A Novel Pixel Circuit Design Using Poly-Si TFTs for AMOLED Displays

• Main Authors: Bo-sin Lin, 林柏辛
• Other Authors: Ching-lin Fan
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/77730141594086568709

碩士 === 國立臺灣科技大學 === 電子工程系 === 96 === 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, and IR-Drop phenomenon. 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. A new pixel design and two modified to promote aperture ratio voltage programming pixel circuits have been proposed, which are 5T2C, 4T2C, and 3T1C, respectively. The 5T2C circuit is first designed, not only the simulation result shows the average error rate of the OLED current is about 1.54% but also the IR-Drop of power line downs to 1 V. result in error rate of the OLED current is about 15%, The circuit will substantially decrease the effects include the threshold voltage and IR-Drop. Subsequently, by way of eliminating a TFT of 5T2C pixel circuit that improve the aperture ratio to become 4T2C pixel circuit, Go a step further, the goal is reached to improve luminance of display. The simulation results show that 4T2C can successfully avoid the threshold voltage of driving TFT and IR-Drop of power line issues. Because the average error rate of the OLED current is about 1.53% and the IR-Drop of power line downs to 1 V. result in error rate of the OLED current is about 15%. Continuously, in order to improve aperture ratio and reduce the average error rate of the OLED current, the 4T2C pixel circuit is modified to cancel a TFT, and a capacitor, and form the 3T1C pixel circuit that can greatly increase aperture ratio. The simulation results show that the average error rate of the OLED current is about 1.41% and the IR-Drop of power line downs to 1 V. result in error rate of the OLED current is below 15%. In conclusion, these three 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.