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Digital Flat Panels

An important difference between CRT monitors and LCD panels is that the former require an analogue signal to produce a picture and the latter require a digital signal. This fact makes the setup of an LCD panel’s position, clock and phase controls critical to obtain the best possible display quality and creates difficulties for panels that do not possess automatic setup features and require these adjustments to be made manually.

The problem occurs because most panels are designed for use with current graphics cards, which have analogue outputs. In this situation the graphics signal is generated digitally inside the PC, converted by the graphics card to an analogue signal, then fed to the LCD panel where it has to be converted back to into a digital signal. For the whole process to work properly, the two converters must be adjusted so that their conversion clocks are running in the same frequency and phase. This usually requires that the clock and phase for the converter in the LCD panel be adjusted to match that of the graphics card.

A simpler and more efficient way to drive an LCD panel would be to cut out the two-step conversion process and drive the panel directly with a digital signal. The LCD panel market is growing from month to month, and with it the pressure on graphics adapter manufacturers to produce products which allow this.

Efforts to define and standardise a digital interface for video monitors, projectors and display support systems were begun in earnest in 1996. But the process moved rather slowly in ensuing years, causing concern among manufacturers desperate for a standard. One of the earliest widely-used digital display interfaces is LVDS (low-voltage differential signalling), a low speed, and low voltage protocol optimised for the ultra-short cable lengths and stingy power requirements of laptop PC systems. Efforts to transition LVDS to external desktop displays foundered when the rival chipmakers – Texas Instruments and National Semiconductor – chose to promote different, incompatible flavours of the technology, FPD-Link and Flat-Link respectively. Other schemes such as Compaq’s Digital Flat Panel (DFP), VESA Plug and Display, and National Semiconductor’s OpenLDI also failed to achieve widespread acceptance.

Finally, the Digital Display Working Group (DDWG) came together at the Intel Developer Forum in September 1998 with the intent to put the digital display interface standard effort back on the fast track. With an ambitious goal of clearing through the confusion of digital interface standards efforts to date, the DDWG – whose initial members included computer industry leaders Intel, Compaq, Fujitsu, Hewlett-Packard, IBM, NEC and Silicon Image – set out to develop a universally acceptable specification. The hope was that Intel’s backing would greatly help in the establishment of an industry standard as it had done previously when it had helped push PCI over VL Bus, and when it stepped in to clear roadblocks for the V.90 modem standard.

In April 1999 the DDWG approved a draft Digital Visual Interface (DVI) specification, and in so doing, brought the prospect of an elegant, high-speed all-digital display solution – albeit at a fairly significant price premium – close to realisation.

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