LIQUID CRYSTAL DISPLAY LCDs

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L
C
D
IQUID
RYSTAL
ISPLAY
By Rodney G. Medina
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• History of LCD
• In 1970, Fergason made the first operating LCD.
• In 1971, the first LCD were demonstrated publicly
  and enthusiastically accepted.
• Early version of LCD were unstable and unsuitable
  for mass production. Only when a British
  scientist discovered "Biphenyl", a stable liquid
  crystal material, that made it possible for LCD
  technology to take off. The first generation LCD
  appeared on calculators, then game sets and
  watches.

Rodney G. Medina
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• What are Liquid Crystals
• LCD stands for Liquid Crystal Display are organic
  substances that reflect light when voltage is
  applied. The liquid crystal display consists of a
  liquid suspension between two glass or plastic
  panels. Crystals in this suspension are naturally
  aligned parallel with one another, allowing light
  to pass through the panel. When electric current
  is applied, the crystals change orientation and
  block light instead of allowing it pass through,
  turning the crystal region dark

Rodney G. Medina
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• Kinds of Liquid Crystal
• Nematic Liquid Crystal types have the rod-like
  molecules oriented parallel to one another but
  have no layer structure.
• Twisted Nematic has a segment appearance and thin
  layer of encapsulated liquid crystal.

Rodney G. Medina
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Conductive Clear Coating
Incident Light
Clear Region
V
Frosted Region
Nemantic Liquid Crystal
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• Kinds of LCD
• Transmissive Field Effect LCD
• Internal light source is on the right and the
  viewer is on the left. Only the vertical
  component of the entering light on the right can
  pass through the vertical light polarizer on the
  right. If there is no applied voltage to the
  conducting surfaces, the vertically polarized
  light enters the liquid crystal region and
  follows the 90 bending of the molecular
  structure. Its horizontal polarization to the
  left hand vertical light polarizer does not allow
  it to pass through, and the viewer sees a
  uniformly dark pattern across the entire display.
  

Rodney G. Medina
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Tranmissive Field-Effect LCD
Vertical light Polarizer
x
Eye
Incident light
Clear conducting surfaces to which applied bias
is connected
Vertical rod
Horizontal rod
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• Reflective Field Effect LCD
• The horizontally polarized Light at the far left
  encounters a horizontally polarized filter and
  passes trough to the reflector, where it is
  reflected back into the liquid crystal, bent back
  into the other vertical polarization, and return
  to the observer. If there is no applied voltage,
  there is a uniformly lit display. The application
  of the voltage results in a vertically incedent
  light encountering a horizontally polarzed filter
  at the left which it will not be able to pass
  through and be reflected.

Rodney G. Medina
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Reflective Field-Effect LCD
Glass
Reflector
x
Incident light
Eye
Clear conducting surfaces to which applied bias
is connected
Vertical Light Polarizer
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• How an LCD work
• LCDs work using these 4 concepts
• Light can be polarized.
• Liquid crystals can transmit and change polarized
  light.
• The structure of liquid crystals can be changed
  by electric current.
• There are transparent substances that can conduct
  electricity.

Rodney G. Medina
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How an LCD works? The cross-section of the TFT
LCD panel looks like a multi-layer sandwich. At
the outermost layer on either side are clear
glass substrates. Between the substrates are the
thin film transistor, colour filter panel that
provides you the necessary red, blue and green
primary colours, and the liquid crystal layer.
Completing the LCD is a fluorescent backlight
that illuminates the screen from beneath. Under
normal conditions when there is no electrical
charge, the liquid crystals are in an amorphous
state. In this state, the liquid crystal pass
through. By subjecting the liquid crystal layer
to varying amount of electrical charges, the
liquid crystal layer will allow different amount
of light to pass through, as they orientate
themselves according to the control center for
the liquid crystals.
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Just like in an ordinary CRT, the red, green and
blue liquid crystal "chambers" make up one pixel
(picture element). By subjecting the red, green,
blue chambers to varying degrees of electrical
charges, different colours can be achieved. An
entire TFT screen is made up of a grid of pixel,
with each pixel having a transistor turning it on
or off. This is where you get your resolution.
Thus, for an LCD to provide a screen resolution
1024 x 768 pixel (SVGA), it must have that number
of pixels.
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• The advantages of LCD monitors
• LCD monitors consume less power
• Do not produce electromagnetic radiation as CRTs
  do
• Do not flicker like CRTs
• Are light and slim in size
• Full viewable size

• Uses of LCD
• Computers 4. Laptops
• Thermometers 5. Cellphones
• Mood Rings

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A simple LCD display from a calculator
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Rodney G. Medina