Document Sample
       By: Rodney G. Medina
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
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
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
                                                Conductive Clear Coating
                             Incident Light

Clear Region


                                    Frosted Region

               Nemantic Liquid Crystal

                                                                      Rodney G. Medina
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. It’s 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
Tranmissive Field-Effect LCD

    Vertical light Polarizer

         Eye                   x           Incident light

                                              Clear conducting
                                              surfaces to which applied
                                              bias is connected

                                          Vertical rod

                                   Horizontal rod

                                                                      Rodney G. Medina
         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
Reflective Field-Effect LCD



                      x          Incident light


                                    Clear conducting
                                    surfaces to which applied
                                    bias is connected

                              Vertical Light Polarizer

                                                            Rodney G. Medina
How an LCD work
  – LCD’s 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

                                                         Rodney G. Medina
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.
                                                             Rodney G. Medina
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.

                                                            Rodney G. Medina
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:
1. Computers           4. Laptops
2. Thermometers        5. Cellphones
3. Mood Rings

                                                       Rodney G. Medina
A simple LCD display from a

                              Rodney G. Medina
Rodney G. Medina

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