FreeLists / si-list / [SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator

["Juergen Flamm" <jflamm@xxxxxxxxxxx>]

A tool from Cadence called SPECCTRAQuest with the Power Integrity option =
will not only allow you to evaluate various capacitor types and =
quantities, but also include their placement locations, their individual =
mounted inductances and a model of the plane pair they are connected to. =
The plane model includes skin effect and dielectric losses. It is not =
only pretty cool to use, but very accurate and shares the same database =
with the Allegro layout tool.=20

Check it out if you like. =20

Regards=20

Juergen Flamm

-----Original Message-----
From: Peterson, James F (FL51) [mailto:james.f.peterson@xxxxxxxxxxxxx]=20
Sent: Monday, August 04, 2003 12:19 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator

Doug,

In regards to :=20

<snip>
1. The reason we wrote the calculator in the first place was because we=20
couldn't figure out how to make the frequency response calculation for =
an=20
arbitrary number of capacitors with arbitrary values, inductance and ESR =

any other way. Then we figured others might have the same problem and =
would=20
like access to the same tool.
<snip>

We've been having excellent results doing this very thing using PSPICE.

We get complete control over ESR and ESL values, qty of caps, and their
values.=20

We plot the results as ohms and freq (log) - which requires a little
config...

regards,
Jim Peterson




-----Original Message-----
From: Doug Brooks [mailto:doug@xxxxxxxxxx]
Sent: Monday, August 04, 2003 1:42 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator


As the author of this calculator, I guess I'd like to throw in my 2 =
cents=20
worth!

1. The reason we wrote the calculator in the first place was because we=20
couldn't figure out how to make the frequency response calculation for =
an=20
arbitrary number of capacitors with arbitrary values, inductance and ESR =

any other way. Then we figured others might have the same problem and =
would=20
like access to the same tool.

2. The calculator helps demonstrate (as does our article) that one thing =

that is REALLY desired for a smooth impedance response is a continuum of =

capacitor self resonant frequencies  (not necessarily simply capacitor=20
VALUES). A large number of caps with the same self resonant frequency =
gives=20
you a single deep zero. Many self resonant frequencies spread over a =
range=20
give you multiple zeros, spreading out the response much more =
effectively.=20
MORE IMPORTANTLY, these zeros (and don't forget the poles in between) =
REACT=20
with each other to provide a smoother response. The calculator helps you =

demonstrate and prove that.

3. Along the way, the results from the calculator provided the evidence=20
(unexpected at the time) that moderate ESR is better than low ESR. The=20
reason is that while low ESRs give you very deep zeros, they also lead =
to=20
very high peaks. Moderate ESR gives you an OVERALL better frequency
response.

4. Finally, the calculator does not address the issue of placement. My=20
input on that question is this: Placement doesn't much matter EXCEPT for =

(a) the electrons must be able to get where they are needed in time=20
(traveling at 6"/ns) and (b) loop areas (including those around and =
through=20
caps) must be minimized for EMI reasons. Most people are aware of these=20
issues, and if they are taken care of, THEN placement is no longer an =
issue.

Hope this helps

Doug Brooks
>

Doug Brooks' new book, "Signal Integrity Issues and Printed Circuit =
Board=20
Design" has just been released by Prentice Hall. See details and =
ordering=20
info at www.ultracad.com
_________________________________________________________________________=
___
__


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