[SI-LIST] Re: Ground problems
- From: "Tom Biggs" <tbiggs@xxxxxxxxxxxxxxxxxxxxx>
- To: "Tom Biggs" <tbiggs@xxxxxxxxxxxxxxxxxxxxx>,<jlevieux@xxxxxxxxxxxxxxxxxx>, <stephanie.goedecke@xxxxxxxxxxx>,<raman@xxxxxxxxxxxxx>
- Date: Fri, 30 May 2003 09:37:33 -0700
I apologize for saying "That is the point he was making", when I should
have said "That is the point she was making".
Of course there could be lots of other reasons for measuring 2v
peak-to-peak between the two planes. It is easy to pick up radiated
noise when the measurement setup has loops in it.
-tom
-----Original Message-----
From: Tom Biggs=20
Sent: Friday, May 30, 2003 8:59 AM
To: jlevieux@xxxxxxxxxxxxxxxxxx; stephanie.goedecke@xxxxxxxxxxx;
raman@xxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Ground problems
A 0 ohm resistor is basically a wire. That isn't the point.
If you are measuring 2v across a '0 ohm' resistor, and lets say that the
0 ohm resistor is really about 0.001 ohms, then ohms law says that there
are 2000 amps going across that resistor. This isn't very likely. More
likely is that the resistor isn't 0 ohms. That is the point he was
making.
-tom
-----Original Message-----
From: John LeVieux [mailto:jlevieux@xxxxxxxxxxxxxxxxxx]=3D20
Sent: Friday, May 30, 2003 8:51 AM
To: 'stephanie.goedecke@xxxxxxxxxxx'; 'raman@xxxxxxxxxxxxx'
Cc: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Re: Ground problems
Stephanie,
What is the difference between the 0 ohm resistor and the wire? Have you
found 0 ohm resistors that do not measure to be 0 ohms? I am working on
a design that has a separated analog and digital ground area that needs
to be connected in the same manner as Ramana described and I would like
to understand the issue with the 0 ohm resistor.
Thanks,
John LeVieux
Littlefeet
Poway, CA
-----Original Message-----
From: stephanie.goedecke@xxxxxxxxxxx
[mailto:stephanie.goedecke@xxxxxxxxxxx]
Sent: Wednesday, May 28, 2003 12:23 AM
To: raman@xxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Ground problems
Hi Ramana,
I think it might not be a 0 Ohm resistor. Would you consider replacing
it with a wire, and repeating the measurement?
regards,
Stephanie
Stephanie Goedecke
Philips - SP3D Chip Design GmbH
Petersbrunnerstr.17
82319 Starnberg / Germany
Phone: +49-8151-270-160
Fax : +49-8151-270-200
=3D20
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To:
<si-list@xxxxxxxxxxxxx> =3D20
cc: (bcc: Stephanie
Goedecke/STN/SC/PHILIPS) =3D20
Subject: [SI-LIST]
Ground problems =3D20
=3D20
"Ramana Rao Rayudu" Classification:
<raman@xxxxxxxxxxxxx>
=3D20
Sent by:
si-list-bounce@freelists
.org
=3D20
2003-05-27 01:45 PM
Please respond to raman
=3D20
=3D20
Hello,
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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