Inductive compensation of operational amplifiers in feedback circuits

Abstract

In this thesis I designed, implemented, and tested an integrated-circuit feedback compensator that uses inductors as compensation elements. Introducing inductors as feedback elements makes it possible to implement lead compensators using shunt topologies, which preserve the closed loop response of a system while compensating the open loop characteristics. My chip consisted of a marginally unstable two-pole amplifier, and a compensated but otherwise identical amplifier. Comparing the step responses of the original and compensated systems proved that the compensator successfully stabilized the unstable system. I used frequency domain analysis to determine how much phase margin my compensator added to the system. After characterizing and canceling out the effects of input and output loading, and the attenuation of my output buffer, I found that my compensator added 41.40 of phase to the system. This was less than the 65° that it was designed for, but more than enough to prove the feasibility of my design.