There is an ancient curse that states, “May you live in interesting times.” Well, “interesting times” is an apt description of the past decade when it comes to the evolution of home electronic displays. Not too long ago, there were three choices for home viewing of vidceo: a direct-view TV set, a rear-projection TV or a front-projection TV. Today, there’s a bewildering array of display technologies with all the growth in flat-matrix imaging. You want acronyms? We’ve got ‘em, from TFT LCD to PDP, D-ILA to DLP, LCoS to P-si. These, too, come in direct-view, rear-projection, and front-projection designs. Not only that, we also have more signals (and acronyms) to hook up to them, from VHS to DVD, 480p to 1080i, and DBS to D-VHS.
Scratching your head right now? So are millions of consumers across the country, trying to decide if their next TV should be a 32-inch CRT, 52-inch rear-projection DLP set, or a 50-inch plasma panel. Are any of these new products viable? Why would you want one over the others? What about reliability? Signal compatibility?
Stop scratching your head and read on.
Holding Fast
Despite the wave of flat-matrix devices now available for consumers, it may surprise you that cathode-ray tube technology is still king of the hill when it comes to home entertainment. CRTs can be cheaply manufactured and they provide good color quality and sufficient resolution for everything from casual channel surfing to full-blown home theaters.
Direct-view CRTs can be purchased for well under $300 in smaller sizes, and models with some degree of DTV signal compatibility can be purchased for under $2000. Rear-projection TV monitors with the capability to show DTV signals range in price from just over $2000 to over $10,000, while front CRT projectors range from about $8000 to over $40,000.
CRT technology is mature. It’s been around a while and has been given new life by the adoption of computer display standards and the introduction of digital television. With skilled hands, you can get some truly amazing pictures from CRTs, particularly those using 8-inch or 9-inch projection tubes to show 720p or 1080i high-definition TV.
While the CRT is holding fast with consumers and home theater afficionados, it’s beating a hasty retreat in the commercial, professional audio-visual, and information-technology markets. The reason is simple: These markets are more focused on simplicity of operation and factors like portability, light output, reduced space requirements and direct digital interfaces.
All of these requirements can be provided by flat-matrix displays, but CRT technology comes up short in more than one area (such as brightness, size and weight). The advantages of some flat-matrix imaging systems are becoming apparent to consumers as well, and these technologies—although still fairly expensive—are beginning to show up in living rooms, dens and family rooms.
Lucy in the Clouds with Diamonds
Let’s take a little tour through each of the flat-matrix technologies you will encounter as you choose that new front, rear or direct-view display for your next installation. To clarify, a flat-matrix device is flat (obviously) and contains a fixed matrix of imaging pixels. Unlike a CRT, the resolution of a flat-matrix device is constant, regardless of whether it is turned on or off. That pixel resolution can be physically measured and is often referred to as the “native resolution” or “sweet spot” of the flat-matrix device. With the exception of plasma panels, all flat-matrix devices are manufactured from silicon wafers—just like integrated circuits.
First up is the Liquid-Crystal Display panel, the grandfather of all flat-matrix devices. The unique property of LCD—birefringence, or the ability to split light into two planes—was observed as far back as the late 1800s. But it took until 1970 for LCD technology to become practical for the mass market.
Today, Sony and Epson churn out practically all of the high-temperature polysilicon (Psi) LCD panels used in desktop/installation, portable, and ultra/microportable video/data projectors. “Polysilicon” describes the chemical formulation of the silicon used to form the tiny, semi-transparent switching transistors that lie atop each of the imaging pixels.
Polysilicon LCDs (and their big brothers, the amorphous LCDs used for the screens on notebook computers) are transmissive, light-shuttering imaging devices. Psi-LCDs require an external projection lamp, and the movement of the tiny liquid crystals in each pixel acts like a miniature venetian blind to make images darker or lighter.
LCD panels as small as 0.7 inches diagonally are commercially available in resolutions up to 1024×768 pixels. The projectors in which they are installed have become quite small and light, creating a new category of coffee-table home theater that is very popular in the tiny rooms of some Japanese households—places where a large rear-projection CRT TV would be impractical.
AM LCD panels are also finding their way into homes, commonly as fold-down TV sets for kitchens and other tight spaces. These panels typically have a maximum resolution of 640×480 pixels (VGA), which is sufficient for viewing TV. In this case, the light source is a fluorescent lamp behind the LCD panel.
