1. Field of the Invention
The present invention relates to a driving method, and more particularly, to a driving method for an active matrix OLED display, as well as a pixel structure using the same.
2. Description of the Related Art
Typically, an active matrix OLED display employs a large number of pixels to present an image, and controls the brightness of each pixel according to a brightness data.
FIG. 1 shows a pixel structure 10 of an active matrix organic light emitting diode (AMOLED). The switching transistor T1 is turned on and a data voltage indicated brightness is applied to a data electrode DATA when the scan electrode SCAN is activated. Thus, the storage capacitor Cs is charged or discharged, and the potential at the gate of the driving transistor T2 may coincide with that of the data voltage. The switching transistor T1 is turned off and the driving transistor T2 is electrically isolated from the data electrode DATA when the scan electrode SCAN is not activated. The data voltage is stored in the storage capacitor Cs, and the potential at the gate of the driving transistor T2 is maintained. The produced driving current I flows to the OLED 20 through the driving transistor T2 according to the voltage (Vgs) between the gate and source of the driving transistor T2. The OLED 20 then continuously illuminates according to the driving current I.
That is, in one display frame, the current received by the OLED is fixed. However, this driving method accumulates carriers inside the OLED 20 which reduce the life of the OLEDs. Moreover, the voltage Vo across the OLED gradually increases over time as shown in FIG. 3. Further, as shown by the formula P=I×V, as the voltage Vo increases over time, the power P also increases. In FIG. 3, curve C1 shows the effect of the voltage Vo of the OLED over time.