[SI-LIST] Re: Switching diff pairs from tightly coupled to loosely coupled and back

Marc, The loose / tight / loose  introduces discontinuities in the even 
mode impedance.  This will creates discontinuities in the even mode that 
establish standing waves that can cause increased jitter due to the 
finite CMR of the receiver.  Eric Bogatin's book "Signal Integrity 
Simplified" deals with the even and odd modes.  I think Eric also just 
posted a notice on a free webinar on differential signaling.

Steve.
Marc Battyani wrote:
> Hi,
>
> I'm re-designing a board initially designed by somebody else and I
> noticed that on layer 1 the diff pairs are tightly coupled while on
> layer 3 they are loosely coupled. (The stackup for the first 4 layers is
> S/G/S/G and there are 2 microvias layers.)
>
> So I'm wandering what will happen to my 5.0Gbps signals when the diff
> pairs go form the layers 1 to the layer 3 and back. As this is on the 2
> sides of the same gnd plane maybe the transition will go smoothly but I
> would be interested by any references (papers, links) or feedback on the
> subject.
>
> Thanks,
>
> Marc
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