Solving Tough Feedback Problems (Without Hair Loss) [Shop Talk: What You Didn’t Learn in School]

You don’t admit it to your colleagues. You may not even admit it to yourself. But deep down, feedback scares you a little bit. Not the everyday dominant pole stuff with generous phase margins and plenty of loop gain. That’s easy. No, it’s that occasional “special” circuit with some peculiar element in the loop, or too many poles lurking around crossover (i.e., unity-gain frequency). In that weird territory, you don’t trust your intuition, your mental constructs don’t hold up, and you find yourself on shaky ground. The sensible response is just to retreat to more familiar surroundings: take the alien elements out of the loop. Crush the bandwidth with a monster capacitor. Run away. Take a management job!