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

Abstract

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 ( $V_{{\mathrm{ REF}}}$ ). Further, the current difference between the current of the driving transistor ( ${I}_{ {D}}$ ) and the programming current, i.e., ${I}_{{\mathrm{ DATA}}}$ , is converted into switching voltage through an amplifier with a shorted resistor, to control the input of a ramp voltage ( ${V}_{{\mathrm{ RAMP}}}$ ). Thus, the degradations in electrical characteristics of the driving transistor can be compensated in real time, and both the influence of threshold voltage ( ${V}_{{\mathrm{ TH}}}$ ) shift and mobility ( ${ {\mu }}$ ) variation are effectively suppressed. The current-error rate of the proposed circuit is less than 3% with ${V}_{{\mathrm{ TH}}}$ shift of ±0.5 V or ${ {\mu } }$ variation of ±15%. In addition, the settling time is less than $4~{ {\mu } }{\text s}$ with the panel loading of 1.5 $\text{K}{ {\Omega }}$ and 100 pF at the OLED current ( ${I}_{{\mathrm{ OLED}}}$ ) levels ranging from 3 ${ {\mu }}\text{A}$ to 200 nA.