Research Of AMOLED Driving Technologies

OLED (Organic Light Emitting Device) is a kind of full solid-state luminescentdevice, and it has already been the research focus in the flat panel display technologydue to its attractive attributes, such as high brightness, high contrast, wide viewingangle, fast response time, strong adaptability, and the easy color tuning. Starting fromthe working principle, circuit model, and approaches to full color of the OLED, theactive matrix driving technology for the OLED is systematically researched in thispaper, and the three main points of this paper are sum up as follows:1. Design of controlling circuit for AMOLED based on FPGABased on the LTPS AMOLED display module of Taiwan CMEL, the displaysystem is constructed, which consists of FPGA, video A/D, SRAM, and the AMOLEDmodule. The functional modules of this display system are achieved by the modulardesign method. And the system hardware and software debugging is realized by FPGA，while the physical map of AMOLED on this system is offered.2. Driving schemes of AMOLED based on a-Si:H TFTIn the conventional2T1C pixel circuit for AMOLED, the threshold voltage (VTH)shifts due to electrical stress over time for a-Si:H TFT may cause non-uniformbrightness. To solve this problem, a new5T1C current-programmed a-Si:H TFT pixelcircuit is proposed. Based on the characteristics of the white OLED and parameters fora-Si:H TFTs, parameters assurance and verification by HSPCE simulation work areachieved for the proposed pixel circuit. Layout of unit pixel and pixel array considering5.7inch QVGA AMOLED display empoying the proposed a-Si:H TFT pixel circuit isdesigned, while the effect of parasitic resistance and capacitance of the scan lines anddata lines for the pixel array is analyzed in the worst case design.3. Driving schemes of AMOLED based on poly-Si TFTIn the AMOLED display panel employing the conventional2T1C pixel circuit, theinevitable variation in threshold voltage (VTH) of poly-Si TFT from one device toanother may cause non-uniform brightness and imprecise gray scale of the panel. Toovercome this issue, a new6T1C voltage-programmed poly-Si TFT pixel circuit is proposed. Through the parameters assurance and verification by HSPCE simulationwork for the proposed poly-Si pixel circuit, it’s verified that the proposed poly-Si pixelcircuit can effectively compensate for the threshold voltage variation of poly-Si TFTand OLED. Meanwhile, an AC driving mode for the OLED is offered by the proposedpoly-Si TFT pixel circuit. Then, the layout of unit pixel and pixel array considering2.8inch QVGA AMOLED display for the proposed poly-Si TFT pixel circuit is achieved,and the2.8inch AMOLED pixel array is simulated and verified in the worst case design,when taking into account the parasitic resistance and capacitance of the scan lines anddata lines.