[SI-LIST] Re: difference b/w CM & DM noise

Hi Latha,
If you want to know the difference between Common-mode and 
Differential-mode noise in conducted emissions (as in a switch mode power 
supply), then a differential-mode noise is the noise between the two wires 
or traces (positive and negative, or live and neutral).  Such a noise can 
be controlled by placing X capacitors across the two wires.  On the other 
hand, a common-mode noise exists in same phase on both the wires or 
traces.  In order to control such a noise, you need to place Y capacitors 
from each wire or trace to Ground.  There are some limitations on the size 
of the Y capacitors you can place in a power supply.  Medical equipment 
have stricter limit on such capacitors.

To get a good understanding of differential and common impedance, you 
should read the book Signal Integrity - Simplified by Dr. Eric Bogatin 
(ISBN 0-13-066946-6).  He has devoted an entire chapter to this subject.

Regards, Ravinder
Server PCB Development
Hitachi Global Storage Technologies


Email: Ravinder.Ajmani@xxxxxxxxxxxxxx



"Latha Devi" <lathadevi@xxxxxxxxxxxxxxxxx> 
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[SI-LIST] difference b/w  CM & DM noise






 
hi, 

i want to clear about what is common mode noise , 

differential mode noise,.in conducted emission. 

and also what is common mode impedance. 



please clearly explain with example 

thanking you 

with regards 

A.latha devi. 

latha 

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