[SI-LIST] Void requirement under Ethernet and E1 Signals

Hi all,
 

I hope this topic was already floated in the Si-list.

 

I would like to get clear idea about this, so please give your reply over
the following queries.

 

I have seen and even I use to provide void over the power planes under
differential signal of Ethernet signal after isolation transformer. 

 

My understanding is to provide void in the power planes, is to avoid noise
(or voltage surge ) couple between the digital planes in the PCB and cable
entering in the front panel of the board.

 

But I had seen people's providing void in the following manner:

 

1.       Void under the Ethernet signals and E1 signals in the secondary
side of the isolation transformer.

2.       Some will not provide void under these signals. They will route
over the ground plane.

3.       Some will provide void just below the isolation transformer, but
not under the differential signals. 

 

In this which methodology is true? Which one have to be followed in the
network application?

 

And what is the reason behind the void under these signals?

 

If anybody will suggest app notes and reasons, that will be great for my
understanding.

 

Thanks & Regards,

Arun Kumar

 



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