[SI-LIST] : Decoupling between non-ground power rails, yes or no??

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From: Greim, Michael ([email protected])
Date: Mon Jan 22 2001 - 08:02:30 PST

Hi All,

I recently saw something on a design that I
felt was questionable and wanted to see what
your thoughts were, especially as there appears
to be a number of folks that have a focus on
PDS and decoupling.

While in the process of performing a PDS analysis
of a new board, I noticed that there was a signi-
ficant amount of decoupling between the power
rails. For instance, there were caps between 5
and 3.3, 3.3 and 2.5, etc. From discussions,
it appears that this is there to facilitate
return currents.

So the obvious question is, Is this accomplishing
what it is believed to be and is there in fact a
better way to do this. Is a properly decoupled PDS
(below target impedance through frequency range)
all that is required. For the sake of argument,
assume that all the planes are whole.

Thanks for your opinions

Best Regards,

Michael C. Greim Sonus Networks
[email protected] 978-589-8336

Making the world safe for digital signals everywhere

And all this science I don't understand
It's just my job six days a week

The time is gone. The email's over
Thought I'd something more to say......

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