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