Ravinder, something seems very wrong with the physics here. I don't know if it is round-off error in your simulation, but Lenz' law agrees with Lee. Differential coupling resists any change. The more tightly you couple the two nets in a diff pair, the more it slows down the transitions. To cause a speed-up, they would have to switch in the same direction. If we could manufacture a machine that accelerated transitions in opposite directions we could solve the world's energy needs. Regards, Steve. At 01:12 PM 10/3/2003 -0700, Ravinder.Ajmani@xxxxxxxx wrote: >One obvious benefit is the reduction in EMI because of reduced loop area. >I have verified this through simulation. However, I am not able to >understand the phenomenon of edge degradation due to close coupling. I >ran some quick simulations on six inch long differential Microstrip nets >under the following conditions: >Case 1: Trace width 9 mils, separation 4 mils, differential impedance 99.3 >ohms >Case 2: Trace width 12.5 mils, separation 40 mils, differential impedance >98.8 ohms > >The driver had a rise time of 250 ps. The only difference I observed >between the two waveforms was that in the first case the propagation time >was 63 ps less than the second case. This is understandable since the >signals in the two branches of differential net have opposite polarity, >the coupling effect will speed them up. > >Next I tried the same simulation for Stripline nets. In this case, there >was practically no difference between two waveforms (less than 5 ps >difference in propagation delay). > >Am I missing something here. > >Regards, Ravinder >Server PCB and Flex Development >Hitachi Global Storage Technologies > >Email: Ravinder.Ajmani@xxxxxxxx > > > > > > >"Lee Ritchey" <leeritchey@xxxxxxxxxxxxx> >Sent by: si-list-bounce@xxxxxxxxxxxxx >10/03/2003 11:41 AM >Please respond to leeritchey > > > To: "Duane Takahashi" <duanet@xxxxxxxxxxxxxxxxxxxxxx>, > si-list@xxxxxxxxxxxxx > cc: > From: si-list-bounce@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 > ------------------------------------------------------------------ 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