Most people would agree that overall,
cathode-ray tubes (CRTs) produce a better on-screen image. So why are so many TV
manufacturers moving away from this tried and trusted technology towards these
newer technologies? Mainly because they are both thinner and lighter and
manufacturers wish to give customers more of what is currently the rage. So,
whether it be plasma, digital light processing (DLP), liquid-crystal display
(LCD), or liquid crystal on silicon (LCoS) - all of these technologies lead to a
new generation of video displays that leave heavy and bulky CRT-based TVs
Plasma, DLP, LCD and LCoS are all 'fixed-pixel displays' - electronic screens made up of a grid of square or rectangular pixels (short for "picture elements"). This is often seen on digital watches, mobile phones and laptop computers. Over the past few years, this mobile technology has also started to gain ground in more permanent-based technologies like large-screen television monitors.
As plasma and direct-view LCD monitors are just a few centimetres deep, they can be hung on the wall like a picture frame. And unlike cathode-ray tube television monitors, their depth doesn't increase proportionally with screen size. While DLP and LCoS can't be used to create flat-panel displays, they (along with LCD) can be used to make front projectors and rear-projection TVs (RPTVs) that are much smaller and lighter than their CRT-based counterparts.
There's a simple reason why fixed-pixel TVs are thinner than tube models. In a CRT, a gun located at the back of the tube 'scans' pictures line by line by firing an electron beam at phosphorescent material covering the tube's front surface. But the pixels in a fixed-pixel display are individually controlled points that can light up without the assistance of a scanning electron beam.
Fixed-pixel technologies have other advantages. For instance, while the three separate tubes used in CRT projection TVs need to be realigned periodically to preserve picture sharpness, fixed-pixel models require almost no maintenance. Another advantage is fixed resolution, which means you know exactly how many pixels are available to create an image. While the source material ultimately determines image quality, the more pixels a display contains, the higher its resolution. Fixed-pixel sets come in a range of resolutions, some as high as 1920 x 1080 - enough to handle 1080i-format high-definition TV (HDTV) programmes. By combining all of these benefits with falling prices - both plasma and DLP prices have dropped huge amounts over the last couple of years - it's clear that it will only be a matter of time before we finally say goodbye to the old picture tube.
Everyone nowadays wants a plasma TV and by looking at one you can easily see why. Just 8 - 15cm deep, plasma TVs can be set up adjacent to or mounted on a wall, preserving precious room space. And just because a plasma set is flat doesn't mean it can't be big. Screen sizes range from 77cm diagonal to a huge cinematic 1m50, allowing everyone (with the necessary amounts of money) able to have a home cinema set-up in a back room.
How It Works
Plasma TV works by suspending an inert gas such as neon or xenon in between two glass plates that are meshed together. Between the glass panels there are generally over 1 million pixel cells capable of producing 16.7 million colours. A series of electrodes located above and below the cells (the top electrode layer is transparent) jolt them with varying amounts of voltage. This excites the gas in the cells, which in turn stimulates the phosphors to produce coloured light that we can see. Plasma is created (hence the name) and causes ultra-violet light to be created. We cannot see UV light, but this light is used to illuminate phosphors built into the glass, creating visible light. Each pixel in a plasma display consists of three gas-filled sub-pixels (cells) coated with red, green or blue phosphors.
Uniformly bright picture over a wide viewing angle—even in a brightly lit room
Svelte design and large screen size
Many models have a wide 16:9 aspect ratio screen and a high enough pixel count to achieve HDTV-level resolution
On many sets, the black portions of the picture - for instance, dark shadows or the letterbox bars on widescreen movies - look dark grey rather than true black. A good tube TV generally produces better blacks than plasma models
Has the potential for burn-in, where an image becomes permanently etched onto the screen - but the danger of this happening is small unless you leave a bright stationary image on the screen for hours at a time. Newer models have burn-in prevention features like a "pixel orbiter" or screensaver which exercises pixels by slowly shifting an image around the display
Most TV manufacturer nowadays makes (or in the case of Bang & Olufsen) buys in the necessary technology made-up and ready for fitting in their own badged cabinet. Prices are still very expensive and technology is expected to improve in the next few years. Don't expect prices to fall too much though as you're likely to get more TV for the same amounts of money.
