Hello Geof, It applies to a single frequency, high or low. Regards, David At 12:56 PM 7/20/2004 +0100, Geoff Stokes wrote: >Hi David > >Thanks for your response. Presumably your "single inductance value" applies >at low frequency rather than high? > >Cheers >Geoff > > > -----Original Message----- > > From: David Siadat [mailto:dsiadat@xxxxxxxxx] > > Sent: 19 July 2004 16:23 > > To: Geoff Stokes > > Cc: 'si-list@xxxxxxxxxxxxx' > > Subject: Re: [SI-LIST] Re: Via modeling & de-embedding > > > > > > Hi Geoff, > > > > I agree with your comments. > > I should also point out that it is quite acceptable to > > replace multiple > > inductance value of a distributed model with a single > > inductance value. > > This does not mean that we are modeling the object with a > > lumped elements. > > 3D field solvers use this to calculate characteristic > > impedance of the object. > > > > Regards, > > David > > > > At 09:21 AM 7/19/2004 +0100, Geoff Stokes wrote: > > >Hi David > > > > > >In your point no. 1 you mention higher order modes. This > > was described very > > >well by Hassan O. Ali. Your point no. 2 mentions > > "characteristics of the > > >via". The RF current is confined to the surface because of > > the skin effect. > > >At the via this surface current changes direction abruptly > > from horizontal > > >to vertical. The discussion seems to indicate to me that there is no > > >purpose in considering characteristics of the plated via > > hole alone, because > > >in the vicinity of the via there are various wave modes. Therefore > > >conventional de-embedding becomes impossible, because it > > uses TEM wave > > >analysis. If the via is sufficiently far from other wave > > discontinuities in > > >the signal path, there will be some value in a TEM model of > > a via together > > >with its connecting traces, and this can be de-embedded to a > > reasonable > > >distance, but not right up to the edge of the anti-pad where > > the higher > > >order modes are quite strong. The varying concentrations of > > field and > > >surface current can be studied in various 3D tools such as > > Ansoft HFSS, CST > > >Microwave Studio or EM3DS. Generally, the TEM mode settles down at a > > >horizontal distance many times larger than the dielectric > > height. In some > > >cases it might be best not to de-embed closer than say 3h, > > and other cases > > >could benefit from a yet larger de-embedding distance. The > > higher order > > >modes provide interactions that are not represented on a two-terminal > > >schematic - at higher frequencies there is no such thing as a simple > > >inductance: that's an approximation suitable only for lower > > frequencies. In > > >the case of a straight wire or plated via, if the impedance > > is significant, > > >it is because the length is a significant part of a > > wavelength, even if the > > >significant part is only a tiny fraction. The lumped > > inductor model is > > >better replaced by a transmission line model, or better still, by a > > >multi-element distributed physical analysis as provided in > > CST Microwave > > >Studio or the like. In practice, for good accuracy, such > > analysis demands > > >single-mode stimulus and termination. > > > > > >So finding the "inductance of a via" or the characteristic > > of the via alone > > >is to chase a rainbow. > > > > > >Cheers > > >Geoff > > > > > > > -----Original Message----- > > > > From: David Siadat [mailto:dsiadat@xxxxxxxxx] > > > > Sent: 16 July 2004 18:04 > > > > To: hassan@xxxxxxxx > > > > Cc: Ivan Ndip; si-list@xxxxxxxxxxxxx > > > > Subject: [SI-LIST] Re: Via modeling & de-embedding > > > > > > > > > > > > Hello Hassan, > > > > > > > > There are two related issues that should be discussed separately. > > > > 1. The required length of the transmission line before the > > > > higher order > > > > modes from > > > > the excitation wave port settle down as Giancarlo > > > > indicated in his email. > > > > 2. How much of the transmission line can be de-embedded to > > > > investigate the > > > > characteristics > > > > of the via its feeding. > > > > > > > > So in a simulation model, you must have long enough > > > > transmission line to > > > > satisfy the first issue > > > > and you should de-embedded to the edge of your anti-pad > > > > radius (assuming > > > > you have a reference > > > > ground plane below the signal layer). > > > > > > > > The impedance of the via consists of the inductance of the > > > > transmission > > > > stub hanging off the via and > > > > the via length as well as capacitance of the via which is > > > > function of via > > > > diameter, pad size (and number of them > > > > in the stack up. you could minimize that by removing pads on > > > > some layers), > > > > anti-pad size ( you could choose > > > > different size at different layers to optimize your impedance). > > > > Lets not forget the via stub length (non terminated > > > > transmission line) that > > > > can oscillate at its resonant frequency. > > > > > > > > I should also point out the importance of return path for the > > > > SINGLE via > > > > model which impacts the inductance value > > > > at lower frequencies. > > > > > > > > Regards, > > > > David > > > > > > > > At 12:17 PM 7/16/2004 -0400, Hassan O. Ali wrote: > > > > >Ivan, > > > > > > > > > >To know how long is long enough, you need first to > > > > understand what a via > > > > >model should > > > > >accomplish. > > > > > > > > > >Assuming a stripline on either side of the via, a TEM wave > > > > gets into the > > > > >via and comes > > > > >out as a TEM wave. At the via itself, though, the incident > > > > signal in TEM > > > > >mode gets > > > > >converted into several other (higher-order) modes and then > > > > back to TEM > > > > >mode as it exists > > > > >the via. The types of higher order modes depend on the > > > > environment around > > > > >the via. Some > > > > >of the modes are evanescent (non-propagating) and some are > > > > propagating > > > > >modes. Some of > > > > >the higher-order propagating modes have much higher > > > > attenuation constants > > > > >(i.e. they die > > > > >off short distance away). Ultimately, one cares only about > > > > the TEM mode > > > > >that propagates > > > > >far into the striplines on either side of the via. > > > > > > > > > >So, in this case, the via model should essentially > > capture the mode > > > > >conversion at the > > > > >via. For that reason, you need to place your reference > > > > planes at points > > > > >where only the > > > > >TEM mode exists (substantially). Unfortunately, the > > > > determination of such > > > > >points is > > > > >problem-dependent. Certainly you shouldn't just use the > > attenuation > > > > >constant of the > > > > >first propagating stripline higher order mode to determine > > > > the location of > > > > >such points. > > > > >That's because you also need to be away from the effects of > > > > evanescent > > > > >(non-propagating) > > > > >modes and other modes that propagate through the via in > > a manner not > > > > >supported by > > > > >stripline. > > > > > > > > > >For each via configuration, I would suggest you start with > > > > very short line > > > > >segments > > > > >(e.g. of length equal to the pad radius) and increase > > the length in > > > > >several steps to > > > > >determine S21 (insertion loss) convergence for the > > frequency band of > > > > >interest. You > > > > >should have to fix your own convergence criterion. I would > > > > be comfortable > > > > >with 0.5% S21 > > > > >covergence. > > > > > > > > > >Regards. > > > > > > > > > >Hassan. > > > > > > > > > > > > > > >On Jul 16, Ivan Ndip <ndip@xxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > Hi Hassan, > > > > > > How "long enough" must the trace segments be? Do you have > > > > any experience > > > > > > in determining the exact length? > > > > > > > > > > > > Best regards, > > > > > > Ivan Ndip > > > > > > > > > > > > Hassan O. Ali wrote: > > > > > > > > > > > > >It seems that "de-embedding" in this thread has been > > > > used to suggest > > > > > that one can > > > > >create > > > > > > >an "isolated" via model that can be used in various > > > > other environments > > > > > such as with > > > > > > >different trace widths and thicknesses; different signal > > > > rates, etc. > > > > > If that is the > > > > > > >case, then I think that suggestion is not accurate enough. > > > > > > > > > > > > > >I tend to believe that via characteristics (hence its > > > > model) cannot be > > > > > isolated from > > > > >the > > > > > > >surrounding environments - especially for higher > > > > frequencies. The > > > > > trace/via-pad > > > > > > >transition itself presents a discontinuity that > > > > contributes to the > > > > > parasitics of the > > > > > > >via. The pads have their own parasitics. Neighboring > > > > ground/power vias > > > > > also can > > > > > > >influence the signal via performance. All of those along > > > > with the via > > > > > barrel > > > > >parasitics > > > > > > >contribute to the overall via characteristics and have to be > > > > > appropriately considered > > > > >in > > > > > > >model creation. > > > > > > > > > > > > > >As to de-embedding, I think you won't get