驅動波形對液晶顯示器特性之影響

Abstract

目前正值TFT-LCD蓬勃發展的時代，如何降低TFT-LCD的生產成本以提高競爭力，是許多人努力的目標。 交大光電所的賴佳成學長在其碩士論文(2001)裡提出，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。發現調變後的驅動波形可以降低TN型TFT-LCD在Data Driver的操作電壓，藉此可以使用成本較低的IC來設計Data Driver以降低成本、提高競爭力。除此之外，調變驅動波形也可使TN型TFT-LCD較易切灰階，不會影響反應速度的時間，不過會造成暗態時的漏光現象。 本論文主要在探討調變驅動波形，對VA型、hybrid 負型液晶型以及hybrid 正型液晶型這三種TFT-LCD特性之影響，並與TN型TFT-LCD相互比較。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，然後實際製作液晶盒來模擬一個TFT-LCD的畫素，加上不同的調變驅動波形後，量測液晶盒的光電特性再與電腦模擬的結果作一比較。 經過模擬與實驗發現，調變驅動波形可以降低VA-LCD、hybrid-負型LCD以及hybrid-正型LCD在data driver的操作電壓，使其較好切灰階並且不會影響到反應速度的時間。除此之外，調變驅動波形會造成hybrid-負型LCD與hybrid-正型LCD在暗態的漏光，但是卻不會造成VA-LCD在暗態時的漏光。 最後我們的結論便是VA-LCD最適合於驅動波形的應用。

TFT-LCD is very popular In recent years. In order to increase the competitiveness, many people study how to decrease the cost. In the Master thesis of Chia-Chen Lai, National Chiao Tung University, 2001, proposed a method to change the conventional driving waveform by modulating the voltage on the common electrode. Finding that using modulated driving waveform in TN-mode TFT-LCD can decrease the operation voltage of data driver. Thus, we can use cheaper driving IC to design Data Driver, then, we can decrease the cost and increase the competitiveness. Besides, Using modulated driving waveform in TN-mode TFT-LCD can make the gray level easier, without effecting the response time, but will induce the leakage of light on dark state. The aim of the thesis is to study the influence of the driving method on the performance of VA-mode TFT-LCD, hybrid negative mode TFT-LCD and hybrid positive mode TFT-LCD. 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. From the results of simulation and experiment, we found that use modulated driving waveform in VA-mode, hybrid negative mode and hybrid positive mode TFT-LCDs can decrease the operation voltage of data driver. And can make the gray level easier, without effecting the response time. Besides, using modulated driving waveform in hybrid negative mode and hybrid positive mode TFT-LCDs will induce the leakage of light on dark stage, but will not when in VA-mode TFT-LCD. The conclusion is that VA-mode TFT-LCD is the better one for the application of modulated driving waveform.