Design And Simulation On Voltage Programmed A-Si TFT AMOLED Pixel Circuit

Now, there are many researches for a-Si TFT AMOLED driving circuit. In the AMOLED panel employing a well-known 2-TFT pixel circuit, the output current for OLED decreases due to the degradation of a-Si TFT used for a current source. Therefore, several compensation pixel circuit based on an a-Si TFT has been reported . There are two main kinds of method called The current programming method and The voltage programming method. The current programming method compensates for threshold voltage shift of a-Si TFT, however, it requires a longer pixel charging time at the data lines compared with a voltage programming method . The voltage programming method can be effective to compensate for the degradation of a-Si TFT . Recently there are more researches for voltage-programmed pixel circuits (CPPCs) . In the paper of J. C. Goh, a kind of 4-TFT parallel -compensation VPPC was proposed, but in this circuit the source node of the driving TFT was connected with a voltage-changed signal line but not the geoelectric source, so the gate-source voltage of the driving TFT is not steady, and the uniformity of brightness of the screen is not steady. In the later paper of J. C. Goh, a kind of improved 5-TFT parallel-compensation VPPC was proposed, in this circuit the source node of the driving TFT was connected with the geoelectric source through the OLED and a switching TFT, but asymmetry of the resistances of OLED and the switching TFT also can lead the varieties of the gate-source voltage of the driving TFT, so there becomes new error .In this paper a new amorphous silicon thin-film transistor (a-Si TFT) pixel circuit for an active matrix organic light-emitting diode (AMOLED) employing a voltage programming has been proposed which consists of five switching TFTs, one driving TFT, and one capacitor. the further simulation results indicate that the proposed a-Si TFT pixel circuit can successfully compensate the varietion of OLED luminance caused by the threshold voltage'difference between a-Si TFTs and also the difference between OLED'resistances,then the gray scale uniformity of the screen can be improved.During the simulation of PSpice,the influence of Vdd voltage,storage capacitor(CS) and W/L ratio of switching TFT (T3,T4,T1),driving TFT (T2) on the output characteristics of this pixel electrode circuit were analyzed in details and...