Behind the Box Tiny Mirrors, Big Impact
How DLP works
The device behind DLP is the Digital Micromirror Device (DMD). The DMD, a microelectromechanical system (MEMS), is a light switch made up of an array of tiny aluminum mirrors that can reflect light in one of two directions. One direction reflects the light out toward a screen; the other—the Off position—directs light away from the screen into a light absorber. The mirrors rotate about 10 degrees to reach their On or Off positions. The DMD itself is composed of a mirror fixed to a post attached to a yoke and hinge. Small spring tips on the yoke help to return the mirror to its original position after deflection. The DMD superstructure sits on a CMOS silicon backplate. Each micromirror represents an individual pixel. The resolution of the display is based on the number or micromirrors.
In single-chip systems a light source is passed through a rotating color wheel and then reflected off the DMD and then through the projection optics onto a screen. Three chip systems use one chip each for red, blue and green light, passed though color prisms. Most business and home theater projectors use single chip designs. The HD1 and HD2 chips being used in HDTV-compatible DLP projectors use DMDs with pixel resolutions of 1280 x 720. The newer HD2 employs a slightly steeper degree of tilt to create deeper blacks in the video image. In current DMD configurations the post on which an individual mirror is mounted protrudes through the mirror. A future DMD will employ a post that does not extend though the mirror.