Persistence pays off for DLP developers

the original research goes even farther back—to 1977 when the airlines were looking to get rid of carbon copies for their tickets.

Apr 1st, 2004

One computer magazine sniffed, "The weirdest technology ever invented," in describing the then-fledgling digital light processing (DLP) chips being introduced by semiconductor giant Texas Industries (TI). Now, six years later, this "weird technology" is the mainstay of many large-screen HDTV sets. Indeed, tech-savvy consumers look for the DLP logo on HDTV sets. And it's a story of dogged pursuit of research that is particularly American.

You may already have seen an industrial-strength DLP film projector at work in your neighborhood movie house—there are almost 200 DLP movie projectors in theaters around the world (check for a theater near you). At the Academy Awards, there were 17 DLP movie projectors displaying the antics of winners to the assembled filmati. And, of course, you can actually buy a 50-inch DLP-equipped TV from Panasonic for around $3,000.

Since 1996, more than two million DLP systems have been shipped to more than 50 manufacturers worldwide, according to TI. Last year DLP sales totalled $340 million for TI, hardly earth-shattering for a $10 billion outfit like TI. But TI is doubling its DLP production this year and exponential growth is forecast in the consumer HDTV market. All this bodes well for TI and vindicates the faith that company executives have had in the technology since the invention of the basic digital micro-mirror device (DMD) in 1987.

And the original research goes even farther back—to 1977 when the airlines were looking to get rid of carbon copies for their tickets. TI, a manufacturer of impact printers that produced tickets, set about making a very different printer using a laser and a flexible membrane. That initial idea was a flop but researchers Larry Hornbeck and Ed Nelson refused to give up. Eventually, the two scientists came up with a micromechanical system with tiny mirrors that could reflect light on and off a screen.

When the Pentagon got wind of the TI research, the Defense Department offered money for the development of a two-million pixel display. At that time, Hornbeck's device supported only 840 pixels. Today, TI is manufacturing DMD chips with more than a million pixels and bigger chips are in research laboratories.

The DMD's micromirrors, mounted on tiny hinges, tilt either toward the light source or away from it, thus creating a light or dark pixel on the projection surface. The bit-streamed image code entering the semiconductor directs each mirror to switch on and off up to several thousand times per second. When a mirror is switched on more frequently than off, it reflects a light gray pixel; a mirror that's switched off more frequently reflects a darker gray pixel.

In this way, the mirrors in a DLP projection system can reflect pixels in up to 1024 shades of gray to convert the video or graphic signal entering the DMD into a highly detailed grayscale image. The trick is to add color with a rapidly-spinning color wheel. The white light generated by the lamp in a DLP projection system passes through a color wheel that filters the light into red, green, and blue, from which a single-chip DLP system can create 16.7 million colors. And the three-chip DMD found in cinema projectors can produce 35 trillion colors.

But TI isn't sitting back and waiting for the big bucks to roll in. TI research has developed a light-eating "dark metal" coat that is applied to the interior of each chip, preventing stray light from traveling to the screen when the mirrors are switched off. Now, photons go only where they're wanted—and contrast ratios are jumping from 800:1 to better than 1500:1. The result: colors are subtler, blacks are richer, whites are brilliant and a room's ambient light can go unnoticed. But, you'll certainly notice the vivid colors that DLP emits.

For that, you can thank the imagination of Larry Hornbeck and long hours of work on the part of TI's scientists and engineers. Persistence pays off.

Jeffrey Bairstow

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