[SI-LIST] current return-path for differential pair on PCB

hi
for a differential pair, like PCIe or SATA, some people (some of my colleagues) 
say, its not needed to have a continous good current return path since the 
differential voltage is referenced only to the other signal-trace in the pair.

I think the current return path has to be continous even for diffpairs, because:
1.) Common mode noise:
if the return path is not continous, then it creates loops for the common mode 
noise, so the common mode noise will be bigger. If the CM noise is bigger than 
it introduces jitter into the differential signal. which is bad.
2.) Impedance:
if the return path is poor, the the return current has to flow around to get a 
path between the source and destination, so on some areas the return current 
doesnt flow unterneath the signal traces so basically their single-ended (odd 
mode) impedances (so the diff impedance too) will be different than its 
calculated in the imp.calculator (polar, or MMTL), which assumes a perfect 
ground plane.

am i right, or wrong? why?

Istvan Nagy
Concurrent Technologies plc, UK.

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