Video Hardware, Part 1 - Flat-Panel LCD Monitors (Page 6 of 12 ) LCD desktop monitors, once seen mainly on the office sets of futuristic TV shows, are now becoming a common choice for use in today's office computing environment. Many users with dual-display-capable video cards have added an LCD panel as a second monitor or use one as their only monitor. LCD monitors offer a number of benefits when compared to conventional CRT "glass tube" monitors. LCD panels feature a larger effective viewable area than CRTs; a 17'' LCD is essentially equal in usability to a 19'' CRT. Because LCDs use direct addressing of the display (each pixel in the picture corresponds with a transistor), they produce a high-precision image. LCDs can't have the common CRT display problems of pin-cushion, barrel distortion, or convergence errors (halos around the edges of onscreen objects). LCD panels are less expensive to operate because they feature lower power consumption and much less heat buildup than CRTs. Because LCD units lack a CRT, no concerns exist about electromagnetic VLF or ELF emissions. Although LCDs offer a comparable mean time between failures (MTBF) to CRT displays, the major reason for LCD failures is the backlight, which is relatively inexpensive to replace. CRT failures usually involve the picture tube, which is the most expensive portion of the display and is often—especially on displays 17'' and smaller—not cost-effective to replace. LCD panels offer a smaller footprint (front-to-back dimensions), and some offer optional wall or stand mounting. Several LCD panels offer a pivoting feature, enabling the unit to swivel 90° and providing a choice between the traditional landscape horizontal mode for Web surfing and the portrait vertical mode for word processing and page-layout programs. LCD panels weigh substantially less than comparably sized CRTs. For example, the ViewSonic VE175, a 17'' LCD, weighs only 13.6 lbs., compared to the 50 lbs. weight of typical 19'' CRTs. There have been two major digital LCD panel standards and specifications: The Digital Flat Panel (DFP) standard approved by the Video Electronic Standards Association (VESA) in February 1999. DFP was previously known as PanelLink; DFP has now been replaced by DVI. The Digital Visual Interface (DVI) standard proposed by the Digital Display Working Group (DDWG) in April 1999. DVI has become a de facto standard supported by most recent mid-range and high-end VGA display cards, including models with dual-display capabilities.
Figure 15.4 shows how DFP and DVI connectors found on some video cards and digital LCDs compare to the standard VGA connector used on conventional video cards, CRTs, and analog-compatible LCDs. 
Figure 15.4 Conventional VGA cards, CRTs, and analog-compatible LCDs use the standard VGA connector. Early digital LCDs and their matching video cards often used the DFP connector. Most recent digital LCD panels use the DVI-D connector, whereas video cards used with both analog and digital displays use the DVI-I connector. Before you rush to the store to purchase an LCD desktop monitor, you should consider several potential drawbacks: If you routinely switch display resolutions (as Web developers do to preview their work), LCD monitors must take one of two approaches to change resolutions. Some older units might reduce the onscreen image to occupy only the pixels of the new resolution, thus using only a portion of a typical 1024x768 LCD panel to display a 640x480 image, whereas newer units might scale the image to occupy the entire screen. Scaling is becoming common because the Digital Display Work Group standard for LCD desktop displays specifies that the scaling must take place in the display panel, the graphics controller, or both places. Look at the quality of a scaled image if using different resolutions is important to you. If you choose an analog LCD panel, you'll usually save money and be able to use your existing video card or onboard video port. However, image quality for both text and graphics can suffer because of the conversion of the computer's digital signal to analog (at the video card) and back to digital again (inside the LCD panel). The conversion can lead to pixel jitter or pixel swim, in which adjacent LCD cells are turned on and off by the display's incapability to determine which cells should stay on and stay off. Most panels come with adjustment software to reduce this display-quality problem, but you might not be able to eliminate it entirely. Digital LCD panels avoid conversion problems when attached to a digital-compatible display card. However, most low-cost, off-the-shelf display cards don't support digital signals yet, and the onboard video circuits built into some motherboards don't support DVI yet.
Note -Video card and chipset makers, such as NVIDIA, Matrox, and ATI, have added support for digital and analog display panels to most of their recent 3D chipsets and video cards. Check the specifications for a particular video card to verify support.
