Patent Publication Number: US-9852688-B2

Title: Pixel and organic light-emitting display apparatus including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2014-0149329, filed on Oct. 30, 2014, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     One or more exemplary embodiments relate to a pixel and an organic light-emitting display apparatus including the same. 
     2. Description of the Related Art 
     Among display apparatuses, organic light-emitting display apparatuses are attracting a lot of attention. The organic light-emitting display apparatus has self-emitting characteristic, and does not use a separate light source, unlike liquid crystal display (LCD) apparatuses, thereby reducing display apparatus&#39; thickness and weight. Also, the organic light-emitting display apparatus shows high-grade characteristics, such as low power consumption, high luminance, and a fast response time. 
     SUMMARY 
     Aspects of one or more exemplary embodiments are directed to a pixel and a display apparatus including the same, which displays an image having uniform or substantially uniform luminance. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     According to one or more exemplary embodiments, there is provided a pixel including: an organic light-emitting diode (OLED); a capacitor connected between a first node and a second node; a first transistor including a gate electrode connected to the second node, a first electrode connected to a first source voltage line, and a second electrode configured to output a current corresponding to a voltage applied to the second node; a second transistor including a gate electrode connected to a first scan line for receiving a first scan signal, a first electrode connected to a data line, and a second electrode connected to the first node; a third transistor including a gate electrode connected to the first scan line, a first electrode connected to the second electrode of the first transistor, and a second electrode connected to the gate electrode of the first transistor; a fourth transistor including a gate electrode connected to a second scan line for receiving a second scan signal, a first electrode connected to the second electrode of the first transistor, and a second electrode connected to an initialization voltage line; and a fifth transistor including a gate electrode and a second electrode connected to an emission control line for receiving an emission control signal, and a first electrode connected to the first node. 
     In an embodiment, the pixel further includes a sixth transistor including a gate electrode connected to the emission control line, a first electrode connected to the second electrode of the first transistor, and a second electrode connected to an anode electrode of the OLED. 
     In an embodiment, during a portion of a period in which a data signal from the data line is transmitted to the first node through the second transistor which is turned on by the first scan signal, the third transistor is turned on by the first scan signal, and the fourth transistor is turned on by the second scan signal to transmit an initialization voltage to the second node. 
     In an embodiment, during an other portion of the period in which the data signal is transmitted to the first node, the fourth transistor is turned off, and a voltage of the second node is set to a value equal to a difference between a threshold voltage of the first transistor and a first source voltage supplied to the first source voltage line. 
     In an embodiment, during a period in which at least one of the first scan signal and the second scan signal is at a first voltage level, the emission control signal is at a second voltage level, and the fifth transistor and the sixth transistor are turned off. 
     In an embodiment, when the fifth transistor and the sixth transistor are turned on by the emission control signal having the first voltage level, a voltage of the first node drops to the first voltage level of the emission control signal, a voltage of the second node changes, and the first transistor is turned on by the voltage of the second node to output the current. 
     In an embodiment, one frame in which the pixel operates includes: a first period in which the first scan signal and the second scan signal are at a first voltage level, and the emission control signal is at a second voltage level; a second period in which the first scan signal is at the first voltage level, and the second scan signal and the emission control signal are at the second voltage level; and a third period in which the first scan signal and the second scan signal are at the second voltage level, and the emission control signal is at the first voltage level. 
     According to one or more exemplary embodiments, there is provided an organic light-emitting display apparatus including: a scan driver configured to sequentially supply a first scan signal to a plurality of first scan lines, and to sequentially supply a second scan signal to a plurality of second scan lines; an emission controller configured to sequentially supply an emission control signal to a plurality of emission control lines; a data driver configured to respectively supply data signals to a plurality of data lines; and a display unit including a plurality of pixels connected to the plurality of first scan lines, the plurality of second scan lines, the plurality of emission control lines, and the plurality of data lines, wherein each of the plurality of pixels includes: an organic light-emitting diode (OLED); a capacitor connected between a first node and a second node; a first transistor including a gate electrode connected to the second node, a first electrode connected to a first source voltage line, and a second electrode outputting a current corresponding to a voltage applied to the second node; a second transistor including a gate electrode connected to one of the plurality of first scan lines, a first electrode connected to one of the plurality of data lines, and a second electrode connected to the first node; a third transistor including a gate electrode connected to the first scan line, a first electrode connected to the second electrode of the first transistor, and a second electrode connected to the gate electrode of the first transistor; a fourth transistor including a gate electrode connected to one of the plurality of second scan lines, a first electrode connected to the second electrode of the first transistor, and a second electrode connected to an initialization voltage line; and a fifth transistor including a gate electrode, a second electrode, and a first electrode connected to the first node, the gate and second electrodes being connected to one of the plurality of emission control lines. 
