Directview LCD Training 10 Theory
THEORY
TFT Element
Pixel Electrode
(Transparent)
Insulator
Semi-conductor
Source
Gate
Drain
Glass Panel
Liquid Crystal Panel
Frame
Prism
Diffusers
Reflector
Light Guide
Data Line
Gate Line
Pixel Electrode
Liquid Crystal
Common Electrode
Color Filter
Polarizer
Polarizer
Transistor
LIQUID CRYSTAL PANEL
Below (on the left) is a cross section of a 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 cell. Color comes from a simple light filter.
An LCD panel from a 15" LCD TV.
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. A TFT is a semiconductor (bottom-right picture), it behaves like a relay
switch.
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