[SI-LIST] Re: Maximum Frequency for S-parameter Extraction of Board Power Plane

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: Rajan Hansa <all.si.list@xxxxxxxxx>
  • Date: Wed, 18 May 2011 04:23:37 -0700

At 3X the package cut-off:
1. You are well-past resonance that occurs just below the cut-off.
2. The amount of energy transferred is typically down 20dB.  The 
impedance of the PCB above this point will have very little impact on 
the power delivery in the IC package.  You could simulate to a higher 
frequency but with little improvement in result accuracy or actionable 
information.  You could also simulate only to a lower frequency, but 
with rapidly increasing uncertainty near what is usually the highest, or 
close to the highest impedance seen by the die.

Steve.
On 5/18/2011 4:12 AM, Rajan Hansa wrote:
> Thanks Steve for being always prompt in reply !!
> Can you please explain how you have got this magical figure, 3 X 
> highest package cut-off frequency ? Why It's not 2 X or 1 X ??
> Rajan
>
> On Wed, May 18, 2011 at 4:21 PM, steve weir <weirsi@xxxxxxxxxx 
> <mailto:weirsi@xxxxxxxxxx>> wrote:
>
>     If you are concerned only with power delivery then simulate to 3X the
>     highest package cut-off frequency of any device you are concerned with
>     that is attached to a given power rail.
>
>     Steve.
>     On 5/18/2011 3:44 AM, Rajan Hansa wrote:
>     > Hello All,
>     >
>     >
>     > I have got a PCB database of one Ethernet Board and I have to
>     extract
>     > s-parameter for all power plane from voltage regulator to  power
>     pin of
>     > chip package. The Board database includes all decap.
>     >
>     >
>     >
>     > As we know extraction time is directly related with maximum
>     frequency So
>     > while setting maximum frequency for s-parameter extraction, I am bit
>     > confused, I would like to know that do I need to set knee
>     frequency ( Fknee
>     > = 0.35/Trise) as maximum frequency OR for board level simulation we
>     > shouldn?t care knee frequency.
>     >
>     >
>     >
>     > As per my understanding, package inductance won?t allow very
>     high frequency
>     > component (switching current component which depends on Trise
>     !!) to travel
>     > to board from chip so voltage regulator in board will never see
>     those high
>     > switching current so I shouldn't simulate/extract s-parameter
>     till knee
>     > frequency.
>     >
>     >
>     >
>     > What?s expert view on this ?
>     >
>     >
>     >
>     > Rgds,
>     >
>     > Rajan
>     >
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>     --
>     Steve Weir
>     IPBLOX, LLC
>     150 N. Center St. #211
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-- 
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV  89501
www.ipblox.com

(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax




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