[SI-LIST] Re: Bypass vs Decoupling capacitors
- From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: <cpad@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>, "steve weir" <weirsp@xxxxxxxxxx>
- Date: Fri, 27 Aug 2004 08:55:00 -0400
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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