The Science Behind ‘Active’ HDMI Cables: Part 1

HDMI 2.0 has forced many to look at new and current active cable devices, not only for bandwidth, but also for length and cable size. In the first of a three-part series, we define the term “active HDMI cable” and what makes them tick.

Jeff Boccaccio

Editor’s Note: This is the first in a three-part series on Active Cables.

With the introduction of HDMI’s new Rev 2.0 and its increased bandwidth, many have focused their attention searching for new products that will support this for 2014. It is looking like the HDMI cable business will become a more “active” one. This has forced many firms to take a closer look at new and current active cable devices, not only for bandwidth, but also for length and cable size.

What makes these active products tick? First let’s define the term “Active HDMI Cable.” It is an HDMI cable, of just about any length, that has an active digital equalizer built into the cable. These devices are placed inside one of the cable connectors, usually at the sink end, or molded in the cable itself. The molded products look like a bulge in the wire where the circuitry is inserted.

Over the course of time these types of equalizers have been used particularly for long-distance applications and were manufactured in several stand-alone form factors (extenders). They were usually built using one of two processing methods known as Pre-Emphasis (Pre-E) and another called De-Emphasis (De-E). They both kind of do the same thing only differently.

During the early days of HDMI under Revisions 1, 1.2, 1.3, and 1.4 these apparati played a huge part in getting HDMI cables over the 7-meter length limitation. The chipsets used in these devices were somewhat large and tended to demand a relatively high amount of supply current, higher than the 55ma HDMI currently supports, so they came equipped with external power supplies.

Over time better semiconductors were designed with smaller form factors and improved power management. These are the chips that you would usually find inside the cable itself making it “active.” Not only was this a major achievement by way of its size, but also for the way it handled its current consumption. As we all know, the HDMI interface uses a 5-volt supply line to support some electronics in the sink with a relatively tight voltage drop spec of no lower than 4.7 volts. So you can see with only a 55ma rating, it doesn’t take much to kill the lifeblood of HDMI.

Now this is where the story begins to get juicy. There was one company that owned and manufactured this type of chipset, truly one of the best achievements in high-speed cable development supporting the HDMI interface. However since the parts’ major role was to be used inside of cables, most of the marketing and exposure of these parts were pretty much under the control of the cable manufacturers that built them. Yep, you guessed it, in China.

It was introduced as a remedy for long-distance applications, but very little emphasis was placed on the technological advancements that the semiconductor company achieved. This inevitably limited the ability for many of the cable manufacturers to take full advantage of this new and advanced technology.

The semiconductor company was called Redmere, based in Cork, Ireland. It was recently acquired by Spectra 7 in Palo Alto, Calif. These are the folks who are now spearheading new cable development for current and future cable products.

When we received the necessary proprietary equipment to analyze the functionality of these parts in our lab it demonstrated a huge potential unknown to many. Notice, I said parts and not part. There are different parts for different applications, not to mention the supporting programming attributes required for each active cable.

In addition, there is a science behind these parts; a very deep and complex science that, again in my opinion, the majority of the cable firms out there did not recognize. I believe that one of the reasons for that confusion – besides lack of knowledge – among manufacturers was due to the large focus China took in branding the name Redmere versus informing cable makers about the potential power and programmability the product line had to offer.

This all became very evident to us as more cable products entered into our labs here at DPL for testing boasting the fact that they were “Redmered”! Who cares – we also receive cables for testing that are “freeze dried.” So what’s the difference? Most companies did not even know there were different parts for different jobs! This all surfaced as some “Redmere” cable products failed to meet DPL minimums, not to mention HDMI speci cation also. Was it the Redmere? Hell no, it was the ignorance of the cable companies.