention. The pixel PX in  FIG. 4  is the same as the pixel PX in  FIG. 2 , and the description will not be repeated. However, unlike the threshold voltage compensation transistor M 4  of  FIG. 2 , a threshold voltage compensation transistor M 4  in  FIG. 4  is selectively turned on by a compensation control signal CCS_ 2  instead of a compensation control signal CSS_ 1 . The compensation control signal CCS_ 2  according to the second exemplary embodiment includes a low-level pulse signal generated from the scan signal with a predetermined phase delay, e.g., a delay equal to one scan pulse. Referring to  FIG. 4 , the compensator  310   b  according to the second exemplary embodiment includes a deterioration detector  316 , a compensation data voltage generator  318 , and a switch SW 4 . 
     The deterioration detector  316  transmits a feedback voltage Vfb that corresponds to the deterioration degree of an organic light emitting diode OLED to the compensation data voltage generator  318  according to the compensation control signal CCS_ 2 . The feedback voltage Vfb according to the second exemplary embodiment is determined by a voltage between an anode and a cathode of the organic light emitting diode OLED when a current I OLED  flows thereto, and increases as the deterioration degree of the organic light emitting diode OLED increases. 
     The deterioration detector  316  includes an analog digital converter A/D and a switch SW 3 . The analog digital converter A/D transmits the feedback voltage Vfb to the compensation data voltage generator  318 . The switch SW 3  includes a first end connected to the analog digital converter A/D and a second end connected to a source of the switching transistor M 2 , and is turned on/off according to the compensation control signal CCS_ 2 . For example, the switch SW 3  according to the second exemplary embodiment is turned on when the compensation control signal CCS_ 2  is low and turned off when the compensation control signal CCS_ 2  is high. Here, the compensation control signal CCS_ 2  according to the second exemplary embodiment of the present invention includes a low-level pulse signal generated from the scan signal with a predetermined phase delay. 
     The compensation data voltage generator  318  calculates the variation amount of the feedback voltage Vfb detected from the deterioration detector  316  and generates the compensation data voltage Vdata_c by compensating a data voltage Vdata as much as the varied amount of the feedback voltage Vfb. The compensation data voltage generator  318  compensates the data voltage Vdata depending on the variation of the feedback voltage Vfb to generate the compensation data voltage Vdata_c. The compensation data voltage generator  318  determines the degree of compensation of the data voltage Vdata according to the variation of the feedback voltage Vfb. In this case, the relationship between the variation of the feedback voltage Vfb and the degree of the compensation of the data voltage Vdata may be stored in a lookup table acquired through experimental methods. 
     In further detail, since an increase of the feedback voltage Vfb implies deterioration of the organic light emitting diode OLED, much more current should flow in the organic light emitting diode OLED for light emission with luminance set in the initial state. In addition, when the driving transistor M 1  is a P-type transistor, deterioration of the organic light emitting diode OLED may be compensated by appropriately decreasing the data voltage Vdata. In this case, the lookup table stores the degree of compensation of the data voltage Vdata according to the variation of the feedback voltage Vfb. The variation of the feedback voltage Vfb implies a difference between a previously measured feedback voltage Vfb and a current feedback voltage Vfb when the feedback voltage Vfb generated according to the current flowing in the organic light emitting diode OLED is measured with a predetermined time gap. 
     The switch SW 4  includes a first end connected to the compensation data voltage generator  318  and a second end connected to the data line D 1 . The switch SW 4  is turned on/off according to the load signal LOAD. For example, the switch SW 4  of the present exemplary embodiment is turned on when the load signal LOAD is low and turned off when the load signal LOAD is high. 
       FIG. 5  illustrates a waveform diagram of a driving method of the display device according to the second exemplary embodiment. Referring to  FIG. 5 , when image data signals DR, DG, and DB are transmitted, the data driver  300  generates a data voltage Vdata corresponding to the image data signals DR, DG, and DB. 
     When the scan signal SS 1  becomes low at a time point P 11 , the switching transistor M 2  is turned on and the data voltage Vdata is transmitted to a gate terminal of the driving transistor M 1 . When the scan signal SS 1  becomes high at a time point P 12 , the switching transistor M 2  is turned off and the light emission control signal EM 1  becomes low. Then, the light emission control transistor M 3  is turned on and a current I OLED  flows in the driving transistor M 1 . 
     The current I OLED  is supplied to the organic light emitting diode OLED through the light emission control transistor M 3  such that the organic light emitting diode OLED emits light. In this case, the feedback voltage Vfb at both sides of the organic light emitting diode OLED varies according to the degree of deterioration of the organic light emitting diode OLED. The feedback voltage Vfb is increased as the degree of the deterioration of the organic light emitting diode OLED is increased. 
     When the compensation control signal CSS_ 2  becomes low at the time point P 12 , the threshold voltage compensation transistor M 4  and the switch SW 3  are turned on. Then, the feedback voltage Vfb is transmitted to the analog digital converter A/D. The feedback voltage Vfb transmitted through the analog digital converter A/D is transmitted to the compensation data voltage generator  318 . The compensation data voltage generator  318  calculates the variation amount of the feedback voltage Vfb, and compensates the data voltage Vdata according to the calculated variation amount to generate the compensation data voltage Vdata_c. That is, luminance of the organic light emitting diode OLED may be constantly maintained by detecting and compensating deterioration of the organic light emitting diode OLED according to the second exemplary embodiment. 
     &lt;Description of Symbols&gt; 
     Display unit  100 , scan driver  200 , data driver  300 , controller  400 , light emission driver  400 , scan lines S 1 -Sn, data lines D 1 -Dm, scan signals SS 1 -SSn, switching transistor M 2 , pixel PX, light emitting signal lines E 1 -En, light emitting signals EM 1 -EMn, input signal IS, horizontal synchronization signal Hsync, vertical synchronization signal Vsync, main clock signal MCLK, image data signals DR, DG, DB, gate ON voltage Von, scan control signal CONT 1 , data control signal CONT 2 , light emission control signal CONT 3 , compensators  310 ,  310   a ,  310   b,  subtractor AD, additive voltage generator  312 , gate OFF voltage Voff, compensation data voltage generator  314 , deterioration detector  316 , compensation data voltage generator  318 , switches SW 1 , SW 2 , SW 3 , SW 4 , analog digital converter A/D, driving transistor M 1 , light emission control transistor M 3 , threshold voltage compensation transistor M 4 , capacitor CST, organic light emitting diode OLED. 
     Exemplary embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.