image“Most of the designs I get pulled into are really design rescues,” Jim Herrmann, Managing Partner & Principal Engineer at AppliedLogix, LLC, said at the 2012 IEEE EMC Global EMC and SI University.

From more than 25 years of hands on, practical design experience, Jim had an epiphany moment that the problems in all the designs he’s rescued have had four key root causes. He says, if you pay attention to these four key design concepts, you will avoid most of the signal integrity design problems in your next design.

 

Concept #1: Treat all interconnects as transmission lines and worry about their return paths as much as the signal paths. Always pay attention to the signal’s return path.

Concept #2: Try to engineer the transmission lines to look as close to a coax as possible, with the return path symmetrical around the signal path. Route in stripline, keep signals away form he edge of the board.

Concept #3: Forget the word “ground”. Board ground is just another piece of copper. Think “return path” and do everything possible to reduce the inductance of the return path.

Concept #4: Do everything possible to reduce the loop inductance of every element in the PDN. Drive out inductance in the PDN path.

Not a bad, concise list of important design guidelines to follow.