FreeLists / si-list / [SI-LIST] Re: Why PDS impedance exceeds target impedeance in low frequency less than 1kHz is OK ?

[Istvan Novak <istvan.novak@xxxxxxxxxxx>]

I wouldnt agree with the statement that exceeding target impedance at 
low frequencies is OK.  As it was pointed out, this might be acceptable 
in the ambiguous scenario when we consider the bypass capacitor network 
only, without the active power source.  This scenario is ambiguous 
because we really need to set the impedance target for the entire 
network, active source, bypass capacitors and PCB structure.  Not doing 
it this way often leads to the wrong design approach when the 
antiresonance between the active source and bypass capacitors is missed. 

There are situations though, when you can convince yourself that it is 
acceptable to have a higher target impedance at low frequencies.  For 
instance, when the rail powers only SerDes devices with a required 
minimum transition density. 

Regards,
Istvan Novak
SUN Microsystems

icer world wrote:
> It's said that PDS impedance  exceeds  target impedeance in low frequency 
> less than 1kHz is OK , can anyone give me some explains?Thanks!
>
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