It depends.
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Carson Au
Sent: Thursday, June 01, 2017 2:42 PM
To: CHARLES.GRASSO@xxxxxxxx
Cc: dmarc-noreply@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Return Path Vias
If I attend a Lee Ritchey class, will I get a different answer?
=P
On Fri, Jun 2, 2017 at 5:52 AM, Grasso, Charles <CHARLES.GRASSO@xxxxxxxx>
wrote:
Carson -
Attend one of Eric Bogatins classes and you will get the answers you
are seeking.
:-)
Thanks
Charles Grasso
(w) 303-706-5467
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Vinu Arumugham
Sent: Wednesday, May 31, 2017 11:55 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Return Path Vias
It depends on the margin you have w.r.t the channel/EMC spec.
If you are able to meet spec. even with one leg of the diff pair
disconnected, that channel is "well designed"! (whether the spec. is
well designed to stress test such configurations for compliance would
be another topic).
Same for return path vias (or lack of them).
Thanks,
Vinu
On 05/31/2017 12:52 AM, Carson Au wrote:
The perennial debate... on SI-List.
SERDES differential channels 10Gbps+. For layer transitions, is it
OK to use just one return path via (both sides of the differential
via sharing one GND return path via, symmetrical/balanced)? Is it OK
to use no return path vias at all (Lee Ritchey advocates for this)?
Is there literature comparing 2x, 1x and NO return path vias?
I can imagine that the common mode conversion would be an issue. But
how much of an issue?
Anecdotal stories that one method "just works" is not sufficient
proof (i.e. for the no return vias case) I have been able to get a
10Gbps+ channel working with only one side of the differential
connected - with a BER better than 10e-15 (ran overnight with no
bit-errors)!! Yet none would say this channel is well designed.
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