Analog Angle Article

“Let’s get physical”: loving Layer 1

We read a lot about the newest and latest connectivity products with more features, advanced user interfaces, and all sorts of wonderful things. Most of this is made possible by highly integrated digital ICs, complex firmware, or upgradable software. So what's left for analog?

The reality is that the standard, multilayered connectivity model, whether the Open Systems Interconnection (OSI) Reference Model with its seven layers (click here, for example), the Internet, or other, needs to physically connect to the channel. Whether it is wired, RF wireless, optical, or other, that connection at Layer 1 is where analog-circuitry issues dominate, and the right analog circuitry is absolutely needed for a successful connection to the medium.

Often, the actual connection at the physical layer is a relatively small part of the overall system, in terms of dimensions and space needed, despite its importance in the signal chain. I think about this when I recall a book I read about the laying of the first trans-Atlantic undersea cable, a major technical accomplishment (this was even before amplifiers!).

One of the challenges in that project was that the undersea cable needed very different amounts and types of insulation and protection, depending on where each part was to be used. The physical enclosure of the copper cable needed to be more rugged closer to shore, where ships or their anchors might scrape or drag it, and it needed to be especially toughened where it came ashore. There was even a picture of a huge blockhouse with a massive cable coming into it from the ocean: that was the undersea cable making landfall, where the relatively thin copper wire inside needed the most real-world protection. To me, this physical ruggedness is symbolic of the physical AND electrical issues that many designers face at the interconnection points.

And if you really want to have fun, try explaining to someone where and how the physical connection is made to “The Internet”. Is there some sort of mega-cable running everywhere that service providers just tap into; similar to a power line with its many drops? How does a dial-up or DSL line from a regular wired or wireless phone-service company actually connect to the Internet? What about a cable TV company: how do they connect to this thing called the Internet? When you get Internet service at your office or company, what is actually connected to, and where? When all is said and done, there has to be a physical connection somewhere to something! ♦

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