Re: New thread on EMI
Joel:
I just realized you had a lot of bad experience with your 100 tx, a twisted
pair Fast Ethernet.
This is totally different from the comments I have provided, which are
optical link.
I also had bad experiences with the twisted pair. Often, I had to redo the
EMI design to pass the EMI test. I did not particularly enjoy it.
All the shielded copper (or twisted pair) cables leak to certain extent.
They are not perfect shield. Therefore, for a copper based link, the whole
EMI headache is shifted to the cable which carries the EMI emission outside
of the cabinet. The good cabinet shield does not help at all. Often the EMI
reading changes very significantly depending on how you lay the cable on the
ground. As you may have noticed, the EMI emission levels of a cable which is
randomly scattered on the ground, or which is left on a reel are
significantly different.
We mostly spent our effort in dealing with the cable EMI problem, but not
equipment.
I am not sure, in a copper link, how much the scrambled IDLE will provide a
difference or relief? I believe the general leaking from the copper cable
and imperfect connector-shield will dominate your EMI design but not IDLE.
In the 10GbE application, I believe the copper connections will be a short
one to interconnect stacked switches. Probably the cable length is a foot,
or two. The whole thing can be inside a big cabinet. I believe those
mechanical engineers will find some way to solve the EMI problem, if there is
one.
<<
Ed
Look at 100tx. There are five components that escape via the port that are
not
clock or clock harmonic related. These are very nasty and climb quite
nicely with
port count. So I don't agree that the IDLE is not a problem. We can agree
to
disagree.
Take care
Joel Goergen >>
Regards,
Ed Chang