How-it-Works: Plasma Display Technology

Since the first plasma TVs appeared on the market less than a decade ago, a lot has changed in plasma display panel technology.

The plasma TV panels of today are more robust, less prone to burn-in, more energy efficient, thinner - some are just an inch-thick - and even more important for a display technology, they are capable of a superior picture. 

It is therefore no surprise that plasma display technology represents by far the most popular video display technology among videophiles and home theater enthusiasts looking for the best cinematic picture over larger big screen HDTVs.

The reality is that if you want the best in overall picture performance, a plasma display can deliver the best shade of black among flat-panel televisions - including the latest and more expensive LED TVs - and rear projection HDTV sets. Only the very best flat-screen CRT TVs can surpass plasmas.

Black-level performance is a most important aspect in picture quality as it helps improve the realism of dark scenes while making colors look richer and more saturated.

But... what is behind this superior performance of a plasma display panel?

Plasma Display Technology Explained

A Few 'Electron Physics' Basics First!

By definition, plasma is a state of matter (gas) where atoms are ionized by adding energy - in this case electrical energy by applying a voltage between two electrodes; this eventually leads to the flow of an electric current. In the process, positive and negative charged particles move fast towards the respectively opposite charged electrodes.

During this fast flow of particles, numerous collisions take place between electrons and atoms. These collisions cause electrons in an atom to jump to a higher energy level. However, it will soon fall back to its original energy level while releasing the extra energy in the form of a light photon.

The photon is that elementary particle responsible for all electromagnetic phenomena; it carries electromagnetic radiation - from gamma to radio. If it falls within the light spectrum, visible or otherwise - it is called a light photon.

The released light photons are in effect ultraviolet photons - meaning that the emitted radiation is invisible to the human eye. Ultraviolet light photons can be used to produce visible light by exciting phosphor atoms. Phosphors are substances that give off visible light photons when their atoms are hit by ultraviolet photons. The collision causes electrons to jump to a higher energy level - which energy is then released in the form of a visible light photon when the electron returns to its normal energy level. Different phosphor formulations yield different colors of light.

How does all this apply to a Plasma Display?

In a plasma display, electricity is used to excite the gas atoms inside the miniature cells forming the display panel; this in turn releases ultra-violet photons. The radiated UV causes the phosphor lining on these minute cells to emit energy in the form of visible colored light - the color of which depends on the type of phosphor used to line the cell.

Cross-sectional view of a plasma flat-panel display image courtesy of  howstuffworks.com

These small cells form the picture elements or pixels of the plasma display panel, and can be thought of an array of miniature colored fluorescent tubes or neon light bulbs. Plasma flat-panel displays consist of hundreds of thousands of such tiny cells that are positioned between two plates of glass. These cells are filled with neon and xenon gas.  Simple mathematics show that a typical wide screen panel with a screen resolution of 1365 x 768 pixels would have over 1-million miniature cells, while a plasma display panel supporting 1080p native screen resolution has almost 2.1 million miniature cells.

Each of these cells is further sub-divided into three sub-cells as will be explained further on, each representing one of the primary light colors (click on the image for more details). Sandwiched between the glass-plates are long electrodes on both sides of the cells. The address electrodes sit behind the cells along with the rear glass plate while transparent display electrodes sit in front of the cells covered by a protective layer along the front glass plate.

'Three' sub-cell structure of a plasma display pixel image courtesy of  howstuffworks.com

When a voltage is applied between the plasma display electrode and the respective address electrode, an electric current flows through the gas in the cell; this simulates the gas atoms to release ultraviolet photons. This ultraviolet radiation excites the phosphor lining on the inside wall of the cell - giving off energy in the form visible light.

The phosphors in a plasma display are arranged to give off colored light - red, green or blue - to build a color image. As already indicated earlier on, each picture element in a display panel is made up of three sub-pixels - each acting as a miniature light source for one for each of these primary light colors.

These colors blend together to create the final color of the pixel; this is very much the same with the way colors blend in CRTs and LCDs.

The pixel brightness in a plasma display is then controlled by using pulse-width modulation techniques. This means that by varying the duration of the voltage pulses applied to the sub-pixel electrodes several thousand times per second, it is possible to control the intensity of the resultant current pulses flowing through the individual cells. This in turn energizes each sub-cell phosphor at different levels to generate increased or decreased intensity of colored light - in line with the picture content. This makes it possible for plasma displays to generate billions of different shades of color - leading to extremely accurate color reproduction and smooth film-like image.