DLP
(Digital Light Processing) A data projection technology from TI that produces clear, readable images on screens in lit rooms. DLP is used in all types of projection devices, from data projectors that weigh only a few pounds to large rear-projection TVs to electronic cinema projectors for movie theaters.
It's All in the Mirrors
The technology uses a spatial light modulator called a "Digital Micromirror Device" (DMD). The DMD is a memory chip covered with hinged, microscopic electromechanical mirrors, one for each pixel on the screen. For example, a 1280x1024 resolution uses more than a million "micromirrors," which tilt 10 degrees forward or backward, acting as light switches. Each mirror is 16 micrometers square, and all of them fit on a CMOS chip the size of a postage stamp.
Tilt and Oscillate
The state of each memory bit (0 or 1) in the video frame causes the mirror to tilt in one direction to direct light through a lens to the screen, or tilt in the other direction to deflect it. Gray scale is created by causing the mirrors to oscillate some number of times within each 16 millisecond video frame.
On one-chip projectors, color is achieved by beaming red, green and blue light onto the chip sequentially. The light source can be a mercury vapor lamp shining through a spinning color wheel or from three LEDs. The oscillating mirrors create the shades of color. Offering longer life and greater contrast, LED-based DLPs began to ship in 2006. More costly three-chip units use three sets of mirrors, one each for red, green and blue, and the resulting three images are combined for projection. See Wobulation, microdisplay and rear-projection TV.
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| DLP Processing |
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| In this one-chip example, each screen frame from the computer is sent to the memory on the DLP chip to provide the data for moving the mirrors. The light source is a mercury vapor lamp beamed through a spinning color wheel or separate red, green and blue LEDs. Drawing less power and producing a higher contrast, the LEDs last 20 years under normal usage, compared to four for the very expensive mercury lamp. |
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| A Single Pixel |
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| Hard to believe, but more than a million of these light switches, only 16 micrometers square, are fabricated onto one CMOS chip. The state of the memory cell (0 or 1) tilts the mirror to reflect or cancel light. Gray scale is achieved by causing the mirrors to oscillate back and forth. (Redrawn from original diagram courtesy of Texas Instruments, Inc.) |
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| DMD Vs. LCD |
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| The gap between the mirrors in a DMD pixel (left) is smaller than the gap in an LCD display (right), resulting in a sharper display. |