     In an embodiment, each of the plurality of pixels further includes a sixth transistor including a gate electrode connected to a corresponding one of the plurality of emission control lines, a first electrode connected to the second electrode of the first transistor, and a second electrode connected to an anode electrode of the OLED. 
     In an embodiment, in a first period of one frame, the scan driver applies the first and second scan signals having a first voltage level, in a second period of the one frame, the scan driver applies the first scan signal having the first voltage level, and to apply the second scan signal having a second voltage level, in a third period of the one frame, the scan driver applies the first and second scan signals having the second voltage level, in the first period and the second period of the one frame, the emission controller applies the emission control signal having the second voltage level, and in the third period of the one frame, the emission controller applies the emission control signal having the first voltage level. 
     In an embodiment, in the first period of the one frame, the second transistor is turned on by the first scan signal having the first voltage level, and a data signal from the data line is transmitted to the first node when turned on, and the third transistor is turned on by the first scan signal having the first voltage level, the fourth transistor is turned on by the second scan signal having the first voltage level, and an initialization voltage is supplied to the second node via the initialization voltage line when turned on. 
     In an embodiment, in the second period of the one frame, while the data signal is being transmitted to the first node, the fourth transistor is turned off by the second scan signal having the second voltage level, and a voltage of the second node is set to a value equal to a difference between a threshold voltage of the first transistor and a first source voltage. 
     In an embodiment, each of the plurality of pixels further includes a sixth transistor including a gate electrode connected to a corresponding one of the plurality of emission control lines, a first electrode connected to the second electrode of the first transistor, and a second electrode connected to an anode electrode of the OLED. 
     In an embodiment, in the third period of the one frame, the fifth transistor and the sixth transistor are turned on by the emission control signal having the first voltage level, a voltage of the first node is dropped to the second voltage level of the emission control signal, a voltage of the second node is changed, and the first transistor is turned on by the voltage of the second node to output the current. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a circuit diagram schematically illustrating a structure of an organic light-emitting display apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a circuit diagram illustrating a pixel according to an exemplary embodiment of the present invention; 
         FIG. 3  is a circuit diagram illustrating a pixel according to another exemplary embodiment of the present invention; and 
         FIG. 4  is a timing diagram for illustrating a method of driving the pixel of  FIG. 3 , according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present exemplary embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the exemplary embodiments are merely described below, by referring to the figures, to explain aspects of the present description. 
     The present inventive concept may have various embodiments, and specific embodiments illustrated in the drawings will be described in detail in the detailed description. The effects and features of the inventive concept will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. The inventive concept may, however, be embodied in different forms and should not be construed as being limited to the embodiments set forth herein. 
     Hereinafter, embodiments of the inventive concept will be described in detail with reference to the accompanying drawings. In addition, in the present specification and drawings, like reference numerals refer to like elements throughout, and thus, redundant descriptions may not be provided. 
     It will be understood that, although the terms “first”, “second”, “third”, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section, without departing from the spirit and scope of the inventive concept. 
     In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the inventive concept. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. Further, the use of “may” when describing embodiments of the inventive concept refers to “one or more embodiments of the inventive concept.” Also, the term “exemplary” is intended to refer to an example or illustration. 
     It will be understood that when an element or layer is referred to as being “on”, “connected to”, “coupled to”, or “adjacent to” another element or layer, it can be directly on, connected to, coupled to, or adjacent to the other element or layer, or one or more intervening elements or layers may be present. When an element or layer is referred to as being “directly on,” “directly connected to”, “directly coupled to”, or “directly mounted to” another element or layer, there are no intervening elements or layers present. 
     As used herein, the term “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. 
     As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively. 
