Circuit and method for driving an organic light emitting diode (o-led)

Abstract

Disclosed is a technique for driving a column of pixels implemented using O-LEDs. The technique includes separate, digitally adjustable current sources on each column conductor of the array. For each column, the digitally-programmed current flow terminates with a reference O-LED and a series NMOS transistor forming the input leg of a novel, distributed current mirror. The current is 'mirrored' to the output leg of the distributed current mirror which can service any one of a plurality of active O-LEDs in the column based on a row select signal. In this way, a transistor on the output leg of the current mirror couples its respective O-LED to a source of operational power. The mirrored charge on the gate of the output leg transistor causes it to apply the same current to the active O-LED as was applied to the reference O-LED through the input leg transistor. Additionally, the voltage drop across the NMOS transistor and the reference O-LED is used to charge a capacitor associated with the selected O-LED. The charging of the capacitor, as a result of the digitally-programmed current supplied through the NMOS transistor to the reference O-LED, allows for continuous driving of the active O-LED during a cycle through. Thus, a reference O-LED in conjunction with an NMOS transistor, services all of a plurality of sequentially-loaded rows within each column.