Istvan, the assumption, is that mounted inductance will make discrete devices ineffective at HF. That assumption then leads to dedicated Vcc / Gnd pairs as necessary with lossy material to damp the cavity, as opposed to Vcc / Sig / Sig / Gnd sandwiches. So we lose the second surface of the GND layer as an image return. Regards, Steve. At 08:55 AM 8/27/2004 -0400, Istvan NOVAK wrote: >Steve, > >I am curious, what do you mean by "it is plane > termination that requires not only the extra >parts, but extra layers"? > >Regards, >Isatvan > > >----- Original Message ----- >From: "steve weir" <weirsp@xxxxxxxxxx> >To: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>; <cpad@xxxxxxxxx>; ><si-list@xxxxxxxxxxxxx> >Sent: Friday, August 27, 2004 2:03 AM >Subject: Re: [SI-LIST] Re: Bypass vs Decoupling capacitors > > > > Istvan, well we do agree on both the points that it requires judgment and > > cost is a big issue, especially if it means adding layers. I can see a > > number of scenarios where it works the other way, and it is plane > > termination that requires not only the extra parts, but extra layers. The > > cost of placements needs to be accounted as well. But then, we get paid >to > > figure out the appropriate compromises. > > > > Regards, > > > > > > Steve. > > At 08:48 PM 8/26/2004 -0400, Istvan NOVAK wrote: > > >Steve, > > > > > >Eventually it is a judgement call of the designer. If you have to > > >increase the number of layers by one (and to keep the stackup > > >symmetry, it is never just one), the board cost may go up by > > >$5-15, depending on the size and complexity. For that money > > >one can buy many hundred resistors and capacitors to quiet > > >the planes. > > > > > >Regards, > > >Istvan > > > > > > > > > > > > > Istvan, yes on most of the points we agree. There are always >exceptions > > >to > > > > any hard rule. A large Vcc plane that does not have thin / lossy > > > > dielectric is subject to resonance at pretty low frequencies. So in >the > > > > cost equation, we have to figure out which costs more: > > > > > > > > 1) Dealing with the increased route complexity of an islanded scheme > > > > 2) Buying lossy dielectric, or special parts / materials to edge >terminate > > > > the planes. > > > > > > > > I am very biased towards 1) > > > > > > > > Regards, > > > > > > > > > > > > Steve. > > > > ------------------------------------------------------------------ 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