# Differential Coupling

#### theTom

Joined May 16, 2006
3
Earlier today I was having a discussion and the term "DIFFERENTIAL COUPLING" was used.
I asked for a clarification of what the term meant and the answer seemed a little shady, so I later googled it and could not find a straightforward definition (surprising!).

Thus, can anyone help me find a concise definition for what _differential coupling_ is?
If anyone has any examples that may additionaly demonstrate the concept I would appreciate those as well.

Thanks!
-t.

#### Papabravo

Joined Feb 24, 2006
16,797
What was the context of the discussion?

The first thing that comes to mind is a shielded cable. If there is a noise source that couples capacitatively then the coupling from the source to the shiled will be different than the coupling from the source to the center conductor. That's kind of the idea of shielding.

#### theTom

Joined May 16, 2006
3
The conversation was about cables, specifically involving high data rates.
There was mention of crosstalk.
So perhaps it is a term used in relation when multiple transmissions are made, the noise may be related to the difference of one transmission to another, coupled onto another line????

I was obviously a little more on the outside of the discussion at hand

#### Papabravo

Joined Feb 24, 2006
16,797
The specifics depend of course on the details of the cable construction and the signaling on the cables. Were you satisfied with the example I gave, or do you want to dig deeper to understand coupling mechanisms and how to minimize them?

#### theTom

Joined May 16, 2006
3
If you have any references for coupling mechanisms and minimization I would appreciate it.
If not that is fine too.
Your example at least got me thinking in the right direction!

#### thingmaker3

Joined May 16, 2005
5,084
It has to do with signal polarity in the cable. Here's an example in UTP cable:

White Paper from Sytimax

IIRC, there's some talk going around about FEXT (far end crosstalk) being due to more than just differential coupling.

I've heard the term used by guys who work with backplanes as well, but I know jack about backplanes.