[SI-LIST] Re: DDR-Length matching
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: karthi keyan <karthiyen@xxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 28 Apr 2011 08:25:16 -0700
+/-10 mils tolerance means that all signals in that group must be within 20
mils of each other.
If your longest trace is 6.253", and your shortest is 6.234", you have met the
spec.
If your longest trace is 6.253", and your shortest is 6.232", you fail the spec.
The spec. could call out '+/-10 mils' or 'within 20 mils', with the same
meaning.
The '+/- 10 mils' verbiage is usually used to align with popular layout tools'
conventions, where you specify +/- xx mils of a defined target. Finding that
target is part of the process for your particular design.
When they specify this kind of tolerance, they usually also insist on routing
on the same layer, so propagation velocity differences don't come into play.
This tight a tolerance (within 20 mils, or about 3-4ps) is usually specified
because experience has proven that it doesn't take CAD folks much longer to
meet a +/- 10 mil spec. than a +/- 100 mil spec., and we can reduce the skew
from routing to essentially zero.
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of karthi keyan
Sent: Thursday, April 28, 2011 2:42 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] DDR-Length matching
Hi experts,
I am working on boards having DDR interface. on layout we are
following the below groupings & length matching
Group1- Data signals,strobe,Mask with in group +/-10 mils tolerance
Group2- Add/Ctrl/Cmd/Clk--with in group +/-10mils tolerance
i am clear on groupings but on length matching i want to know how
to calculate the exact Min & max length matching tolerance .
can you please let me clear on DDR length matching?
Thanks,
Karthikeyan
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
