[SI-LIST] Re: Input impedance of Power trace
- From: "Andrew Ingraham" <a.ingraham@xxxxxxxx>
- To: "Si-List" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 25 Aug 2004 09:59:14 -0400
> It seems to me that only DC exists on the trace ...
> It depends on what frequency components will be on that trace. ...
I would put more emphasis on the fact that even a DC power trace handles AC
signals. You almost can't avoid it. Even if the voltage is ostensibly DC,
the currents are not.
Remember that when a driver switches, it causes an output current to flow on
the signal trace, and this output current also flows through the power
and/or ground nets to get to the output driver that switched. That current
has all the same high frequency switching characteristics as the output
signal itself ... same sub-ns risetimes, etc. With good bypassing close to
the driver, the highest frequency components don't need to travel far
through power traces, but they do propagate.
With one power trace feeding dozens of output drivers, the problem is
magnified.
And there's stuff like crosstalk to consider.
So you really can't treat a power trace as a DC-only net, unless you have so
much local bypassing that the transients just can't get out.
Regards,
Andy
------------------------------------------------------------------
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 FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//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
Other related posts:
