RE: [SI-LIST] : Bead-choking the power supply--everywhere!

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From: Boris Yost (yost@rainbowdisplays.com)
Date: Thu Sep 14 2000 - 07:56:12 PDT


It's not analog. There are two (...2...) components that have internal
PLL's. They have separate power and ground pins, and they should get
special treatment.

Everything else is traditional, synchronous logic.

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Ingraham, Andrew
Sent: Thursday, September 14, 2000 10:00 AM
To: si-list@silab.eng.sun.com
Subject: RE: [SI-LIST] : Bead-choking the power supply--everywhere!

> Is this "decoupling" scheme overkill, useful, or a disaster waiting
to
>happen?

I can't say for sure, but perhaps the designer wanted those filters on the
critical analog components (to keep noise from getting into them from
everything else, and maybe to reduce the tendency to oscillate with too many
wide bandwidth analog devices sharing the same power rail). But it sounds
like someone got carried way.

Or maybe this EMI expert got bitten once by a bad design that radiated out
all the cables and openings, and is now trying to "play it safe."

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