I recently served on a panel where I was asked, “At what point does signal integrity become a problem?” The intent of the question was to ask at what frequency did signal integrity become an issue for board designers, but as stated, the question was more general. And that got me thinking about how broad the term “signal integrity” really is, even though we have come to think of it terms of more narrowly defined highspeed issue. A not-really-facetious answer to the question is that we have a signal integrity problem whenever the signal begins to lose its integrity! And this is not related to frequency. Two of the more obvious and common ways a signal can lose integrity are when it becomes distorted or when the signal-to-noise ratio (S/N) begins to degrade.