On Sun, March 11, 2012 11:03 am, Spehro Pefhany wrote:
> At 11:31 AM 3/11/2012, you wrote:

>>My wife, also a computer "geek" but without an EE inclination was asking
>>me why anyone would design with a jack without built-in magnetics these
>>days.
>>
>>Could anyone clue me in?
>>
>>Thanks,
>>    Bill
>
> To save a bit of money. The combination of an external transformer and a
> passive jack is still a bit less costly (used to be a LOT less costly,
> but the integrated ones have come down a lot in cost). Putting it in the
> can costs more and probably involves as much _total_ labor but saves on
> the footprint and PCB assembly costs.

In a previous life, I did Ethernet physical layer design/testing on
servers for a major computer manufacurer (rhymes with "Hell").  Without
fail, the first pass of Ethernet designs done would not pass the IEEE
802.3 physical layer specifications, *unless* they used an integrated
magnetics.  Return loss, signal integrity, or Hipot- doing the design
right (for interoperability) is quite hard.

It is pretty easy to get Ethernet to talk over a short cable, but if you
want to meet the BER ratings at maximum distance and minimum distance,
while also meeting safety specs (Ethernet (not PoE) is designed to be
electrically isolated) is far from a trivial exercise.

Using integrated magnetics saves a *huge* amount of time and vastly
improves your chances of design success.

Matt Bennett
Just outside of Austin, TX
30.51,-97.91

The views I express are my own, not that of my employer, a large
multinational corporation that you are familiar with.
--=20
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