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Liquid Crystal Displays. T.N. Ruckmongathan Raman Research Institute Bangalore 560080. Introduction. Liquid crystal displays are popular because of: Low power consumption Low voltage operation Flat panel with thin profile Flexible size, format and shape. Classification of LCDs. - PowerPoint PPT Presentation
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Liquid Crystal Displays
T.N. RuckmongathanRaman Research InstituteBangalore 560080
IntroductionLiquid crystal displays are popular because of:
Low power consumptionLow voltage operationFlat panel with thin profileFlexible size, format and shape
Classification of LCDsPassive matrix LCD:Intrinsic nonlinear characteristic is exploited for matrix addressing
Active matrix LCD:A nonlinear element (thin film transistor) is used in each pixel
Electro-optic EffectsTwisted Nematic (TN) Super Twisted Nematic(STN)Electrically Controlled Birefringence (ECB) Polymer Dispersed Liquid Crystals Pi- CellIn Plane SwitchingBi Stable devices: ferro-electric, Zeninthal, Chiral Nematic, etc.
Molecular alignment
Twisted Structure
Twisted Nematic LCD
Electro Optic Response
Driving LCDsStatic or Direct (Non-multiplexed)Matrix Addressing (Multiplexing)Line-by-line addressingMulti-line addressingActive addressing (all the rows)
Active MatrixDiodesThin Film TransistorsMIM, Varistors etc.
Static (Direct) Drive
Matrix LCDs
Line by Line Addressing
LCD with Drive Electronics
Passive Matrix LCDThe Contrast and viewing angle decreases with multiplexingSupply voltage also increases with multiplexing
Multi-line addressing techniqueReduced supply voltageGood brightness uniformity
Color in LCDsUsing color filtersRGB sub-pixelsReduces light throughput
Gray shades1-bit2-bits3-bits4-bits5-bits6-bits7-bits8-bits
Gray scale in images 1-bit 2-bits 3-bits 4-bits 5-bits6-bits
Gray Shades in PMLCDFrame modulationPulse width modulationAmplitude modulationSuccessive approximationSpatial ditheringArea modulation
PMLCD eight gray shades
Active Matrix LCD
AMLCD Color
Active Matrix LCDThe contrast is independent of matrix sizeHigh contrastComplex manufacturing process
a-Si TFTIntegration of drivers with poly- silicon
LCD TV
Some gadgets using LCDCamcordersLCD monitorsLCD Screens CamerasMobile phones PDAs
LCD TV (23 and 30)
LCD TV 54