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

  • From: Hassan Ali <hali@xxxxxxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Mon, 10 Sep 2001 19:10:40 -0400

> -----Original Message-----
> From: MikonCons@xxxxxxx [mailto:MikonCons@xxxxxxx]
> Sent: Monday, September 10, 2001 6:30 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Tightly coupled VS loosely coupled diff pairs


> Another major contributor in edge rate degradation is non-symmetrical 
> coupling to adjacent signal traces and pins in connector pin 
> fields. Contrary 
> to recommendations made by another well-known consultant for AMP HS-3 
> connectors, I have conclusively demonstrated superior eye 
> diagram performance 
> of pairs that bracket the signal pin rows, as opposed to the 
> ground pin rows.

Thanks, Mike, for an enlightening response.

Some folks claim that loose coupling is better because it results in less
reflection due to intra-pair trace spacing changes (hence impedance
mismatches) in connector pin fields, in device break-out area and associated
vias. You didn't say much about that. Just wondering, have you ever
quantified that particular reflection effect?

Around the same impedance matching issue, is it not the case that in some
applications there is a need to tightly match both single-ended and
differential impedances? If that is the case, is it then always right that
tight coupling is better than loose coupling?


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