[SI-LIST] Re: Diff.Pairs

  • From: Scott McMorrow <scott@xxxxxxxxxxxxx>
  • To: bmgman@xxxxxxxxxx
  • Date: Sat, 11 Oct 2003 15:43:22 -0700

Mike

see below

>
> Scott,
> how did the difference  between the noise voltages get to be common 
> mode?  Given identical noise voltages on both traces, the difference 
> is zero - and that is differential noise.  The CM noise is the average 
> of the two noise voltages (sum/2) 


I am talking about a case where Lee has suggested that the differential 
pair can be split between two different routing layers.  The stackup 
might be as follows:

Ground

diff layer 1

Power 1

Ground

diff Layer 2

Power 2


The noise on each of these layers is totally different.  Thus at any 
point along the differential pair there is a common mode voltage 
differential that occurs, causing a net current flow in one direction or 
the other.  You are correct for signals that are referenced to the same 
layer.

Oh, and your point is well taken.  -1.5 dB of loss would be 1.5 dB of 
gain.  Oops!


regards,

scott

-- 
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com




------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:     
                //www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
  

Other related posts: