The Technology Behind DLP Televisions

DLP is a fully digital projection technology found in big-screen TVs and front projectors. At the heart of every DLP display is a DLP chip, also known as a Digital Micromirror Device, or DMD chip. It was invented by a physicist at Texas Instruments in 1987.

Though small (less than an inch on a side), a DLP chip holds a rectangular array of hundreds of thousands of hinge-mounted microscopic mirrors (see photo, below). The gaps between mirrors are also tiny, allowing the mirror array to create images that are sharp and seamless.

A simplified view of a DLP light engine. A high-powered lamp (out of view, left) shines light through the segments of the spinning color wheel. The colored light strikes the DLP chip, creating the full-color image that is projected through the lens.

Though small (less than an inch on a side), a DLP chip holds a rectangular array of hundreds of thousands of hinge-mounted microscopic mirrors (see photo, below). The gaps between mirrors are also tiny, allowing the mirror array to create images that are sharp and seamless.

The Texas Instruments HD2 DLP chip (left) creates images using 921,600 microscopic mirrors. Pictured at right, an ant's leg against a mirror array. Each individually controlled mirror is a single pixel in a 1280 x 720-pixel array.

The DLP chip doesn't generate its own light; that's supplied by a high-powered lamp. If the lamp's white light could shine directly on the DLP chip, the image generated would be grayscale — black and white. Each individual mirror can tilt independently, and the direction and degree of tilt determines the shade of gray created.

If a mirror tilts to the "ON" position, the maximum amount of the lamp's light is reflected toward the lens — the pixel appears white. If the mirror tilts in the "OFF" position away from the lamp, no light is reflected and the pixel appears black. The micromirrors are switched on and off thousands of times each second by a digital clock. The intensity of light output from any given mirror depends on the ratio of its "ON" cycles to its "OFF" cycles. This system can generate up to 1024 shades of gray.

As with all color displays, the entire color spectrum can be created from just three fundamental colors — red, green, and blue. DLP-based displays that use a single DLP chip (including all current DLP big-screens) create color through the use of a rotating "color wheel" with red, green and blue filter elements. (A few high-end front projectors don't have a color wheel because they use three DLP chips: one each for red, green, and blue.)

The color wheel is positioned between the lamp and the DLP chip (see illustration, above). Its rate of spin is precisely synchronized to the mirror array by a control signal, so the correct color of light is projected when each signal is driving the mirrors. When you combine the DLP chip's grayscale with the colored light created by the color wheel, you get a palette of over 16 million colors.

Because the colors are projected sequentially rather than all at once, it's up to our brains to assemble this color information into a continuous whole. And for most people, it works beautifully, resulting in smooth images with gorgeous, natural colors. But the color wheel is also responsible for the "rainbow effect" that some people notice (see below).

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