LCD Technology

LCD Technology Introduction

LCD Technology Working principles:

LCDs are made from liquid crystals, an intermediary substance between a liquid and a solid. When liquid crystals are inserted between alignment layers, they line up with the grooves of the layers. Light then follows the direction in which the liquid crystal molecules are arranged. When an electrical charge is applies, the molecules re-arrange themselves in a vertical pattern and light passes through without being twisted.

A combination of polarizing filters along with alignment layers and liquid crystal molecules form a liquid crystal display. Two types of drive panels are used to control an LCD, active and passive. An active matrix display contains a transistor while a passive one does not. A transistor allows for superior picture quality and faster response times. All Vision Touch LCDs contain a transistor.

When two polarizing filters are arranged along perpendicular axes, as in the first illustration, light passes through the lead filter and follows the helix arrangement of the liquid crystal molecules. The light is twisted 90 degree, thus allowing it to pass through the lower filter. When voltage is applied, however, the liquid crystal molecules straighten out of their helix pattern. Light is blocked by lower filter and the screen appears black because of there being no twisting effect.

The Figure left shows the typical structure of a TFT LCD. This simplified illustration omits the transparent electrodes and alignment layers for twisted nematic (TN) liquid crystal that are placed on the inner surfaces of the glass substrates.

 

Above 2 figures shows how signal voltage controls the transmission of light in a TN-type LCD. The arrangement of liquid crystal molecules varies between the two states illustrated below. The various arrangements are caused by an electric field corresponding to the signal voltage between the transparent electrodes on arrangement; light transmission is controlled by the signal voltage.