RE: [SI-LIST] : Fwd: Probing power plane with analyzer.

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From: Dawson Yee (dawsony@microsoft.com)
Date: Thu Sep 28 2000 - 14:15:33 PDT


If you are doing A vs B comparisons, then just use some resistors to safely
voltage divide the input voltage, present a high enough measurement
instrument input impedance (preventing the power plane from "seeing" 50
ohms!), feed with a coax cable and then use the measurement instrument
attenuator if needed. If you use DC blocking caps you have to be concerned
about frequency roll-off (the higher frequencies rolls-off, tricking you
into thinking that there are no high frequency issues). With this technique
you can (sort of) ascertain the Power and Ground plane noises when used with
a spectrum analyzer (don't connect the ground lead, but be aware of what
potential it is at).

I've used this technique for many, many years (despite a lot of skeptics),
have not blown out any instruments, and have had a lot of real world, high
volume success.

Regards, Dawson

------- Start of forwarded message -------
 
To: "'EMC - PSTC Forum'" <emc-pstc@majordomo.ieee.org>
Cc: Roman Seifert <Seifert@ali.com.au>
Subject: Probing power plane with analyser.
From: "Cameron O'phee" <O'phee@ali.com.au>
Date: Thu, 28 Sep 2000 11:59:24 +1100

Hello All,

I have been asked by one of our design engineers if I can measure the RF
signature on the 3v plane on one of our PCB designs. The purpose of this is
to compare it to proposed changes for cost reduction, ie removal of bypass
caps. I would assume I need some sort of CDN but I have no designs for this
application. Does anyone have any ideas on how I can safely probe a 3v DC
power rail with an EMC analyser (HP8591E)?

Regards,

Cameron O'Phee.
EMC & Safety Precompliance.
Aristocrat Technologies Australia.

Telephone : +61 2 9697 4420
Facsimile : +61 2 9663 1412
Mobile : 0418 464 016

Thanks.
Best Regards,
Barry Ma <bma@anritsu.com>
ANRITSU www.anritsu.com
Morgan Hill, CA 95037
Tel. 408-778-2000 x 4465
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