DISPLAY units are an integral component of any computer system. We depend on it to see the output of any given instruction. Most of us regularly come in touch with it to learn the result of an executed task, to play games, watch movies, listening to music or any other activity on our computers. At this moment, the most common display technology is Cathode Ray Tube (CRT). CRT monitors look bulky, and continually expose us to gamma rays which are detrimental to our health.

Ever since researchers realized these drawbacks, they have worked on display technologies to make them less harmful to our health as well as eliminate the structural limitations. Presently, different display technologies are readily available in the market, namely Liquid Crystal Display (LCD), plasma display, touch screen, Organic Light Emitting Diode (OLED) and others. However, all display technologies, except CRT are expensive as they have embedded some advanced features. In this article I make a comprehensive survey of CRT, LCD, plasma display, touch screen and OLED that hopes to provide a clearer picture of existing display technologies.

Cathode Ray Tube (CRT)

The era of CRT monitors is approaching its conclusion. Surprisingly, large numbers of TV sets and computer monitors continue to be based on CRT technology. The underlying reasons for continuing CRT's dominance is its ability to produce a crisp and vibrant image.

The entire circuitry within the monitor can be grouped into three main categories: video signal processing and amplification, horizontal/vertical deflection and synchronizing and power supply. The operation of a CRT monitor is not very complex. A heating element in a CRT monitor heats the cathode and causes it to emit electrons, which are accelerated and focused on a phosphor screen through high voltage grids. An image (raster) is displayed by scanning the electron beam across the screen. Since the phosphor's luminance

begins to fade after a short time, the image needs to be refreshed continuously. In order to eliminate this flicker, most monitors refresh the screen at a 60 Hz rate.

Consumers with a limited

budget are likely to be most attracted to CRT monitors as it is a low cost solution and generates better image than LCD monitors. For general purposes such as preparing documents and watching movies or videos enjoy, 15 inches is usually enough but graphics and multimedia performances are better achieved by 17 inches monitors.

Liquid Crystal Display (LCD) LCD monitors break the trend of traditional display technologies. They are slim, lightweight and consume much less power than LED and gas-displays because they work on the principle of blocking light rather than emitting it. Most portable devices like laptops, PDAs and nowadays many desktop PCs used LCD technology.

Two common variations of LCDs are passive matrix and active matrix display. The active matrix LCD is also known as a thin film transistor (TFT) display. The

passive matrix LCD has a grid of conductors with pixels located at each intersection in the grid. A current is sent across two conductors on the grid to control the light for any pixel. An active matrix has a transistor located at

each pixel intersection, requiring less current to control the luminance of a pixel. For this reason, the current in an active matrix display can be switched on and off more frequently, improving the screen refresh time.

A Dual scanning technique is used in some passive matrix LCD's. In this scheme, the grid can scan twice with the same electricity and time as it took for the original technology to scan only once. Despite this advantage, the active matrix still leads the LCD world.

Plasma Display

The inside story of a plasma display is it illuminates tiny, color fluorescent lights to produce an image. Each pixel is made up of three fluorescent lights; red, green and blue. The charge causes the gas in the fluorescent light to emit ultraviolet rays, which causes the phosphor to emit color. The amount of charge

determines the intensity, and the combination of the different intensities of red, green and blue produce all the colors required.

Plasma displays were initially monochrome, typically orange, but color displays have become

very popular and are used for home theater and computer monitors as well as digital signs. Plasma technology is similar to the way neon signs work combined with the red, green and blue phosphor technology of a CRT. Plasma monitors also consume significantly more electricity than LCD-based monitors.

Plasma displays are not able to show TV programs if there is no TV tuner bundled with it. A TV tuner is a device that receives a television signal and interprets it to create a video image. Like LCD monitors, plasma displays are simply monitors that display a standard video signal. To watch TV programs on plasma display one needs to install a separate unit that has its own TV tuner.

Touch Screen

Touch screen is an exciting technology that allows users to give input through monitor. Currently two types of touch screen technology are used the

most frequently, which are the resistive system and capacitive system.

The resistive method is completely pressure sensitive. It uses a plastic layer on top of a metallic-coated glass layer that is separated by spacers. When a user touches the screen the two layers make contact on that spot. As a result, the electric field changes and the computer detect it to determine coordinates. Then a special driver translates the touch into a format that is compatible with the operating system.

The capacitive method uses a metallic coated glass panel, but without the plastic overlay. It senses the change in electricity from the electricity in your finger or from a stylus wired to the computer that emits a charge. The capacitive system transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits 75 percent, giving the capacitive system better picture quality than the resistive system.

Organic Light Emitting Diode (OLED)

It is a thin-film, light-emitting device that typically consists of a series of organic layers between two electrical contacts (electrodes). OLEDs can be made using small-molecular weight organic materials (SM-OLEDs) or polymer-based materials (PLEDs, LEPs). Unlike LCDs and FEDs, which are constructed of layered materials, OLEDs are monolithic devices, because each layer is deposited on the other, creating a single unit.

In May 2005, Samsung demonstrated a 40" OLED panel for use in future high-definition TV sets. Initially developed for display applications, OLEDs offer bright, colorful images with a wide viewing angle and low power. They do not need backlights like LCD screens. OLEDs are commonly constructed on glass, but can also be fabricated on plastic and other flexible substrate films, such as Universal Display's Flexible OLED (FOLED).

References: www.wikipedia.com www.howstuffworks.com