Four-Thin Film Transistor Pixel Electrode Circuits for Active-Matrix Organic Light-Emitting Displays

Constant-current, four-thin-film-transistor (TFT) pixel electrode circuits, based on hydrogenated amorphous silicon (a-Si:H) TFT technology for active-matrix organic light-emitting displays (AM-OLEDs), have been designed, fabricated, and characterized. Experimental results indicate that continuous pixel electrode excitation can be achieved with these circuits. The pixel electrode circuits use a current driver to automatically adjust their current level for threshold voltage shifts of both the organic light-emitting devices and the drive TFT. Consequently, these pixel electrode circuits have excellent electrical reliability even when a large threshold voltage shift is present. A high output current level and a good output-input current linearity have been demonstrated with these circuits.