Voice of the Experts: Signal Integrity

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Routing 112 Gbps PAM4 signals through a system poses many challenges for designers. In this piece, SI expert Scott McMorrow explains what causes signal degradation and offers a path forward.

As Dave Dunham from Molex Corp. likes to say, "When designing high-speed serial links beyond 10 GB/s, everything matters." In order to ensure first time success at these speeds, accurate channel modeling is a prerequisite. This is especially true for long backplane channels.

We worry about via stubs in high-speed designs because they cause unwanted resonant frequency nulls which appear in the insertion loss plot (IL) of the channel. But are all via stubs bad? Well, as with most answers relating to signal integrity, “It depends.”