Creating the Picture
The heart of an SED-TV is the millions of miniature CRTs, called surface-conduction electron emitters (SCEs). An SCE is microscopic, and it consists of a layer of carbon with a gap down the center. One half of the carbon layer connects to a negative electrode, and the other connects to a positive electrode. When the circuitry delivers about 10 volts of current to the SCE, electrons appear at one side of the gap.
An SED-TV has millions of these SCEs arranged in a matrix, and each one controls the red, green or blue aspect of one pixel of the picture. Rather than directing electrons to create the image one row at a time, the matrix activates all the SCEs needed to create the picture virtually simultaneously.
As with a CRT set, the inside of an SED-TV is a vacuum. All of the SCEs are on one side of the vacuum, and the phosphor-coated screen is on the other. The screen has a positive electrical charge, so it attracts the electrons from the SCEs.
When they reach the screen, the electrons pass through a very thin layer of aluminum. They hit the phosphors, which then emit red, green or blue light. Your eyes and brain combine these glowing dots to create a picture.
Any part of the screen that's not used to create pixels is black, which gives the picture better contrast. There's also a color filter between the phosphors and the glass to improve color accuracy and cut down on reflected light.
To tie it all together, when the SED-TV receives a signal, it:
- Decodes the signal
- Decides what to do with the red, green and blue aspect of each pixel
- Activates the necessary SCEs, which generate electrons that fly through the vacuum to the screen
When the electrons hit the phosphors, those pixels glow, and your brain combines them to form a cohesive picture. The pictures change at a rate that allows you to perceive them as moving.
This process happens almost instantaneously, and the set can create a picture sixty times per second. Unlike a CRT, it doesn't have to interlace the picture by painting only every other line. It creates the entire picture every time.
The idea of a big-screen picture with CRT quality in a package that's about a quarter of an inch thick is pretty amazing. We'll look at the pros and cons of this TV technology next.