accurate > > > > results if your > > > > > reference (de- > > > > > > >embedding) plane is right at the transition. In > > other words, an > > > > > accurate via model > > > > > > >should include trace segments long enough to ensure that > > > > the field at > > > > > the segment > > > > >ends > > > > > > >are mainly of the dominant mode of field propagation. In > > > > fact most (if > > > > > not all) de- > > > > > > >embedding techniques make that assumption. > > > > > > > > > > > > > >Regards. > > > > > > > > > > > > > >Hassan. > > > > > > > > > > > > > > > > > > > > >On Jul 15, David Siadat <dsiadat@xxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > >>Hello Ivan, > > > > > > >> > > > > > > >>De-embedding the transmission line feeding the via is > > > > limited to the > > > > > > >>edge of the anti-pad region that the transmission line > > > > is referenced to. > > > > > > >>That could mean an additional 17.5 mil transmission > > > > line for 35mil > > > > > diameter > > > > > > >>anti-pad. The inductance value of this transmission > > line can be > > > > > significant > > > > > > >>compare with the inductance of the via itself. > > > > > > >> > > > > > > >>Regards, > > > > > > >>David > > > > > > >> > > > > > > > > > > > >------------------------------------------------------------------ > > > > >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 FAQ wiki page is located at: > > > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > > > > > > >List technical documents are available at: > > > > > http://www.si-list.org > > > > > > > > > >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 FAQ wiki page is located at: > > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > > > > > List technical documents are available at: > > > > http://www.si-list.org > > > > > > > > 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 > > > > > > > > > > > > > > > > >_________________________________________________________ > > > > > >Zetex Semiconductors - Solutions for an analog world > > > > > >EID Award Winners for 'Best Use of Technology' 2003 for the > > >AcoustarTM ZXCW8100 End-to-End Digital Audio Amplifier Controller > > > > > >http://www.zetex.com > > >_________________________________________________________ > > > > > >############################################################# > > ######### > > >E-MAILS are susceptible to interference. You should not assume that > > >the contents originated from the sender or the Zetex Group > > or that they > > >have been accurately reproduced from their original form. > > >Zetex accepts no responsibility for information, errors or > > omissions in > > >this e-mail nor for its use or misuse nor for any act committed or > > >omitted in connection with this communication. > > >If in doubt, please verify the authenticity with the sender. > > >############################################################# > > ######### > > > > > >------------------------------------------------------------------ > > >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 FAQ wiki page is located at: > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > > >List technical documents are available at: > > > http://www.si-list.org > > > > > >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 > > > > > > > >_________________________________________________________ > >Zetex Semiconductors - Solutions for an analog world > >EID Award Winners for 'Best Use of Technology' 2003 for the >AcoustarTM ZXCW8100 End-to-End Digital Audio Amplifier Controller > >http://www.zetex.com >_________________________________________________________ > >###################################################################### >E-MAILS are susceptible to interference. You should not assume that >the contents originated from the sender or the Zetex Group or that they >have been accurately reproduced from their original form. >Zetex accepts no responsibility for information, errors or omissions in >this e-mail nor for its use or misuse nor for any act committed or >omitted in connection with this communication. >If in doubt, please verify the authenticity with the sender. >###################################################################### > >------------------------------------------------------------------ >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 FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >List technical documents are available at: > http://www.si-list.org > >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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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