Internal and external op-amp compensation: a control-centric tutorial

Frequency compensation of two-stage integrated-circuit operational amplifiers is normally accomplished with a capacitor around the second stage. This compensation capacitance creates the desired dominant-pole behavior in the open-loop transfer function of the op-amp. Circuit analysis of this compensation leads to a mathematical observation of "pole splitting": that as the compensation capacitance is increased, the parasitic poles of the amplifier separate in frequency. Treatment of op-amp compensation as minor-loop feedback, instead of pole splitting, greatly simplifies and generalizes the analysis and design of op-amp frequency response. Using classical-control techniques instead of direct circuit analysis, insight and intuition into the behavior and flexibility of the system are gained.