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(lái)決定光的路徑。以顯示出

2、對(duì)比，並利用color filter來(lái)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(guò)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(guò)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(guò)施加電壓後，已失去了旋轉(zhuǎn) 光路徑的功能，因此光線無(wú)法透過(guò)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%VVthVthVth: :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)

13、移曲線光電轉(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(méi)有不易發(fā)生 1. Cst on Common 2. Cst on Gate液晶畫素TFTGate LineData LineCs液晶畫

14、素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(lái)使上述金屬層間之分隔避免之間用來(lái)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

15、要作用為控制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(lái)臨前可將先前之信號(hào)儲(chǔ)存於信號(hào)來(lái)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