Liquid Crystal on Silicon projection display technology differs from an LCD in that it is a reflective, not a transmissive, technology.

In a “standard” LCD, light passes though the device from a backlight behind the display surface. Liquid crystals in the path of the light selectively block or allow light to pass through red, green, and blue filters to create the image. Think of it as stained glass that can change the shape of the various colored bits. In a desktop or laptop, this light is created by a long thin fluorescent lamp coiled behind the screen, and in a projector this light comes from a high-intensity halogen lamp.

An LCoS display uses liquid crystals as well, but instead of letting light pass through, the crystals change light as it reflects off of the surface of the display. Think of it as a mirror that can change the way it reflects light to create an image.

This is similar in operation to a digital-micromirror-based DLP chip, which uses millions of microscopic mirrors, each representing one pixel, that selectively reflect light to make a picture. The primary difference is that there are no moving parts in an LCoS display. In addition, in an LCoS display the pixel pitch can be tighter, as there is no need to have clearance between the pixels.

The advantages include the ability to scale up display resolution without changing the size of the chip itself. In an LCD, since the light has to pass through the display, there is a limit on the size of the pixel since the transistors in it are opaque. This means that the pixels can only be shrunk to a certain size before light transmission is compromised, forcing high-resolution projection LCDs to increase in size to accommodate more pixels. This problem also exists in DLP chips, but due to mechanical considerations of the mirrors and clearances needed. An LCoS chip has its transistors behind immobile pixels, and therefore does not share either shortcoming.

Yet another advantage to having the transistors behind the pixel is that you can then add more than control transistors to each pixel. This allows you to add features like video memory and logic on-chip. Intel is now making LCoS chips with that extra functionality using 0.13-micron process technology, and will be flooding the market with cheap high-performance LCoS chips that promise to push the cost of a HDTV with 1080p resolution to under $1,800 by mid-2005.

Lastly, unlike CRT and Plasma, LCoS monitors will never suffer from burn-in under any circumstances..

Update 22 Oct. '04. - Intel has dropped plans to field the devices at all. This increases the chance that this excellent technology will never find its niche in the marketplace. Wimps.

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