[SI-LIST] Re: 10-Layer Stack up
- From: steve weir <weirsi@xxxxxxxxxx>
- To: arpad.muranyi@xxxxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 23 May 2005 13:22:58 -0700
Shhh, that's a secret!
At 12:04 PM 5/23/2005 -0700, Muranyi, Arpad wrote:
>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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