Enough SED?
Tim Dean
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Aug 2, 2006 10:50 AM
Is the next generation flat screen technology worth waiting for?
Just when you thought it was safe to sell your old CRT (Cathode Ray Tube) display and buy a flat screen, another competing technology comes along. It’s hard enough choosing between LCD or plasma screens, let alone the new arrival, OLED (Organic Light Emitting Diode) -- see Focus, PC Authority, issue 100. And while OLED has grabbed our attention, another technology has been gaining momentum, and may dominate in a few short years.
It’s called SED, otherwise known by its catchy full name: Surface-conduction Electron-emitter Display. Interestingly, it has more in common with your old-school CRT than with the latest generation of flat panel displays. This means that if its developers Toshiba and Canon can pull it off, SED could theoretically fuse all the strengths of CRT technology with those of LCD (Liquid Crystal Display) and plasma, without any of the weaknesses. Sounds too good to be true, right?
State of play
Before we dive into the guts of SED technology, it’s worth pausing for a moment and asking the question: do we need another flat screen technology? Aren’t LCD and plasma -- along with OLED for smaller screens -- good enough?
Each of these screen types has its strengths and weaknesses, and none have been able to compete with relatively primitive CRTs in some key areas.
CRTs have been available for nearly 90 years so they’ve had time to mature. Even with the recent advances in LCD and plasma, CRTs are still best for black level, contrast and response time.
However, CRTs have a lot of unattractive qualities, such as the space they take up. They’re also susceptible to a range of unpleasant visual artefacts, such as moiré (interference pattern that leaves a grid or curved lines across the screen), geometric distortion (such as representing a circle on screen as an oval or ellipse), screen regulation (where the screen jumps in size when displaying a bright image compared to a dark image) and many more. They’re also limited in the size they can reach, with the largest practical CRT TVs topping out at around 107cm (42in), compared to an astounding 262cm (103in) found in Panasonic’s latest leviathan of a plasma screen.
Plasma screens can be much larger and thinner than CRTs, and have a higher peak brightness level and a black level close to that of a CRT. However, plasma screens consume vast amounts of power, and still struggle with fine colour gradation and detail at low brightness levels.
LCD delivers the highest definition, due to its small and tightly packed pixels, has decent brightness and is starting to become available in sizes above 107cm (42in), as was demonstrated by the monstrous 208cm (82in) Samsung LCD screen demoed at the 2006 CES event. On the other hand, LCD still suffers from below average contrast, relatively poor colour reproduction and pixel response time, plus they’re still extremely expensive, especially in larger screen sizes.
OLED, the poster child of screen technology, has much promise, but at this stage it looks more likely to evolve into a small screen product using the cheaper passive flavour of the technology rather than the larger ‘active’ form. This means it’ll be more commonly found in watches or mobile phones (rather than taking pride of place in the living room), at least for a few years yet.
OLED has potential when it comes to resolution, contrast and motion, but it has some large hurdles to leap before it becomes a viable big screen technology. Researchers are trying to overcome short screen lifetimes, the relative brightness of the different coloured pixels and reducing the cost of large active displays. The screens are also very susceptible to damage from moisture, which increases cost of manufacture due to the need to make them watertight.
What we need is a screen that combines the strengths of all the other technologies, without any of the weaknesses. Step forward SED.
The principle behind SED is simple. The screen employs the same technique that CRTs have used for a century --shooting electrons at phosphors embedded in the screen, which then emit light. However, instead of using a single large electron gun (or three for an RGB colour screen) firing electrons through a vacuum tube, as in a CRT, an SED screen has a tiny electron emitter placed directly behind each pixel on the screen.
The trick has been designing an equivalent of an electron gun that is hundreds of times smaller and doesn’t consume huge amounts of power. Toshiba and Canon have worked together and come up with an innovative solution.
An SED screen has two plates of glass separated by a vacuum, one plate coated in red, green and blue phosphor sub-pixels, while the other is coated with a matrix of electron emitters. On the side with the electron emitters is a channel only a few nanometres wide -- with one side of the channel positively charged and the other negatively charged. When a small voltage of around 10V is applied across this channel electrons flow from one side to the other. Some get scattered rather than flowing smoothly to the other side of the channel. At this point, another set of electrodes take over. These electrodes run at a much higher voltage, in the order of 10kV, and they propel the scattered electrons towards the phosphor elements on the other plate of glass.
The result is like having a miniature electron gun on each and every coloured sub-pixel, giving pixel precision in drawing the screen, much as an LCD or plasma screen does. There’s no need to deflect a single electron beam across the whole screen, so screen sizes can be considerably larger than CRTs. Canon suggests screens of 40in (102cm) or higher that are only several centimetres thick.
Furthermore, because a SED screen doesn’t have a backlight, like a LCD, when the emitters are not firing, there’s virtually no light emitted. This means a SED display has superior black levels. This could result in unprecedented contrast levels of many thousands to one -- surpassing the contrast of even the best CRTs and high-end plasma screens. Because each pixel has its own electron emitter which can be individually switched on or off, pixel refresh times are also very high -- in the order of 1ms -- which makes motion blur practically non existent.
SED resolutions are as high as 720p today, with 1080p screens being slated for availability at launch. Toshiba and Canon have already demoed screens around 30 inches (76cm) in size, with screens above 50 inches (127cm) in size coming around launch time. The million-dollar question is: when will SED screens actually launch?
Canon has been beavering away on SED since the mid ‘80s, and teamed up with Toshiba in 1999 to produce a commercial product. As of 2004, the plan was to begin mass production in 2005 for the initial launch. That date has been pushed back several times, and in March Toshiba announced that mass production wouldn’t kick off until July 2007, with a late ‘07 retail launch, in time for the 2008 Beijing Olympics - a big catalyst for purchases of large flat screen TVs.
Based on Toshiba and Canon’s track record, it’s uncertain whether the Q4 2007 launch is realistic. And when the first SED screens hit the streets, they’re likely to be rambunctiously expensive. Expect it to take a few years before they drop to the price of plasma displays, let alone LCDs.
Still, SED seems to have a lot going for it. It brings the high contrast, fast response times and excellent colour response of CRT, along with the slim form factor of LCD and plasma screens, at lower levels of power consumption. All we need are real screens to evaluate to determine whether the reality lives up to the hype.
High definition(s)
With all this talk of high definition screens, it’s worth reflecting on the state of high definition content in this country. Just to make sure we’re all thoroughly confused during these transition years from analogue to digital television, the Government has endorsed not one flavour of high definition digital television, but three.
Currently, the most popular high definition standard worldwide is 1080i, which runs at an interlaced resolution of 1920 x 1080. This standard is being used by a majority of broadcasters around Australia, including Nine, Ten, WIN, NBN, Southern Cross Ten and Tas Digital. 720p, which runs at 1280 x 720 pixels is only supported by the ABC, while the poor cousin of ‘true’ high definition, 576p (720 x 576), is broadcast by Seven and SBS.
The final high definition standard, the monster 1080p, will only be available on next-generation discs (such as HD-DVD and the competing Blu-Ray), the supply of which is severely restricted at the moment. Furthermore, only a few commercial high definition DVD players can output 1080p, and it’s viewable on only the most expensive screens available today.
What does that mean for us? If you want to protect your investment in terms of high definition, then invest in a screen that can handle at least 1080i, preferably with a digital HDMI connector to preserve image quality. Most high definition DVD players also output or downscale to 1080i, so you won’t miss any content. 1080p is a nice concept, but is too rare and expensive to be worth considering, at least for a few years.