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twisted nematic (display) (TN)

LCD displays are based on liquid crystal cells in TN(twisted nematic) technology. This technology exploits the effect that polarized light passing through liquid crystal molecules is rotated in its plane of polarization. When an electric field is applied to the liquid crystal cell, the liquid crystal molecules orient themselves parallel to the electric field, cancelling the rotation of the plane of polarization.

A TN cell consists of two glass plates coated with transparent electrodes. On both glass plates are polarizers, which polarize the light in different planes of polarization. The glass plates are coated with transparent electrodes and between the glass plates is the nematic liquid crystal. The passive method uses a mirror located below the TN cell to reflect the light.

When no voltage is applied to the electrodes, unpolarized light enters the TN cell and is rotated 90° as it passes through the liquid crystal, allowing it to pass through the second polarizer rotated 90°. It hits the mirror from which it is reflected and exits the TN cell again. The resulting display appears silvery gray.

Structure of the passive TN cell

Structure of the passive TN cell

If a voltage is applied to the electrodes, the light is not rotated in the TN cell and thus cannot pass the second polarizer. The display remains dark. In this TN technology, the angle of rotation of the polarized light is 90 degrees, the segments are switched on or off, grayscale is possible in principle, but not common. On the display, the characters are shown in gray and the background in black.

The various twisted nematic (TN) technologies

The various twisted nematic (TN) technologies

In order to increase contrast, color representation and viewing angle, TN technology has been modified by various manufacturers and improved variants such as DSTN (D, Double), CSTN (C, Color), FSTN (F, Film) and TSTN (T, Triple) have emerged alongside the classic TN technology, to name just a few. The simple TN black and white displays have the widest distribution of all liquid crystal technologies and are based on LCD technology. They are used millions of times in watches, calculators, in display elements and display modules, in displays of measuring instruments, etc. They also form the basis for LCD displays because of their low latency.

Informations:
Englisch: twisted nematic (display) - TN
Updated at: 24.10.2015
#Words: 364
Links: lost calls delayed (LCD), crystal (XTAL), terminal node (TN), light, polarization
Translations: DE
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