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.