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Digital Micromirror Devices
The DMD is a chip that has anywhere from 800 to more than 1 million tiny mirrors on it, depending on the size of the array. Each 16-µm2 mirror (µm = millionth of a meter) on a DMD consists of three physical layers and two "airgap" layers. The airgap layers separate the three physical layers and allow the mirror to tilt +10 or -10 degrees.
 Photo courtesy Texas Instruments Exploded view of an individual mirror on a DMD |
When a voltage is applied to either of the address electrodes, the mirrors can tilt +10 degrees or -10 degrees, representing "on" or "off" in a digital signal.
 Photo courtesy Texas Instruments A blow-up of two mirrors on the DMD, one "on" and one "off" |
In a projector, light shines on the DMD. Light hitting the "on" mirror will reflect through the projection lens to the screen. Light hitting the "off" mirror will reflect to a light absorber. Each mirror is individually controlled and is totally independent of all the other mirrors.
Incoming light hits the three mirror pixels. The two outer mirrors ("on") reflect the light through the projection lens and onto the screen, producing square, white pixel images. The central mirror is tilted ("off") and reflects light away from the projection lens to a light absorber -- no light reaches the screen at that particular pixel, so a square, dark pixel image is produced. In the same way, the remaining mirror pixels reflect light either to the screen or away from it. |
Each frame of a movie is separated into its red, blue, and green components and digitized into 1,310,000 samples for each color. Each mirror in the system is controlled by one of these samples. By using a color filter wheel between the light and the DMD, and by varying the amount of time each individual DMD mirror pixel is on, a full-color, digital picture is projected onto the screen.
 Photo courtesyTexas Instruments White light is forced down onto a color wheel filter. This wheel spins in sequence with the red, green and blue video signals being sent to the DMD. Mirrors are turned "on" depending on where and how much of each color is needed for each TV field. The human visual system integrates the sequential color and sees a full-color image. |
 Photo courtesy Texas Instruments This digitized photograph of a parrot demonstrates the seamless, film-like DMD picture. |
Because the micromirrors are only 1 µm apart, an image takes up a larger percentage (89 percent) of space on the DMD chip's reflective surface, as compared to a typical LCD (12 to 50 percent). This reduces the pixelation of the image.
 Photo courtesy Texas Instruments Close-up photo of the parrot's eye projected through a three-panel poly-silicon VGA resolution LCD projector (left image) and a one-chip VGA resolution DMD projector (right image). Both the LCD and DMD photos were taken under the same conditions, with each projector optimized for focus, brightness and color. |