[PCB_FORUM] Re: Diff pair setup in Constraint Manager
- From: "Shaw, Christopher" <chris.shaw@xxxxxxxxxxxxxx>
- To: "icu-pcb-forum@xxxxxxxxxxxxx" <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Fri, 15 Feb 2013 15:46:55 +0000
We have found that if you back annotate from physical to schematic then, no
matter what packaging option is set (changes only or override) the physical
diff pair constraints always win. Therefore, as our schematic and layout design
is often concurrent, we have had some very frustrated schematic designers! So
now we just do the bare diff pair definition plus phase tolerance in the
schematic, and do the rest of the diff pair constraints in physical.
Regards,
Chris
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Macindoe, Gary
Sent: Friday, February 15, 2013 9:37 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Diff pair setup in Constraint Manager
Thanks for the reply Randy.
One thing I notice is that if you set up your diff pairs under Physical, there
is no way to specify the phase tolerance (difference in length allowed between
the positive and negative signals within the diff pair) nor uncoupled length
(necessary for breakout, etc.). These two parameters can only be specified
under the Electrical tab.
If I understand it correctly, you could set up diff pairs under Physical, but
still need to set the above two parameters under Electrical, right? So, just
set it up completely under Electrical sounds right to me.
Regards,
Gary MacIndoe
Senior PCB Design Engineer
EbD R&D Hardware
Surgical Solutions Group
Covidien
5920 Longbow Drive
M/S A20
Boulder, CO 80301
303.476.7458
www.covidien.com<http://www.covidien.com/>
From:
icu-pcb-forum-bounce@xxxxxxxxxxxxx<mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx>
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Randy Dawson
Sent: Friday, February 15, 2013 8:02 AM
To: icu-pcb-forum
Subject: [PCB_FORUM] Re: Diff pair setup in Constraint Manager
Hi Gary,
If you set it up as an electrical constraint, its dimensions will change with
stackup changes (as the impedance is stackup dependent).
As a physical constraint, they do not.
There are reasons to do it either way, for example you want to preserve or
reuse some physical routing rules from a prior design, you would set
constraints as physical, and adjust stackup accordingly.
Likewise, if you are modifying stackup, you want the dimensions to track your
changes to maintain impedance.
Randy Dawson
________________________________
From: Gary.Macindoe@xxxxxxxxxxxx<mailto:Gary.Macindoe@xxxxxxxxxxxx>
To: icu-pcb-forum@xxxxxxxxxxxxx<mailto:icu-pcb-forum@xxxxxxxxxxxxx>
Subject: [PCB_FORUM] Diff pair setup in Constraint Manager
Date: Fri, 15 Feb 2013 14:47:50 +0000
Hey guys,
You know, this has always been a mystery to me, where to set up diff pairs in
CM.
Should you create a differential impedance Electrical Constraint Set under the
Electrical tab, or a Physical Constraint Set under the Physical tab?
It appears that you can set it up in either place and get it to work.
How do you guys do it, and why?
Regards,
Gary MacIndoe
Senior PCB Design Engineer
EbD R&D Hardware
Surgical Solutions Group
Covidien
5920 Longbow Drive
M/S A20
Boulder, CO 80301
303.476.7458
www.covidien.com<http://www.covidien.com/>
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