Prathap, You can expect faster convergence with S-parameters only if you do not have sufficient number of samples at lower frequencies and your S-parameter model have wrong asymptotes at DC. It often happens with S-parameters measured for a channel with AC coupling capacitors. The insertion loss goes to very small values at lower measured frequencies and "intuitive" extrapolation may be something close to 0 dB loss at DC. In reality the insertion losses increase at extremely low frequencies (depends on the values of the capacitors). It can also happen with modeled S-parameters if you do not set up frequency sweep from DC with sufficient resolution at lower frequencies. Restriction on lower frequencies in the frequency-domain analysis of a channel with AC coupling caps may be a good alternative to the use of resistors instead of caps discussed here. Though, I have not seen investigations of accuracy for such analysis. Best regards, Yuriy Shlepnev www.simberian.com -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of prathap sirishe Sent: Friday, July 08, 2011 10:49 AM To: Andy Haas Cc: Newbie Pugal; Roopesh Badala; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: trouble simulating with AC coupling capacitors in topology Hello Roopesh, I remember facing same issue before. From what I recollect, apart from all the solutions mentioned so far, you can try to generate a s-parameter model for an ac coupled differential trace pair using another simulation tool like Hyperlynx and use the resultant ".s4p" file in Cadence tool set, replacing differential trace segment with 4-port s-parameter model. Hope this helps! Regards, Prathap On Fri, Jul 8, 2011 at 11:31 AM, Andy Haas <andyhaas@xxxxxxxxxxx> wrote: > Hi guys, > > There should be no issue in simulating nets with series caps within > the Cadence SI environment. Initial conditions can also be used if you > use the right model. Feel free to contact me offline and I'd be happy to help. > > Regards, > Andy > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx > [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of Newbie Pugal > Sent: Friday, July 08, 2011 9:50 AM > To: Roopesh Badala; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: trouble simulating with AC coupling capacitors > in topology > > Hi Roopesh, > I have faced similar problem in the past and went to cadence for the > support but did not worked out. With the AC caps in the cadence the P > and N waveforms will not come as expect. Later I simulated using > HSPICE with initial condition settings or else you need to run a long > bits for the settled waveforms. > > Regards > Pugal > > > ________________________________ > From: Roopesh Badala <roopesh.badala@xxxxxxxxx> > To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx> > Sent: Friday, 8 July 2011 4:54 PM > Subject: [SI-LIST] trouble simulating with AC coupling capacitors in > topology > > Hi All, > I am trying to simulate a topology which has AC coupling capacitors in it. > > Using Cadence Allegro PCB SI tool set , i am unable to get the > expected output. > > but when I simulate the same topology by removing the AC coupling > capacitors in signal path, I get a perfect waveform. > > Is this a tool limitation..? can some body suggest me if they have > faced similar issue. > > > Thank you > > Roopesh > > > ------------------------------------------------------------------ > 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 > > 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 > > 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 > > 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 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 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu