[SI-LIST] Re: Tightly coupled VS loosely coupled diff pairs

  • From: MikonCons@xxxxxxx
  • To: si-list@xxxxxxxxxxxxx
  • Date: Thu, 6 Sep 2001 14:51:04 EDT


Loose versus tight coupling: The obtainable degree of coupling for 
edge-coupled traces is very limited; however, the tighter the better. Both 
source coupling and victim coupling is reduced by closer spacing of the 
traces, as is radiated emissions. The use of loosely coupled traces makes 
life easier for the layout designer, but is NOT technically better from the 
design margin standpoint.

Losses: Because the degree of coupling is not major (i.e., typically 15%) for 
"closely" coupled traces, the bulk of the current still flows in adjacent 
reference planes and the added losses are minor. In some cases, one might 
prefer the added high frequency (i.e., harmonics) attenuation to soften the 

I use tightly coupled trace pairs within the limits of the vendor's 
manufacturing process to the maximum extent practical.


Michael L. Conn
Owner/Principal Consultant
Mikon Consulting

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