*From*: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>*To*: "Vinu Arumugham" <vinu@xxxxxxxxx>, "Scott McMorrow" <scott@xxxxxxxxxxxxx>*Date*: Tue, 16 Sep 2008 08:12:31 -0700

Vinu, I stand by my statement and have data to support it. Lee > [Original Message] > From: Vinu Arumugham <vinu@xxxxxxxxx> > To: Scott McMorrow <scott@xxxxxxxxxxxxx> > Cc: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>; Michael Rose <mrose@xxxxxxxxxxxx>; si-list <si-list@xxxxxxxxxxxxx> > Date: 9/15/2008 4:26:45 PM > Subject: [SI-LIST] Re: plane-to-plane decoupling > > Scott, > I was not suggesting that capacitors connecting split planes were a > "clean" solution. I just wanted to point out that Lee's statement, > "There are no capacitors that work at 3.125 Gb/S for decoupling.", is > not entirely true. > > Thanks, > Vinu > > > Scott McMorrow wrote: > > Vinu > > > > Not quite. As long as there is a ground plane underneath, and close > > to, the capacitor, some return path energy will get across. But, > > there is a mismatch in impedance between the capacitor and plane, and > > here is still an inductive loop for the return energy to get to the > > capacitor. Because of this, quite a bit of the common mode energy > > will be reflected back into the near end power/ground plane cavity. > > > > regards, > > > > Scott > > > > Scott McMorrow > > Teraspeed Consulting Group LLC > > 121 North River Drive > > Narragansett, RI 02882 > > (401) 284-1827 Business > > (401) 284-1840 Fax > > > > http://www.teraspeed.com > > > > Teraspeed® is the registered service mark of > > Teraspeed Consulting Group LLC > > > > > > > > Vinu Arumugham wrote: > >> Lee, > >> The capacitor used for AC coupling on the signal path, should be able > >> work just as good if it were placed on the return path as a decoupling > >> capacitor for that signal. > >> Each signal trace will of course need a dedicated capacitor to avoid > >> additional crosstalk. > >> > >> Thanks, > >> Vinu > >> > >> Lee Ritchey wrote: > >> > >>> Michael, > >>> > >>> There are no capacitors that work at 3.125 Gb/S for decoupling. The way to > >>> provide this path is by placing the planes close to each other. I use 3 > >>> mils all of the time for this purpose. Works greast! > >>> > >>> Lee Ritchey > >>> Speeding Edge > >>> > >>> > >>> > >>> > >>>> [Original Message] > >>>> From: Michael Rose <mrose@xxxxxxxxxxxx> > >>>> To: SI-List <si-list@xxxxxxxxxxxxx> > >>>> Date: 9/15/2008 10:01:17 AM > >>>> Subject: [SI-LIST] plane-to-plane decoupling > >>>> > >>>> I looking for some suggestions regarding decoupling between co-planar > >>>> plane splits. I'm working on a backplane with a number of 3.125Gbps diff > >>>> pairs. I've specified a dual stripline stackup assigned as follows: > >>>> > >>>> 1 - P > >>>> 2 - G > >>>> 3 - S > >>>> 4 - S > >>>> 5 - P > >>>> 6 - G > >>>> and so on > >>>> > >>>> Some diff pairs on L4 will cross power plane splits (actual different > >>>> power sources and loads) and I wanted to provide an effective AC path > >>>> for any common-mode return currents. I was thinking about placing some > >>>> nearby decoupling caps from plane-to-plane across the split. Do you > >>>> think it would be better to decouple from plane-to-ground on both sides > >>>> to steer the current through the L6 ground layer? L5 and L6 are already > >>>> coupled through the inter-plane capacitance (they're about 4mils apart). > >>>> Which will provide a lower inductance path? > >>>> > >>>> Mike > >>>> ------------------------------------------------------------------ > >>>> 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: > >>>> http://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: > >>>> 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@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx 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

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