Scott, I suspect you are right, but the thread was about decoupling power planes. > [Original Message] > From: Scott McMorrow <scott@xxxxxxxxxxxxx> > To: <leeritchey@xxxxxxxxxxxxx> > Cc: Vinu Arumugham <vinu@xxxxxxxxx>; Michael Rose <mrose@xxxxxxxxxxxx>; si-list <si-list@xxxxxxxxxxxxx> > Date: 9/15/2008 12:53:27 PM > Subject: [SI-LIST] Re: plane-to-plane decoupling > > Lee > I believe that Vinu is speaking of using a capacitor as a series pass > element, rather than as a shunt element. > > 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 > > > > Lee Ritchey wrote: > > Vinu, > > > > Can you show me a capacitor that works at 3.125 Gb/S for decoupling? > > > > Lee > > > > > > > > ----- Original Message ----- > > *From:* Vinu Arumugham <mailto:vinu@xxxxxxxxx> > > *To: *Scott McMorrow <mailto:scott@xxxxxxxxxxxxx> > > *Cc: *Lee Ritchey <mailto:leeritchey@xxxxxxxxxxxxx>; Michael Rose > > <mailto:mrose@xxxxxxxxxxxx>; si-list <mailto:si-list@xxxxxxxxxxxxx> > > *Sent:* 9/15/2008 12:24:44 PM > > *Subject:* Re: [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: > >>>>> //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 > >>>>> 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 technical documents are available at: > >>>> http://www.si-list.net > >>>> > >>>> 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 technical documents are available at: > >>> http://www.si-list.net > >>> > >>> 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 technical documents are available at: > http://www.si-list.net > > 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 technical documents are available at: http://www.si-list.net 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