       FIG. 1  is a circuit diagram schematically illustrating a structure of an organic light-emitting display apparatus  10  according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , the organic light-emitting display apparatus  10 , according to an exemplary embodiment, includes a display unit (or pixel unit)  110 , a scan driver  120 , a data driver  130 , an emission controller  140 , a power supply  150 , and a controller  160 . 
     The display unit  110  includes a plurality of scan lines SL 11  to SL 2   n  (where n is an integer greater than one), a plurality of data lines DL 1  to DLm (where m is an integer greater than one), and a plurality of pixels PX. The plurality of scan lines SL 11  to SL 2   n  are arranged in rows and are separated from each other at certain intervals, and transfer (e.g., transmit) scan signals. The plurality of data lines DL 1  to DLm are arranged in column to be separated from each other at certain intervals, and respectively transfer data signals. The plurality of scan lines SL 11  to SL 2   n  and the plurality of data lines DL 1  to DLm are arranged in a grid-like (e.g., matrix-like) manner, and the plurality of pixels PX are respectively provided at crossing portions between the plurality of scan lines SL 11  to SL 2   n  and the plurality of data lines DL 1  to DLm. The display unit  110  may further include a plurality of emission control lines EL 1  to ELn. The plurality of emission control lines EL 1  to ELn are arranged in row to be separated from each other in parallel, and transfer emission control signals. 
     The scan driver  120  is connected to the scan lines SL 11  to SL 2   n  of the display unit  110 , and generates the scan signal based on a combination of a gate-on voltage and a gate-off voltage according to a second control signal CONT 2  to apply the scan signal to the scan lines SL 11  to SL 2   n . When the scan signal has the gate-on voltage, a switching transistor of a pixel connected to a corresponding scan line is turned on. 
     The data driver  130  is connected to the data lines DL 1  to DLm of the display unit  110 , and respectively applies the data signals representing gray scale levels to the plurality of data lines DL 1  to DLm according to a first control signal CONT 1 . The data driver  130  converts input image data having a gray scale level, input from the controller  160 , into a data signal corresponding to a voltage or a current. 
     The emission controller  140  is connected to the emission control lines EL 1  to ELn of the display unit  110 , and generates an emission control signal according to a third control signal CONT 3  to apply the emission control signal to the emission control line EL 1  to ELn. A width of a gate-on voltage section of the emission control signal is set to be equal to or broader than that of a gate-on voltage section of the scan signal. In the exemplary embodiment of  FIG. 1 , the emission controller  140  is separately provided. However, the emission controller  140  may be omitted, and the scan driver  120  may apply the emission control signal to the emission control signals EL 1  to ELn. 
     The power supply  150  generates a first source voltage ELVDD and a second source voltage ELVSS according to a fourth control signal CONT 4 . The power supply  150  applies the generated first source voltage ELVDD and second source voltage ELVSS to the display unit  110 . A voltage level of the first source voltage ELVDD is higher than a voltage level of the second source voltage ELVSS. The power supply  150  generates an initialization voltage Vinit according to the fourth control signal CONT 4  to apply the initialization voltage Vinit to the display unit  110 . 
     The controller  160  receives, from an external graphic controller, input image data and an input control signal for controlling the display of the input image data. The input control signal includes, for example, a vertical sync signal Vsync, a horizontal sync signal Hsync, and a main clock MCLK. The controller  160  transfers (e.g., transmits) input image data to the data driver  130 , generates the first control signal CONT 1  to transfer the first control signal CONT 1  to the data driver, and generates the second control signal CONT 2  to the scan driver  120 . The first control signal CONT 1  includes a horizontal sync start signal STH, indicating the transfer of input image data to pixels PX of one row, and a clock signal. The second control signal CONT 2  includes a scan start signal SSP indicating the start of scan and a plurality of clock signals SCLK. The controller  160  generates the third control signal CONT 3 , and transfers the third control signal CONT 3  to the emission controller  140 . The controller  160  generates the fourth control signal CONT 4 , and transfers the fourth control signal CONT 4  to the power supply  150 . 
     Each of the scan driver  120 , the data driver  130 , the emission controller  140 , the power supply  150 , and the controller  160  may be implemented as a separate integrated circuit (IC) chip or one IC chip, and thus may be directly mounted on a substrate on which the display unit  110  is provided, mounted on a flexible printed circuit film, attached to a substrate in a tape carrier package (TCP), or directly provided on a substrate. 
