14 DAY TRIAL // The graphics card would be useless without a decent monitor which displays millions or even billions of colors, unless you?ve somehow managed to get those latest spiffy holographic projectors. This article will present common types of PC monitors and all-purpose displays that can connect to a PC as of 2006. Remember that the actual tendency is to incorporate High Definition resolutions of 1920 X 1020 pixels in all these displays, further promoting the newly introduced HD-DVDs and Blue-Ray medias for improved content quality.
In the beginning, there was the CRT In the CRT (cathode ray tube) monitor, the images are displayed on the largest part of the tube (the screen). The back of the vacuum tube has a negatively charged cathode, or electron gun. The electron gun shoots electrons down the tube and onto the positively charged screen. The screen is coated with a pattern of red, green and blue (RGB) phosphorescent dots (usually made up of transition metals or rare earth elements) that will glow when struck by the electron streams. Each cluster of three dots constitutes one pixel (picture element).
The image on the monitor screen is made up from hundreds of thousands of such pixels glowing on commands coming from the graphics card. If the distance between pixels is too great, the picture will appear fuzzy, or grainy. The closer together the pixels are, the sharper the image on screen. The distance between pixels on a computer monitor screen is called its dot pitch and is measured in millimeters. Most monitors have a dot pitch between 0.22 and 0.28 mm. The interior side of the phosphor layer is often covered with a layer of aluminum. The phosphors are usually poor electrical conductors which lead to the deposition of residual charge on the screen, effectively decreasing the energy of the impacting electrons due to electrostatic repulsion (an effect known as "sticking"). The aluminum layer is connected to the conductive layer inside the tube, and disposes of this charge. Additionally, it reflects the phosphor light in the desired direction (towards the viewer), and protects the phosphor from ion bombardment.
Around the collar of the cathodic tube there a couple of magnets, which bend the beam of electrons, in order to light every spread pixel from the screen (magnetic deflection). The beam is bent (scanning process) across the monitor from left to right and top to bottom to create, or draw the image, line by line. The number of times in one second that the electron gun rescans the entire image is called the refresh rate and is measured in hertz (acceptable refresh rates start with 75 Hz).
Time for an important historical fact. The earliest recorded version of a CRT was a cold-cathode diode, a modification of the Crookes tube with a phosphor-coated screen, sometimes called a Braun tube. The first version to use a hot cathode was developed by John B. Johnson (who gave his name to the term Johnson noise) and Harry Weiner Weinhart of Western Electric, and became a commercial product in 1922.
There are two CRT standards that are included in present-day monitors. According to each standard, the pixels are either packed together in strips (as in aperture grille designs) or clusters (as in shadow mask CRTs). Current CRT monitors have three electron guns, one for each primary color, arranged either in a straight line or in a triangular configuration (the guns are usually constructed as a single unit). Each gun's beam reaches the dots of exactly one color; a grille or mask absorbs those electrons that would otherwise hit the wrong phosphor. Since each beam starts at a slightly different location within the tube, and all three beams are perturbed in essentially the same way, a particular deflection charge will cause the beams to hit a slightly different location on the screen (called a 'subpixel'). Color CRTs with the guns arranged in a triangular configuration are known as delta-gun CRTs, because the triangular formation resembles the shape of the Greek letter delta.
Let there be liquid crystals! CRTs became quite ?space-consuming? with the introduction of wider 19 or 21? displays and they got damn heavy, too. We really need something thinner and lighter. How about that LCD technology?
The liquid crystal display (LCD) technology is quite different from the CRT one. In an LCD we still find pixels, but these ones consist of a layer of liquid crystal molecules aligned between two transparent electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each other. Liquid crystals are very important here, because, without their insertion between the polarizing filters, light passing through one filter would be blocked by the other.
