Karbosguide.com - Module 7a.6

The flat panel monitors


The contents:

  • Introduction to flat panel monitors
  • Eye Ergonomics
  • The Digital Interface
  • Next Generation Monitors?
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  • The Digital Flat Panel Monitors

    The big, heavy traditional CRT monitors will eventually be phased out. To day we see them replaced by the flat andLCD (Liquid Crystal Display) monitors, also known from labtops.

    It may be a few years before this technology will be dominating, but it is bound to happen. The the flat panel monitors are excellent, and they are available; the prices have gone down. Today a 17.3" LCD costs as much as a 21" CRT monitor did 4 years ago.

    The LCD screen is flat, since it contains no cathode ray tube (CRT). Instead the screen image is generated on a flat plastic disk, where millions of transistors create the pixels.

    Here you see a Siemens Nixdorf 3501T. It was my first TFT monitor (from 1997), and it produces a sharp high resolution image - better than any other I had ever seen:


    Eye Ergonomics

    The digital flat panel monitors are also called "soft" screens, since their images seems to have a "softer" quality than those from traditional CRT monitors. The image does not flicker thus causing less eye strain.

    People, like myself, who have become accustomed to these soft images will not return to the traditional monitors. I cannot express this with enough emphasis: The flat display is the best monitor available. It is so good to your eyes!

    Modern research has shown that a steadily illuminated screen image is a very important element in a good work environment. The eye responds to all light impressions, and the brain interprets all light impressions continually. When a mediocre monitor flickers, the brain will continually receive superfluous light impressions "noise" to sort out. Thus the brain works permanent overtime interpreting the screen flicker. No wonder that people get tired from watching their monitors.

    At the same time the LCD screen is by far the most environmentally safe product. These flat screens emit zero radiation, and they consume significantly less power than the traditional monitors. Another reason to expect LCD screens to become the monitors of the future.

    No refresh rate

    A big advantage in the LCD screen is that it does not flicker. Traditional CRT monitors flicker all the time which is not ideal. Of course the best CRT monitors have a high refresh rate (85 Hz or more), which provides a very stable image with no noticeable flicker. But the LCD screen does not flicker at all (when digitally connected). They have a refresh rate of 0 Hz!

    Please notice that looking at LCD displays, you may read information like:

  • Pixel Frequency 65MHz
  • Horizontal 30 ~ 50KHz
  • Vertical: 55 ~ 70Hz

    This indicates that there is a refresh rate. There is, but it is only working when the screen image is changing. So if you move a window across the screen, the changes will be updated with a refresh rate of 60 Hz or what ever you choose.

    To many users this does not really matter; using Office programs, most of the time the screen image does not change, hence it does not flicker. Obviously it is a problem if you expect to use your flat panel monitor to show full motion videos or games.


    The digital interface

    The most important thing about the flat panel monitor is that it is connected to a digital graphics port. Unfortunately, this is not always the case.

    Back in 1997, when I got my first flat panel monitor (the Siemens 3501T mentioned above) it was only available with a (total proprietary) digital graphics adapter. This was a 1st generation flat panel monitor. Later the manufactures found out to add an analog port in the displays. This way people could buy a flat panel monitor and reuse their exixting graphics adapter. It is a marketing stunt, which should not be followed!

    The only way to benefit from a flat panel monitor is to feed it digitally.

    Our latest monitor

    In spring 2001 I bought a new flat panel monitor; it is a Dell model 1701FP. A nice 17.3" monitor, which I paid around $900 for (the price have decreased later). The monitor holds both an analog (VGA-) port and a digital port (DVI).

    A 17.3" flat panel monitor has a visible area much bigger than that from a traditional 17" CRT monitor - you can compare it to a 19" CRT. The 17.3 inches is the visible diameter.

    I was told, that it should work fine using the analog port with my existing Matrox G400 graphics controller. The manual emphased that one should use the 60Hz mode. I installed the hardware, and it worked fine. Only the image was terrible! It was flickering and very unsharp, kind of "dirty".