One company—Sharp—has introduced a large widescreen (16:9) LCD panel for home and commercial use. It has a native resolution of 1280×768 pixels, which is enough to view high-definition TV and widescreen DVDs fed through a video scaler. This panel and the tiny panels in front LCD projectors still work the same way, using the motion of LCs to shutter light and create grayscale images. Color is added by built-in filters on large AM LCDs and by using three panels with color filters with Psi LCDs.
LCD projectors have the look and feel of older slide projectors, but they are a lot brighter. While LCD designs are very popular in the corporate, institutional and educational markets, they haven’t caught on as well with consumers. The single-lens design and simple operation does appeal to many people, and the bright images can be used with large screens. In fact, a large front screen and LCD projector can cost less than a big-screen CRT TV set.
The limitations of LCDs are largely in the quality of images they produce. LCD panels are never really “off” like a CRT is when powered down. Some light always leaks through the panel even in its fully-closed state. As a result, the black levels that result aren’t really black, but a very dark gray.
In a room with normal to high ambient light levels, these levels of black aren’t even a consideration. But in a home theater, much of the shadow detail in TV programs and movies is lost, or crushed. The other problem is the native resolution. LCD panels always look best when the input signal source matches the native resolution of the panel. Anything higher or lower will require resizing, or scaling. As you can imagine, this is not an easy process, particularly when converting interlaced video with motion to progressive-scan video.
Right now, the choice of an LCD projector for home use is often based on price. Front LCD projectors can be had for under $5000, and there are a couple of 16:9 models available from Sony (VPL-VW10HT) and Toshiba (MT-7) for under $10,000. Unlike front CRT projectors, they won’t need convergence. In fact, about the only service LCD projectors do require is a new lamp from time to time, and cleaning or replacement of the air filter.
Bring in the Silicon
LCD panels can also be manufactured as reflective devices. These panels fall into a fast-growing class of Liquid-Crystal on Silicon displays, and there are plenty of companies jockeying for market position. LCoS panels are marketed and branded under a variety of names, such as JVC’s Digital Image Light Amplifier (D-ILA) and Samsung’s Ferroelectric LCD (Fe-LCD). To date, only JVC has been able to produce LCoS devices with acceptable manufacturing yields over 80%. Their D-ILA product looks very much like a conventional Psi-LCD panel, except it has a highly polished mirror surface and an opaque backing. It measures 0.9 inches diagonally and has a native resolution of 1365×768 pixels (SXGA).
In an LCoS panel, the driving electronics are mounted directly to the backplane of the LCD. This provides a big advantage over transmissive LCD light efficiency. Typically, transmissive LCD panels throw away 50% of the light passing through them due to polarization losses, but reflective LCDs can do much better than that.
The down side is that the optical path for a 3-panel LCoS projector or RPTV is much more complicated than that seen in a transmissive LCD projector. That’s because the light is traveling in both directions at the same time, although polarized in two different planes.
JVC’s early D-ILA projectors were pretty large, but there have been size and weight reductions since then. Right now, JVC has re-introduced the D-Ahlia, a 3-panel D-ILA RPTV ($13,999) that features a 61-inch 16:9 screen and uses special 1280×1028 non-square pixel D-ILA devices. It is also adequate for viewing of HDTV content.
Again, LCoS front projectors and RPTVs do not require convergence (you’d be nuts to try it anyway; it requires laboratory-grade equipment) and their maintenance will consist of cleaning the air filter and changing the lamp as needed. One caveat: The lamp used in the D-Ahlia is a short-arc xenon, and it isn’t cheap. Expect to get about 1000 hours from this lamp and pay about $700 for a replacement.
Donna in the Lake with Pizzas
There’s another way to make images from reflected light, and (oddly enough) this technology was originally intended for use in laser printers. Texas Instruments’ Digital Light Processing is based on the digital micromirror device, another silicon-based, flat-matrix widget that contains thousands of tiny mirrors on its surface. Each mirror can tilt a maximum of 10˚ from off to on. There’s no in-between; so how does the DMD produce grayscale images? Simple. By using a technique known as pulse-width modulation. During any given time interval, the number of off states and their duration compared to the number of on states and their duration determines an absolute grayscale value. Increase the ratio to favor on states, and the image gets brighter. Favor off states, and the image becomes darker.
DLP is currently the only 100-digital flat-matrix imaging system on the market, and TI has been very active with numerous partners to build DLP technology into everything from microportable projectors to 3-chip, super-bright projectors for electronic cinema.
