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Basic information

• Liquid crystal was discovered by an Austrian botanist Fredreich

Rheinizer in 1888.

• "Liquid crystal" is neither solid nor liquid (an example is soapy

water).

• Important: in the mid-1960s, it was shown that liquid crystals

when stimulated by an external electrical charge could

change the properties of light passing through the

crystals. • The early prototypes (late 1960s) were too unstable for mass

production. But all of that changed when a British researcher

proposed a stable, liquid crystal material (biphenyl).

• Today's color LCD TVs and LCD Monitors have a sandwichlike

structure .

What is TFT LCD?

• TFT LCD (Thin Film Transistor Liquid Crystal Display) has a

sandwich-like structure, liquid crystal fills the space between

two glass plates.

• TFT Glass has as many TFTs as the number of pixels

displayed, while a Color Filter Glass has color filter which

generates color.

• Liquid crystals rotate according to the difference in voltage

between the Color Filter Glass and the TFT Glass.

• The amount of light supplied by Back Light is determined by

the “amount” of rotation of the liquid crystals.

• How it works?

The source of light produces a light. The light passes through

liquid crystal, its intensity is influenced by other layers,

especially by liquid crystal.

Basic structure: two layers made of glass, liquid crystal

between them.

• The flow of light is controlled by the voltage applied to the

liquid crystal (between color filter glass and TFT glass).

• According to the voltage applied, the structure of the liquid

crystal rotates (different angle for different pixel/subpixels) –

thus for each pixel/subpixel different amount of light passes

through the liquid crystal.

• TFT glass – transistors are on the surface, each of them

controls the voltage brought to ITO electrode.

• Front glass – Colored RGB filters on the surface. They develop

each color in the intensity corresponding to the amount of light

passing through the liquid crystal.

• The electrode on the side of screen is common for all pixels.
• The voltages brought to signal lines are derived from values transferred through DVI (from graphics adapter to monitor).
• On the glass layer, the number of transistors is the same as the number of pixels multiplied by 3 (each pixel consists of 3 subpixels) – the number of TFTs might be a problem from the 11 technological point of view (the association with the resolution required).
• Each subpixel has its own transistor, ITO electrode and capacitor.
• Note: in mono monitor there should be no subpixels but just one TFT (transistor) for each pixel.
• By scanning the gate bus-lines sequentially, and by applying signal voltages to all signal lines in a specified sequence, we can address all pixels. One result of all this is that the addressing of an LCD is done line by line.
• Mono LCDs are designed to produce gray levels - intermediate brightness levels between the brightest white and the darkest black a unit pixel can generate. There can be either a discrete numbers of levels - such as 8, 16, 64, or 256 - or a continuous gradation of levels, depending on the LCD monitor.