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Transcript

  • 1. Liquid Crystal Displays IQxplorer
  • 2. LCD Overview
    • LCDs are a type of light modulating display device. LCD technology does not directly emit light in order to create visualizations, it rather modifies the transmission of light to represent images.
      • On the other hand Plasma displays, CRT and OLED devices are all light emitting display devices.
    • LCDs are rapidly becoming the most popular display device available.
      • 2006 - Nearly 33% of all TVs sold in North America were LCDs
      • 2007 - Expected to surpass 50%
  • 3. History and Development of LCDs
    • Discovery of liquid crystals
      • 1888
        • Friedrich Reinitzer discovers liquid crystals
      • 1904
        • Otto Lehmann publishes work on liquid crystals
    • Innovation
      • 1963
        • Richard Williams and George Heilmeier suggest using
        • liquid crystals for making a display device
      • 1968
        • First operational LCD created by RCA using Dynamic Scattering Method (DSM)
      • 1971
        • First LCD using Twisted Nematics (TN) produced
  • 4. History and Development of LCDs (cntd)
    • Applications
      • 1970’s
        • First commercial LCDs came into existence. The technology was first used in the quartz watch and in early calculator displays.
      • 1990’s
        • Early use of colour LCDs for digital cameras and computer monitors
      • 2000’s
        • Technological improvements led to larger LCDs suitable for home theatre use.
        • Full HD 1080p displays produced
        • Currently the largest LCD panel is 108”
  • 5.
    • Basic operation of a TN (twisted nematic) LCD
      • The panel consists of a number of layers:
        • Liquid crystal layer
        • 2 transparent conductors
        • 2 perpendicular polarizing filters
        • Colour filter
      • In their natural state the liquid crystals align themselves in a helical structure. The nature of the molecules rotates the polarization of light as it passes through.
    How LCDs work
  • 6. How LCDs work
      • When an electric field is applied to the liquid crystals the twisted structure gets distorted to varying degrees depending on the voltage applied. The change in the structure subsequently causes a change in how drastically the light is rotated. This ultimately decides how much light will pass through the filters and determine the brightness of the sub-pixel.
      • When light passes through the first polarizing filter, half of it is blocked. The remaining light normally gets rotated by the liquid crystals and can pass through the second perpendicular polarizing filter. If it isn’t rotated at all, then no light will pass.
  • 7. Types of LCDs
    • Direct Electrical Connections vs Multiplexing
      • In small LCD devices, such as watches with 7-segment displays, it is possible to have a direct connection to control each segment.
      • This is not feasible for larger displays, like colour monitors. Millions of individual connections would be required. Therefore the pixels must be controlled by a multiplex array. Multiplexing reduces the connections required substantially.
      • There are associated problems with multiplexing since some of the inactive pixels will still be effected by the voltage running through their row or column. This was solved through “switching” where thin film transistors are used in the multiplex array, ensuring only activated pixels are effected.
  • 8. Types of LCDs
    • Passive vs Active Matrix
      • Passive
        • Each pixel must retain it’s state without a steady electric charge
        • Scanned one pixel at a time
        • Poor contrast, and very slow response times
      • Active
        • Electric charged is stored between refreshes
        • Scanned one row at a time
  • 9. Types of LCDs
    • A light source is required for LCDs
    • Types of lighting
      • Transmissive
        • Backlight is used to light the display
          • Poor performance outdoors or in bright light. Solutions: Brighter backlight or less reflective surface
      • Transflective
        • Backlight and a reflective mirror surface are both used
          • Good overall performance in all lighting conditions
      • Reflective
        • Only ambient light is used via a mirror surface
          • Ie. Watches
  • 10. LCDs
    • Advantages
      • thin and lightweight
      • low power consumption
        • Plasma: 200-1000W+ LCD: 100-200W
      • relatively cheap and getting cheaper
      • higher resolutions for less
        • 1080p
      • size range
      • lifespan
    • Disadvantages
      • poor contrast ratio
        • “ Backlight bleed”
      • response times
      • viewing angles
  • 11. Future
    • LCD will continue to close the gap with Plasma
      • Technological advances will further improve the contrast ratio and response time of LCDs
      • LCD will likely be the prominent display device for the foreseeable future
    • 3D LCD
      • Stereoscopic vision without the need for glasses or other aids
        • Projects a different image to each eye
    • Sharp Dual Directional Viewing
      • Using similar technology to the 3D LCD, two distinct images can be displayed to two different viewers
        • Triple viewing
        • Privacy
    • OLED Displays
      • Can be put onto flexible surfaces
      • Better colours, contrast, brightness, more efficient
      • Lifespan issues though
  • 12. References
    • P. Engardio, E. Woyke, M. Ihlwan, K. Hall. 2007. Flat Panels, Thin Margins. Business Week. Issue 4023. pg. 50-51.
    • Jeffrey A. Hart. Technology, Television and Competition. Cambridge University Press, 2004.
    • D.J. Channim, A. Sussman. Liquid-Crystal Displays, LCD. Topics in Applied Physics Volume 40: Display Devices . Ed. J. I. Pankove. New York, 1980.
    • Liquid Crystal Display http://en.wikipedia.org/wiki/Liquid_crystal_display

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