Understanding How SED-TV Functions

For decades, televisions have relied on the cathode ray tube (CRT)) to produce clear, vibrant images. While CRTs are still used for their excellent color reproduction, they are large and cumbersome, unable to accommodate the larger screens desired by modern consumers.

Many of the latest television models have improved upon CRTs' size and weight, but they often fall short when it comes to picture quality. Issues like limited viewing angles, poor black levels, burn-in, and other visual distortions can mar the viewing experience.

The surface-conduction electron-emitter display (SED) offers another breakthrough in television technology. Unlike other models, it merges the superior picture quality of a CRT with the slim design of a flat-panel plasma screen. With an SED-TV, you can enjoy a massive screen with excellent clarity, all in a device just a few centimeters thick.

This article will delve into the inner workings of how an SED-TV produces stunning visuals. We’ll begin by exploring the mechanics of CRTs, and then we’ll examine the process behind creating the tiny components that make up an SED-TV.

A Look Back at CRTs

Many people view CRTs as outdated, especially in comparison to newer technologies like LCD, plasma, DLP, and LCoS. However, CRTs still have their advantages, and understanding how they work is crucial to grasping the principles behind SED-TV.

In essence, a CRT directs electrons at a phosphorescent screen. When an electron strikes the screen, it lights up that specific point, or pixel. Typically, three electron streams are used, each activating a different phosphor: red, green, and blue. Your eye and brain merge these glowing points to form the image you perceive.

The electrons in a CRT are produced by a heated filament known as a cathode. The cathode is a negatively charged electrode, much like a filament in a light bulb. When current passes through it, electrons are emitted and directed towards the positively charged anode, which accelerates them toward the screen. Electromagnetic steering coils guide the electron streams, enabling them to create the image one line at a time, from top to bottom.

The electron gun, consisting of cathodes, anodes, and electromagnets, is the core component of a CRT television. You can explore more about the electron gun and its role in picture creation in How Television Works.

An SED-TV generates an image in a similar fashion. It's a flat-panel TV that replaces a single electron gun with millions of tiny CRTs. These micro CRTs are known as surface-conducting electron emitters (SCEs). For each pixel, there are three SCEs -- one for red, one for green, and one for blue. A large widescreen HD set can contain over 6 million SCEs.

Let’s examine how these SCEs generate electrons and create the image.

How the Image is Created

At the core of an SED-TV are millions of tiny CRTs, known as surface-conduction electron emitters (SCEs). Each SCE is minuscule, consisting of a layer of carbon with a central gap. One side of the gap is connected to a negative electrode, and the other to a positive electrode. When the circuit applies about 10 volts of current, electrons appear at one side of the gap.

An SED-TV features millions of SCEs arranged in a matrix, with each one controlling the red, green, or blue component of a single pixel. Instead of gradually building the image row by row, the matrix activates all the necessary SCEs to create the image almost at once.

Like a CRT, an SED-TV operates in a vacuum. The SCEs are positioned on one side of the vacuum, while the phosphor-coated screen is located on the opposite side. The screen holds a positive charge, which attracts the electrons from the SCEs.

When the electrons reach the screen, they pass through a thin layer of aluminum and collide with the phosphors, which then emit red, green, or blue light. Your eyes and brain merge these glowing dots to form the picture.

The areas of the screen that aren’t used to create pixels remain black, enhancing the picture's contrast. Additionally, a color filter sits between the phosphors and the glass, improving color accuracy and reducing reflected light.

To summarize, when an SED-TV receives a signal, it:

When the electrons strike the phosphors, the corresponding pixels light up, and your brain merges them to form a complete image. The images refresh at a rate that makes them appear as smooth motion.

This happens almost instantly, and the TV can generate a new picture up to sixty times per second. Unlike a CRT, there is no need to interlace the image by painting only alternate lines. It renders the entire image in each cycle.

The concept of a large-screen display with the quality of a CRT, yet only about a quarter-inch thick, is truly impressive. Let’s now explore the advantages and drawbacks of this TV technology.

Pros & Cons of SED-TV

SED-TVs were expected to launch in 2006, and early reviews from CES and other electronics expos highlight their impressive picture quality. SED-TVs offer all the advantages of CRT TVs, such as excellent color accuracy and deep blacks, without the bulk and weight of traditional CRTs. The wide viewing angle and SCE structure eliminate edge blurring seen in some CRT models. These sets are compact, lightweight, and more energy-efficient than other flat-panel TVs.

Determining the drawbacks of owning an SED-TV will be challenging until more people begin using them. However, many anticipate that the high cost will be a major hurdle, with rumors suggesting that a 55-inch model might start at around $10,000.

The release of the SED-TV has faced several delays. Initially set for spring 2006, Toshiba and Canon later pushed the launch to late 2007 due to cost concerns. By spring 2007, the companies announced a vague release date, citing issues with patents, supply, and production challenges [source: Reuters].

For more detailed information on SED-TVs and other TV technologies, check out the links in the following section.