[SI-LIST] Re: Dual referenced stripline?

Chris-

To a high frequency signal, there is no difference between "GND" 
and "Vcc".

The problem is that there must be a discontinuity at the location 
where the signal changes return path from only the PCB GND plane (or 
SMA ground) to also including Vcc plane as well.

For example, if an SMA cable connects to a PCB.  The return path of 
the signal inside the cable is external conductor of the cable, which 
is likely connected to the GND plane on the PCB.  In order for the 
return current to travel on Vcc, it must travel either through the 
impedance of either a bypass capacitor or the impedance between 
planes (whichever way is lowest impedance).  This will cause an 
impedance discontinuity.

The problem is that this impedance discontinuity is very application 
specific.  Each design will be different at this transition.  As with 
a lot of SI issues, it's very difficult to generalize.  I recommend 
the best way to understand this issue is to use a field solver.

Regards,
Ryan Satrom
Everett Charles Technologies

--- In si-list@xxxxxxxxxxxxxxx, "Christopher Rodenberg" 
<c.k.rodenberg@...> wrote:
>
> Hi folks, not sure if dual-ref is the right term, but I'm looking 
for
> info on stripline with one ground plane and the other at Vcc. I'm
> trying to gauge the effects of this configuration versus normal
> "ground sandwiched" line. Any tips/sources?
> 
> Chris
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