Even so, the biggest potential market for DLP remains with consumers.At present, three companies—Panasonic, Hitachi and Mitsubishi—have presented large-screen (52-inch to 65-inch) rear-projection DLP TV sets. Each model uses a special 16:9 DMD, adapted from TI’s 1280×1024 (SXGA) designs. This 1280×720 DMD comes with its own color wheel, synchronized to the on and off states of the mirrors to produce a full-color image. These sets range in price from $13,000 to $18,000. Sharp and PLUS showed front projectors incorporating the 1280×720 DMD at the recent Winter CES, but don’t expect these models to show up until the end of 2001. Both will be close to (if not over) $10,000 in price when they become available.
TI recently announced the availability of a widescreen SDTV DMD, this time with 848×480 pixel resolution. Three companies, SIM2 Multimedia, PLUS and InFocus, have all announced plans to build front-projectors or RPTVs around this wide-VGA DMD, which will probably target the under-$5000 market.
DLP technology brings many advantages to the table. Again, there is no convergence required with a single-chip DLP front or rear projector. Maintenance will typically be limited to replacing bulbs and cleaning air filters. Unlike the D-Ahlia (and like LCD projectors and RPTVs), a lower-cost short-arc mercury vapor lamp is used (UHP, UHE, NSH, etc.), which will last between 1500 and 2000 hours.
Fast From the Gate
While all of these technologies are trickling into homes across the country, there is one imaging system that has really taken off in a hurry. The Plasma Display Panel has captured the imagination of consumers, dealers and industry writers because of its unique combination of big, bright images and thin profile.
Plasma technology has been around for quite a few years and dates its birth back to 1964 in the bowels of the University of Illinois-Champaign campus. The principle of plasma is very similar to the operation of a fluorescent lamp. A combination of rare gases (typically xenon and neon, or argon and neon) within a sealed pixel are stimulated by an electrical discharge through the pixel.The phosphors glow, and the duration of that glow and its intensity are determined by the write-sustain-clear cycle of charges and discharges. What actually makes the phosphors glow is a burst of ultraviolet radiation caused by the temporary ionization of the rare-gas mixture. When ionized, the gases can conduct electricity momentarily as they have changed into a plasma state. Hence, the name.
Plasma panels aren’t all that different than CRTs in operation, but they can be manufactured into much bigger screens with considerably less weight. The manufacture of super-large cathode-ray tubes (over 40 inches) has been discontinued, but companies such as Pioneer, NEC and Fujitsu can crank out 42-inch and even 50-inch diagonal plasma panels with ease.
Plasma panels have some neat tricks. Their images are viewable over a very wide angle, 80˚ horizontally and vertically. They can also crank out the brightness (commonly over 100 nits or 33 foot-Lamberts), although the jury is still out on how long plasma panels will last at these levels.
More importantly, plasma panels are manufactured with native resolutions that are a good match for widescreen DVDs and SDTV/HDTV viewing. Most 42-inch panels have a wide-VGA matrix (852×480 pixels), but some specialized models sold by Sony and Fujitsu have much higher resolution (1024×1024 non-square pixels).
Because of price reductions across the board in plasma, there is now more interest in 50-inch models. These typically have wide-XGA resolution (either 1280×768 or 1365×768 pixels) and direct HDTV compatibility. Even so, the 50-inch designs are less than 6 inches thick, and some models weigh less than 100 pounds.
But the size wars continue. NEC Technologies recently showed a 61-inch plasma panel at the NAB 2001 show, and LG/Zenith and Samsung have also shown 60-inch prototypes at Winter CES. NEC has so much confidence in the future of plasma that it has discontinued the manufacture of direct-view CRT monitors completely.
Plasma panels have their advantages and disadvantages. One drawback in particular is false contouring, or the inability of a panel to resolve enough shades of gray in an image. The result is an unnatural contour between low level shades of gray that often resembles creeping moss. Another problem with plasma is that the pixels can easily burn in (or even burn out) if the panel is driven too hard with bright images for too long. Most manufacturers are claiming a half-life of 15,000 to 20,000 hours for a plasma panel, but they do not specify the necessary preset brightness levels to achieve that number.
Plasma panels – or PDPs, for short – are popping up in all kinds of home theater installations. In many cases, the 42-inch models replaced a CRT-type RPTV, while the 50″ panels are finding favor over front projectors. Many are being flown from the ceiling or built into hidden recesses. Look for this market to continue growing as 40- and 42-inch panel prices drop to below $5000 by early next year, and 50-inch panels come down to the $10,000–$12,000 range.
Peter H. Putman owns PHP Communications, Doylestown, Pennsylvania. He is the author of The Toastmasters Guide to Audio/Visual Presentations.
