Pixels and Mirrors
At the heart of the DLP system is a digital micromirror device (DMD). The DMD is tiny -- you could hold it in the palm of your hand. But if you could get a close-up look at one while it was working, what you would see would resemble a photo mosaic.
Photo courtesy Michael Jastremski for openphoto.net
Colorado Blue Mountain Flower Mosaic
When you look closely at a photo mosaic, you see a group of tiny, square photographs. But when you step away from the mosaic, the photos blend together to create a larger image. This is what happens with a DMD, except that it uses light instead of tiny photographs. If you looked at it very closely, you would only see tiny, square mirrors reflecting light. But, from far away (or when the light is projected on a screen), you would see a picture.
A DMD contains as many as two million microscopic mirrors, and each mirror corresponds to one pixel of the finished picture. The aluminum mirrors are sixteen microns square and weigh only a few millionths of a gram. Each one is attached to a yoke and a hinge that moves the mirrors to the on and off positions.
A DMD can support a maximum of 1,280 by 720 pixels, but some high-definition images require 1,920 by 1,080 pixels. Hewlett-Packard has developed a technique called wobulation, which allows each mirror to create two of the image’s pixels, improving the resolution. It should be available to consumers in late 2006. [ref]
A DMD chip is a micro electro-mechanical system (MEMS). MEMS devices combine microscopic machines with the same silicon used in a computer. See How Semiconductors Work for more information.
In addition to the mirrors, the DMD unit includes:
- A CMOS DDR SRAM chip, which is a memory cell that will electrostatically cause the mirror to tilt to the on or off position, depending on its logic value (0 or 1).
- A heat sink
- An optical window, which allows light to pass through while protecting the mirrors from dust and debris
In the next section, we'll explore how this tiny device creates a black-and-white digital picture.