[SI-LIST] Re: Questions on GND Ref Plane and Diff pair coupling
- From: "Yassin, Adnan" <adnan.yassin@xxxxxxxxx>
- To: <Ravinder.Ajmani@xxxxxxxxxxxxxx>, "shemshak" <shemshak1@xxxxxxxxx>
- Date: Tue, 18 Mar 2008 16:32:55 -0700
Hi Ravinder,
What if there is no GND plane (e.g., 2 layer PCB), is the loosely
coupled scheme still favored over the tightly coupled one?
Thanks,
-Adnan
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Ravinder.Ajmani@xxxxxxxxxxxxxx
Sent: Tuesday, March 18, 2008 1:18 PM
To: shemshak
Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Questions on GND Ref Plane and Diff pair coupling
Hi Shemshak,
The coupling between the two lines is much smaller than the coupling
each=20
line has with the adjacent plane. Hence any discontinuity in the return
plane will affect signal propagation. Absence of a ground plane will
also=20
result in higher crosstalk.
If you are not short on routing space then loosely coupled traces are=20
better than the tightly coupled. In such a configuration you need not=20
route traces next to each other, and it is easier to maintain equal
length=20
around vias etc.
Regards, Ravinder
Server PCB Development
Hitachi Global Storage Technologies
Email: Ravinder.Ajmani@xxxxxxxxxxxxxx
shemshak <shemshak1@xxxxxxxxx>=20
Sent by: si-list-bounce@xxxxxxxxxxxxx
03/18/2008 12:37 PM
To
si-list@xxxxxxxxxxxxx
cc
Subject
[SI-LIST] Questions on GND Ref Plane and Diff pair coupling
Hi all,
I have two questions which I really appreciate your feedback on them.
1) If we have differentail pairs which they can reference to each other=20
(one signal and the other as the return path), then do still need to
have=20
GND plane adjacent to these signals for the return path? I think the=20
answer is yes, we need GND plane, but why?
2) When do we use loosly coupled vs tightly coupled differential pairs?=20
When would be better to use one over the other.
thanks,
Shemshak
=20
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