Digital Light Processors or back to Mechanical Television!

Have you heard about the "DMD"? A device invented by the Texas Instrument engineer, Dr. Larry J Hornbeck and his TI colleague, Dr. W. E. Nelson. First demonstrated in 1994, The DMD is a Digital Micromirror Device, consisting of thousands of teeny, tiny mirrors, fabricated on hinges on top of a static random access memory. Each mirror is able to switch or move into two states, +10 degrees for "on" or -10 degrees for "off" and thereby control an individual pixel of light.

To use the DMD in a television system, the video signal must undergo a digital processing technique developed for this purpose, that converts it to pulse width modulation (PWM). By electrically addressing the memory cell below each mirror with the PWM signal, each mirror in the DMD array is electrostatically tilted to the on or off positions and the pulse width modulation controls how long the mirrors remain in either of the two positions. The rapid response of the mirrors allows a digital gray scale or color reproduction. The combination of the DMD and the processing is what together make up the digital light processor or a DLP. At this point, the DLP becomes a simple optical system. The light from a projection lamp is passed through condensing lenses, a color filter system, onto the DMD, through the projection lens and finally to the screen. For color, a single DLP with a color wheel has been used. More recently three DLPs are being used, one each for the colors red, green and blue.

The DLP system is best suited for large image applications. It is presently replacing many of the Eidopror systems that were providing theater size screens (check this site for information on the Eidophor).

So here we are again. This is mechanical television. The early mirror drums might have had 30, maybe 60 mirrors. But each mirror took care of producing a whole line. Maybe more. However, with the DMD, each mirror takes care of only one pixel. And modern high-resolution images of today have a lot of pixels. So it should be no surprise that the DMD must have a lot of mirrors. That's right... the DMD has over a half a million (500,800 in a 848 X 600 matrix). To give you an idea of the size of these mirrors; if they were the size of a pin head (.075"), the mirror array would be 5.3 feet by 3.75 feet. Actually, the device is about 1 X 1 inches.

In the early years, they just could not make mirrors small enough (they tried) or fast enough (they tried) and locate and control them accurately enough (they tried that too). We have come a long way since those early years, but many times it appears we just improve on old ideas. (Not that that's so easy!)

This information in this section is based on that found on the Texas Instrument web site. If you would like to learn more about the DMD and DLP, you can go directly to the TI site.

Peter Yanczer

If breaking a mirror can lead to 7 years bad luck... I wonder what happens if you burn out one of these DLPs?
WOW! I don't even want to think about it!