Analog small-signal modeling-part I: behavioral signal path modeling for analog integrated circuits

Abstract

This paper describes the transformation of small-signal modeling of analog integrated circuits into control system modeling. Transforming a small-signal circuit into a control system equivalent results in a behavioral signal path (BSP) model. A BSP model gives insight in the operation of a circuit because it shows all the different conversions from current to voltage and vice versa, including poles and zeros which cause a decrease-increase in transfer along the signal path. The different poles are a function of the small-signal parameters of the different devices and are modeled with small symbolic equations, which make them fully comprehensible. This enables the designer to accurately control the sizing process by enabling pole/zero placement. On a BSP model, all theorems of control theory as well as typical design approximations can be performed. The methodology and its applications are illustrated with several examples.