驅動波形對扭轉線狀液晶顯示器特性之影響

Abstract

驅動波形對扭轉線狀液晶顯示器特性之影響 研 究 生 ： 賴 佳 成 指導教授 ： 王 淑 霞 國立交通大學光電工程研究所 摘 要 本論文主要在探討驅動波形對主動矩陣式驅動的扭轉線狀液晶顯示器特性之影響，我們提出了利用共通電極調變的方式，將原來使用的驅動波形作一調變以達到改變驅動波形的目的。我們從液晶連續體彈性形變理論著手，再配合瓊斯矩陣（Jones Matrix）以電腦模擬液晶顯示器的光電特性，然後將電腦模擬的結果與實驗結果作一比較。 當我們使用傳統的驅動波形探討靜態光學特性時，因為液晶分子間的彈性力與固定的電壓交互作用，最後會達到一個平衡態，此時液晶盒的光穿透率是液晶指向矢排列分佈所造成的光的總體相位延遲，但是當我們給的電壓並不是一個恆定的電壓而是一個固定週期重複的調變電壓時，液晶指向矢會達到一個我們稱之為動態穩定的情況，反應於光學也是如此。因為人眼有視覺暫留特性，所以只要此調變電壓的重複頻率夠快，光學上是可以騙過人眼的。利用這種調變驅動波形的結果，我們可以達到降低液晶顯示器臨界電壓的特性，當然，並非液晶本身的臨界電壓真的被降低了，而是降低了從訊號源供給液晶畫素，以克服液晶彈性力使之重新排列分佈（reorientation）的電壓。而我們也使得穿透率對電壓的曲線變緩了，使可切灰階的電壓範圍擴大了，使得各灰階電壓忍受系統所造成的雜訊電壓的能力增加或可增加灰階的數量。但是我們也發現了，此種驅動方式會使此種正常白的扭轉線狀液晶顯示模式有暗態漏光的現象，而我們發覺只要讓液晶的驅動波形的調變部分電壓頻率加快的話，可以降低這種漏光現象。另外，我們也針對了調變與不調變驅動波形的灰階變換的反應時間作一探討，由動態反應曲線圖即可明顯看出反應時間並無多大差異。

The Influence of the Driving Waveform on the Performance of TN-LCD Student：Chia-Cheng Lai Advisor：Shu-Hsia Chen Institute of Electro-Optical Engineering College of Electrical Engineering and Computer Science National Chiao Tung University ABSTRACT The aim of the thesis is to study the influence of the driving method on the performance of TN-LCD, which is droved by active matrix. We have proposed a method to change the conventional driving waveform by modulating the voltage on the common electrode. We began from continuous elastic deformation theory of liquid crystal and Jones Matrix. We studied the electro-optical performance by using a computer simulation. The cell of liquid crystal of a single pixel was also fabricated, and its electro-optical characteristics were measured for various driving waveform and compared it to the simulation results. Because of the interaction of the elastic force of liquid crystal and the constant electrical voltage, the directors of liquid crystal will get a stable distribution after some time passing. When we study the static optical characteristics by conventional driving waveform, we mean that the transmittance of the cell is the result of total phase retardation of the orientation of the director of liquid crystal. But if we don’t drive it by using a constant voltage, instead modulated driving waveform repeated in a constant period, the directors will come to a situation, which we name it “dynamic stability”. The same situation responds to optical transmittance, too. Because the man’s eyes have the characteristics of persistence of vision, so the variation of transmittance will not be seen if the frequency of the frame is high enough. By this method, we could lower the threshold voltage of TFT-LCD down but not the liquid crystal. The slope of T-V curve could also be altered by various modulated waveforms and the range for the division of gray level is expanded. That is good to tolerate the noise margin of the system or useful for more gray levels. But the leakage of the dark state was found in this mode of normally white twisted-nematic. Then we discover increasing the frequency of the segment of modulation would reduce this phenomenon. In the aspect of dynamic behavior, we found that the response time is not much different to that of using a conventional waveform.