The skin-effect will be significant if the traces are longer. It is true in the case of PCB where traces are normally longer than 2 inches. In the case of packages, where most of the traces are ~1-2cm long, the skin effect may not be significant. Tight coupling may be desirable because of trace density. Amit Agrawal Broadcom Corp. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Lee Ritchey Sent: Friday, October 03, 2003 11:41 AM To: Duane Takahashi; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Diff.Pairs More than that, it does not have any benefit. Tight coupling of differential pairs forces the traces to be narrower increasing the skin effect losses. Also, this tight coupling is going to result in good old cross talk that actually degrades the edges. How the notion of tight coupling of differential pairs as beneficial got started is a mystery to me. There are several references that show that tight coupling is not beneficial, one of them is Howard Johnson's latest book, at least one column he has written and my recently released book. Lee Ritchey > [Original Message] > From: Duane Takahashi <duanet@xxxxxxxxxxxxxxxxxxxxxx> > To: <si-list@xxxxxxxxxxxxx> > Date: 10/2/2003 3:58:59 PM > Subject: [SI-LIST] Re: Diff.Pairs > > Hi Juergen: > > Aligning the stack up for the broadside coupled diff lines is expensive. > You can do this, but it drives up the cost of the board. > > Duane > > > Hi Juergen, > > You can find lots of application notes > > especially with respect to process variation > > on differential pairs here: > > > > > > www.polarinstruments.com/support/cits/cits_index.html > > > > In particular this one may be of interest: > > > > > > How measured impedance may vary from field solver calculations when > > using woven glass reinforced > > <http://www.polarinstruments.com/support/cits/AP139.html>laminates > > > > www.polarinstruments.com/support/cits/AP139.html > > > > > > And this note: > > > > Copper thickness, edge coupled lines and > > characteristic > > <http://www.polarinstruments.com/support/cits/AP151.html>impedance > > > > > > www.polarinstruments.com/support/cits/AP151.html > > > > > > > > Hope this helps.... > > > > > > Kind regards > > Martyn Gaudion > > www.polarinstruments.com > > T: +44 1481 253081 > > F: +44 1481 252476 > > M: +44 7710 522748 > > E: martyn@xxxxxxxxxxxxxxxxxxxx > > > > ============================================ > > Controlled Impedance & Signal integrity tools > > for the Printed circuit fabrication industry > > ============================================ > > > > > > > > > > > > > > At 19:00 02/10/2003, you wrote: > > > >>I am seeking help in finding enlightenment regarding electrical > >>performance pros and cons and how manufacturing tolerances play a role > >>when comparing side by side and tandem differential pairs. I'd appreciate > >>your opinion, experience, analysis, pointers to papers and articels, etc. > >> > >>In return, I would offer to share a summary of the finding/discoveries > >>with interested parties. > >> > >>Thanks > >> > >>Juergen > >> > >> > >> > >>------------------------------------------------------------------ > >>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 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 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 > > > > -- > Duane Takahashi phone: 408-720-4200 > Greenfield Networks fax: 408-720-4210 > 255 Santa Ana Court email: duanet@xxxxxxxxxxxxxxxxxxxxxx > Sunnyvale, CA 94085 > > * MOVING! Please note new numbers and address * > > ------------------------------------------------------------------ > 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 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 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 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