Re: R:[SI-LIST] : Comment on Johnson's article (Now BuriedCapacitance)

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From: Istvan NOVAK (istvan.novak@worldnet.att.net)
Date: Wed Nov 10 1999 - 17:57:59 PST


Roberto,

One early document showing plane resonances was the Buried Capacitance
Guide, the 1995./1996 version of which is now available on-line on the HADCO
website: www.hadco.com. Figure 12 on page 21 shows measured impedances of a
bypass capacitor and a buried capacitance test board. Upon close
examination, the testboard impedance curve shows some ripple at high
frequencies. The figure also shows the asympthotical inductance as being
0.7nH. The 0.7nH figure tells us that the reason why we do not see bigger
ripple in the impedance profile, is probably the connecting inductance,
which masks out the plane inductance and impedance minima. The spreading
inductance of a 2-mil pair is around 40-120pH, depending on frequency and
where we are on the plane, so the measurement setup seemed to have
approximately ten times higher residual inductance.

A recent set of measurement results is posted in the slides from the
October RMCEMC meeting (Richard Charbonneau, Charles Grosso) titled:
Embedded Capacitance: The next step in PWB Design. It is available from
http://www.ewh.ieee.org/r5/denver/rockymountainemc/. Slides 26-34 show
impedance profiles of various test board structures, some of them exhibit
large resonances. Some impedance profiles on the slides are smooth, which
may be due to several reasons, some of these reasons: a) the measurement
discontinuities mask out resonances (note that the smooth impedance profiles
are those where the impedance curves have the overall lowest values), or b)
the
dielectric material is lossy enough at and above the lowest resonance
frequency (referring to the loss tangent of the material), or c) depending
on the size of the test board, the lowest resonance frequencies may be
pushed out to such high frequencies that the dielectric loss suppresses the
resonances (referring to the size of the structure). Here items b) and c)
are interrelated: if we assume more-or-less frequency independent loss
tangent, the actual parallel loss conductance varies linearly with
frequency. Also, the resonance frequencies are roughly scaled by the size
(side dimension) of planes. so if we take a smaller-size plane, the
high-frequency conductance at the resonance frequencies (which are now
higher) may succesfully dampen resonances. But the same material in
bigger-size planes may exhibit bigger resonances.

Simulated self and transfer impedance profiles (with good correlation to
measured values) were published at EPEP98 and IEEE CPMT August issue,
downloadable from http://home.att.net/~istvan.novak/index.html. Measuring
techniques to allow to measure low impedances at high frequencies were
published at DesignCon99; accuracy considerations of plane simulation models
and also measured proofs that plane pairs with the same dielectrics but
different sizes have slightly different resonance behaviour, was published
at EPEP99,
both downloadable from the same site.

Best regards

Istvan Novak
SUN Microsystems

----- Original Message -----
From: Vigliarolo Roberto <Vigliarolo@asamrt.interbusiness.it>
To: <si-list@silab.eng.sun.com>
Cc: <istvan.novak@worldnet.att.net>
Sent: Friday, November 05, 1999 6:01 AM
Subject: R:[SI-LIST] : Comment on Johnson's article (Now BuriedCapacitance)

> ----------
> Da: Istvan NOVAK[SMTP:istvan.novak@worldnet.att.net]
> Risposta a: si-list@silab.eng.sun.com
> Inviato: mercoledý 3 novembre 1999 14.15
> A: MikonCons@aol.com; Dr. Edward P. Sayre
> Cc: si-list@silab.eng.sun.com
> Oggetto: Re: [SI-LIST] : Comment on Johnson's article (Now
> BuriedCapacitance)
>
>For repetitive (periodical) excitation, resonances due to
>the finite sizes do occur, unless the structure itself is lossy
enough to
>sufficiently suppress the resonances. The steady-state transfer
impedance
>profile may show impedance peaks, which are sometimes even bigger
than the
>impedance magnitude at the excitation point. Consequence: at a
remote
>point, the noise from a given source is bigger than at the source
itself.
>This effect was simulated and measured on various structures
independently
>by different people, and has been documented/published in several
articles
>at (among others) EPEP conferences and also in the IEEE Tr. CPMT
August 1999
>issue. Some of those articles are also available on-line.

............................

>For physically large and/or high-current designs, however,
>the power-distribution-impedance requirement and the needed measurement
>resolution may be in the milliohm range. One possible way to achieve such
>measurement resolution was published at DesignCon99 (also available on
>line).

.......................
Could you please tell me where I can find (on-line) the articles you
mentioned?
Thank you!

Roberto Vigliarolo

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