RF Active Inductors Small-Signal Design by Means of Conformal Transformations

In this work we present a synthesis method for the design of RF and microwave Active Inductors (AI) based on S-parameters and conformal transformations. The proposed approach allows to study and define the desired AI characteristics directly managing the transfer function of an equivalent two-ports network, thus overcoming the difficulties relative to the characterization of the classical closed-loop architecture that characterizes both the proposed AI architecture and the classical gyrator-C capacitor scheme. By analyzing the obtained AI open-loop transfer function, it is possible to define the design criteria useful to obtain a single port equivalent network showing an inductive behavior at the desired frequency. An example of application of the proposed approach is also provided and the obtained AI is used for the design of a low-power active filter. Measurements are in good agreement with the simulation results, demonstrating the feasibility of the proposed design approach.