At the recently concluded Embedded Systems Conference, I moderated a session on Specialized Data converters which included a very unusual presentation. Michael K. Mayes, a senior design engineer at Linear Technology Corp discussed a high-performance delta-sigma A/D converter he had designed.
What I found fascinating, in addition to the performance specifications he achieved, was his recounting that he had not used any EDA tools in the design. Instead, to realize absolute highest performance, he looked at every source and timing of noise, imperfection, coupling, and other extremely subtle effects. Then he systematically reduced them, designed them out, compensated for, or worked around each, using manual layout. Using this “hand-crafted” analog, Mayes' design achieves linearity of better than 1 part per million over the entire voltage-input range, along with excellent noise rejection, and it allows for seamless conversion speed change.
Now, I am not expecting designers to drop their EDA tools and go the manual route en masse. This simply can't and won’t happen in designs with significant digital content, large silicon complexity, or a function that is radically different from an A/D converter, such as a state machine. But sometimes it's nice to know that while automated tools are great, that sometimes, in order to really approach perfection, you have to apply the human, creative, innovative touch. Just following design rules to perfection, as EDA tools do, won't achieve the goals, especially in the precision analog world where you have major thermal, current flow, ground noise, and coupling issues with which to contend.
At least that's the case, for now!
Bill Schweber , Site Editor, Planet Analog