[SI-LIST] Re: Power Plane resonance analysis

  • From: Aleksandr Oysgelt <aleks@xxxxxxxxxxxxxxxxxx>
  • To: Istvan Novak <istvan.novak@xxxxxxx>
  • Date: Thu, 27 Aug 2009 14:06:14 -0700

How do you figure out propagation delay through planes?  Is it sqrt(L/C) so
L is about 32pH/mil of separation (sheet inductance) but what is C (which is
area dependent - no concept of "sheet capacitance")?
Thank you
Aleks

On Thu, Aug 27, 2009 at 5:25 AM, Istvan Novak <istvan.novak@xxxxxxx> wrote:

> Hi San,
>
> If you have the good luck to have rectangular plane shapes, you can
> simply calculate the
> modal resonance peak frequencies from the propagation delay along each
> of the two sides
> of the rectangle.  1/(2*tpd) gives you the lowest resonance peak, and
> you will get all of
> the harmonics, so it becomes a double infinite series.  On typical PCB
> dimensions today,
> the first five or ten resonance peaks matter in self impedance; the
> higher-order modes
> will tend to blend together into an inductive slope.
>
> For more complex shapes the modal resonance frequencies need to be
> calculated by
> an appropriate software.  You can go from simple and low-cost tools like
> EZPlane
> (http://www.ems-plus.com/ezpowerplane.html) to more sophisticated tools
> like
> Sphinx (http://www.e-systemdesign.com/products.aspx) to high-end tools
> such
> as Ansoft SiWave or HFSS.  For HFSS and correlation on power planes, you
> can
> check out the Unofficial HFSS User forum (http://www.hfss-forum.com/).
>
> To make sure that resonances do not create a problem, best and cheapest
> defense
> is to make sure you dont excite them.  You can do this by creating a
> stackup to
> minimize signal-return currents going through unrelated power-ground
> cavities.
> To reduce the resonances themselves, you can either sprinkle the planes
> with many
> capacitors, match the planes or use thin laminates, or a combination of
> these. If
>  you sprinkle the planes in the old-fashioned brute-force manner, you
> could use the
> same capacitance value, say 0.1uF or 1uF.  Key is minimizing the inductance
> in the capacitor connections because with the cumulative inductance of
> all capacitors
> on the plane you want to stay below a couple of percents of the plane's
> inductance.
> You can read more on these design options at
> http://www.electrical-integrity.com/,
> go to Paper download.  In the Tool download section you can also find
> simple
> illustration tools for plane resonances.
>
> For measurement options, you can look at the paper "Frequency Domain Power
> Distribution Measurements - An Overview" from DesignCon 2003 East, Boston,
> MA, June 23-25, 2003.  You will find it at the site above.  For more
> details and
> tips, you can look at the book Frequency-Domain Characterization of Power
> Distribution Networks, Artech House, 2007.
>
> Regards,
>
> Istvan Novak
> SUN Microsystems
>
>
>
> Sandhya I. M. wrote:
> > Hi SI experts,
> >
> > If any one can help me in doing PCB Power Plane resonance analysis by
> > sharing documents or by explaining how it occurs.
> >
> > What are the causes of PCB Power Plane resonance analysis
> > How can we measure resonant frequency
> > How decoupling caps helps in suppressing resoinance in planes.
> > What are the factors we should consider while doing resonance analysis.
> >
> >  Thank you
> >
> > Regards
> > san
> >
> >
>
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