| Summary: | 博士 === 國立交通大學 === 電子工程系 === 89 === Compared with thin film transistor (TFT) liquid crystal displays (LCDs), the supertwisted nematic (STN) LCDs have become the enabling technology of low-cost flat panel displays. However, STN LCDs are still too sluggish to show video-rate images for the increasing multimedia demands. Trying to resolve this problem by reducing the response time of STN LCDs is only partially successful, because the phenomenon of frame response occurs. It is the reason, which makes the fast response STN LCDs to have low brightness, low contrast and flickering. Active addressing is a new driving technology, by which frame response could be eliminated and video-rate images could be shown in the fast response STN LCDs. As the active addressing technology is used to show gray scale images, two main methods had been proposed. However, they encounter various problems of hardware implement. The pulse height modulation (PHM) active addressing method could show unlimited gray levels, but it needs complex hardware for computation, including summation, square and square root. Besides, as row number is increased, its hardware requirement is tremendous, because it is proportional to the row number. The row voltage modulation (RVM) method needs less hardware. However, it is only feasible for displays with fewer grays scales, because the bit-time interval frequency becomes unreasonably high as the gray scales are increased.
In this thesis, the gray-shading active addressing techniques are investigated for showing the TFT-like images. There are several key researches for this work.
(1) At the beginning, the mathematical descriptions are given to analyze the gray-shading active addressing techniques. On this basis, various hardware problems for gray scales by active addressing methods could be easily seen.
(2) Then, a modified active addressing technique, which combines the ideas of subgroups and PHM active addressing, is proposed to resolve the tremendous hardware problem that the PHM active addressing faces. The proposed technique has the same gray-shading capability as the PHM active addressing technique, but its hardware requirement is dramatically limited for a large-row-number STN LCD.
(3) With this proposed technique, a generalized architecture and its circuit design are available for the hardware realization.
Finally, to demonstrate the proposed technique and its feasibility, a hardware architecture for 480 320 STN LCDs is available to implement the 4-bit modified active addressing display system. Based on the architecture, the circuits of the LCD controller and the required digital-to-analog (D/A) converter are implemented into ICs using CMOS logic process.
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