[SI-LIST] Re: Bypass vs Decoupling capacitors

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.
> >
> >


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