Researchers are currently pursuing a number of technologies aimed at the development of flat screens to replace television and cathode ray tube (CRT) display devices. The research is driven not so much by the needs of the home entertainment industry-although the idea of a three by four foot wall-hung television screen only one-inch thick is appealing-but by the portability inherent in the lighter and less bulky flat screen devices, their lower power consumption and freedom from geometric distortion.. Much of the research is targeted at defense industry applications.
The electroluminescent (EL) approach creates pictures using a myriad of microscopic elements, similar to single light bulbs. The illumination source is a network of narrow channels, each containing a single metallic electrode surrounded by gases. Another type of flat screen uses liquid crystal displays (LCD) similar to those in electronic watches.
In television applications EL flat-screens require unique circuitry to hook up their drive, signals with electrodes along the- extremities of the TV's picture area. Drive signals are sequenced so that they light up single photo elements, or pixels, as they connect at the intersection of horizontal rows and vertical columns. In contrast, LCD's advantage is in using very little power. Industry experts are estimating pixel density for both systems at 50 to 70 elements per inch, which means outstanding graphics resolution. A 50-inch screen could create over 1200 horizontal color elements-or about three times more pixel density than TV stations can now transmit.
Color is no problem for flat-screen TV. It's simply a matter of applying phosphors in the correct areas for EL units. The liquid crystal display material originates as color. The big challenge for the engineers in both systems is getting the cost down to affordable consumer levels. Because the sets will be solid- state, this should be possible. In fact, there are already predictions that small portable sets will become as inexpensive as a digital watch display. Hitachi has demonstrated a working model LCD pocket TV with limited resolution.
The Army is developing an EL attaché case sized videodisk player, which may be available by 1985, and would permit training in the field with on-site equipment. LCD display units offer the potential for battery powered portable terminals for automation applications.
One U.S. company-Grid Systems Inc.- has developed a portable computer which uses EL flat screen technology-the Compass Computer. Filling only one half of a brief case, the Compass fits in a magnesium case just two inches thick and weighs only 9-1/4 lb. By comparison, IBM's Personal Computer which, it is claimed does not match the Grid machine's power, weighs five times as much and takes up 13 times as much space. The basic price of the Compass is $8,150, or at least 20 percent higher than a comparably equipped computer from IBM.
The Compass Computer features a pop-up electroluminescent flat screen. The display is 1/4 inch thick and measures 6 inches diagonally. It is designed to provide finer resolution and greater flexibility in mixing graphics and text than the bulkier CRT screens used in' other personal computers. The screen is reported to cost $700, which is more than ten times as much as a standard CRT display screen.
