[SI-LIST] Re: 10-Layer Stack up

Couldn't someone finally invent a non-inductive
conductor?!?!?  - Just a joke...   :-)

Arpad
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of steve weir
Sent: Monday, May 23, 2005 11:55 AM
To: tmcgonigle@xxxxxxxx; sunil_bharadwaz@xxxxxxxxx; =
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 10-Layer Stack up

Thomas, contrary to popular folklore, the main benefit of a thin =
sandwich=20
is not more capacitance but lower inductance.

If you have any doubts, consider that with a high Er dielectric you =
could=20
achieve equivalent plane cavity capacitance with a much thicker =
dielectric=20
but also much higher inductance.  I believe that if you model that, it =
will=20
become clear to you that Larry Smith's battle cry:  "It's the inductance =

stupid!" is on the mark.

It is low inductance that presents a low impedance to high=20
frequencies.  The planes present a lower inductance than the bypass=20
capacitors, but for it to be useful as a shunt on its own through the=20
cavity capacitance, you have to cross the AR created by the cavity with =
the=20
discrete bypass capacitors.  Because of the problems that presents we =
have=20
seen many proposals to try and find better damping, whether it be any of =

the resistive techniques or high ESR capacitors that Istvan has =
proposed,=20
or raising the net ESR of the discrete network using Larry's F^N=20
technique.  Since by and large most people do not use any of the =
techniques=20
either Istvan or Larry have proposed to solve that problem, they live =
with=20
it for better or for worse.  Under those conditions, more capacitance =
can=20
be as much of a problem as it can be a benefit.  But lower inductance =
helps=20
no matter what.

Steve.
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