The surfaces of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using a cloth (the direction of the liquid crystal alignment is defined by the direction of rubbing). Important factors to consider when evaluating an LCD monitor include resolution, viewable size, response time (measured in milliseconds), matrix type (passive or active), viewing angle, color support, brightness and contrast ratio, aspect ratio, and input ports (e.g. DVI or VGA). These factors are important because the incipient LCD technologies had several problems concerning the response time, the viewing angles and the brightness/contrast ratios.
Let us concentrate on computer-related LCDs. The PCs are usually accompanied by TFT LCDs, which use Thin-Film Transistor (TFT) technology to improve their image quality. TFT LCDs use the most common type of LCD active matrix. They are used in both flat panel displays and projectors. In recent years, TFT flat panel displays have rapidly displaced competing CRT supremacy and their prices are dropping by the month. They are commonly available in sizes between 12 and 30 inches. As of 2004, they have also made inroads on the television market, threatening the old technologies that lasted for more than 20 years.
There are several types of TFT LCDs on the market: - TN + Film ? the most common consumer display type, due to its lower price. The pixel response time on modern TN panels is sufficiently fast to avoid the shadow-trail artifacts that were a cause for complaint in the past. This fast response time has been a heavily marketed aspect of TN displays, although in most cases this number does not reflect performance across the entire range of possible color transitions. However this marketing strategy, combined with the relatively lower cost of production for TN panels, has led to the dominance of TN in the consumer market. However, there still are some limitations for this type. The TN display suffers from limited viewing angles, especially in the vertical direction, and some are unable to display the full 16.7 million colors (24-bit truecolor) available from modern graphics cards. Overall, color reproduction and linearity on TN panels is poor. Shortcomings in display color gamut (often referred to as a percentage of the NTSC 1953 color gamut) can also be attributed to backlighting technology. It is not uncommon for displays with CCFL (Cold Cathode Fluorescent Lamps) based lighting to range from 40% to 76% of the NTSC color gamut, whereas displays utilizing white LED backlights may extend past 100% of the NTSC color gamut - a difference quite perceivable by the human eye.
-IPS ? In-Plane Switching technology was developed by Hitachi in 1996 to improve the poor viewing angles and color reproduction of TN panels. Most also support true 8-bit color. These improvements came at a loss of response time, which was initially on the order of 50ms. IPS panels were also extremely expensive. The newer S-IPS (Super-IPS) technology comes in two flavors, which are meant to improve the older IPS: AS-IPS - Advanced Super IPS, also developed by Hitachi in 2002, improves substantially on the contrast ratio of traditional S-IPS panels to the point where they are second only to some S-PVAs. A-TW-IPS - Advanced True White IPS, developed by LG Philips for NEC, is a custom S-IPS panel with a TW (True White) color filter to make white look more natural and to increase color gamut. This is used in professional/photography LCDs.
-MVA (Multi-domain Vertical Alignment) was originally developed in 1998 by Fujitsu as a compromise between TN and IPS. It achieved fast pixel response (at the time), wide viewing angles, and high contrast at the cost of brightness and color reproduction.
Analysts predicted that MVA would corner the mainstream market, but instead, TN has risen to dominance. A contributing factor was the higher cost of MVA, along with its slower pixel response (which rises dramatically with small changes in brightness).
-PVA (Patterned Vertical Alignment) and S-PVA (Super Patterned Vertical Alignment) are more advanced versions of MVA technology offered by Samsung. Developed independently, a PVA suffers from the same problems as MVA, but boasts very high contrast ratios such as 3000:1. S-PVA panels all use true 8-bit color electronics.
Medic! Some plasma, on the double! A plasma display panel (PDP) is an emissive flat panel display where visible light is created by phosphors excited by a plasma discharge between two flat panels of glass. The gas discharge contains no mercury (contrary to the backlights of an active matrix LCD); an inert mixture of noble gases (neon and xenon) is used instead. Plasma displays are bright (1000 lx or higher for the module), have a wide color gamut, and can be produced in fairly large sizes, up to 262 cm (103 inches) diagonally. They have a very high "dark-room" black level, creating the "perfect black" desirable for watching movies. The display panel is only about 6 cm (2? inches) thick, while the total thickness, including electronics, is less than 10 cm (4 inches). Real life measurements of plasma power consumption find it to be much less than that normally quoted by manufacturers. Nominal measurements indicate 150 watts for a 50" screen.
