Home > Hd TV and monitors > Technology Behind LCD TV

Technology Behind LCD TV

December 21st, 2010 Leave a comment Go to comments

This article is for the laymen to understand what LCD TV technology is all about in a peripheral manner and thus no rigorous attempt is made to describe LCD TV technology threadbare

While discussing LCD technology it is pertinent to discuss about Liquid Crystals first.

Liquid crystals are so named because this substance can manifest the behavior of liquid in some aspects and solid (Crystal) in some other aspects. That is the Liquid Crystal can co-exist both as solid and liquid states simultaneously although being closer to liquid state. It has two melting points from solid to a turbid liquid state and then another melting point converts the turbid liquid to clear liquid state. It is the intermediate state of turbid liquid which also partially behaves as solid crystal that is utilized for LCD TV technology. As the molecules of this hazy Liquid crystals tend to maintain their orientation like solid crystals and at the same time can also partially move in different positions like natural liquid molecules, the name of ‘Liquid Crystal’ has been given to this type of substance.

Liquid crystals are available in a variety of properties. The ones used in LCD TV manufacturing have a naturally twisted molecular structure and are referred as Nematic Phase Liquid crystals. Nematics are rod shaped molecules of the liquid crystal substance (used for LCD TV) of about 20 angstroms length which can be oriented suitably by application of a small electrical voltage for a small current to flow and/or by a microscopically grooved surface (called directors) in contact with the liquid crystal solution. Flow of the current through these Nematics untwists the crystals in varying degrees in an anticipated and controllable manner depending on the applied voltage. Now this property of Nematic Phase Liquid crystals is made to interact with (polarized) light to form the basic technology in making an LCD TV.

Then we must understand what is a pixel as digital images are always measured in pixel both length and breadth wise. A pixel is a tiny square (normally invisible to naked eye) that represents a color value of a very small area on a digital display; millions of such pixels forming the total color image on the display screen. A pixel is somewhat like one small colored mosaic tile amongst hundreds on a wall or floor. When viewed from a distance the boundaries of these individual tiles become obscured and a whole pleasing colored image is perceived. However if we blow up or zoom an image 500% or more individual pixels may become visible as tiny squares in a whole graphic

In numeric terms, a 3-mega pixel camera may have 2048 pixel columns wide and 1536 rows tall making a total of 5048*1536=3145728 pixels or little over 3 million pixels or in short 3-mega pixels. So pixels are very small picture elements the combined effect of which represents the whole image on display.

The typical LCD display assembly may consist of two polarizing films on two glass plates between which the liquid crystal solution is sandwiched. Either LED or fluorescent back light is made incident upon the first polarizing film on the first glass plate which allows vertical vibrations only of light incident on it blocking rest of the vibrations. The vertical vibrations of the so polarized light pass through the first glass plate which has microscopic grooves on its inner side that has the same direction as the polarizing filter. These grooves cause the first layer of the liquid crystal molecules to align with the direction of the grooves or in other words the direction of the polarizing filter. The light from the first filter thus freely enters the naturally twisted rod shaped molecules and takes the twisted course of these molecules and reaches the second glass plates. The molecules form the picture element or pixels of the display. A transparent electrode matrix is placed in between the first glass plate and the liquid crystal solution, so that the applied signal voltage (suitably amplified) can untwist the twisted molecules to an extent depending upon the amplitude of signal voltage. The resultant current passing through the liquid crystals untwists the crystals to varying degrees depending on signal amplitude. In the process lights plane of vibration changes to that of the crystal molecules and at the entry of the second glass plate more or less or no light passes through the second polarizing filter on the face of the display.

A color filter layer is paced between the liquid crystal solution and the front glass plate. This filter selectively allows red, green and blue light waves to three sub-pixels formed by the molecules of the liquid crystal solution. The three colors of the sub-pixels form a tiny picture element or one pixel.

Thus if each red, green and blue sub-pixel can display 256 different intensities of their respective color, then each pixel can produce a possible combination of 16.8 million (256x256x256) colors. That is why LCD TVs are so vivid in color representation out-matching the conventional CRT TVs.

However in today’s era of high resolution, high speed image display technology, thin film transistors or TFT (along with associated capacitors) are used in place of electrodes and arranged in a matrix, one TFT each to control one sub-pixel, so that the signal voltage can be applied to each sub-pixel individually thereby reducing color overlaps and improving response time creating images of amazing quality and vivid colors. This type of TFT matrix is called active matrix in LCD TV parlance.

Categories: Hd TV and monitors Tags:
  1. No comments yet.