Search

This paper proposes a new pixel circuit using low-temperature polycrystalline silicon thin-film transistors (LTPS TFTs) for use in mobile active matrix organic light-emitting diode (AMOLED) displays. The purpose of a pixel circuit is to supply stable and uniform currents to current-driving devices of OLEDs. The proposed pixel circuit uses overlapping compensation times to extend the period of precise sensing of $V_{\mathrm {TH}}$ variations of LTPS TFTs. Moreover, the proposed circuit prevents a current from flowing into an OLED when the OLED is not operated in the emission stage to avoid image flicker. An 1.3-in panel that uses the proposed pixel circuit is fabricated. Measurement results verify that the increased $T_{\mathrm {COMP}}$ of 33.3 $\mu \text{s}$ results in higher contrast ratio and lower required data voltages than those at $T_{\mathrm {COMP}}$ values of 4.3 and 2.2 $\mu \text{s}$. Red, green, and blue images displayed by the fabricated panel with a $T_{\mathrm {COMP}}$ of 33.3 $\mu \text{s}$ with a 255 gray level are all much more uniform than with $T_{\mathrm {COMPS}}$ of 4.3 and 2.2 $\mu \text{s}$. White images with a $T_{\mathrm {COMP}}$ of 33.3 $\mu \text{s}$ for 16 and 8 gray levels on the fabricated panel confirm that the serious line and spot defects in the images with $T_{\mathrm {COMP}}$ values of 4.3 and 2.2 $\mu \text{s}$ are effectively eliminated. Therefore, the proposed pixel circuit is suitable for use in mobile AMOLED displays. [ABSTRACT FROM AUTHOR]

This brief suppresses threshold voltage (${V}_{\text {TH}}$) variations in low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs) with a new current scaling ratio modulation method for the application of active-matrix organic light-emitting diode displays. With a newly proposed 3T2C LTPS TFT-based pixel circuit, high-current scaling ratios at low gray levels and low ratios at high gray levels are achieved. Thus, the programming time at low gray levels can be reduced, and the driving currents of the OLED are efficiently generated over the entire data range without consuming extra power for the current source. The driving currents are also independent of the threshold voltage of the driving TFT and the power line voltage, guaranteeing the uniformity of the current. Simulation results demonstrate that the relative current error rates are below 3.7% as the threshold voltage varies ±0.5 V and below 5.3% as the threshold voltage varies ±0.5 V and the power line voltage drops by 1 V; the programming time can be as short as only $12~\mu \text{s}$. [ABSTRACT FROM AUTHOR]

This paper presents a simple pixel structure that uses the voltage-programmed method to compensate for the electrical characteristic variations in low-temperature polycrystalline-silicon thin-film transistors and the current-resistance ( \(I\) – \(R\) ) voltage drop in the power line for active-matrix organic light-emitting diode displays. Based on the experimental results, the functionality of the pixel circuit can be operated correctly during each operation phase. Moreover, the pixel current exhibits high uniformity against the threshold voltage and mobility variations in the driving TFT. [ABSTRACT FROM AUTHOR]