Tim,
Happens all the time, especially as modern ASICs or FPGAs may require several different I/O rails. You can't spend a plane pair on all of them, nor suffer split-crossings if you cut up and share a reference layer. A shape on a routing layer can make perfect sense. Something to ask yourself though, is how much extra pFs / reduction in PDN impedance am I really getting from this tiny shape as opposed to say a fat trace?
-peter arnold
-----Original Message-----
From: si-list-bounce (AT) freelists (DOT) org on behalf of Nash, Timothy J
Sent: Wed 11/03/2009 4:49 PM
To: si-list (AT) freelists (DOT) org
Subject: [SI-LIST] Potentially Dumb Question About Routing Layers
SI Gurus:
How common is the practice of sharing a routing layer with a power or
ground region (i.e. an
FPGA core voltage plane)? If I can find a
reasonable return path for the signals, at face value, it appears to be
ok. But something screams inside of me that this isn't a good idea, but
I can't really explain why.
Thanks in advance,
Tim
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list
For help:
si-list-request (AT) freelists (DOT) org with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
http://www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request (AT) freelists (DOT) org with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list
For help:
si-list-request (AT) freelists (DOT) org with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
http://www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu