Conduction avenues for the non-power signals.
We’ve discussed the importance and care required when routing the power delivery network (PDN) of modern printed circuit boards. From how to support current supply needs, loop inductance, and defining layer stack-ups, it may seem we’ve addressed all the power concerns one could have. This is just a fraction of the considerations a designer needs to keep in mind, however. The PDN has an important secondary role that has nothing to do with power delivery. Often forgotten, the PDN is responsible for roughly 50% of the conduction avenues for the non-power signals.
Commonly referred to as return path, this routing “completes the loop,” enabling current to flow. It can be as influential (and problematic) to signal quality as the transmission lines we study in detail. In fact, failure to address the return path is a leading cause of signal integrity issues. Perhaps more troubling, they frequently go undetected even in the setting of comprehensive simulation.
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