RE: [SI-LIST] Re: Ground problems

From: "Michael Poimboeuf" <Michael_Poimboeuf@xxxxxxxxxxxxxx>
To: <tbiggs@xxxxxxxxxxxxxxxxxxxxx>, <jlevieux@xxxxxxxxxxxxxxxxxx>,<stephanie.goedecke@xxxxxxxxxxx>, <raman@xxxxxxxxxxxxx>
Date: Fri, 30 May 2003 09:57:09 -0700

First, what is a CRO?

Second, 2v pk-pk over what bandwidth?

A few observations.

You shouldn't try to measure this with single ended probes.

When using differential probes you must insure that the probe
dc offset is calibrated. I recommend doing a null before doing
the measurement.

Even when using differential probes, common mode pickup can
easily swamp out the tiny voltage levels you're trying to=20
measure. I use a common mode choke in series with the probe
to block this.



---
mkp=20

...



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We are testing the power supply (VRM 8.5 compatible) for our processor
board.

We have a split ground - the power supply ground and the digital ground
shorted at one single point with a 0 ohm resistor. There is no signals
crossing over and I do not think there are any loops.


The voltage difference between the 2 grounds is very large. The CRO
shows a p-p of 2V when measuring between the 0 ohm resistor.


What could be the reason for this and what could the remedies.


Thanks and Regards

Ramana Rao Rayudu
Real Time Systems Group
Centre For Development Of Advanced Computing
No.1 Old Madras Road, Byappanahalli
Bangalore - 38, India
Ph 91-80-5244059

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RE: [SI-LIST] Re: Ground problems

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