Signals Crossing Plane Splits - Intel Pentium M Processor Design Manual

12.9.6

Signals Crossing Plane Splits

Signals that cross an adjacent layers plane boundary is undesirable for two reasons:
•
The return current that runs in the reference plane wants to share its current with the adjacent
layers reference plane it just crossed over. The return current now has to find a return path on
the adjacent layer which will cause signal delay.
•
The impedance of the trace will changes each time it crosses a plane.
Figure 170
routing is done on layer 2 while layer 1 (striped area) contains power and ground. Signals should be
routed in a way to avoid this issue such as routing on a different layer or repositioning the signals to
avoid the adjacent layers plane boundary.
Figure 170. Signal Crossing Plane Splits
Layer 2 Signals
Design Guide
®
Intel Pentium
shows the improper method of signals crossing adjacent layers plane boundaries. Signal
Layer 2
Signals crossing plane splits
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M Processor and Intel
High-Speed Design Concerns
Layer 1
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E7501 Chipset Platform
241