Organic light emitting display

1. An organic light emitting display comprising:

a first transistor having a gate electrode connected to a first selection signal, a source electrode connected to a data signal, and a drain electrode connected to a second node;

a second transistor having a gate electrode connected to the first selection signal, a source electrode connected to a power voltage, and a drain electrode connected to a first node;

a third transistor having a gate electrode connected to a second selection signal, a source electrode connected to a reference voltage, and a drain electrode connected to the second node;

a capacitor connected between the first node and the second node; and

a fourth transistor having a gate electrode connected to the first node, a source electrode connected to the power voltage, and a drain electrode connected to an organic light emitting diode (OLED),

wherein during a first period, the data signal is supplied to the second node by switching the first transistor and the power voltage is supplied to the first node by switching the second transistor, and during a second period, the reference voltage is supplied to the second node by switching the third transistor such that a voltage relating to the power voltage, the data voltage and the reference voltage is charged at the first node, and

wherein the reference voltage is different from the power voltage.

2. The apparatus according to claim 1 , wherein the first through fourth transistors are the same type.

3. The apparatus according to claim 1 , wherein a driving current independent of the power voltage flows through the fourth transistor under the control of the second transistor.

4. A display device having a plurality of pixels, each pixel of the display device comprising:

a first transistor having a gate electrode connected to a first selection signal, a source electrode connected to a data signal, and a drain electrode connected to a second node;

a second transistor having a gate electrode connected to the first selection signal, a source electrode connected to a power voltage, and a drain electrode connected to a first node;

a third transistor having a gate electrode connected to a second selection signal, a source electrode connected to a reference voltage, and a drain electrode connected to the second node;

a capacitor connected between the first node and the second node; and

a fourth transistor having a gate electrode connected to the first node, a source electrode connected to the power voltage, and a drain electrode connected to a light emitting element,

wherein during a first period, the data signal is supplied to the second node by switching the first transistor and the power voltage is supplied to the first node by switching the second transistor, and during a second period, the reference voltage is supplied to the second node by switching the third transistor such that a voltage relating to the power voltage, the data voltage and the reference voltage is charged at the first node, and

wherein the reference voltage is different from the power voltage.

5. The display device according to claim 4 , wherein the display device is an organic light emitting display.

6. The display device according to claim 4 , wherein the light emitting element includes an organic light emitting diode.

7. The display device according to claim 4 , wherein the first through fourth transistors are the same type.