Information Display Symposium: Displays become more than dumb panels
With underlying technologies stabilizing, engineers must turn to system-level approaches for display improvements.
By Ron Wilson, Executive Editor -- EDN, June 14, 2006
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The Society for Information Display International Symposium in San Francisco last week offered its usual stunning range of display devices, ranging from the enormous (50-in. television screens) to the wearable (goggles and spectacle-mounted displays). The range of underlying technologies was just as impressive. But to the attendee examining the products on display and talking to the knowledgeable, a couple of interesting trends became evident.
First, underlying display technologies have become remarkably stable. TFT LCDs and plasma displays dominate the large flat-panel business, both for home television viewing and for static commercial signage. OLED (organic LED) technology, still an emerging entrant, is looking increasingly viable as a third alternative.
In smaller displays, the world still belongs to various flavors of LCDs, because the pixel size of plasma displays renders them inappropriate for smaller panels. This is especially true for notebook PCs. However, OLEDs may establish their first strong foothold in smaller, moderate-resolution industrial displays.
"OLED technology will catch up," said Steve Atwood, CTO of Capstone Visual Product Development. Indeed, reliability and efficiency are increasing. OSRAM, for instance, is reporting lifetime of more than 50,000 hours and good energy efficiency on images that aren't primarily white pixels. And the technology doesn't require nearly the level of infrastructure investment necessary for LCDs.
"If there's a perception problem with OLEDs now," Atwood continued, "it may be because the pioneers just over-hyped the technology far too early. In the display business, it's a 20-year path from initial technology to commodity production. You can't short-circuit that process."
We are likely to see a future with four or five mature display technologies coexisting, each with its own strengths and market niches, Atwood said. Interestingly, at least from an historical perspective, it appears that the CRT (cathode ray tube) will not be one of those technologies. In fact, several observers noted that the show floor this year displayed not one CRT—a giant change when one considers the huge market share and infrastructure the devices used to enjoy.
System-level view
If technology stability is one trend, the other major trend is nearly the opposite. The unrelenting quest for better image quality, across all display sizes and technologies, is no longer purely a matter of display-device design. It is now a system-design issue, and this has created a rich, turbulent brew of system-level approaches.
Take the issue of moving images, for example. One of the few remaining weaknesses of TFT LCD technology is that the slow response time of the liquid-crystal cells means that objects in rapid motion across the display tend to blur. This has not been much of a problem for notebook screens, which have traditionally been called upon to display relatively static images. But it is becoming an issue across the industry as video content begins to appear everywhere.
Consumers who have just dropped $3500 for a high-end notebook PC, or even more than that for a huge flat-panel TV, tend to be humorless about blurry images during their favorite sports events or action-adventure flicks. Worse yet for the LCD makers, plasma and OLED technologies both boast considerably faster response times, giving them an inside track on moving-image quality.
So panel manufacturers, their customers, and their customers' vendors are all pitching in to attack the motion problem at the system level. For example, panel manufacturers are reducing the viscosity of the liquid in their cells as much as possible to reduce response time. And some are revisiting a previously explored and rejected technology called OCB (optically compensated bend) mode, which aims to improve response time by requiring the crystals to bend only slightly, rather than twisting.
At the same time, driver vendors are attempting to add overshoot correction to their circuits, and some vendors are investigating backlight-modulation schemes. In some backlight schemes, the backlight flashes every 1/60 or 1/120 of a second rather than staying on continuously, acting like the shutter in a movie projector. Ideally, this illuminates the screen only when all pixels have reached their steady state but before they begin to visibly decay. Reports indicate that the technique does indeed eliminate blurring. However, it can render motion jerky, and some people can perceive the flicker.
Beyond this, many vendors are looking at digital image-processing techniques to alter the incoming signal, thus making it easier for the panel to compensate for blur. In this approach, a motion-detection algorithm—not unlike those used in video-compression schemes—identifies moving objects in the image and pre-distorts them to the advantage of the panel.
Engineers are increasingly combining panel physics, driver capabilities, backlight technology, and image-processing techniques to improve image quality, according to a number of sources. In fact, Atwood says, today one has to think of the flat-panel display not as a dumb peripheral device, but as an image-processing subsystem that happens to display its results.
