Video Hardware - Upgrading and Repairing PCs - page 826

LCD and DLP Projectors
Originally, data projectors were intended for use in boardrooms and training facilities.
However,withtheriseofhometheatersystems,theincreasingpopularityofworkingfrom
home,andmajorpricereductionsandimprovementsinprojectortechnology,portablepro-
jectors are an increasingly popular alternative to large-screen TVs and plasma displays.
Two technologies are used in the construction of data projectors:
• Liquid crystal display (LCD)
• DLP
Instead of using triads of subpixels as in a flat-panel or portable LCD, an LCD projector
works by separating white light into red, green, and blue wavelengths and directing each
wavelength through a corresponding LCD panel. Each LCD panel's pixels are opened or
closed according to the signals received from the signal source (computer, DVD, or video
player) and are combined into a single RGB image that is projected onto the screen. A
relatively hot projection lamp must be used to project LCD images, so LCD projectors re-
quire some cool-down time before they can be stored.
The other major technology for presentation and home theater projectors uses Texas In-
struments' own DLP technology. DLP projectors use a combination of a rapidly spinning
color wheel and a microprocessor-controlled array of tiny mirrors known as a digital mi-
cromirror device (DMD). Each mirror in a DMD corresponds to a pixel, and the mir-
rors reflect light toward or away from the projector optics. Depending on how frequently
the mirrors are switched on, the image varies from white (always on) to black (never on)
through as many as 1,024 gray shades. The color wheel provides color data to complete
the projected image. Compared to LCD projectors, DLP projectors are more compact, are
lighter, and cool down more quickly after use. Although DLP projects were originally
more expensive than LCD projectors, they are now about the same price. Most current
projectors also support HDTV resolutions of 720p and 1080i, enabling a single projector
to work as either a PC or a TV display.
Figure 12.25 illustrates how a DLP-based projector produces the image.
Figure 12.25 How a typical DLP projector works.