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Liquid Crystal Displays

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.

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Liquid Crystal Displays

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  1. Liquid Crystal Displays T.N. Ruckmongathan Raman Research Institute Bangalore 560080

  2. Introduction Liquid crystal displays are popular because of: • Low power consumption • Low voltage operation • Flat panel with thin profile • Flexible size, format and shape

  3. Classification of LCDs • Passive matrix LCD: Intrinsic nonlinear characteristic is exploited for matrix addressing • Active matrix LCD: A nonlinear element (thin film transistor) is used in each pixel

  4. Electro-optic Effects • Twisted Nematic (TN) • Super Twisted Nematic(STN) • Electrically Controlled Birefringence (ECB) • Polymer Dispersed Liquid Crystals • Pi- Cell • In Plane Switching • Bi Stable devices: ferro-electric, Zeninthal, Chiral Nematic, … etc.

  5. Molecular alignment

  6. Twisted Structure

  7. Twisted Nematic LCD

  8. Electro Optic Response

  9. Driving LCDs • Static or Direct (Non-multiplexed) • Matrix Addressing (Multiplexing) • Line-by-line addressing • Multi-line addressing • Active addressing (all the rows) • Active Matrix • Diodes • Thin Film Transistors • MIM, Varistors etc.

  10. Static (Direct) Drive

  11. Matrix LCDs

  12. Line by Line Addressing

  13. LCD with Drive Electronics

  14. Passive Matrix LCD • The Contrast and viewing angle decreases with multiplexing • Supply voltage also increases with multiplexing • Multi-line addressing technique • Reduced supply voltage • Good brightness uniformity

  15. Color in LCDs • Using color filters • RGB sub-pixels • Reduces light throughput

  16. Gray shades 3-bits 1-bit 2-bits 6-bits 4-bits 5-bits 7-bits 8-bits

  17. Gray scale in images 1-bit 2-bits 3-bits 4-bits 5-bits 6-bits

  18. Gray Shades in PMLCD • Frame modulation • Pulse width modulation • Amplitude modulation • Successive approximation • Spatial dithering • Area modulation

  19. PMLCD eight gray shades

  20. Active Matrix LCD

  21. AMLCD Color

  22. Active Matrix LCD • The contrast is independent of matrix size • High contrast • Complex manufacturing process • a-Si TFT • Integration of drivers with poly- silicon

  23. LCD TV

  24. Some gadgets using LCD Camcorders PDAs Mobile phones LCD monitors Cameras LCD Screens

  25. LCD TV (23” and 30”)

  26. LCD TV – 54”

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