DisplayPort: Technicals & Advantages

We already talked a fair bit about DisplayPort in our earlier article on Luxtera's CMOS Photonics technology, but only with a focus on cable length given the advantages of Luxtera's technology. Now that we're talking of DisplayPort receivers in general, it's also important to consider other dynamics that influence the DisplayPort vs HDMI vs DVI battle.

DisplayPort's advantages over LVDS are quite obvious, as briefly discussed on Page 2, but it's much less obvious why anyone should care in the PC market. Dual-link DVI already has provisions for higher bit depths and refresh rates and DisplayPort's bandwidth isn't much higher, so why even bother besides the lack of royalties and the marketing appeal of new technology? Well, there certainly are several other reasons:

  • Smaller connectors and ports; this will make GPUs with 4 display ports per board possible, as well as making DisplayPort a more viable alternative to VGA in notebooks than DVI ever was. Lower EMI also helps there.
  • DisplayPort is currently the only standard which supports 'AC-Coupling'; this makes the transition to smaller process nodes for transmitters (i.e. on the GPU) much easier. HDMI 1.3 still doesn't support that, although it has been claimed that the next revision will.
  • Truly open standard, unlike HDMI or even DVI. This is what made support for Luxtera's CMOS Photonics solutions possible, for example. It has also been claimed that some are unhappy with the way HDMI versions have been handled, with no clear roadmap and a significant timing advantage for Silicon Image.
  • Potentially cheaper overall; in its standard implementation for LCDs, DisplayPort uses 4 pairs of wires, while DVI requires 7 for a dual-link connector (6 data and 1 clock). IDT couldn't yet confirm whether the receivers will actually be cheaper though, as they are not yet sampling products.
  • Support for a number of minor goodies, including two-way communications for touch screens, support for audio data (like HDMI), slightly higher bandwidth (enough for 2560x1600 10bpc, unlike dual-link DVI), and more. Also supports implementations with fewer wires/lanes for markets where that could make sense, such as handhelds.

And then interestingly, there's something else that DisplayPort makes possible: ultra-thin displays. How is that even related? Well, previous standards were made with the assumption that all displays would have a front-end and an integrated scaler (although Dell's 3007 doesn't have the latter, but we're not sure if that's even spec-compliant in theory). DisplayPort, on the other hand, allows the graphics card to "direct drive" the LCD.

The primary advantages to this are cost and sleekness. Both are because the LCD manufacturer can get rid of a fair bit of electronics this way (scaler/front-end controller and TMDS receiver, internal LVDS bus, etc.) - and the results speak for themselves:

Dell's upcoming Direct Drive-based DisplayPort LCD. It's just 0.5 inches thick.
[Source: Engadget]