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Altera_Forum
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13 years ago

PDN Tool Zh = Zs + Zv

Hello All! The PDN Tool shows the impedance between the decoupling network and BGA on the graph as Zh = Zvia + Zspreading, but if I leave the plane and BGA vias unchanged, the Zh value changes ...
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Altera_Forum
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13 years ago

Hi Ken,

See Page 1-22 of the PDN tool user guide here: http://www.altera.com/literature/ug/ug_pdn_gen_device.pdf

In the PDN guide for combining rails your supposed to choose the one with the highest Feffective. Feffecitve is the frequency above which PCB decoupling caps cease to help, due to the inductance between them and the die, due to bga vias spreading, etc. So it makes sense that in my PDN tool for VCC I see that when Zh becomes significant (is this the 3dB point?), that is where Feffecitve is, so there must be some relationship between the two, but in general I don't think you have to worry about Zh. You're also supposed to combine the current for all rails, and design for the lowest ripple voltage.

Steve