Assuming i chose to route an impedance controlled signal with a power plane as a reference plane instead of ground (microstrip or stripline), and assuming i'll make sure the signal won't cross power planes.

Does it matter if the reference power plane is the VCC of the driver driving the signal or it can be any VCC i have on my PCB?


Theoretically it does not matter as long as you provide proper coupling between different reference planes. The following animations illustrates the current flow in transmission line, Wikipedia gif. Moving dots illustrate local charges. As one can see, the charges oscillate along conductors, including the reference plane. When you switch planes, you need to shunt the gap with appropriate capacitor, to provide continuity. The coupling with MLCC caps might be tricky however, since the impedance of caps can turn into inductive branch for high-frequency signals, so the caps need to be selected carefully (and placed in near proximity to microstrip trace).

This animation also illustrates why any discontinuity in ground plane are bad for characteristic impedance uniformity - cuts in reference plane are obstructing the current oscillations.

ADDITION: Here I found a nice article about the fundamental importance of Return Current" in HS design, which partially touches the topic of split reference planes, "The Ground Myth", see Slide 93.

  • \$\begingroup\$ Can you erase the thing about the cap, so I can upvote your answer? This is not good for a number of reasons. Just think about what frequencies this would work for and compare to what you need for typical digital stuff today. \$\endgroup\$ – Rolf Ostergaard Jan 26 '17 at 10:08
  • 1
    \$\begingroup\$ @RolfOstergaard, sorry, I can't erase the stuff about the cap. When a reference plane is split, you have to provide a continuity for return current. Since the planes are at different potential, only a cap can do this. But the caps are what they are, so one needs to be careful. See one example piers.org/piersonline/pdf/Vol3No7Page1144to1147.pdf \$\endgroup\$ – Ale..chenski Jan 26 '17 at 18:29

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