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MEMS made this pico-projector palm-sized

Posted: 07 Jan 2008 ?? ?Print Version ?Bookmark and Share

Keywords:Microvision pico-projector? MEMS? digital projector?

Digital projectors revolutionized mobile presentations by harnessing mass-produced LCD technology to stand-in for viewgraphs!enabling high-output light bulbs to shine through the LCD instead of through plastic sheets. While digital-projector companies progressively downsize their LCDs, making units smaller and lower power, digital micro-mirror technology stands poised to leapfrog digital projectors down to the size of cellphones

At this week's Consumer Electronics Show, Microvision Inc. will showcase a prototype of its pico-projector, which uses MEMS to downsize a digital projector to a palm-sized battery-powered unit.

Texas Instruments Inc. has been privately showing a cellphone-sized prototype of its digital-light projector (DLP), which uses a MEMS chip with a million micromirrors to project images. Now, Microvision claims to have downsized the pico-projector by replacing TI's million-mirror MEMS chip with its own single-mirror MEMS chip, which Microvision explains can be produced cheaply enough to become standard equipment on future cell phones.

"Our MEMS chip is fundamentally different [from TI's DLP]," said Russell Hannigan, senior product marketing manager at Microvision. "TI's DLP dedicates a separate mirror to each pixel, requiring a million micromirrors for a million-pixel display. Instead, we use a single mirror to create all the pixels!enabling our device to be much, much smaller and less expensive."

Microvision's pico-projector won last year's innovation award for consumer electronics devices from Frost and Sullivan Research. Microvision has already signed up a few customers: Motorola's Mobile Devices division, for its handheld projector modules; an unnamed automotive supplier for in-vehicle use of its pico-projector; and an unnamed Asian "large consumer electronics manufacturer," for cellphones, digital cameras and personal media players. The company promises to announce new OEM deals this year, when it begins delivering its first modules to customers.

Decade in development
Almost a decade in development, Microvision's MEMS-based pico-projector is based on a unique MEMS technology platform that makes use of laser scanning technologies borrowed from the company's successful barcode reader product. Solid-state lasers combined in the same tiny module with a single digital micromirror simplify the whole projection system by not requiring any optical lenses. Control circuitry aims the lasers in a raster-scanning pattern, modulating its coherent beam onto each pixel of the display by moving the single mirror to keep the image in focus regardless of distance.

"We arrange it so the image is always in focus!with no need to adjust it with a lens!from about 200mm [8 inches] to maybe 2m [80 inches] away, so you can literally move the image from the wall to the ceiling and it will always be in focus," said Hannigan.

No lens required
The single mirror scans from pixel-position to pixel-position like a cathode-ray tube, but instead of using an electron beam it uses red-, blue- and green-lasers. As a result, there is no focusing lens required, because the lasers already render razor-sharp points without external optics. This enables the full spectrum of colors and shades of gray to be illuminated on a million-pixel display by a pico-sized projector that's 7mm thick and taking up just 5cm3 of total volume.

The mirror itself is round, about 1mm in diameter, and is deflected in both the x- and y-planes simultaneously. As the mirror scans left-to-right and top-to-bottom, the three-lasers are modulated so that each pixel in the display receives the appropriate mixture of red, green and blue light to render a scene accurately.

The main disadvantage of Microvison's pico-projector is that it only has a brightness of about 10 lumens!compared with 100 lumens or more for suitcase-sized digital projectors offered today. However, the pico-projector also uses much less power than today's competing technologies, because it does not depend on constantly-on high-intensity light bulbs.

"Our device is much lower in power--typically half the power of our competitors," said Hannigan. "With a DLP, for instance, the light source must always be on, but our light source is only on when we need it, which is incredibly important for battery-powered devices."

The palm-sized unit will have 2.5 hours of battery life when released in mid-2008, but the prototype to be shown at CES will only achieve about 1.5 hours of battery use. The prototype uses a widescreen, WVGA (848 x 480 pixels), format for DVD-like quality images.

"You really need to see the DVD-quality of our image in a two- to four-inch format to appreciate how good it looks," said Hannigan.

Microvision said they expect customers to use its pico-projector in locations where other small projector technologies are too bulky and power-hungry!such as watching YouTube videos while sitting in bed, or MSN newscasts at the breakfast table, or to project PowerPoint presentations on a cocktail napkin at lunch. For portable media players, the unit will provide enough battery life to watch a complete feature-length film on a plane.

The company expects the unit to be initially offered in stand-alone portable projectors you attach to an iPod during 2008, but by 2009 it also expects OEMs to begin incorporating the 5cm3 unit into cellphones and portable media players.

- R. Colin Johnson
EE Times

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