FUBOCO: Structure Synthesis of Basic Op-Amps by FUnctional BlOck COmposition

Abstract

This article presents a method to automatically synthesize the structure and initial sizing of an operational amplifier. It is positioned between approaches with fixed design plans and a small search space of structures and approaches with generic structural production rules and a large search space with technically impractical structures. The presented approach develops a hierarchical composition graph based on functional blocks that spans a search space of thousands of technically meaningful structure variants for single-output, fully differential, and complementary operational amplifiers. The search algorithm is a combined heuristic and enumerative process. The evaluation is based on circuit sizing with a library of behavioral equations of functional blocks. Formalizing the knowledge of functional blocks in op-amps for structural synthesis and sizing inherently reduces the search space and lessens the number of created topologies not fulfilling the specifications. Experimental results for the three op-amp classes are presented. An outlook how this method can be extended to multi-stage op-amps is given.