Analog small-signal modeling-part II: elementary transistor stages analyzed with behavioral signal path modeling

Abstract

This paper describes the practical application of behavioral signal path modeling to the small-signal modeling of analog integrated circuits. The method brings a new viewpoint to how small-signal transfer functions are built up. The composition of the signal path is revealed in a detailed way. This allows the derivation of design relationships and requirements, useful for manual or automatic state-of-the art design. The paper is written from a design point of view, where the emphasis is on analysis. Various elementary transistor stages are analyzed, and design requirements are derived, more complicated examples are tackled to show that the method remains manually applicable and the obtained models manageable. The method provides qualitative insight and offers an organized, structured approach to circuit analysis, making the use of fuzzy design heuristics unnecessary and unwanted. It allows one to obtain insight in circuit structures where other methods fail.