       FIG. 2  is a circuit diagram illustrating a pixel according to an exemplary embodiment of the present invention. 
     For convenience of description,  FIG. 2  illustrates a pixel PX 1  that is connected to an arbitrary data line DLm to receive a data signal DATA, connected to an nth first scan line SL 1   n  and an nth second scan line SL 2   n  to receive a first scan signal S 1 [ n ] and a second scan signal S 2 [ n ], and connected to an nth emission control line ELn to receive an emission control signal EM[n]. 
     Referring to  FIG. 2 , the pixel PX 1  according to an exemplary embodiment includes first to sixth transistors T 1  to T 6 , a capacitor Cst, and an organic light-emitting diode OLED. 
     The first transistor T 1  includes a gate electrode connected to a second node N 2 , a first electrode connected to a first source voltage line through which the first source voltage ELVDD is applied, and a second electrode connected to a first electrode of the sixth transistor T 6 . The first transistor T 1  acts as a driving transistor, and supplies a current, corresponding to a voltage applied to a second node N 2 , to the organic light-emitting diode OLED. 
     The second transistor T 2  includes a gate electrode connected to the first scan line SL 1   n , a first electrode connected to the data line DLm, and a second electrode connected to a first node N 1 . When the first scan signal S 1 [ n ] having a gate-on voltage is supplied to the first scan line SL 1   n , the second transistor T 2  is turned on, and transfers (e.g., transmits) the data signal DATA, supplied through the data line DLm, to the first node N 1 . 
     The third transistor T 3  includes a gate electrode connected to the first scan line SL 1   n , a first electrode connected to the second electrode of the first transistor T 1 , and a second electrode connected to the gate electrode of the first transistor T 1 . When the first scan signal S 1 [ n ] having the gate-on voltage is supplied to the first scan line SL 1   n , the third transistor T 3  is turned on, and diode-connects the first transistor T 1 . 
     The fourth transistor T 4  includes a gate electrode connected to the second scan line SL 2   n , a first electrode connected to the second electrode of the first transistor T 1 , and a second electrode connected to an initialization voltage line through which the initialization voltage Vinit is applied. When the second scan signal S 2 [ n ] having the gate-on voltage is supplied to the second scan line SL 2   n , the fourth transistor T 4  is turned on, and transfers the initialization voltage Vinit to the third node N 3 . 
     The fifth transistor T 5  includes a gate electrode connected to the emission control line ELn, a first electrode connected to the first node N 1 , and a second electrode connected to the initialization voltage line. When the emission control signal EM[n] having a gate-on level is supplied through the emission control line ELn, the fifth transistor T 5  is turned on, and changes a voltage value of the first node N 1  to a voltage value of the initialization voltage Vinit. 
     The sixth transistor T 6  includes a gate electrode connected to the emission control line ELn, the first electrode connected to the second electrode of the first transistor T 1 , and a second electrode connected to an anode electrode of the organic light-emitting diode OLED. When the sixth transistor T 6  is supplied with the emission control signal EM[n] having the gate-on voltage through the emission control line ELn, the sixth transistor T 6  is turned on, and supplies a current from the first transistor T 1  to the organic light-emitting diode OLED. 
     The capacitor Cst is connected between the first node N 1  and the second node N 2 , and is charged with a voltage equal to the difference between a voltage of the first node N 1  and a voltage of the second node N 2 . 
     The organic light-emitting diode OLED includes the anode electrode connected to the second electrode of the sixth transistor T 6 , and a cathode electrode connected to the second source voltage ELVSS. The second source voltage ELVSS has a lower level than that of the first source voltage ELVDD. The organic light-emitting diode OLED generates light having certain luminance in response to an amount of current supplied from the first transistor T 1 . 
     The pixel PX 1  of  FIG. 2  uses the initialization voltage Vinit for sustaining a data voltage corresponding to a data signal of the first node N 1 , and for initializing the gate electrode of the first transistor T 1 . Therefore, the voltage for sustaining the data voltage and the voltage for initializing the gate electrode of the first transistor T 1  cannot be set as optimal voltages. 
       FIG. 3  is a circuit diagram illustrating a pixel according to another exemplary embodiment of the present invention. 
