超扭轉矩液晶顯示器之改良式主動尋址技術

Abstract

與薄膜電晶體液晶顯示器相較，超扭轉矩液晶顯示器提供了一種較低廉的平面顯示器技術。然而，使用超扭轉矩液晶顯示器來顯示動態影像，其反應速度仍嫌太慢，以致無法滿足與日俱增的多媒體需求。過去幾年當中，從液晶材質著手，改善液晶分子的反應速度以求提昇其動態響應，並無法得到滿意的結果。因為隨著液晶分子反應速度的加快，使用傳統的方式來驅動液晶顯示器將使得畫面亮度變低、對比變差甚至發生閃爍的現象。主動尋址技術是一種新的液晶顯示器驅動方法，可以用來克服上述之現象與問題，達到在快速反應的液晶面板上顯示動態影像之目的。然而在使用主動尋址技術以顯示灰階影像方面，兩種主要的主動式尋址灰階顯示技術卻都有硬體製造與設計上的困難。脈衝高度調變主動尋址的方式可以顯示無限階層的灰階影像，然而此法需要複雜的加法、平方以及開根號運算。隨著螢幕的尺寸變大，列數變多，硬體的大小亦隨列數成正比增加，最後整個硬體線路會變得十分的龐大。列電壓調變主動尋址的方式對硬體之需求較少，然而隨著灰階數之增加，整體驅動線路之操作頻率將變得很高，並不實用。因此，列電壓調變的驅動方式僅適用於灰階數較少之液晶螢幕。 在本論文中，將探索主動尋址之灰階顯示技術，以求在快速反應超扭轉矩液晶顯示器上達到和薄膜電晶體液晶顯示器一樣高品質之映像。整個論文裡有幾個關鍵的研究主題，包括： (1) 首先，我們使用數學導證來分析灰階主動尋址技術，以此為基礎，使用主動尋址技術來顯示灰階影像的原理及問題所在將可以很容易地去了解。 (2) 然後，我們提出了改良式主動尋址技術。此法結合了子群以及高度脈衝調變主動尋址之觀念，和脈衝高度調變技術一樣，此法能顯示無限階層的灰階影像，但是對於列數較高之液晶面板，拜子群概念之賜，驅動線路之運算硬體又增加有限，因此非常適合實際之運用。 (3) 對於此一改良式主動尋址技術，我們化簡其數學模型，並提出了一個通用的硬體架構及其電路設計方法以供實際運用之參考。 最後，為了展示所提之技術以及其可行性，我們設計了一個改良式四位元主動尋址系統給480×320超扭轉矩液晶顯示器用。在這系統裡，我們使用互補式金氧半邏輯製程把驅動線路控制器以及欄訊號數位類比輸出線路分別做成積體電路。

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.