TFT Guide Part 3 - Digital Interfaces

Who's Leading The Race?

Using a standard VGA connector with a TFT display is an almost absurd situation. A digital signal, which is inherently generated in the graphics board, is converted into an analog signal for transmission, only to be converted back into a digital signal again inside the display. It is obvious that this double conversion leads to a loss of display quality and increased hardware costs. A digital interface would obviously make more sense for flat panel displays. However, the situation today is something of a dilemma. Several specifications are simultaneously struggling for the acceptance of the general buyer.

In this article we intend to briefly discuss the history of the development of the digital interfaces, to inform you about the most important of them and obviously to present our prime candidate to you.

Analog Or Digital - The Biggest Difference Of The Interfaces

Flat panel displays with an analog VGA interface continue to dominate the market. The reason why digital interfaces have not been able to penetrate the market is basically due to the uncertainty of the buyer. Well, that isn't surprising in view of the sheer number of standards such as LVDS, TDMS, GVIF, P&D, DVI and DFP - just to name a few. It's obvious that there are far too many. A similar situation arose in the 80's when video standards such as VHS, Beta and Video2000 sparred for market domination. The VHS system finally emerged as the winner, although Beta was technically superior.

The ultimate winning system for digital TFT interfaces now appears to be fixed, but first let's take a look at a few facts:

Analog flat panel displays have had a justified existence for a long time as hardware to control a digital equivalent did not exist. The lack of suitable standards and the objective of the graphic board manufacturers to sell volume also helped their short-term dominance. From today's point of view, analog TFTs are absolutely unnecessary, but they are still successful on the market. The reason for this is that these devices are mainly sold for specific projects and are often part of large tenders. The buyers, normally large companies and government departments, already have an existing infrastructure, which they do not want to change. The majority of these customers simply wants to exchange their old workspace monitors for new flat panel displays and therefore need to be able to plug the new displays into the analog VGA connector of their existing graphic boards. This approach isn't exactly visionary, because it is then impossible to upgrade to digital interfaces in the future.

At this stage we'd like to touch on the subject of pixel jitter , which is almost certainly one of the most unpleasant effects of analog TFTs. This shimmering effect occurs when the clock and phase are not synchronized 100% with the analog signal. Individual pixels then start to swim, which is most apparent and annoying in characters and lines. Digital TFTs avoid the need to trim the clock and phase completely and therefore don't have this problem. If you own one of these digital displays you only need to change the brightness and contrast according to your needs. The technical frills are dropped entirely, and this makes it much easier for you.

A look at today's turnaround situation allows us to be optimistic. The question of standards has been practically resolved and graphic boards are now available with the corresponding digital outputs. The following table gives you an overview of the most important points: