1、Chapter 2 LCD顯示原理1液晶以分子排列分類Nematic liquid crystal線狀液晶LCD用液晶之主流排列特點:分子傾向指著某個特定方向2液晶之介電異向性液晶之介電常數值越大產生的induce dipole越大介電異向性決定LC之轉動3Induced Dipole04LC birefringence n定義n|nn= n|- nLCLCn會改變入射光的偏振進而讓LCD產生顯示的效果EEEEEE5液晶配向之方法配向過程: 配向膜印刷 rubbing process 玻璃對組注入LCInject LCPanel assemblyAttach SpacersApply Seal

2、antRubbingCell ProcessApply PI FilmSeal6Homogenous alignment (ECB)Homeotropic alignmentTwisted alignment (Twisted nematic)Hybrid alignment配向過程: 配向膜印刷 rubbing process 玻璃對組注入LC常見液晶配向排列模式Alignment film7晶體光學光入射液晶之可能現象和效應吸收(absorption)和穿透(transmission)折射(refraction)和反射雙折射效應(birefringence effect) 旋光效應(pol

3、arization rotation effect)散射(scattering)繞射(diffraction)色散(dispersion) 8Polarized WaveLinear PolarizationCircular PolarizationLeft-hand/Right-handElliptical Polarization9Polarization of Optical Waves光偏極化之物理機制: (1) Dichroism (selective absorption)(2) Birefringence (double refraction)(3) Reflection(4)

4、ScatteringEx: dichroism10相位延遲與偏振狀態之關係 = 0 或 時, 電場為線偏極化, 偏振方向與x軸之夾角 = /2 且 時, 電場為圓偏極化(正號為左圓;負號為右圓偏振) 若 時, 電場為橢圓偏極化且主軸在x或y軸上(3)其餘狀況為橢圓偏振0/2-/2-/43/4-/4-3/4E=Ex(z,t)+Ey(z,t)11為相位差12=0Time increases線偏振圓偏振=/2ExEyEyExEyExExEyExEyEyExEyExExEy(Assume Eox=Eoy)圖示相位延遲與偏振狀態之關係13雙折射晶體種類光在一晶體內傳播時若看到兩種折射率則此晶體為雙折射晶

5、體(例如液晶)光在雙折射晶體內的折射率值跟光的入射角度和偏振有關單光軸晶體nx=ny nz雙光軸晶體nx ny nz14k正單光軸晶體之折射率橢圓球nxnynzneffno正單光軸晶體 nx=ny01. 顯示器用液晶為正單光軸液晶2. 棒狀液晶為正單光軸光入射時單光軸晶體之雙折射特性短軸 no=nx=ny光入射晶體時:晶體之兩個折射率值分別為k垂直平面和折射率橢圓球產生之橢圓截面之長短軸橢圓截面長軸15k負單光軸晶體(negative uniaxial)之折射率橢圓球nxnynzneffno負單光軸晶體 nx=nynzBirefringence n=neff-no 時,旋光效應NWV=0As

6、V increasesi.e. u1,=90o, =0o1st minimum and polarization rotation effect(NW)43TN之e-mode和o-mode入射光偏振和第一層LC分子平行e-mode入射光偏振和第一層LC分子垂直o-mode44對比的定義CR對比高對比低NW黑畫面電壓白畫面電壓45視角的定義CR10No Gray-Scale Inversion Color Dispersion (uv0.004)46顯示器座標定義Normal= 0: Viewing Angle: Viewing Direction=0=180=270=90=0=180=270=

7、90Normal= 0: Viewing Angle: Viewing Direction上下左右47Iso-Contrast Contour204060800030609012015018021024027030033048TN-LCD的視角限制Bright stateDark stateLC residual phaseLC optical anisotropy視角不足等對比(iso-CR)圖CR=1049TN-LCD的視角限制LC directorUpperRightLowerLeftTop ViewUpperLowerGlass substrateSide ViewLC directo

8、rGlass substrateGrey Scale Inversion50GSI angleGray Scale Inversion(GSI)的定義51n=0Gray Scale Inversion(GSI)原理LC (液晶分子)光52Gray Scale Inversion(GSI)原理V1V1V2V2V1V2V1V2Gary scale inversion灰階反轉53灰階反轉(Gray Scale Inversion)54CIE (Commission Internationale de lEclairage ) x-y色座標顏色用座標來表示越靠近邊界顏色越飽和白色座標?55GSICol

9、or dispersion視角的定義56NTSC Ratio(色域)的定義National Television System CommitteeEBU: European Broadcasting Union NTSC ratio = 100 %NTSCRGBcolor gamutColor saturation index 57High NTSC ratioLow NTSC ratioNTSC ratio 色彩飽和度58Equivalent Circuit of a PixelCapacitorLC layer59LCD Module StructureModulePolarizerCF

10、(Color Filter)LCArrayCell (Panel)Back Light + PCBPolarizer60Definition of Resolution 1-pixel including R,G,B 3-sub-pixel1-G-sub-pixel61CF頻譜Backlight頻譜LCD顯色原理B/LCF= outputx62RGBCMYWRGB混色關係63Aperture Ratio of a PixelEffective area= Aperture Ratio64QVGA: 320 xRGBx240VGA: 640 xRGBx480SVGA: 800 xRGBx600X

11、GA: 1024xRGBx768SXGA: 1280 xRGBx1024SXGA+: 1400 xRGBx1050UXGA: 1600 xRGBx1200Some terminology of display resolution NTSC: 525-linePAL: 625-lineHDTV: 1920 x1080VCD: 352x288DVD: 720 x576QCIF+a: 220 x176QCIF: 144x176Data DisplayVideo Display65Passive Matrix LCD (PM-LCD) vs. Active Matrix LCD (AM-LCD) PM-LCD: TN/STN 1.無開關元件 2.沒有操作的畫素會受其他 畫素寫入電壓的影響 3.中低解析度, 低單價產品AM-LCD: 1.以TFT作為畫素(pixel)開關及儲 存電容 2.適合高解析度66TFT的作用因TFT元件的動作類似一個開關(Switch)，液晶元件的作用類似一個電容，藉Switch的ON/OFF對電容儲存的電壓值進行更新/保持。SW ON時信號寫入(加入、記錄)在液晶電容上，在以外時間 SW OFF，可防止信號從液晶電容洩漏。在必要時可將保持電容與液晶電容並聯，以改善其保持特性.保持電容- 儲存電容TFT元件加入電壓液晶67GDSDSGT