LCD 基本驅(qū)動(dòng)原理

1、課程大綱課程大綱 顯示的基本原理顯示的基本原理 1. 偏光片的使用 2. Rubbing的定向 3. 液晶的定向 4. 加入電場(chǎng)後的液晶 5. 液晶與偏光片的效應(yīng)組合 LCD基本驅(qū)動(dòng)原理基本驅(qū)動(dòng)原理 1. 液晶與外加電場(chǎng)的關(guān)係液晶與外加電場(chǎng)的關(guān)係 2. TFT的基本驅(qū)動(dòng)的基本驅(qū)動(dòng) （a）TFT的機(jī)構(gòu)的機(jī)構(gòu) （b）TFT的簡(jiǎn)易等效電路的簡(jiǎn)易等效電路 （c）面板的各種極性與）面板的各種極性與Common 的不同驅(qū)動(dòng)的不同驅(qū)動(dòng) （d）Cst on Common & Cst on GateLCD的顯示原理 基本上，LCD是藉由電場(chǎng)加於液晶，改變其雙折射現(xiàn)像，並配合偏光片來決定光的路徑。以顯示出

2、對(duì)比，並利用color filter來呈現(xiàn)出色彩。 (1). 偏光片的使用偏光片的使用 ：使用偏光片，可決定光的行進(jìn)路線。 (2).Rubbing的定向：的定向：可使液晶分子呈現(xiàn)規(guī)則的排列 (3). 液晶的定向液晶的定向：可使液晶分子呈現(xiàn)規(guī)則的排列後，達(dá)到扭轉(zhuǎn)的功 能；不同型態(tài)之LCD有不同的扭轉(zhuǎn)角。(4). 加入電場(chǎng)後的液晶：加入電場(chǎng)後的液晶：當(dāng)所加的電場(chǎng)強(qiáng)度高於液晶的臨限電壓時(shí)， 改變?cè)械呐まD(zhuǎn)排列狀態(tài)。 (5). 液晶與偏光片的效應(yīng)組合：液晶與偏光片的效應(yīng)組合： 未加電壓未加電壓：當(dāng)光線通過上層偏光片，以一特定的方向進(jìn)入LCD後，藉 由液晶的扭轉(zhuǎn)將光路徑旋轉(zhuǎn)至特定之角度，而得以穿透下 層

3、偏光片的透過軸向。 施加電壓施加電壓：原有液晶分子排列的狀態(tài)經(jīng)過施加電壓後，已失去了旋轉(zhuǎn) 光路徑的功能，因此光線無法透過直交的偏光片。 TFT基本驅(qū)動(dòng)ClcTFT SubstrateColor Filter SubstrateRGBClcClcRBGTFT 基本的剖面圖基本的剖面圖舉例：舉例：TFT LCD 等效電路等效電路Gate DriversSource Driver1H1HClcCsCsCsCsCsCsCsCsCsClcClcClcClcClcClcClcClcGlassGlassGate Metal DepositionGate PatterningSiNx Depositioni

4、a-Si Depositionn+ a-Si DepositionActive PatterningData Metal DepositionData Metal Patterningn+ a-Si EtchSiNx DepositionVia Hole PatterningITO DepositionPixel PatterningPixelDataPassivation SiNxn+ a-Sii a-SiGateinsulatorSiNxGateVia holeFrame TimeGate123N1HL1L2L3DATAtF = 16.7mstg (gate on time)G0G1G2G

5、3+V1+V2V3offoffoffonononoffoffoffoffoffoffCst Scanning at-a-line - Vgh is applied to a gate line - All TFTs on a gate line are turned on - Current flows from data line to pixel and pixels on the gate line are charged up to data voltage - Vgl is applied to a gate line - All TFTs on a gate line are tu

6、rned off and pixels on the gate line holds the charged voltageDisplay FormatResolutionVGASVGAXGASXGAUXGAQXGAGate-on-time480 x640 xRGB600 x800 xRGB768x1024xRGB1024x1280 xRGB1200 x1600 xRGB1536x2048xRGB34 s27 s21.7 s16 s13 s10 sPixel Size (in 15.1”)480 m X 160 m384 m X 128 m300 m X 100 m234 m X 78 m19

7、2 m X 64 m150 m X 50 mRefreshing time tF ( Frame time ) ( dominated by the Pixel design tg )Refreshing rate = 1/ tF Gate switching time tg ( Gate-on time ) tg ( Gate-on time ) = tF ( Frame time ) / total Gate line ( dominated by product resolution)For example: tg ( Gate-on time ) = 16.7 ms / 768 ( f

8、or 14.1” XGA ) = 21.7 sR/G/B: 若各以6 bits訊號(hào)控制,則可各得 26=64 scales1 dot: R/G/B 所組成所以螢?zāi)簧弦粋€(gè)點(diǎn)由6X3=18 bits所控制故每個(gè)點(diǎn)顏色階數(shù)可有218=256K scalesFull color (True color) scale: 24 bits= 17M scales1M=1024K, 1K=1024bitsColor scale Depends onThe charging capabilityT-V (Transmission versus Voltage) curveTN liquid crystal: N

9、ormally WhiteTFT mobility (ie carrier mobility, 載子移動(dòng)率)Transmission (%)Voltage像素 Pixel dimension: 88X264 mm2 點(diǎn)距 Dot dimension: 264X264 mm2 面板的各種極性變化方式：Column inversionLine inversionDot inversionFrame inversion1st field2nd fieldPositive voltageNegative voltage246810121416Gate_EvenGate_OddData_EvenData

