Before flat screens as we know them today, there were squashed versions of the CRT (cathode ray tube) invented by German physicist Ferdinand Braun in 1897. An electron gun at one end fired on a fluorescent surface at the other. So they were straight and long. As the cathode ray tube approached its hundredth birthday there were several attempts at modifying it. They all flopped.
In the early 1980s Sinclair announced a £5 million, four year investment programme in a pocket FM radio/television receiver to be called Microvision. But the idea of a squashed tube was already doomed. At the Tokyo Electronics Show in 1980 Toshiba unveiled a pocket TV with a 2in monochrome LCD. The pictures were rotten, and smeared on motion, but it signposted the future.
The Sinclair Microvision’s 3in black and white screen was made from a flat sandwich of two glass plates. Electrons fired from a gun at one end and were bent by electrostatic plates through 90 degrees to strike a phosphor screen on the back plate. This created a TV image which was viewed through a transparent tin oxide electrode on the front plate.
To reduce power consumption the image was squeezed before projection through an anamorphic lens, rather like a Cinemascope movie. Sinclair put a Fresnel plate over the screen to expand it. The pictures were poor. Sinclair promised a domestic set using back projection from three tubes to give colour. But it never happened.
Sony competed with its own squashed tube and the Watchman black and white pocket TV. The pictures were better but the set was too expensive, and quickly disappeared as LCDs started to roll off Japanese production lines. The Watchman was later recycled as a video entryphone.
Scrapped components for the Microvision turned up a few years later in a bargain basement catalogue. The circuitry was going for 30p and the casings cost £2.
Sony’s Beam Index tube was superficially similar to the squashed CRT used by Sinclair, but whereas these screens gave only black and white pictures, the BI tube gave colour. The electron beam was turned through 90 degrees to scan an angled screen on the side of the tube.
As with a conventional colour tube, the screen was coated with red, green and blue phosphor strips. But whereas a conventional tube has three guns, with masking to direct each gun beam only onto one set of colour phosphors, the BI tube used a single gun whose single beam was continually switched in position to land on different coloured phosphors. Beam positioning had to be very precise, so extra ‘index’ phosphors were deposited between the colour phosphors. The extra phosphors generated light which was sensed by detectors which controlled the beam position.
Sony sold the Indextron portable TV set in Japan. Its 4in BI tube looked very similar to an LCD screen. The tube TV was larger than an LCD set of similar screen size, but cost 30% less. The falling cost of LCDs soon undercut Beam Indexing, killing the system and writing off Sony’s investment.
Panasonic lost out too, because the company had designed a 6in BI-style tube for mounting in the backs of airline seats. Panasonic also lost out on 20 years of research into another CRT modification, called Beam Matrix. Although the names are similar, the technologies were very different.
In 1990 Cambridge researchers discovered that poly p-phenylenevinylene plastics emit light when fed 5 volts. Cambridge Display Technology (CDT) took up the idea and in 1996 struck a deal with Seiko Epson. CDT also did a deal with Philips, and the Dutch company dropped its legal opposition to CDT’s patents. In early 1998 CDT generated press interest by demonstrating a Light Emitting Polymer (LEP) screen.
Seiko had used LCD production techniques and an inkjet printer to paint a fine mosiac of LEP dots on glass panels, sandwiched with a grid of fine metal eletrodes and thin film switching transistors. Instead of holding an open press conference, with crossfire Q&A, CDT staged two days of one-to-one meetings with CEO Daniel Chapchal who “thought the device was too small to be the centre of a large event”.
The device was indeed small; it measured 450mm diagonally and showed a Wallace and Grommit clip in monochrome black-and-green. Resolution was 236 lines, but the pictures look sharp on the tiny screen. The image was however overlain with a swirl of granular video noise, and the electrode grid was clearly visible.