Classification of LCD
There are four common LCD monitors:
1.TN-LCD (Twisted NemaTIc-LCD, Twisted Nematic LCD) 2.STN-LCD (Super TN-LCD, Super Twisted Nematic LCD)
3. DSTN-LCD (Double layer STN-LCD, double layer super twisted nematic LCD) 4. TFT-LCD (Thin Film Transistor-LCD, thin film transistor LCD)
From a structural point of view, TN-LCD and STN-LCD seem to have little difference, but in essence their working principles are completely different: ①The twist angle in the TN liquid crystal cell is 90 °; the twist angle in the STN liquid crystal cell is 270 ° Or nearby values;
② In the TN liquid crystal cell, the polarizing axis of the polarizer is parallel to the long axis of liquid crystal molecules on the surface of the upper substrate, and the polarizing axis of the analyzer is parallel to the long axis of liquid crystal molecules on the surface of the lower substrate, that is, the upper and lower polarizing axes are at 90 ° to each other; In STN liquid crystal cells, the upper and lower polarizing axes and the long axes of the upper and lower substrate molecules are not parallel to each other, but form an angle, generally 30 °.
â‘¢ The TN liquid crystal cell works by using the optical rotation characteristics of liquid crystal molecules, while the STN liquid crystal cell has an angle of polarization of the incident rays through the polarizer and the liquid crystal molecules, so that the incident light is decomposed into two kinds of normal beam and abnormal beam. The beam of light produces an optical path difference and interferes when passing through the analyzer. Therefore, the STN liquid crystal cell works by utilizing the birefringence characteristic of liquid crystal.
④TN liquid crystal cell works in black and white mode; STN liquid crystal cell generally works in the case of optical path difference of 0.8μm, the interference color is yellow. When a voltage greater than Vth is applied, white light can pass through the liquid crystal layer, but it is significantly weakened when passing through the analyzer. The liquid crystal cell has a black appearance, which is called the black / yellow mode. If the optical axis of the analyzer is rotated left by 30 ° with respect to the long axis direction of the liquid crystal molecules on the exiting light side, it is the white / blue mode. That is, when no voltage is applied, the liquid crystal cell is blue; when voltage is applied, the liquid crystal cell has a colorless appearance. Therefore STN is a colored mode.
Because TN cannot display delicate characters, it is usually used in electronic watches and calculators. TN series LCD monitors have been basically eliminated as displays. STN has a larger twist angle and displays finer characters than TN. It also supports basic color displays and is mostly used for LCD TVs, video camera LCD monitors, and handheld game consoles. The subsequent DSTN and TFT were widely made into liquid crystal display devices. DSTN LCD screens were mostly used in early notebook computers. Because of the limited number of colors supported, they are also called pseudo color displays. TFT is not only used in notebook computers, but also gradually entered the mainstream desktop display market.
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