1.  Field
Aspects of embodiments according to the present invention relate to a stage circuit and a scan driver using the same. 
2.  Description of the Related Art
Recently, flat panel displays (FPDs) with reduced weight and volume in comparison to cathode ray tubes (CRT) have been developed.  The FPDs include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and an organic light emitting display. 
Among the FPDs, the organic light emitting display displays an image using organic light emitting diodes (OLEDs) that generate light by re-combination of electrons and holes.  The organic light emitting display has high response speed and is driven with low power consumption.  A typical organic light emitting display supplies current corresponding to data signals to the OLEDs using transistors formed in pixels so that light is emitted by the OLEDs. 
The organic light emitting display includes a data driver for supplying the data signals to data lines, a scan driver for progressively supplying scan signals to scan lines, and a display unit including a plurality of pixels coupled to the scan lines and the data lines. 
The pixels included in the display unit are selected when the scan signals are supplied to the scan lines to receive the data signals from the data lines.  The pixels that receive the data signals generate light components with set or predetermined brightness corresponding to the data signals and display a predetermined image. 
On the other hand, the scan driver includes stages respectively coupled to the scan lines.  Each of the stages includes a plurality of transistors in order to supply the scan signals to the scan lines.  P-type (for example, PMOS) or N-type (for example, NMOS) transistors that constitute the stages are concurrently (e.g., simultaneously) formed in a panel together with the pixels.  When the stages are concurrently (e.g., simultaneously) formed in the panel together with the pixels, manufacturing cost may be reduced. 
However, when the stage is realized by the N-type transistor, the turn-off of the transistor is not controlled by the threshold voltage (Vth) shift of the transistor so that an erroneous operation is caused.  That is, in the case of the N-type transistor, as illustrated in FIG.  1, Vth is negatively shifted with respect to time so that the transistor is not turned off in a state where a voltage Vgs between a gate and a source of the transistor is 0V (that is, Vgs=0V). 
On the other hand, a method of driving the organic light emitting display is divided into a progressive emission method and a concurrent emission method.  In the progressive emission method, data are progressively input by scan lines, and pixels progressively emit light in units of horizontal lines in the same order as the input of the data. 
In the concurrent emission method, data are progressively input by scan lines, and pixels concurrently (e.g., simultaneously) emit light after the data are input to all of the pixels.  In order to realize the concurrent emission method, scan signals are to be concurrently (e.g., simultaneously) or progressively supplied to the scan lines.