1/Z1 + 1/Z2 + 1/Z3 = 1/ZT ... Actually they are complex impedances so
you need to do a vector sum but never mind adding up all the
impedances. Can you do 2-5 mil traces with 5 mil air gap? That sounds
like less than 5 and 5 to me. My PCB vendor is only certified to 6 and
6. Your normal shop can't do this one.
> Also it seems to me that I want to have some amount of coupling between
> the two traces so that any noise that gets injected into these traces will
> have a canceling effect.
Don't worry about this kind of noise. That's why you use differential
transmission. Common mode signals are automatically removed.
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