High-quality LCD panels of either digital or analog type are great for displaying sharp text and graphics. But they often can't display as wide a range of very light and very dark colors as CRTs can. Many LCDs don't react as quickly as CRTs. This can cause full-motion video, full-screen 3D games, and animation to look smeared onscreen. To avoid this problem, look for LCDs that offer a response time of 16ms or faster. Some LCDs now have response times as low as 12ms. These displays use an improved control method called feed forward driving (FFD) technology developed by Mitsubishi.
Note -Instead of applying the same voltage level to LCD cells when the image changes, FFD uses the optimum voltage level for each cell when it changes. Because cells require different voltage levels depending on the shade needed, FFD displays reduce blur by improving display performance. FFD displays first became available at retail late in 2002.
Thanks to price decreases, larger panel sizes, improved performance, and widespread support for DVI digital connectors on current video cards, this is the best time ever to consider buying an LCD panel for your desktop PC. Be sure that you use the following criteria when you consider purchasing an LCD monitor: Evaluate the panel both at its native resolution and at any other resolutions you plan to use. If you're considering a digital LCD panel, determine whether your existing video card supports the features you need. Features you might find necessary include OpenGL and high-speed 3D support (for gaming), VGA-to-TV support (for video producers), and DVD playback software (for watching DVD movies). Because most mid-range and high-end video cards based on the latest NVIDIA and ATI chipsets do offer a DVI port for connection with current and forthcoming digital LCD panels, you can upgrade to a high-performance video card that will support your display. Even though some notebook computers now support DVI displays, most still feature only analog VGA connectors. Look for displays that support both analog and DVI inputs if you want to use the same display on different systems. Because LCD panels are much lighter and smaller than normal CRT displays, they're a natural choice for connecting to both desktop and notebook computers. If you use multiple computers in a small work area, you might also want to look for displays that support multiple inputs, which enables you to connect two computers to one screen. Make sure your system has a suitable expansion slot for the recommended video card type. Many low-cost systems today feature onboard AGP video but no AGP slot, which can't be upgraded unless the user opts for the obsolescent (for video) PCI slot. As the move to LCD panels continues, more of these systems should feature built-in support for LCDs, but this could be a problem for some time to come.
Note -Although many recent chipsets with integrated video—such as NVIDIA's nForce2; ATI's Radeon IGP; and Intel's 865G, 845G, and 845GE—feature DVI support, most motherboards using these chipsets do not provide a built-in DVI port. Instead, an optional add-on card that plugs in to the AGP slot is used to enable DVI support. Otherwise, the onboard video can be disabled and replaced with a dual-display video card with VGA and DVI ports.
Evaluate the panel and card combo's performance on video clips and animation if you work with full-motion video, animated presentation programs, or games. Although active-matrix (analog) and digital LCD monitors have much wider viewing areas than do passive-matrix and dual-scan LCD panels used in older notebook computers, their viewing angles are still usually much less than CRTs. This is an important consideration if you're planning to use your LCD monitor for group presentations. To improve the horizontal viewing area, several vendors have developed patented improvements to the basic TFT display, such as Hitachi's in-plane switching (IPS), Fujitsu's multidomain vertical adjustment (MVA), and Mitsubishi's FFD—all of which have been licensed to other leading LCD makers. A high-contrast ratio (luminance difference between white and black) makes for sharper text and vivid colors. A typical CRT has a contrast ratio of about 245:1. Although LCD panels in the May 23, 2000 PC Magazine test had contrast ratios ranging from a low of 186:1 to a high of 370:1, newer LCD panels have even higher contrast ratios (up to 400:1). Panels could be viewed at an average horizontal angle of as much as 129° without loss of contrast. Features such as integrated speakers and Universal Serial Bus (USB) hubs are pleasant additions, but your eyes should make the final decision about which panel is best for you. Because reviews of LCD panels often don't provide detailed analysis of horizontal and vertical viewing angles and contrast ratios, check display units in stores yourself. Be sure to view the displays from several angles. If you're adding the panel as a second display, be sure to check its off-axis image quality. Look for pivoting displays that enable you to rotate the display to match an upright page layout if you use your computer for text-editing or page layout. This feature is supported by many LCD panels—particularly those that are 17'' or larger—but the display performance in portrait mode is usually lower than in normal landscape mode, especially for rapid motion. If possible, test the display in portrait mode if you plan to use this mode frequently.
 | This chapter is from Upgrading and Repairing PCs, 16th edition,by Scott Mueller. (Que Books, 2004, ISBN: 0789731738). Check it out at your favorite bookstore today. Buy this book now! |
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