Abstract
The pixel circuit of an active matrix organic light-emitting diode (AMOLED) display uses thin-film transistors (TFTs) for the switching and driving components. However, the electrical characteristics of TFTs may vary due to fabrication process variation or long-term operation. Additionally, the efficiency of OLED material will degrade gradually, resulting in brightness nonuniformity and luminance decay. Numerous pixel compensation circuits have been proposed and exhibit effective compensation capability in 2D displays, whereas for three-dimensional (3D) displays, the short programming time causes incomplete compensation of TFT threshold voltage, and thus influences the image quality of 3D AMOLED display.In order to solve the issues mentioned above, this thesis proposes three novel pixel circuits. The first two pixel circuits adopt current-programming structure to operate in 2D displays. The first 6T1C circuit has immunity against the variation of threshold voltage of TFT and reduces the charging time at low grayscale. The simulation results demonstrate current error rate is under 5% with TFT threshold voltage variation, and the luminance degradation is 3% over 540 hours while the efficiency of OLED drops from 17.26 (cd/A) to 14.69 (cd/A). However, the aperture ratio of this circuit is reduced because of the excessive components and complex control signals. The second 3T1C circuit with few components and control signals increases aperture ratio and improves the defects in charging time as mentioned above. The simulation results show the current error rate is under 10% with TFT threshold voltage variation. Due to characteristics limitation for 3D displays, the third 3T1C circuit uses the voltage-programming approach to maintain brightness uniformity. The design of the driving signal can simultaneously compensate for TFT threshold voltage variation of the entire panel, shortening the operation time to meet the specifications required in 3D displays. Based on the simulation results, while the circuit operates at 240Hz, 360Hz, and 480Hz, the current error rate is 4.4%, 4.3% and 4.4% respectively.
The proposed pixel circuits in this thesis improve the brightness nonuniformity caused by the variation of the transistor characteristics. The first circuit can compensate for luminance decay due to OLED material aging and accelerates the operation speed. The second circuit focuses on simplifying the number of pixel elements, although it can’t compensate for OLED luminance decay, the aperture ratio is higher. The third circuit maintains a higher aperture ratio and can be applied to 3D display technology. The presented circuits improve the display image and will significantly contribute to AMOLED applications in the future.
| Date of Award | 2011 |
|---|---|
| Original language | Chinese (Traditional) |
| Supervisor | Chih-Lung Lin (Supervisor) |