As 2006 builds momentum, the flurry of new products and pricing announcements from the manufacturers of liquid-crystal display (LCD) and plasma display panel (PDP) monitors is reaching fever pitch. Larger screen sizes, lower prices, higher pixel density and improved picture quality are all part of the buzz.
Both technologies are strong contenders for digital signage applications. Both have their own “exclusive” turf, and the battle lines keep shifting every year. These aren’t minor skirmishes – this is serious stuff, particularly when a company has invested billions of dollars in new LCD or plasma fabrication lines (fabs).
As a consultant, analyst, and reporter specializing in display products, I find the LCD/PDP battles to be highly entertaining. One company shows a 102-inch plasma; they are trumped a year later by a 103-inch model. Another manufacturer claims they have the world’s largest LCD (82 inches diagonal), and barely eight months have passed before the ante is raised to 100 inches.
And so it goes. One side has faster line addressing; the other has better motion. One claims to have the best color, but the other shows a different backlighting system that vaults past the first company with wider color gamuts. Black levels, grayscales, pixel density, power consumption – these are all smaller battles in the overall flat-panel war.
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LCD displays operate by polarizing light when a pixel is to be dark, preventing it from passing through the front of the panel. |
Behind The Glass: LCD
To better understand what all the fuss is
about, let’s
review the differences between the two technologies. LCD imaging uses
arrays of pixels containing tiny liquid crystals. These crystals exhibit birefringence,
or the ability to polarize light that passes through them into two different
planes.
The alignment of the crystals determines how much light passes through each pixel. By using polarized light to begin with, we can construct a simple monochromatic light shutter that is transmissive in operation. That’s pretty much it in a nutshell.
LCD technology evolved out of scientific principles observed in nature back in the 1880s, believe it or not. Much of the development work in modern LC displays took place at RCA in the 1950s and 1960s. But companies like Casio and Sharp really picked up the ball in the 1970s and 1980s, leading to the modern LCD displays we see today.
There are numerous companies making LCD panels, which find their way into TVs and monitors. The largest of those include Sharp in Japan, Samsung and LG.Philips in Korea (a joint venture), and AU Optronics and Chi Mei Optoelectronics in Taiwan (China).
At present, LG.Philips has the crown for the largest LCD panel at 100 inches, unveiled in early March. The largest sizes that are shipping in quantity are 45, 46, and 47 inches, with 52-, 54-, 55-, 57-, and even 65-inch sizes having been shown in commercial models.
LCD panels require a backlight source, which is typically a cold-cathode fluorescent lamp (CCFL). These lamps can put out some really bright images, and it’s not unusual to measure 400+ nits from an LCD monitor showing a full white image. (One nit is equal to one candela per square meter.)
As bright as LCD panels are, they aren’t completely effective as light shutters. Even while the pixels are turned off, some light always passes through the panel, so black levels are fairly high – typically over 1 nit, and often in the 1.5- to 2.5- nits range. Since the LC light-shuttering process is monochromatic, tiny red, green, and blue color filters must be applied to each pixel to show full-color images.
One big advantage LCDs have is their high resolution, even in smaller panel sizes. Panels from 15 inches to 37 inches are available with 1,280x768-pixel arrays (Wide XGA), while newer panels coming to market offer 1,920x1,080 pixels from 37 inches and up. Because the CCflis always on, the light-shutter operation cannot cause image burn-in – there are no phosphors to age, only the small color filters (usually due to UV light).
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PDP (or plasma) panels operate by generating an electrical discharge, causing the colored phosphors in the pixel to glow. |
Behind The Glass: Plasma
You might be surprised to learn that
plasma displays were invented at the University of Illinois in 1964. Since then,
a host of companies including IBM, Fujitsu, and Corning have worked to commercialize
the technology, but it was Fujitsu who rolled out the first full-color plasma
monitor in 1993. Today, the PDP industry is dominated by five companies: Panasonic,
Pioneer, and Hitachi in Japan, and LG and Samsung in Korea.
Plasma technology has a lot in common with a cathode-ray tube (CRT). A plasma display panel has rows of tiny pixels, created by putting two etched pieces of special glass together to form barrier ribs and pixels. Color phosphors are coated into the pixels and three electrodes are attached. Finally, each pixel is filled with a combination of xenon and neon gas (sometimes helium is also added).
