[SI-LIST] Power Integrity Question
- From: "Avtaar Singh" <avtaarenator@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 6 Nov 2008 18:22:54 +0800
Dear All:
I have a very basic Power Integrity question.
Lets say a Power Delivery Network (PDN) has an impedance peak at 100MHz. I
add a capacitor that dips the impedance exactly at 100 MHz, and creates 2
smaller peaks at, lets say, 20 MHz and 250 MHz. According to the theories of
Physics, these peaks should have their impedance value little bit lesser
than the impedance value of the PDN, at those 2 frequency points, before
this capacitor was added. But we do not always see that in simulation tools.
Sometimes we see that the 2 peaks that are formed have higher impedance than
the impedance that existed at those frequency points before this last
capacitor was added. This seems weird to me, because even though the ESR of
the caps should decide how sharp or blunt the Z peaks are, but an added Z in
parallel should always mean lesser impedance rather than more impedance. Can
someone please explain this paradox?
Thanks for the kind guidance.
Regards,
Avtaar Singh
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