YMMV In my experience, most measurements and equations for FR4 Er fail to factor in the internal inductance. This tends to exaggerate the Er increase at lower frequencies. Once you remove internal inductance from most measurements of Er, I find that the curves are quite flat from several hundred MHz to 10 GHz. But, then you have to use a field solver that correctly models internal inductance. Few of those exist in the 2D world, and in the 3D world it makes for some extremely long solve times. 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 Ihsan Erdin wrote: > Ryan, > > In High Speed Digital System Design by Stephen Hall, et al., Steven > Mumbhy's emprical formulation is quoted as: > er(freq)=6.32 - [2.17 + 0.168 x log10(freq in kHz)] x Vrsn > where Vrsn is the volume content of the resin, which is approximated > as 1-(thickness of the glass cloth/thickness of the dielectric layer) > I didn't see the actual source and don't know how that relation was > derived but according to the book, the relation was experimentally > validated from 1kHz to 1Ghz. Hope that helps. > > Regards > > Ihsan > > > > On 1/17/07, ryansatrom <ryan.satrom@xxxxxxxxxxx> wrote: > >> Thanks for your feedback. Sometimes, living in the simulation world, >> you forget the real-world effects of boards. >> >> Lee: Is there any way to predict this frequency dependency of er? >> >> Fred: Is the frequency dependence of R and G caused by the same issues >> Lee is discussing (dielectric constant over frequency)? Are there any >> other causes of this? >> >> (As a side note, the equation suggests R and G to be fixed in >> frequency, while L and C are the frequency dependent values. I guess >> that's why the lumped element model breaks down and models are more >> accurately viewed as distributed full-wave EM models) >> >> Thanks again for the comments. >> >> Ryan >> >> ------------------------------------------------------------------ >> 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: >> http://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: >> http://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: > http://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: > http://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: http://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: http://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