[SI-LIST] Re: Diff.Pairs
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Chris Cheng" <chris.cheng@xxxxxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Sat, 4 Oct 2003 11:37:55 -0700
I've had both on the same design for many years. Don't get you point.
> [Original Message]
> From: Chris Cheng <chris.cheng@xxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 10/3/2003 1:03:30 PM
> Subject: [SI-LIST] Re: Diff.Pairs
>
> I thought you are old enough to remember the days when board traces are
wide
> (6-8 mils were state of the art) and technology don't mix (either you have
> ECL or CMOS as critical highspeed design on the system but not both). It
is
> easy to justify tight coupling of different pairs then. It still makes
sense
> for many designs where differential I/O is the only thing you care (e.g.
> FCAL or 3GIO subsystems or clusters).
>
> -----Original Message-----
> From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx]
> Sent: Friday, October 03, 2003 11:41 AM
> To: Duane Takahashi; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Diff.Pairs
>
>
> More than that, it does not have any benefit. Tight coupling of
> differential pairs forces the traces to be narrower increasing the skin
> effect losses. Also, this tight coupling is going to result in good old
> cross talk that actually degrades the edges.
>
> How the notion of tight coupling of differential pairs as beneficial got
> started is a mystery to me. There are several references that show that
> tight coupling is not beneficial, one of them is Howard Johnson's latest
> book, at least one column he has written and my recently released book.
>
> Lee Ritchey
>
>
>
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