Poly-Si Driving Circuits for Organic EL Displays

摘要

In order to realize a fully integrated polycrystalline silicon thin-film transistor organic electro-luminescent display (poly-Si TFT-OELD) with good image quality, problems caused by spatially non-uniform device characteristic in TFTs must be addressed. In TFT-OELDs, spatial variation of threshold voltage (ΔV_T) in TFT driving circuits leads to non-uniform brightness and poor grayscale accuracy. Consequently, special pixel driver circuits are designed to overcome such difficulties. TFT-OELD analog and digital pixel driver circuits are closely examined and design difficulties are pointed out. For example, in an analog driver circuit, one difficulty is to minimize the power consumption give the spread of ΔV_T; whereas in a digital driver circuit, one of the difficulties is how to maximize the number of grayscales. Performances of important circuits are analyzed and compared through circuit simulations using a poly-Si TFT model. Finally, suggestions of grayscale accuracy improvement are made.