Fixed-pixel technology isn't just for flat TVs. Projection sets also benefit from Digital Light Processing (DLP) - especially rear-projection TVs, which can be slimmed down to a depth of less than 60cm when chips are used in place of CRTs.
How It Works
At the heart of every DLP™ projection system is an optical semiconductor known as the Digital Micromirror Device (DMD) which was invented by Texas Instruments in 1987. The DMD chip is probably the world's most sophisticated light switch. It contains a rectangular array of up to 1.3 million hinge-mounted microscopic mirrors; each of these micromirrors measures less than one-fifth the width of a human hair, and corresponds to one pixel in a projected image. DLP sets fall mainly into two camps:
single-chip front- and rear-projection TVs filter white light from the lamp through a colour wheel to produce colour
three-chip front projectors - which are generally much more expensive - dedicate one chip each to the red, green and blue primary colours
If the three tubes used in a CRT projector to
beam an image onto the screen aren't kept perfectly aligned, the edges of lines
will appear discoloured. But since DLP images derive from a chip whose alignment
characteristics don't 'age' there's no need to tweak the picture periodically.
While its reproduction of dark scenes isn't yet up to CRT standards, DLP achieves deeper, more realistic shadows and blacks than every other fixed-pixel technology. That's because the pivoting mirrors on a DLP chip create black by reflecting light away from the screen. Also, because the DLP mirrors are so close together, the sets generally don't have a problem with 'screen door' effects (a faint image of the pixel grid)
There is no danger of screen burn-in with DLP
DLP front projectors can be reasonably priced
DLP rear-projection TVs are more expensive than the same-size CRT sets
Single-chip DLP sets are prone to a 'rainbow' effect. Although the colour wheel that separates the white light spins extremely fast, you may see streaks of primary colour if you look closely enough, especially from one side of the image to the other. However, faster colour wheels that can dramatically decrease this effect are appearing in newer sets.
Again, many manufacturers offer DLP-based TVs which are increasing in size year by year. Again, prices are falling over time, too.
The oldest of fixed-pixel display technology, LCD (liquid-crystal display) technology first appeared in watches and pocket calculators in the early 1970s. LCD technology is a jack of all trades, capable of powering front projectors, rear-projection TVs and flat-panel displays. LCD screens have already caught on in the computer world, but they've only recently begun to make headway in domestic television sets. This can be attributed in part to picture-quality issues. But there are also size limitations; until recently, the largest flat-panel LCD screen available was around 72cm (diagonally-viewed), although the technology already exists to price them as wide as 1m30.
How It Works
Whether spread across a flat-panel screen or placed in the heart of a projector, all LCDs are pretty much the same. A matrix of thin-film transistors (TFTs) supplies voltage to liquid crystal-filled cells sandwiched between two sheets of glass. As with plasma panels, a trio of red, green, and blue cells make up one pixel. When hit with an electrical charge, the crystals 'untwist' to an exact degree to filter light generated by a lamp behind the screen (for flat-panel TVs) or one shining through a small LCD chip (for projection TVs).
