» Microdisplay chips for rear projection televisions

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“Microdisplay” refers to the one or more microchips containing millions of pixels being used for the new generation of rear projection televisions. Digital Light Processing (DLP), Liquid Crystal Display (LCD), and Liquid Crystal on Silicon (LCoS) are the three competing chip types. Constant improvements to each technology from its supporters have narrowed the differences them.

Microdisplay rear projection televisions are opening up a less expensive option to widescreen plasma and LCD screens.

Digital Light Processing (DLP)

Texas Instruments DLP technology, is fabricated silicon chips with anywhere from 800,000 to more than one million tiny, electromechanical mirrors. The microscopic mirrors move (vibrate) to reflect the correct amount and color and light for each screen pixel. Texas Instruments, the sole technology supplier, supplies numerous DLP chip models to television (and projector) manufacturers including Samsung, Toshiba, Mitsubishi, Panasonic and LG.

Because of DLP chips lightening fast response time in varying the light for each pixel, DLP microdisplay rear projection televisions can use a single chip combined with a color wheel configuration. In comparison, LCDs require a three-chip configuration because of their slower response times.

The DLP projection configuration involves light from a projection lamp passing through a color wheel, the different segments of which provide the primary (red, green and blue + sometimes white) colors. The primary colors shine sequentially onto the DLP chip where each micro-mirror reflects the correct amount of light for each pixel out through the projection lens. The technology relies on the stream of sequential colors being fast enough that the slow response time of the human eye blends them together into a single combined color for each pixel.

A commonly reported problem with early DLP technology, “rainbow effects” (brief steaks of color some people can detect resulting from their perception of the sequence of red, green and blue colors from the color wheel), has been significantly reduced with the advent of faster, more segmented color wheels.

Other DLP technology improvements have been announced by Samsung (LED light source instead of traditional lamp) and Mitsubishi (laser powered DLP). See our article New Generation of DLP Rear Projection TVs for more details.

Brillian Corporation, developer of the believe that scaling up chip pixel density for high definition television (1080p and higher) will be a problem for DLP technologyBrillian Corporation, developer of the Gen II LCoS technology, believe that scaling up chip pixel density for high definition television (1080p and higher) will be a problem for DLP technology.

“Furthermore, as demand moves from 720p to 1080p and higher resolutions, DLP technology encounters issues with scaling its pixels to smaller sizes. This limits the speed with which this technology can support higher resolutions at a cost-effective price.”

Texas Instruments has developed the “Smooth Picture” technology which orients the digital micromirrors in a diamond pattern rather than a rectangular one. An optical actuator shifts the light path by one half-pixel sideways on alternate frames allowing reproduction of all the pixels for a high-definition image using only half the number of micromirrors therefore, generating an obvious cost advantage.

Liquid Crystal Display (LCD)

Unlike DLP, LCD microdisplays are “transmissive” – controlling the light passing through them like a valve by using the polarization effects of the chips liquid crystals. LCD microdisplay projection systems separate the projection lamps light into red, green, and blue light using wavelength (color) splitting dichroic filters The separate light colors pass through the microdisplays and are then recombined to form the full-color image. The LCD pixels in the microdisplays (made of high-temperature polysilicon - HTPS) control the amount of each color that passes through to be recombined for the final required color and brightness.

Early LCD microdisplays suffered from noticeable spaces between pixels on the screen. The effect was caused by the opaque circuit carrying boundaries around the transparent liquid crystals – producing an effect similar to shining a light through a screen door. However, manufacturers have reduced the width of the opaque boundaries so that recent high-resolution LCD microdisplays have practically no screen-door effect beyond twice the screen width viewing distances.

LCD chips do not produce as deep blacks as DLP microdisplays but, they are improving their position. LCD also can have some slight discoloration problems in images that have large white areas.

LCD microdisplay manufacturers have established the 3LCD Group to promote the technology. Members include Epson, Fujitsu, Hitachi, Sanyo, Panasonic, and Sony. The group promote their LCoS approach and using their 3LCD logo as a counter to the DLP technology brand marketing efforts of Texas Instruments.

Liquid Crystal on Silicon (LCoS)

The field of manufacturers working with LCoS technology has narrowed with Mitsubishi, Philips and Toshiba dropping the technology. This most probably reflects the reality that the technology and associated manufacturing processes are difficult to perfect. The remaining players all have differing approaches LCos.

LCoS can be viewed as a combination of both the reflective approach of DLP and the transmissive approach of LCD. In LCoS, liquid crystals are applied to a reflective mirror substrate with the polarization of liquid crystals being used light transmission control and the mirror below reflecting the light or not as required by the image requirements. LCOS microdisplays are mostly of a three-chip configuration for the three primary colors. As with DLP microdisplays LCoS relies on projecting the three primary colors rapidly enough so that the eye combines them into a single color.

Some LCoS advantages are:

• inherent high resolution due to minimal space between pixels on the chips,
• pixel edges tend to be smoother compared to the sharp edges of the micro-mirrors in DLP,
• superior color saturation (shared with DLP) over LCD however LCD can produce more than adequate color saturation.

Some LCoS Limitations are:

• contrast of about 600:1 trailing most DLP products,
• Lamp life and replacement costs tend to be more expensive than for LCD or DLP.

Manufacturers producing LCoS rear projection televisions include:

• Sony’s SXRD (Silicon X-tal Reflective Display),
• Syntax-Brillian’s Gen II LCoS, and
• JVC’s D-ILA (Digital Direct Drive Image Light Amplifier).

JVC (HD-ILA): In 2004, JVC offered a line of rear-projection sets employing their own LCoS technology variation, HD-ILA (Direct Drive Image Light Amplifier). Read Presentation Technology Reviews post on JVC’s HD-ILA line of rear projection, high definition TVs

Sony (SXRD): Sony has named their variation of the LCoS chip SXRD (Silicon X-tal Reflective Display or Silicon Crystal Reflective Display). Sony has based its SXRD (silicon-crystal-reflective-display) technology on high-temperature polysilicon liquid crystals. Read our review of Sony’s KDS-R60XBR1 and the 50” KDS-R50XBR1 which employ Sony’s SXRD technology