[SI-LIST] Re: Input impedance of Power trace
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: <cgrassosprint1@xxxxxxxxxxxxx>, "Si-List" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 24 Aug 2004 21:18:41 -0700
Once a customer was having problems with an oscillator on a board. The nice
perfect 50% duty cycle we expected to see was totally distorted. Other
similar oscillator circuits were on the same mother board without similar
issues. We eventually traced the problem (sorry about the pun) down to the
power run for the local bypass cap to the IC's Vdd pin. It was a 50 Ohm net
just like the signal runs on the rest of the board. The current spikes on
the power pin were being treated just like any other signal that propagated
down similar traces. We could see the Vdd voltage collapse at the IC and
that would propagate down the Vdd trace until it reach the cap. The cap
would then recharge the line.
So a microstrip used for power distribution will act just like any other
microstrip. It will present itself as a 50 Ohm (or whatever) impedance as
the source impedance of the power supply until the PDS has the time to
recharge the line.
So, if your load is purely DC then the R of the trace is OK to use. If you
have any AC components on the net you have to treat it as a transmission
line of characteristic impedance.
Tom Dagostino
Teraspeed Consulting Group LLC
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Charles Grasso
Sent: Tuesday, August 24, 2004 9:10 PM
To: Si-List
Subject: [SI-LIST] Input impedance of Power trace
Good evening all..
I have a question regarding the distribution of power on a printed circuit
board with a trace (i.e a microstrip) rather than a plane.
It seems to me that only DC exists on the trace then the input impedance of
the microstrip configuration simply become the total DC resistance of the
current loop.
Is this correct?
if not how does one estimate the input impedance of a microstrip trace (long
and thin) used for power distribution?
Thanks
------------------------------------------------------------------
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
------------------------------------------------------------------
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:
