[SI-LIST] Re: Question regarding return current in a differential pair

  • From: Ke Wang <wolfkid72@xxxxxxxxx>
  • To: mkotson@xxxxxxxxxxx, si-list@xxxxxxxxxxxxx
  • Date: Thu, 20 Apr 2006 10:04:33 -0700 (PDT)

Hi Mike,

Basically I think you are right. However the coupling
between the two signal traces and ground determines
how much return current go through ground. For
example, if the two signal traces are well separated,
the return current will be mostly through ground. If
the two signal traces are tightly coupled and far to
ground (e.g., twist pair), most return currnt will be
on one trace.

Thanks,
Ke

--- Michael Kotson <mkotson@xxxxxxxxxxx> wrote:

> Hello Gurus,
>     I have a question regarding the return current
> for a high speed
> differential signal.  I've seen a couple of sources
> that state that all
> of the signal return current is handled by the other
> half of the
> differential pair. It seems more logical to me that
> there must be some
> amount of return current (not just common mode) on
> the reference
> plane(s) as well.  What's the truth?
> 
>  
> 
> Thanks in advance,
> 
> Mike
> 
>  
> 
> Michael Kotson
> 
> Project Engineer
> 
> VT Miltope 
> 
> 4900 Pearl East Circle Suite 106
> 
> Boulder, CO 80301
> 
> (303) 473-0388 x132
> 
> http://www.miltope.com <http://www.miltope.com/> 
> 
>  
> 
>  
> 
> 
> 
>
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