[SI-LIST] Re: PDS simulation
- From: Cosmin Iorga <ci249534@xxxxxxxxx>
- To: John Kwan <jkwan@xxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 9 Jun 2009 09:01:55 -0700 (PDT)
Hi John,
This may be a clue to your question: The VRM has certain impedance also
dependent
on frequency. At low frequencies the VRM
impedance is very low and tends to â??shortâ?? the planes; but it is not a
â??zeroâ?? Ohm
impedance. At high frequencies, however,
the VRM impedance increases and at very high frequencies it is so high that it
is negligible compared to the impedance of the decoupling capacitors. I assume
in your case the VRM was not
represented by any frequency-dependent model, so shorting it would approximate
the impedance at low
frequencies and leaving it open would approximate the impedance at high
frequencies.
Cosmin Iorga,
NoiseCoupling.com
http://www.noisecoupling.com
________________________________
From: John Kwan <jkwan@xxxxxxxxxxx>
To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Sent: Monday, June 8, 2009 8:13:16 PM
Subject: [SI-LIST] PDS simulation
I heard people talking about "open circuit Impedance" and "short circuit
Impedance" of the power plane of a PCB.
Which one of them tells us about the impedance of the planes cavity?
How do we tell the IR drop from this information?
Why do we use Z11 and Z22 for the impedance rather than Z21 or Z12?
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