To “fire” a plasma pixel, a priming charge must first be applied across the pixel electrodes. Once this voltage rises to a certain point (usually a couple hundred volts), it will arc across the electrodes. The gas mixture inside ionizes as current flows through the pixel, giving off a broadband burst of electromagnetic energy. (When the gas conducts electricity, it is said to be in a “plasma” state – hence, the name.) Some of that electromagnetic energy contains ultraviolet light, and it is this UV burst that causes the phosphors to glow. The operation is very similar to that of a fluorescent light. Once the pixel is turned on, a lower “sustain” voltage is used to keep it on. Eventually, a third voltage is applied to discharge the pixel and start the process all over again.
Plasma’s biggest difference from LCD technology is that it is emissive, not transmissive. The light source varies in intensity, and is not shuttered, just like a CRT monitor. That means that black levels are much lower, colors are highly saturated, and viewing angles will be wider – after all, the viewer is looking directly at the source of illuminated color.
The higher operating voltages do have some drawbacks, most notably higher power consumption than an LCD monitor. And there has to be some mechanism in place to regulate current flow with high-brightness images. Otherwise, the color phosphors will be severely stressed and age prematurely, a phenomenon known as “burn-in” or “differential aging” in the AV and home theater industries.
Still, plasma display panels can achieve very high contrast, with average readings in the 300:1 to 500:1 range and peak contrast readings in excess of 2,500:1. PDPs are not practical to make in sizes smaller than 32 inches and in fact are not sold in sizes smaller than 37 inches outside of Japan. Pixel resolution is not as dense as LCD in sizes to 42 inches (1,024x768 is the current maximum at 42 inches), with Wide XGA (1,280x768 and 1,366x768) a common pixel count in 50- to 65-inch panels.
What’s Next
In the flat-panel display world, even minor
technological disadvantages can be seen as serious marketing impediments. For
LCD, the problems of motion smear (insufficiently-fast LC twist time), narrower
viewing angles, black levels, and low contrast are all being tackled with vigor.
A technique known as black frame insertion, along with pulsing the backlight
on and off in sync with video frames, has resulted in cleaning up fastmotion
smear artifacts.
Different liquid crystal alignment schemes are being used to improve viewing angles and contrast, including Sharp’s Advanced Super View (ASV), Samsung’s Super Patterned Vertical Alignment (S-PVA) and LG.Philip’s Super In-Plane Switching (S-IPS) all contending. Polarization-compensating films for LCD panels have been shown that extend practical viewing angles well past 45 degrees in any plane.
The issues of color are being tackled with light-emitting diodes (LEDs) and enhanced CCFLs. But LED backlights will increase power consumption, unless they are operated in a pulse-width mode manner. The current move to LEDs is also motivated by the desire of government bodies to phase out the use of toxic metals in everyday products, such as mercury (found in CCFLs) and lead (The European Union has started this year to pressure manufactures to phase out such metals).
For plasma, motion smear has never been a problem, but addressing pixels quickly enough on large panels requires the use of parallel line addressing, adding to complexity and cost. At the International Consumer Electronics Show (CES) 2006, most of the “Big Five” PDP companies announced their move to single-line addressing, in addition to unveiling 1,920x1,080 pixel matrices in 50-inch, 55- inch, and 60-inch prototypes.
New high-contrast films are allowing increases in image brightness from PDPs, which are impaired by having both anti-glare and EMI coatings in their glass surfaces. And larger plasma screens aren’t just for showing off – the manufacturing costs of plasma are lower for a given screen size than LCD, and in fact the costs per square inch decline with larger PDP screen sizes.
Just Warming Up
This battle is far from over. Every signifi- cant
technological advance in one camp is met with a similar advance in the other,
with major shows like CES and InfoComm as the bragging grounds. Consider that
some manufacturers are spewing out in excess of 50,000 LCD panels and 100,000
plasma panels a month, and you can see the incentive to maintain and grow market
share by constantly tweaking and fine-tuning each technology.
The good news for end-users is that LCD and plasma screen sizes are bigger than ever. Prices continue to fall every quarter, thanks to competition. And manufacturers are getting market-savvy about add-ons, like expansion slots, IP/LAN interfaces, and plug-in media servers. So no matter what happens, you win.
But it’s still fun to watch these guys slug it out, isn’t it?
