Abstracts:A novel pixel circuit with low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) for driving active-matrix organic light-emitting diode (AMOLED) displays is proposed. The pixel circuit is built on two adjacent pixels with six p-type LTPS-TFTs and a capacitor, and thus the equivalent circuit is 3T0.5C in each layout area, which has a superior aperture ratio. The pixel circuit can compensate for the threshold voltage (VTH) deviation of the driving TFT and provide a reverse bias on the OLED to ameliorate the OLED’s lifetime. The simulation results show that the pixel circuit can provide a stable driving current to AMOLED displays and the average error rate of the driving current was 1.8% when the driving TFT threshold voltage deviated by ±0.33 V. Therefore, the proposed pixel circuit with a superior aperture ratio can show high immunity to the driving TFT threshold voltage deviation and significantly improve the uniformity of brightness of AMOLED displays.

Abstracts:This paper proposes a new gate driver circuit using depletion mode a-IGZO TFTs. The proposed gate driver circuit can prevent Q node, the gate node of pull-up TFT, from discharging during the output pulse duration. For that purpose, our circuit applies sufficient negative gate-to-source bias (Vgs) to the switch TFTs connected to the Q node during that time. Consequently, the leakage current through them is suppressed even though they have a negative threshold voltage (Vth). The proposed circuit has eleven transistors and two capacitors and it requires only two clock signals, which enables us to adopt the circuit at minimum extra cost. It works properly even when Vth is as low as −7.1 V. The normalized power consumption of the proposed circuit is also lowered compared with the previously reported circuits when the transistor has negative Vth. The power consumption of the proposed circuit for Vth of −5 V increases only nine times that for Vth of 3 V.