The Novel AMOLED Pixel Design with AC bias for Improving the Brightness Uniformity

• Main Authors: Yan-Wei Liu, 劉晏瑋
• Other Authors: Ching-Lin Fan
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/44706639484340079438

碩士 === 國立臺灣科技大學 === 電子工程系 === 97 === As a result of flat panel displays have the potential for slim profile, light weight, low power consumption, wide viewing angle, full color, etc. Therefore flat panel displays are essential for various applications. Among of numerous different flat panel displays, Organic Light Emitting Diode (OLED) display has some fingerprint as high brightness, wide viewing angle, light weight, low power, and producing light by itself, Display industry will pay attention to OLED display. In this thesis, voltage programming method of driving circuits for active-matrix-organic light-emitting-diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) have been investigated. Contrasting to amorphous silicon (a-Si) TFTs, LTPS-TFTs are provide with the higher current driving capability and the better reliability, and used to implement pixel circuits and driving circuits on a single glass substrate. But LTPS-TFT process by ELA, enable LTPS-TFT to produce the mutant problem of the characteristic. Therefore, the new voltage programming method of pixel circuit has been proposed, in order to compensate issues on variation of the threshold voltage, IR-Drop phenomenon and OLED degradation. First of all, conventional 2T1C pixel circuit is interpreted for simulation results and discussions. The simulation results show that output current of conventional 2T1C pixel circuit is instable owing to various characteristics in TFTs. In order to compensate the threshold voltage deviation, we propose an modified 4T2C pixel circuit. And we propose two 2T1C AC driving pixel circuits (2T1C AC Ⅰ), ( 2T1C AC Ⅱ) which can compensate the threshold voltage deviation and OLED degradation. And then we propose two pixel circuit (3T1C AC Ⅰ), ( 3T1C AC Ⅱ), which can compensate the threshold voltage deviation and IR-Drop of VDD power line. The simulation result shows the average error rate of the OLED current in 2T1C AC driving pixel circuits is about 4%. And the error rate of the 3T1C AC driving pixel circuit with IR-Drop of VDD power line is about 15%, The circuit will substantially decrease the effects include the threshold voltage and IR-Drop. In conclusion, these four proposed pixel circuits all successfully compensate for characteristics variation of LTPS-TFT and the threshold voltage variation of driving TFT and improve the current uniformity for AMOLED greatly. Therefore, the circuit designs possess the potential for the AMOLED panel application in the future.