Monday, August 29, 2005
Plasma Displays: An Overview
Since the day television was invented, TV technology has certainly been refined quite a bit, but the core concept has remained the same. Even today most of the televisions are built on the age old Cathode Ray Tube (CRT) technology which no doubt has been modified to make bigger, better screens to give a larger crisper picture and subsequently, a much better viewing experience. There are limitations to CRT that are being felt increasingly as the need for higher resolution televisions increase each day. For instance, consider that even the lowest resolution that you can get on the computer monitor you are viewing is 640x480 whereas the best resolution that the finest analog TV can give you is a maximum of 480 horizontal lines. Compare this to at least 1024x768 resolution that we are used to seeing on our desktops and you can see why there is such a hue and cry about finding a whole new system for televisions.
The search and the subsequent research has led to quite a lot of technologies and standards being spewed out of labs, and of course add to that the conundrum of interlaced, progressive, high-definition and other such standards. Needless to say, you have nice soup that no one is sure consists of what exactly. At CoolTechZone.com, we have been doing a technology series to bring to you the various options that are available, and one of the strongest contenders is Plasma Display. The most amazing aspect of plasma TVs, apart from the new attractive technology they use instead of the mundane CRT, is that they are the same size or larger than the largest CRTs with their width averaging approximately four inches.
Principle:
If you have any idea as to how a television works, you will know that RGB or Red, Green and Blue are the three basic colors that combine in various amounts to give you all the colors in the spectrum. The core concept in plasmas is the same: manipulation of the RGB elements to display an image on the screen.
So, what exactly is plasma? Plasma by definition is one of the four states of matter (apart from solid, liquid and gas) and consists of positively and negatively charged particles, which are added in roughly the same quantity. This obviously makes the gas more or less inert but ensures that the charged particles are free to conduct electricity. Plasma can be produced if a gas is energized enough to split the molecules into positive and negatively charged ions. Mostly, the plasma displays use a mixture of noble gases like Neon and Xenon.
Imagine you have plasma inside a covered vessel (this is not entirely possibly but just for the sake of an example, imagine…). When electricity is passed into the plasma, the electrons from the current (free electrons moving around is basically how current travels) collide with the inert atoms and result in the ionization (ionization signifies that the atom no longer consists equal number of positively and negatively charged particles but one or the other has the upper hand) of the atom.
The negatively charged ions are attracted towards the positive electrode of the battery while the positively charged ions are attracted towards the negative electrode of the battery. While the particles are moving towards the appropriate battery terminal, they may or may not collide with each other. If they do collide, then it leads to the dropping of electrons from one state of energy to another, which results in releasing light photons in the process (If you have read our Organic Light Emitting Diode (OLED) Technology: An Overview, you already know how the LED lights produce light photons. The concept is pretty similar here.).
Now the problem in plasma (unlike OLED) is that the light photons thus released belong to the Ultraviolet band and are therefore invisible to human eyes. This was where researchers got hitched until someone came up and suggested that they use these UV photons to incite visible light photons. Now to better understand this concept, lets look at how a normal plasma display is constructed.
Construction:
The plasma televisions of today use Xenon and Neon gases inside. There are two sheets of glass that sandwich between them, thousands and thousands of tiny little cells filled with a mixture of Xenon and Neon. Each of these cells can be considered a pixel and is further divided into three sub-pixels or cells, each making up one of the three colors (Red, Green or Blue). Along the glass plates, these cells are surrounded by electrodes on both sides; the electrodes along the glass plate at the rear are called address electrodes. The electrodes in the front are of course made of transparent material (to facilitate seeing the emitted photons, of course) and are covered in insulating material to prevent conduction of electricity outside the display, which would otherwise give users a disturbing shock.
Both electrode sets, in conjunction with each other, span the entire screen creating a grid similar to active matrix displays. In order to ionize the gas in any cell, electric current is passed through the electrodes forming the cell a few thousand times within a second. Each time a different colored cell is charged, this charges the atoms and converts them to ions and facilitates the release of UV photons due to the ionic collision.
The inside wall of the cell is meted with a special treatment of a phosphor coating. This is done to exploit the phosphors property of giving out light when it comes in contact with other light.
Since the UV photons are released inside the cell, they hit this phosphor and one of the phosphor’s electrons gets an energy boost and heats up, thus jumping to a higher energy state. Since the hit from the photon is not a continuous process, in the sense that once it has hit an electron, that electron will not get additional energy, the electron comes back to its original state and gives up some of the energy it has which is of course released in the form of a light photon, only this time, they are in the visible spectrum.
The concept of RGB is attained by coating three sub-cells (remember how each cell in the matrix was sub divided into three smaller cells?) with red, green and blue coatings respectively, so whichever color is required, that sub cell is charged. Of course, if you need more colors, you’ll need to mix and match the RGB cells to give the final color to the pixel. This process is repeated cell after cell and pixel after pixel to give you the final brilliantly bright picture that you see on a plasma TV.
This in essence is how plasma TV displays images. An interesting offshoot of this technology is the great viewing angle. This is because each pixel is lit up individually from within, which ensures that we are able to view it from most angles.
The main advantage apart from the great viewing angle is the fact that the displays are amazingly slim and have the most awesome flaunt value in your living or TV room, however, the style comes at a pretty steep price with a 42-inch screen costing you between $1500 to $2000.
Plasma technology definitely holds great promise for the future but as with all "emerging" technologies, prices need to come down for mass acceptance, which is required for mass production, faster market adoption rate and overall product costs. However, until prices are somewhat lower than they are currently, hopefully manufacturers will refine and advance Plasma TVs to make them a desirable option.
source:http://www.cooltechzone.com/index.php?option=content&task=view&id=1733&Itemid=0&limit=1&limitstart=2
