A Fast Ramp-Voltage-Based Current Programming Driver for AMOLED Display

A new source driving circuit to compensate characteristics variations of thin-film transistors for AMOLED displays with high resolution is presented in this brief. The second-generation current conveyor is implemented for rapid current sensing of the feedback line, which is biased with a constant reference-voltage (VREF). Further, the current difference between the current of the driving transistor (ID) and the programming current, i.e., IDATA, is converted into switching voltage through an amplifier with a shorted resistor, to control the input of a ramp voltage (VRAMP). Thus, the degradations in electrical characteristics of the driving transistor can be compensated in real time, and both the influence of threshold voltage (VTH) shift and mobility (μ) variation are effectively suppressed. The current-error rate of the proposed circuit is less than 3% with VTH shift of ±0.5 V or μ variation of ±15%. In addition, the settling time is less than 4 μs with the panel loading of 1.5 KΩ and 100 pF at the OLED current (IOLED) levels ranging from 3 μA to 200 nA.