Asymmetry in broadside configuration

摘要

The broadside-coupled layout in Figure 1 in-cludes two traces, A and B, that begin on the surface layer of the pc board. They then pass through layer 2 into a broadside-coupled stripline configuration on layers 3 and 4. The plane-stitching via X resides 4 mm from signal via Y. The return current for trace A (dotted line) therefore has to divert 4 mm out of its way to find the plane-stitching via, plus another 4 mm to get back, giving a total estimated additional delay of (4 mm)·2·(4 psec/mm)=56 psec. If this same asymmetry exists at both ends of the broadside configuration, the total additional delay on trace A equals 112 psec.