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Large Tiled LCDs Present Seamless Images

Photonics Spectra
May 2000
Aaron J. Hand

For years, manufacturers and research groups have struggled to develop effective large, flat screens. Although liquid crystal displays (LCDs) dominate the flat panel display market, large versions have been impractical.

Rainbow Displays Inc. has developed a technology that extends the realm of liquid crystal displays into larger sizes by joining four standard-size panels into one large, apparently seamless display. To date, the relative newcomer has achieved an 800 x 600-pixel display as large as 38.6 in.

The developer has managed to hide its seams through such tricks as precision mechanical alignment, optical stacking and a tight control of light, said Stephen P. Sedaker, vice president of marketing and sales.

Rainbow Displays has developed a seamless 38.6-in. liquid crystal display despite tiling it from four separate panels.

One key involves making the pixel pitch (the space between pixels) within a given tile the same as that between tiles. Large displays typically use a larger pixel pitch, in this case about 1 mm compared with the typical 0.23 mm found in desktop monitors.

Although this reduces resolution for viewers who are standing too close to the screen, it bears little relevance because the large screen would likely be viewed from a distance of at least 6 ft., Sedaker said. Nevertheless, the company's future versions will have a pixel pitch of less than 0.8 mm, and researchers are working to get that figure even smaller.

To shield the seams from viewers' sight and to keep stray light from escaping around the cells, apertures are incorporated into the display stack and the entire screen is covered with a mask. The display also incorporates microlens arrays to enhance the viewing angle to >160°.

Also important is the precise alignment of the glass panels. Rainbow Displays recently entered a joint development agreement with Philips Flat Display Systems of San Jose, Calif., which is making the glass panels. Philips owns a minority stake in Rainbow Displays.

Although Rainbow Displays aims to reach display sizes of 42 in. or larger, Sedaker said, its first stop is to create a slightly smaller screen in a 16 x 9 format, which is more desirable for large screens than the standard 4 x 3 cathode-ray tube aspect ratio. The company's first commercial product -- expected this year -- will be an 853 x 480-pixel, 37.5-in. display, followed later this year by a 1280 x 768-pixel version.

Tiled liquid crystal displays will compete primarily with plasma displays for the large flat panel market. Rainbow Displays expects the price of its displays to be lower than that of comparable plasma displays. A key advantage, Sedaker said, is that his company's displays rely on thin-film transistor technology, which is relatively mature.

"Other technologies are still going through a learning process," he said. "We think we can stay ahead of that."

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