Re: [SI-LIST] : Measuring Ground Noise

Istvan NOVAK (istvan.novak@worldnet.att.net)
Wed, 24 Jun 1998 21:00:41 -0400

Andy,

The noise between the power and ground plane effects primarily the
electronics, as Larry pointed out. The noise on one of the planes or on
both of them appears as a common-mode noise, as will mainly cause EMI
problems. One possible way to measure it without the need of long
interconnecting wires is to have an extra plane parallel to the one that you
want to measure. If the quiet plane is connected to the active plane at one
point only, it will not carry whatever noise or signal-return currents there
may be on the active plane. Probing the signal between the quiet plane and
active plane, the measured voltage is just what otherwise appears on the
active plane between the point of measurement and the point where the two
planes are connected.

Regards,

Istvan Novak

-----Original Message-----
From: Andrew Ingraham <Andrew.Ingraham@digital.com>
To: si-list@silab.Eng.Sun.COM <si-list@silab.Eng.Sun.COM>
Date: Wednesday, June 24, 1998 8:14 AM
Subject: RE: [SI-LIST] : Measuring Ground Noise

>> Agreed on all points. What follows, however, is that you can measure
>> localized noise on your ground plane - you just need to figure out
>what
>> your reference point will be.
>
>But, to measure noise _across_ your ground plane, requires attaching
>probe wires some distance apart ... which requires wires of some length.
>How to do that effectively and believe the results? (And in the first
>place, what is the significance of noise across the ground plane?)
>
>Regards,
>Andy Ingraham
>
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