Video Hardware, Part 1 - LCD and DLP Projectors

Originally, data projectors were intended for use in boardrooms and training facilities. However, with the rise of home theater systems, the increasing popularity of working from home, and major price reductions and improvements in projector technology, portable projectors are an increasingly popular alternative to large-screen TVs and plasma displays. They can be used with Windows XP Media Center PCs and video players as well as their traditional partners, conventional laptop and desktop computers.

Two technologies are used in the construction of data projectors:

• Liquid crystal display (LCD)

• Digital light processing (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.

LCD projectors are relatively low in cost (some 800x600 SVGA models are available for under $1,000) but require some cool-down time before they can be stored.

The other major technology for presentation and home theater projectors uses Texas Instruments' own digital light processing (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 micromirror device (DMD). Each mirror in a DMD corresponds to a pixel, and the mirrors 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; however, they are more expensive.

Figure 15.5 illustrates how a DLP-based processor produces the image.

Figure 15.5 How a typical DLP projector works.

The earliest DLP projectors used a simple three-color (RGB) wheel, as shown in Figure 15.5. However, more recent models have used a four-segment (RGB and clear) or a six-segment (RGBRGB) wheel to improve picture quality.

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Note -For more information about digital light processing, see the official Texas Instruments Web site about DLP technology at http://www.dlp.com.

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This chapter is from Upgrading and Repairing PCs, 16th edition,by Scott Mueller. (Que Books, 2004, ISBN: 0789731738).  Check it out at your favorite bookstore today. Buy this book now!

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