     For convenience of description,  FIG. 3  illustrates a pixel PX 2  that is connected to an arbitrary data line DLm to receive a data signal DATA, connected to an nth first scan line SL 1   n  and an nth second scan line SL 2   n  to receive a first scan signal S 1 [ n ] and a second scan signal S 2 [ n ], and connected to an nth emission control line ELn to receive an emission control signal EM[n]. 
     Referring to  FIG. 3 , the pixel PX 2  according to an exemplary embodiment includes first to sixth transistors T 1  to T 6 , a capacitor Cst, and an organic light-emitting diode OLED. 
     The first transistor T 1  includes a gate electrode connected to a second node N 2 , a first electrode connected to a first source voltage line through which the first source voltage ELVDD is applied, and a second electrode connected to a first electrode of the sixth transistor T 6 . The first transistor T 1  acts as a driving transistor, and supplies a current, corresponding to a voltage applied to a second node N 2 , to the organic light-emitting diode OLED. 
     The second transistor T 2  includes a gate electrode connected to the first scan line SL 1   n , a first electrode connected to the data line DLm, and a second electrode connected to a first node N 1 . When the first scan signal S 1 [ n ] having a gate-on voltage is supplied to the first scan line SL 1   n , the second transistor T 2  is turned on, and transfers (e.g., transmits) the data signal DATA, supplied through the data line DLm, to the first node N 1 . 
     The third transistor T 3  includes a gate electrode connected to the first scan line SL 1   n , a first electrode connected to the second electrode of the first transistor T 1 , and a second electrode connected to the gate electrode of the first transistor T 1 . When the first scan signal S 1 [ n ] having the gate-on voltage is supplied to the first scan line SL 1   n , the third transistor T 3  is turned on, and diode-connects the first transistor T 1 . 
     The fourth transistor T 4  includes a gate electrode connected to the second scan line SL 2   n , a first electrode connected to the second electrode of the first transistor T 1 , and a second electrode connected to an initialization voltage line through which the initialization voltage Vinit is applied. When the second scan signal S 2 [ n ] is supplied to the second scan line SL 2   n , the fourth transistor T 4  is turned on. 
     The fifth transistor T 5  includes a gate electrode and a second electrode, which are connected to the emission control line ELn, and a first electrode connected to the first node N 1 . When the emission control signal EM[n] having the gate-on voltage is supplied through the emission control line ELn, the fifth transistor T 5  is turned on and diode-connected, and changes a voltage value of the first node N 1  to a voltage value of the gate-on voltage of the emission control signal EM[n]. 
     The sixth transistor T 6  includes a gate electrode connected to the emission control line ELn, the first electrode connected to the second electrode of the first transistor T 1 , and a second electrode connected to an anode electrode of the organic light-emitting diode OLED. When the sixth transistor T 6  is supplied with the emission control signal EM[n] having the gate-on voltage through the emission control line ELn, the sixth transistor T 6  is turned on, and supplies a current from the first transistor T 1  to the organic light-emitting diode OLED. 
     The capacitor Cst is connected between the first node N 1  and the second node N 2 , and is charged with a voltage equal to the difference between a voltage of the first node N 1  and a voltage of the second node N 2 . 
     The organic light-emitting diode OLED includes the anode electrode connected to the second electrode of the sixth transistor T 6  and a cathode electrode connected to the second source voltage ELVSS. A voltage value of the second source voltage ELVSS is set lower than a voltage value of the first source voltage ELVDD. The organic light-emitting diode OLED generates light having a certain luminance in response to an amount of current supplied from the first transistor T 1 . 
       FIG. 4  is a timing diagram for describing a method of driving the pixel of  FIG. 3 , according to an exemplary embodiment of the present invention. 
     In a first period T 1 , the first scan signal S 1  [n] having a high level is applied to the first scan line SL 1   n , the second scan signal S 2 [ n ] having a high level is applied to the second scan line SL 2   n , and the emission control signal EM[n] having a high level is applied to the emission control line ELn. Therefore, the first to sixth transistors T 1  to T 6  are turned off. 
     In a second period T 2 , the first scan signal S 1 [ n ] having a low level is applied to the first scan line SL 1   n , and the second scan signal S 2 [ n ] having a low level is applied to the second scan line SL 2   n . The emission control signal EM[n] having a high level is applied to the emission control line ELn. 