Direct-view models are only a few centimetres deep
LCD front projectors and RPTVs can deliver slightly better colour than DLP sets because the three chips can be individually adjusted, although newer DLP models are narrowing the gap with six-segment colour wheels that use two segments each for the red, green and blue primary colours to improve colour fidelity
Using the same wattage lamp, a typical LCD projector will create a brighter image than a DLP model - but most DLP projectors produce enough light for just about any home cinema
Out of all the fixed-pixel technologies, LCD has the biggest problem producing true blacks. Some light always passes through when the liquid crystals untwist, so the best black on most LCD panels is a very dark grey
Because of the way light passes through an LCD cell, direct-view LCDs usually have a narrower viewing angle than plasma TVs
Low-resolution LCDs exhibit distinct pixilation and screen-door effects when blown up to big screen sizes. For front projection, using a model with XGA (1,024 x 768 pixels) or higher resolution will reduce screen-door effects
While LCD TVs are very popular in the Far East, elsewhere the story has been a little lacklustre. This, again, is due to the high cost factor and the relative poor screen results when compared to other technologies. However, technology is again increasing in leaps and bounds and with much more work to be done on R&D, the technology will be around - and will increase in quality - for a long time to come. Again, as in all the cases of mass demand, prices will plummet in the coming future.
The least-familiar player at the fixed-pixel poker table, LCoS (Liquid Crystal on Silicon) owes most of its technological heritage to LCD. But it outperforms LCD in many respects because it allows for smaller-size pixels that provide higher resolution and almost eliminate the screen-door effect. LCoS has tremendous potential for home cinema, but at the moment it's only available in a handful of products.
How It Works
At the heart of a LCoS projector or rear projection television are between one and three LCOS Semiconductors. The LCOS micro-displays use a twisted Nematic Liquid Crystal. When an electric field is applied to the crystal the amount of twist varies. Using this principle a beam of light is passed through a polariser to make the light waves travel in a single direction. The Twisted Nematic Liquid Crystal causes direction of the polarised light to change. This light is then reflected off the LCOS reflective coating and providing it is in the correct direction it then passes through a second polariser (called the 'analyser').
The cost is its biggest bugbear - with relatively few of these designs being built costs are not likely to fall rapidly in the near future
While costs remain high, LCos is not likely to become a serious contender in fixed-panel displays. However, the resolution capabilities offered by the system make it very attractive and with more R&D work, over time costs may well come down to make it more appealing to manufacturers and consumers alike.
Flat screen televisions –
Quality versus Price: A Bang &
" More and more often Bang & Olufsen get questions and comments about the pricing of our flat screen portfolio - often with a clear indication that "similar" screens are offered much cheaper from other manufacturers. Apart from the fact that other distribution channels operate with significantly lower margins, the pricing issue also has a lot to do with important differentiation in terms of product quality.
In order to substantiate the quality differentiation in the Bang & Olufsen range of flat screen products in a documentary and easy-to-grasp way we are at the moment producing a short DVD movie with a content that focuses on all the differentiation elements contained in a Bang & Olufsen television. This DVD will be made available to all Bang & Olufsen dealers very soon.
In addition hereto we have some important information we would like to share with you right away.
The LCD and plasma components applied in a Bang & Olufsen flat screen television is not just at an average market level. The specifications and quality that Bang & Olufsen requires is the best any supplier can manufacture. We are cooperating with the world leading suppliers within LCD and plasma technology (from Japan, Korea and Taiwan), and we are also demanding the newest models - manufactured by the newest technology - thereby offering the absolute best picture quality in terms of e.g. viewing angle, blackness, dynamic properties, noise, contour and colour naturalness. We set our specifications so high that our suppliers often must sort their flat screen production to find enough panels meeting the Bang & Olufsen requirements. We know that even high-ranked global brands in the consumer electronics industry today offer not just older generations, but also panels at a lower quality level compared to the ones we are using - with a direct link to the price point these brands can offer.
The figure below shows in principle how prices on flat screen panels are influenced by specifications and quality from different flat screen generations (actual model, one year old model and 2 years old model), and by sorting in different specification classes (grade 1, 2 and 3), e.g. regarding damaged pixels. Bang & Olufsen are requiring today's generation and the highest grade - but this is definitely not the case for many of the flat screen brands we find on the market place."
Source: Bang & Olufsen Product Information - November 2004
BeoTech © 2006 All rights reserved