[SI-LIST] Re: Differential Signals with changed ground references

 Depends.  If your image current does not travel the other leg of the 
differential pair but the PCB ground plane then you may excite one of the 
cavities .  Any common mode coupling will image the ground structure and could 
excite as well.
-Jory



----- Original Message ----
From: ryansatrom <ryan.satrom@xxxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Tuesday, February 26, 2008 10:36:20 AM
Subject: [SI-LIST] Differential Signals with changed ground references


I 
am 
currently 
trying 
to 
determine 
the 
performance 
of 
an 
interface 
where 
the 
PCB 
ground 
planes 
and 
the 
device 
grounds 
are 
not 
tied 
together 
(except 
on 
the 
very 
outside 
of 
the 
PCB).

I 
recognize 
this 
is 
a 
design 
flaw 
(I 
didn't 
design 
the 
PCB), 
and 
I 
also 
recognize 
that 
this 
causes 
floating 
signals 
for 
all 
single-ended 
signals.

However, 
my 
intuition 
tells 
me 
that 
the 
differential 
signals 
would 
perform 
okay 
(ignoring 
any 
failures 
due 
to 
PDS 
- 
strictly 
from 
a 
signal 
integrity 
perspective).

Am 
I 
correct 
in 
this 
assumption?  
Or 
would 
it 
be 
based 
on 
the 
device 
design 
and 
how 
the 
device 
reads 
the 
differential 
inputs/outputs?

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