Everything about Lcos totally explained
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 15,000:1 using a dynamic iris.
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) and
JVC's
D-ILA (Digital Direct Drive Image Light Amplifier. Every company which produces and markets LCoS rear-projection televisions uses three-panel LCoS technology,. Sony and JVC also produce and market front-projection displays that use three LCoS panels.
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.
Developers and manufacturers of LCoS panels who are now defunct, or have exited LCoS, include: Philips, Microdisplay Corporation, Spatialight, Syntax-Brillian.
Display system architectures
There are two broad categories of LCoS displays: three-panel and single-panel. In three-panel designs, there's 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, one by Microdisplay Corporation and one from Forth Dimension Displays. Forth Dimension Displays have a Ferroelectric LCoS display technology (known as TDI) (available in SXGA and 720P resolutions) which is mainly, but not exclusively, used in high resolution NTE applications such as Training & Simulation.
Further Information
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