Embedded Tutorial ET1: Pole-Zero Analysis of Low-Dropout (LDO) Regulators: A Tutorial Overview

Summary form only given: We discuss the low-dropout (LDO) voltage regulator pole-zero analysis in this tutorial. A priori knowledge of poles and zeros assist in choosing the right topology and appropriate frequency compensation techniques before implementing the transistor level design, as the location of poles move with output load current. The objective of this tutorial is to provide a step-by-step procedure for analyzing poles and zeros in LDO regulators. To this end, two recent state-of-the-art LDO regulators from the literature are analyzed, explaining several intricacies involved. We explain step-by-step procedure in developing the small-signal model, breaking the voltage/current loop and techniques for quickly arriving at simple and approximate pole-zero equations. During the process, several frequency compensation techniques are elucidated. The derived analytic expressions for poles and zeros help in developing intuition of circuit behavior.