Current Programming Method with Voltage-Variation-Sensing and Current-Feedback Operations for Active Matrix Organic Light-Emitting Diodes

Abstract

In active matrix organic light-emitting diodes (AMOLEDs), there are two driving methods: voltage programming and current programming methods. The voltage programming method has a short programming time, but its uniformity is sensitive to the characteristics of driving thin film transistors (TFTs). On the other hand, the current programming method is insensitive to the characteristics of driving TFTs but has a long programming time. Therefore, we propose a new driving method with voltage-variation-sensing and current-feedback operations to resolving these problems. The proposed driving method is carried out to detect the voltage variations of a current digital-to-analog converter (DAC), and a fast charging/discharging panel using an additional current source. A programming method using an additional current source is a successive approximation method. In successive approximation methods, charging or discharging through the voltage variation of the current DAC is selected. However the voltage variation of the current DAC is small, thus, we proposed a detection circuit using a unit gain operational amplifier. Simulation results show that the current through an organic light-emitting diodes (OLEDs) reaches a values of 17 nA in 20 µs when the data programming time is 52 µs in a 2.2-in. quarter-video graphic array (qVGA) of AMOLEDs. For the remaining 32 µs, the current DAC compensates the current difference.