**From:** Istvan NOVAK (*[email protected]*)

**Date:** Wed Nov 10 1999 - 17:57:59 PST

**Next message:**Joel Jorgenson: "Re: [SI-LIST] : Plane Capacitance"**Previous message:**Charles) Kin P. Cheung: "Re: [SI-LIST] : Free 3D Planar EM simulator"**In reply to:**Vigliarolo Roberto: "R:[SI-LIST] : Comment on Johnson's article (Now BuriedCapacitance )"

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 <[email protected]>

To: <[email protected]>

Cc: <[email protected]>

Sent: Friday, November 05, 1999 6:01 AM

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

*> ----------
*

*> Da: Istvan NOVAK[SMTP:[email protected]]
*

*> Risposta a: [email protected]
*

*> Inviato: mercoledì 3 novembre 1999 14.15
*

*> A: [email protected]; Dr. Edward P. Sayre
*

*> Cc: [email protected]
*

*> 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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