Liquid crystal on silicon

Liquid crystal on silicon (LCOS or LCoS) is a "micro-projection" or "micro-display" technology typically applied in projection televisions. It is a reflective technology similar to DLP projectors; however, it uses liquid crystals instead of individual mirrors. By way of comparison, LCD projectors use transmissive LCD chips, allowing light to pass through the liquid crystal. In LCoS, liquid crystals are applied directly to the surface of a silicon chip coated with an aluminized layer, with some type of passivation layer, which is highly reflective.

LCoS technology can produce much higher resolution images than liquid crystal display and plasma display technologies, which makes it less expensive to implement in such devices as televisions.

At the 2004 CES, Intel announced plans for the large scale production of inexpensive LCoS chips for use in flat panel displays. These plans were cancelled in October 2004. Sony has made it to market (December 2005) with the Sony-VPL-VW100 or "Ruby" projector, using SXRD, 3 LCoS chips each with a native resolution of 1080p (1920 × 1080), with a stated contrast ratio of 15,000 using a dynamic iris.

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History and implementations

LCoS technology has the potential to enable the manufacture of big-screen high-definition televisions with very high picture quality at relatively low cost. LCoS, while conceptually straightforward, can be a difficult technology to master; a number of companies have dropped out of the LCoS business in recent years. Nonetheless, as of June 2006, proprietary methods for mass-producing LCoS developed, and at least four manufacturers now produce LCoS-based rear-projection televisions for the consumer market.

Commercial implementations of LCoS technology include: Sony's SXRD (Silicon X-tal Reflective Display), Syntax-Brillian's Gen II LCoS, JVC's D-ILA (Digital Direct Drive Image Light Amplifier), and MicroDisplay Corporation's Liquid Fidelity. Nearly every company which produces and markets LCoS rear-projection televisions uses three-panel LCoS technology,^{[citation needed]} with the exception of MicroDisplay Corporation, which uses a single LCoS panel capable of producing true 1080p resolution with two million pixels on a single chip. Sony and JVC also produce and market front-projection displays that use three LCoS panels. Another provider of third-party LCoS chips is a Novato-based firm, Spatialight.

Direct-view LCoS devices such as the single-panel LED-illuminated devices made by Displaytech and Forth Dimension Displays (Dalgety Bay, Fife, Scotland) (formerly known as CRLO Displays) are also used as electronic viewfinders for digital cameras and within Near to Eye (NTE) applications such as Head Mounted Displays (HMDs). These devices are made using ferroelectric liquid crystals, which are inherently faster than other types of liquid crystals.

Display system architectures

There are two broad categories of LCoS displays: three-panel and single-panel. In three-panel designs, there is one display chip per color, and the images are combined optically. In single-panel designs, one display chip shows the red, green, and blue components in succession with the observer's eyes relied upon to combine the color stream. As each color is presented, a color wheel (or an RGB LED array) illuminates the display with only red, green or blue light. If the frequency of the color fields is lower than about 540 Hz, an effect called color breakup is seen, where false colors are briefly perceived when either the image or the observer's eye is in motion. While less expensive; single-panel projectors require higher-speed display elements to process all three colors during a single frame time, and the need to avoid color breakup makes further demands on the speed of the display technology.

Three-panel designs

In a DLP device the light is separated into three components and then combined back: Two beam splitters are needed. In LCoS devices the light is additionally polarized and then analyzed; four beam splitters are needed. In most DLP sets a color wheel separates colors from a lamp, using one chip for all three colors; SXRD sets use three separate chips, one for each color.

One-panel designs

There were three single-panel LCoS displays in production. One by Philips, and one by Microdisplay Corporation. MicroDisplay Corp's display products were used in HDTVs produced by Uneed Systems of South Korea from 2004–2006, and are currently an integral component of all Liquid Fidelity HDTVs. Finally, Forth Dimension Displays have a Ferroelectric LCoS display technology (known as TDI^TM) (available in SXGA and 720P resolutions) which is mainly, but not exclusively, used in high resolution NTE applications such as Training & Simulation.

See also

• Comparison of display technology
• DLP
• SXRD