ELECTRASCAN ELECTRONIC REPAIR

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Liquid Crystal on Silicon

LCOS is a relatively new LCD technology. In contrast to nematic twisted LCDs, in which the crystals and electrodes are sandwiched between polarized glass plates, LCOS devices have the crystals coated over the surface of a silicon chip. The electronic circuits that drive the formation of the image are etched into the chip, which is coated with a reflective (aluminized) surface. The polarizers are located in the light path both before and after the light bounces off the chip. The advantages of this setup are:

	The LCOS devices are easier to manufacture than conventional LCD displays.
	They have higher resolution because several million pixels can be etched onto one chip.
	They can be much smaller than conventional LCD displays.

While LCOS devices have been made for projection TVs (such as those made by Philips), they can also be used for microdisplays used in near-eye applications like wearable computers and heads-up displays.

Photo courtesy Colorado MicroDisplay, Inc.
Example of LCOS device used for a microdisplay

For an LCOS projector, the following steps are involved:

A digital signal causes voltages on the chip to arrange in a given configuration to form the image.

The light (red, green, blue) from the lamp goes through a polarizer.

The light bounces off the surface of the LCOS chip.

The reflected light goes through a second polarizer.

The lens collects the light that went through the second polarizer.

The lens magnifies and focuses the image onto the screen.

There are several possible configurations when using LCOS: A projector might shine three separate sources of light -- red, green and blue -- onto different LCOS chips; it might use one chip and one source with a filter wheel; or it might utilize some combination of these two options.

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