Gee at first I thought this came from Lee Ritchie "Show me the data....." Doug At 10:19 AM 4/21/2006, steve weir wrote: >Doug, I am amiss to find another reference that supports the idea that the >fields reshape concentrating around the two lines during the bit >interval. If we are not talking about an audio frequency diff pair but a >digital one where plane penetration is not an issue then I see the >relative coupling line to line versus line to image plane as varying very >little across the signal spectra. If you have references that show >differently would you share them? > >Regards, > > >Steve. > >At 09:50 AM 4/21/2006, Doug Brooks wrote: >>Mmmmmmm, >>Well.............. >>Draw a picture of an *ideal* trapezoidal repetitive waveform and then think >>about what you said. >>During transition time, there is a high di/dt component. (hence a high >>coupling component to the plane). >> >>During the part of the waveform where the signal has *stabilized* the >>instantaneous di/dt is very low or zero (hence a lower coupling component >>to the plane). >> >>Nevertheless that part of the signal changes polarity twice a cycle. If you >>want to think there is no AC component there, that is your prerogative. I >>happen to think there is. >> >>Doug Brooks, PhD >> >> >> >> >> >>At 11:16 AM 4/20/2006, Scott McMorrow wrote: >> >Doug >> > >> >I beg to differ. If the signal has "stabilized" there is therefore no AC >> >component. If there is no AC component, there is nothing to radiate. >> > >> >Scott >> > >> > >> >Scott McMorrow >> > >> > >> >Doug Brooks wrote: >> >> >> >>In my humble opinion, and not counting common mode currents: >> >> >> >>During the signal rise and fall times, the return current tends to flow on >> >>the reference plane, just as signals on single-ended traces do. >> >> >> >>During the time that the signal is "stabilized," there is no coupled >> signal >> >>on the plane and the loop is around from one trace of the differential >> pair >> >>to the other. >> >> >> >>It is during this latter phase of the signal that loop area (as in EMI) >> >>might be an issue. During my signal integrity seminars I show some >> >>animations that illustrate this pretty clearly. >> >> >> >>Doug Brooks >> >> >> > >> >___________________________________________________________________ >> _________- >> >Check out UltraCAD's differential impedance and skin effect calculators at >> >http://www.ultracad.com >> >>------------------------------------------------------------------ >>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 > > ____________________________________________________________________________- Check out UltraCAD's differential impedance and skin effect calculators at http://www.ultracad.com ------------------------------------------------------------------ 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