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The general principle of the LCD screen

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The general principle of the LCD screen

The LCD screen uses liquid crystal to control the passage of backlight. The basic structure

of a TFT-LCD (Thin Film Transistor) screen may be thought of as two glass substrates

sandwiching a layer of liquid crystal molecules. The whole screen has been divided into

many columns and rows. In each cross of a column and a row is the display unit (pixel). The

front glass substrate is fit with a color filter which gives each pixel its own color, while the

back glass substrate has transistors fabricated on it. When a positive or negative voltage is

applied through a transistor to a pixel, the liquid crystal changes direction and allows

backlight to pass through the pixel as shown in Figure 1.

In Figure 1, the gate driver sends a line selection pulse to the top line and turns on the first

line TFT. The data (analog voltage) is transferred from the source driver to the pixels in the

first line. After the first line data is updated, the gate driver selects the second line. After the

last line is scanned, the picture on the whole screen is updated which is referred to as a

frame update. Then the gate driver starts from the first line again and begins the next frame

update.

Figure 1.

LCD screen layout