     The second transistor T 2  and the third transistor T 3  are turned on by the first scan signal S 1 [ n ] having a low level. The fourth transistor T 4  is turned on by the second scan signal S 2 [ n ] having a low level. 
     When the second transistor T 2  is turned on, the data signal DATA supplied through the data line DLm is supplied to the first node N 1 . When the fourth transistor T 4  and the third transistor T 3  are turned on, the initialization voltage Vinit is supplied to the second node N 2 . The initialization voltage Vinit is set as a lower voltage than a voltage of the data signal DATA. 
     That is, in the second period T 2 , the gate electrode of the first transistor T 1  is initialized, and the data signal DATA is applied to the pixel PX 1 . 
     In a third period T 3 , the first scan signal S 1 [ n ] having a low level is maintained on the first scan line SL 1   n , the emission control signal EM[n] having a high level is maintained on the emission control line ELn, and the second scan signal S 2 [ n ] applied to the second scan line SL 2   n  is shifted to a high level. Therefore, the fourth transistor T 4  is turned off. At this time, because the first transistor T 1  is diode-connected, a voltage value of the second node N 2  is set as a value that is obtained by subtracting a threshold voltage of the first transistor T 1  from a voltage value of the first source voltage ELVDD. The capacitor Cst is charged with a voltage difference between the first node N 1  and the second node N 2 . 
     That is, in the third period T 3 , the threshold voltage of the first transistor  1  is compensated for. 
     In a fourth period T 4 , the second scan signal S 2 [ n ] having a high level is maintained on the second scan line SL 2   n , the emission control signal EM[n] having a high level is maintained on the emission control line ELn, and the first scan signal S 1 [ n ] supplied to the first scan line SL 1   n  is shifted to a high level. Therefore, the second transistor T 2  and the third transistor T 3  are turned off. 
     Subsequently, in a fifth period T 5 , the emission control signal EM[n] having a high level is shifted to a low level. Therefore, the fifth transistor T 5  and the sixth transistor T 6  are turned on. When the fifth transistor T 5  is turned on, a voltage value of the first node N 1  is dropped to a low-level voltage value of the emission control signal EM[n]. That is, the voltage value of the first node N 1  is dropped from a voltage value of the data signal DATA to the low-level voltage value of the emission control signal EM[n]. In this case, the third transistor T 3  is turned off, and thus, the second node N 2  is floated, whereby a voltage value of the second node N 2  is dropped in correspondence with the voltage value of the first node N 1 . For example, the voltage value of the second node N 2  is dropped by a voltage of the data signal from a voltage value, which is obtained by subtracting the threshold value of the first transistor T 1  from the first source voltage ELVDD. 
     Then, the first transistor T 1  supplies a current, corresponding to a voltage value, which is applied to the second node N 2  during the fifth period T 5 , to the organic light-emitting diode OLED via the sixth transistor T 6 , and thus, the organic light-emitting diode OLED generates light having a certain luminance. 
     The pixel PX 2  of  FIG. 3  uses a low-level voltage of the emission control signal EM[n] as an auxiliary voltage for maintaining the data signal independently from the initialization voltage Vinit that initializes the gate electrode of the first transistor T 1 . An optimal voltage value is set by differentially applying a data signal maintenance voltage and a gate electrode initialization voltage of the driving transistor. Also, by diode-connecting the fifth transistor T 5  to the emission control line ELn, a voltage is stably applied, and the data signal is maintained. Also, by diode-connecting the fifth transistor T 5  to the emission control line ELn, a separate auxiliary voltage is not needed. Therefore, a degree of free of a design of a pixel and a region margin are enhanced. 
     In the present embodiment, each of the transistors of a pixel circuit is a P-type transistor. In this case, a gate-on voltage for turning on the transistors is a low-level voltage, and a gate-off voltage for turning off the transistors is a high-level voltage. However, the present embodiment is not limited thereto, and each of the transistors of a pixel circuit may be an N-type transistor. In this case, a gate-on voltage for turning on the transistors is a high-level voltage, and a gate-off voltage for turning off the transistors is a low-level voltage. 
     As described above, according to the one or more of the above exemplary embodiments, the display apparatus displays an image having uniform or substantially uniform luminance. 
     It should be understood that the exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other exemplary embodiments. 
     While one or more exemplary embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various suitable changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims, and equivalents thereto.