    The weird thing is, that the Dell manual holds almost nothing on these issues. But through testing we found out that the 75 Hz analog mode was the best possible. But it was not satisfactory, not at all. Having paid quite a lot of money, we decided to go for a digital graphigs controller. We found an ATI Radeon VE, which turned out to be a great card at a reasonable price:

    From the box, the product seems to be aimed gamers. To those I am sure, that the RADEON chipset and the 32 MB of DDR RAM is fine. To us, the very important issue was, that there is a DVI connector on the board:

    With the DVI connector in use, the DELL flat panel monitor works absolutely perfectly. Thinking about it, it is incredible, that the company does not tell this in the manual. With digital interface the image is extremely sharp and completely flicker free.

    A flat panel monitor is digital by nature. There is no analog electronics included, and that is the big advantage of this technology. Hence, the monitor should not be connected through an analog interface. In fact, using the analog interface, you get to conversions, which both add noise to the final image. First the graphics adapter has to convert the digital data of the PC to analog electronical signals. Then these analog signals have to be converted back til digital information to feed the display.

    Using the digital interface, each pixel consists of three transistors, which each is mapped to the corresponding memory cell holding the image info. A purely digital to digital transmission with no electronical noise involved - that is the way to produce a stunning image!

    Here you see an illustration of the differences between the two setups:

    The A/D (analog to digital, the RAMDAC of the video card) and D/A (digital to analog) conversions only reduce image quality on a flat panal monitor - nothing else! Hence, the digital interface by-pass the RAMDAC of the graphics controller:


    Panel Quality

    It is difficult to produce a flat panel display without flaws. Most panels sold have a few defect pixels, where one or more transistors are gone.

    The bigger the panel gets, the more flaws you find (due to the increasing number of transistors). This helps keeping up the prices - the manufactures have to throw away a large percantage of the production - you cannot repair flawed pixels.

    All vendors have some kind of quality policy in this area. Some only accept up to 3 or 5 pixel flaws per panel. Others accept up to 15, if they are not situated in the middle of the display. When you buy a flat panel display you should make sure that you can return it if the number of pixel-flaws is to big. This can be hard to achieve.

    In the summer 2001, a German survey showed that some vendors take advantage of the consumers ignorance in this area. More than 30% of the flat panel monitors were of second range quality and should not have been brought to the shops. Obviously it has been tempting to some companies to sell some of the displays, which should have been dismissed.

    Screen savers

    Using a LCD display, you should remember to install the Windows screen saver. I use "Black screen" after 5 minutes. Like in the "old days", the monitor may get damaged from longer periods of showing the same image.


    Next Generation Monitors?

    The monitor technology is advancing very rapidly. An interesting development comes from a British invention LEP - Light Emitting Plastic . It is an ordinary thin, flexible plastic (polymer), which is sandwiched together with a thin film of indium tin oxide and aluminum. Thin-film transistors control the oxide layer, causing the huge plastic polymer molecules to become light emitting.

    These LEP screens should have these advantages:

  • They are completely flat and lightweight.
  • They consume only small amounts of electric power.
  • They do not require background illumination, which the LCD crystals do.
  • They emit light, which is visible from all angles of view.

    These screens was expected to be available in year 2002/2003, but lately there have been no much indication that they will come. Currently work is being done with prototypes, which have a resolution of 200 dpi. That corresponds to a resolution of 2200 X 1600 pixels in a 15" screen. So maybe we can look forward to an extremely high screen resolution.

    I would like to fantasize about future Coca-Cola bottles with a built-in video display in the plastic bottle! By the way, these polymer plastic materials are finding their way into other parts of the data processing technology. Work is being done on developing different storage media, hard disks in terabytes size and RAM modules based on polymers. These "organic" storage media should also be significantly cheaper to produce that the traditional products.

    See Cambridge Display Technology web .


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    To learn more

    Read about sound cards in Module 7c.

    Read about digital sound and music in Module 7d .

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