10、_OddSpareVgh = +15VVgl = -15Vtg = 100sVdh = +5VVref = 0VVdl = -5VVghVglVdhVdlVref246810121416Gate_EvenGate_OddData_EvenData_OddSpareVgh = +15VVgl = -15Vtg = 100sVdh = +5VVref = 0VVdl = -5VVghVglVdhVdlVref246810121416Gate_EvenGate_OddData_EvenData_OddSpareVgh = +15VVgl = -15Vtg = 100sVdh = +5VVref =

11、0VVdl = -5VVghVglVdhVdlVref246810121416Gate_EvenGate_OddData_EvenData_OddSpareVgh = +15VVgl = -15Vtg = 100sVdh = +5VVref = 0VVdl = -5VVghVglVdhVrefCommon電極的驅(qū)動(dòng)方式 Common電壓固定不變的驅(qū)動(dòng)方式 Common電壓不停變動(dòng)的驅(qū)動(dòng)方式Direct Driving of TFT LCDs DC Bias of CommonGrayScale Voltage V0V1V2V62V63V63V62V2V1V01 Frame / 1 LineAC

12、 Driving of TFT LCDsV0V1V2V62V63V63V62V2V1V0Common WaveformGraylevel Voltage1Frame / 1 LineT100%VVthVth:Vth:液晶的操作臨界電壓液晶的操作臨界電壓Vcom:共通電極訊號(hào)位準(zhǔn)共通電極訊號(hào)位準(zhǔn)正極性正極性訊號(hào)時(shí)光電轉(zhuǎn)移曲線負(fù)極性負(fù)極性訊號(hào)時(shí)光電轉(zhuǎn)移曲線Vth負(fù)極性負(fù)極性時(shí)臨界電壓正極性正極性時(shí)臨界電壓5V3.5V6.5VT100%V5V-1.5VVth正極性正極性訊號(hào)時(shí)訊號(hào)時(shí)共通電極訊號(hào)位準(zhǔn)共通電極訊號(hào)位準(zhǔn)負(fù)極性負(fù)極性訊號(hào)時(shí)訊號(hào)時(shí)共通電極訊號(hào)位準(zhǔn)共通電極訊號(hào)位準(zhǔn)正極性正極性訊號(hào)時(shí)訊號(hào)時(shí)光電轉(zhuǎn)移

13、曲線光電轉(zhuǎn)移曲線負(fù)極性負(fù)極性訊號(hào)時(shí)訊號(hào)時(shí)光電轉(zhuǎn)移曲線光電轉(zhuǎn)移曲線VthCommon inversion固定與變動(dòng)Gate inversion固定與變動(dòng)Data inversion只能使用固定的Common電極電壓Dot inversion只能使用固定的Common電極電壓Common inversion明顯垂直與水平方向都容易發(fā)生Gate inversion不明顯水平方向容易發(fā)生Data inversion不明顯垂直方向容易發(fā)生Dot inversion幾乎沒有不易發(fā)生 1. Cst on Common 2. Cst on Gate液晶畫素TFTGate LineData LineCs液晶畫素

14、TFTCommonGate LineData LineCsCs Cst on ComCst on GateHigher Open Ratio名詞解釋名詞解釋: M metal 金屬金屬 GE / SD / ITO I Insulator 絕緣層絕緣層 AS / BP 用來使上述金屬層間之分隔避免之間用來使上述金屬層間之分隔避免之間 ShortCst on Gate即使用即使用ITO/GE作電容儲(chǔ)存作電容儲(chǔ)存畫面上一個(gè)點(diǎn)為三個(gè)畫面上一個(gè)點(diǎn)為三個(gè)pixel所組成所組成( R 紅紅,G 綠綠 ,B 藍(lán)藍(lán) )而每個(gè)而每個(gè)pixel之組成要素則為之組成要素則為1.TFT device 主要作用為控制主要

15、作用為控制pixel信號(hào)之傳遞信號(hào)之傳遞2. Cst 主要功用為儲(chǔ)存電荷之用主要功用為儲(chǔ)存電荷之用,確保在下一次更新確保在下一次更新 信號(hào)來臨前可將先前之信號(hào)儲(chǔ)存於信號(hào)來臨前可將先前之信號(hào)儲(chǔ)存於pixel內(nèi)內(nèi)3. ITO 與彩色濾光片共同組成上下兩電極板提供電場(chǎng)使兩者之間之與彩色濾光片共同組成上下兩電極板提供電場(chǎng)使兩者之間之 液晶角度變化以控制液晶角度變化以控制pixel之亮暗程度之亮暗程度ClcCsClcCsCommonCommon (N-1)thScan Line (N-1)thScan LineNth Scan LineNth Scan LineCs on Common Mode Cs on Gate ModeCgdCgd液晶電容儲(chǔ)存電容掃描電極資料電極共通電極Mth Data LineMth Data Line資料電極掃描電極:Clc:Cs:Com:Cgd寄生電容液晶畫素電容:Clc+CsCst on Common & Gate的簡(jiǎn)單電路SourceDrainGateVgppVsppVgon-minVgoff-minVshVdhVslVdlVgdVghVglVgdComm