D52WLCD
18
OVERVIEW
THEORY
LIQUID CRYSTALS
Matter has three distinct states; solid, liquid, and gas
(and what some consider a fourth state beyond gas,
plasma). However, there are states of matter that may
fall between these states. Liquid crystals fall between a
liquid and a solid. Basically they are crystals that hold
their orientation (shape) but can flow similar to liquids.
Their molecules point in the same direction with respect
to each other like in a solid, but they are free to change
position like a liquid. Think of a handful of pencils. They
all point the same direction and hold their shape at
rest, but (collectively) change shape when you squeeze
or let go of them.
There are different phases and types of liquid crystals
that perform differently. Small amounts of pressure, heat,
and/or electricity can cause liquid crystals to change in
some way. Therefore liquid crystals are used in many
different ways, not just for displays. Other uses are
thermometers, window coatings, soap, etc. The types
of liquid crystals used in LCDs are called Twisted Nematics.
As the name implies, they are twisted. By applying an
electrical current to them they will untwist.
TFT Element
Pixel Electrode
(Transparent)
Insulator
Semi-conductor
Source
Gate
Drain
Glass Panel
Data Line
Gate Line
Pixel Electrode
Liquid Crystal
Common Electrode
Color Filter
Polarizer
Polarizer
Transistor
LIQUID CRYSTAL PANEL
Below is an exploded view of the Liquid Crystal Panel.
The key to an LCD's operation is the polarizers. The
polarizers only allow a certain wavelength of light to
pass through. The two polarizers are mounted at a 90
degree angle with respect to each other, which prevents
light from passing through. The liquid crystals are used
to twist the light beam 90 degrees and allow light to
pass through that pixel.
Each sub-pixel or cell (a red, green, and blue sub-pixel
equals one pixel) is controlled by a Thin Film Transistor
(TFT). This provides accurate control of each cell and
makes for an accurate picture. Some methods used in
the past that didn't involve a switch and current could
leak to surrounding cells resulting in a blurred image.
LIQUID CRYSTAL PANEL CROSS-SECTION
THIN FILM TRANSISITOR
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