The main advantage of plasma display technology is that a very wide screen can be produced using extremely thin materials. Since each pixel is lit individually, the image is very bright and has a wide viewing angle. Most cheap consumer displays appear to have an insufficient color depth - a moving dithering pattern may be easily noticeable for a discerning viewer over flat areas or smooth gradients; expensive high-resolution panels are much better at managing the problem. Anyway, the lifetime of the latest generation of plasma displays is estimated at 60,000 hours (this actually is the estimated half-life time).
?Right SED Fred? A surface-conduction electron-emitter display (SED) is a flat panel display technology that uses surface conduction electron emitters for every individual display pixel. The surface conduction emitter emits electrons that excite a phosphor coating on the display panel, the same basic concept found in traditional cathode ray tube (CRT) televisions. This means that SEDs use small cathode ray tubes behind every single pixel (instead of one tube for the whole display) and can combine the slim form factor and contrast ratios of LCDs and plasma displays with the superior viewing angles, black levels, and pixel response time of CRTs. Canon also claims that SEDs consume less power than LCD displays. Being nearly as slim as LCDs, the SED sports some impressive capabilities: exceptional contrast rates of as much as 100,000:1, response times of less than 1 ms and a viewing angle of 180 degrees.
Hey, my display is alive! An organic light-emitting diode (OLED) is a special type of light-emitting diode (LED) in which the emissive layer comprises a thin-film of certain organic compounds. The emissive electroluminescent layer can include a polymeric substance that allows the deposition of very suitable organic compounds, for example, in rows and columns on a flat carrier by using a simple "printing" method to create a matrix of pixels which can emit different color light. Such systems can be used in television screens, computer displays, portable system screens, and in advertising, information and indication applications. OLEDs can also be used in light sources for general space illumination. OLEDs lend themselves for the implementation of large areal light-emitting elements. OLEDs typically emit less light per area than inorganic solid-state based LEDs which are usually designed for use as point light sources.
One of the great benefits of an OLED display over the traditional LCD displays is that OLEDs do not require a backlight to function. This means that they draw far less power and, when powered from a battery, can operate longer on the same charge. It is also known that OLED based display devices can be more effectively manufactured than liquid-crystal and plasma displays.
As always, there have to be some drawbacks too. The biggest technical problem left to overcome has been the limited lifetime of the organic materials. For example, blue OLEDs typically have lifetimes of around 5,000 hours when used for flat panel displays, which is much lower than typical lifetimes of LCD or Plasma technology. However, recent experimentation has shown that it's possible to swap the chemical component for a phosphorescent one, if the subtle differences in energy transitions are accounted for, resulting in lifetimes of up to 20,000 hours for blue PHOLEDs.
Also, the intrusion of water into displays can damage or destroy the organic materials. Therefore, improved sealing processes are important for practical manufacturing and may limit the longevity of more flexible displays.
All the above-mentioned display types are battling for supremacy. LCDs are en vogue for now, but several future technologies, such as the laser or the holographic displays promise life-like colors and 3D imagery. As previously stated, LCDs become more and more affordable and may soon be proclaimed the industry's standard. Plasma displays see a slower market penetration, but they too tend to become cheaper. The interesting SED will be available worldwide as soon as Q1 2007, with more than decent prices and this will make them a true competitor for LCDs and Plasmas. OLED still has some issues to resolve, but it may become a reliable display type for mobile devices. What about CRTs? Well, they are quite outdated and many companies have already decided to stop their production. 2007 may be the last year for CRT mass production. I say it?s all for the best. And that's a wrap. I think we'll go on with the hard disk drives in the next article. Stay tuned.
