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Don't the new LCD monitors look impressive? Thanks to ongoing cost reduction and performance enhancements in flat panel display (FPD) technology, the new LDD desktop displays are finally poised to enter the PC mainstream. On the surface this represents an enticing opportunity to upgrade the desktop PC monitor to a purely digital interconnect and display technology.

As with any new PC peripheral device, the transition to digital FPD displays presents a complex set of technical and business challenges for the industry. History has shown that major PC transitions evolve over five or more years. For example, the PC industry shipped most PCs with both 5.25-inch and 3.5-inch floppy disk drives for a period of 10 years as it moved to higher capacity floppy disk drives.

In an effort to agree on an FPD digital standard interface, Intel and eight other companies announced the formation of the Digital Display Working Group (DDWG) on September 17, 1998, at the Intel Developer Forum in Palm Springs, CA. This group is working to bring to the industry a single standard for making the digital interface work between the PC and the monitor. This is not the first time this has been tried. VESA (Video Electronic Standards Association) has been working on a digital interface encompassed in the Plug & Display (P&D) standard. P&D has not won broad support due to cost, various factions competing for specific digital standards, such as, GVIF, LVDS and TMDS, and lack of clear support for existing equipment -- the legacy compatabilitycompatibility issue.

Analog RGB Legacy Support

The inertia of analog RGB video is enormous. The installed base of PCs with analog RGB outputs is approaching 1 billion units (according to David Mentley of Stanford Resources, Inc.) This huge installed base will continue to influence FPD monitor sales and feature sets until they match CRT cost structures. The problem is two-fold: PC OEMs need to support the installed base of analog RGB monitors in order to sell upgraded PCs, and monitor makers need to support existing PCs with analog RBG video outputs. Educated buyers always demand compatibility with their existing PC equipment.

Some PC OEMs are planning to bundle FPD monitors using digital interfaces with custom digital video cards. This helps digital monitor acceptance but does not help upgrade PCs when the old monitor remains. Most corporate IS managers require new PC systems be compatible with their installed base of CRT monitors. Interchangeability of monitors and PCs in large offices is a must to allow the flexibility to reallocate monitors and PCs to meet changing needs in their organizations.

Does the new digital interface make a difference to the consumer? Proponents argue that image quality is better, the costs are comparable and the standard will see easy adoption. We already see a huge legacy issue, let's talk about the other issues.

Equal Image Quality

Proponents of digital interfaces have claimed "outstanding image clarity" for FPD monitors using a pure digital interface. They also claim that the analog interface image quality suffers from "numerous anomalies" resulting from the conversion from digital to analog to digital.

New technology in ADCs and PLLs has closed the image-quality gap with the digital interfaces. In fact, this current generation of high-speed ADC and PLL technology -- now in high volume production monitors -- is winning awards for image quality. According to Windows Magazine, the Eizo FlexScan L34 monitor with an analog interface was the first FPD monitor selected to their Windows 100 Hardware List because "it has unmatched image quality" and "cleaner color blending and uniform scaling than that of rivals."

Analog Costs Less Than Digital

All OEMs are sensitive to how much the consumer is willing to pay for a PC system. Analog RGB video offers lower overall system costs due to greater economies of scale. Leading desktop graphics vendors such as Matrox, ATI Technologies, S3, 3DFX, nVidea and Intel supply graphics controllers with analog RGB outputs using low-cost, embedded RAMDACs. Digital interfaces such as LVDS, GVIF, and TMDS (Panelink) add cost because they require special shielding to connectors and cables in order to match the performance of their analog counterpart.

Interface costs are the sum of component, cable and connector costs. The analog interface uses the industry-standard VGA cable and connectors that are produced in quantities of over 100 million units per year. Recent advances in high-speed ADC technology have reduced the total analog interface cost per monitor to less than $25. Using CMOS technology, the entire analog interface has been integrated on a single chip such as Analog Devices' AD9884.

The digital interface such as VESA's Plug and Display and DFP (Digital Flat Panel) currently uses more expensive cables and connectors as a result of lower production volumes and additional shielding (twin coaxial) to ensure compliance with EMI emission standards. The difference in the cable cost is about 4x. The costs of a digital interface for an SXGA FPD monitor starts at $35 (a 30% premium) broken down in Table 1 for a typical 1280 x 1024 lines display.

In order to gain acceptance, a monitor maker may bundle a video card with a digital FPD. These special video cards include the required digital interface circuits and can add an additional $150 to the cost of the monitor.

The Analog Interface is the Only Industry-Wide Standard for FPD Monitors

Consumers simply don't have the time or the expertise to decide among competing technologies to make their PC systems work properly, depending on PC industry standards to obtain plug-and-play performance right out of the box.

The Digital Display Working Group has the right idea in trying to define an open industry standard but their work is only starting. Today, there are multiple cable configurations for the competing digital interfaces. that make it virtually impossible for consumers to ensure compatibility. This confusion among the connectors led PC guru John Dvorak to recommend, "The problem is that we'll probably see various new connectors on the market at the same time, and if you choose the wrong one you may end up with a white elephant. Until this shakes out, stick with the 15-pin VGA plug."

Conclusion

The analog interface is helping gain market acceptance for FPD monitors simply because it works! The analog interface offers legacy compatibility, with over 1 billion PCs worldwide, has the lowest total cost, and is the only industry-wide standard interface for FPD monitors. FPD displays using the latest analog interface technology have shown comparable image quality to that produced by the best digital interfaces. Today, consumers are overwhelmingly buying FPD monitors with an analog RGB interface.

It would only make sense that the industry and DDWG move toward a digital interface for FPD monitors while embracing the analog interface. This philosophy will enable consumers and MIS professionals to support existing equipment, enjoy ease of use, and upgrade at a pace that fits the company or an individual's budget.

The Authors

Dale Stolitzka is chief systems architect for Analog Devices' computer product line. He is located at ADI's facility in Santa Clara, California.

Doug Bartow is strategic marketing manager for Analog Devices' interface product line and is located at the company office in Greensboro, North Carolina.

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