The Evolutionary Era - Toward the Golden Age of Active Inductors

Active inductors (AIs) implemented using gyrator-C configurations have become a cornerstone of radio frequency integrated circuit (RFIC) and analog design, providing wide tunability, small size, and CMOS compatibility compared with their passive spiral counterparts. This chapter is dedicated to the in-depth study of single-ended gyrator-C active inductors, starting from the basic operation principles, parasitic effects, and equivalent impedance modeling of this family of circuits. Several simple configurations are first reviewed, followed by the effective evolution overview and the main performance enhancement techniques developed up to the mid-2000s. Such techniques have included the use of resistive feedback, cascode and regulated cascode topologies, auxiliary capacitors, and advanced biasing schemes, analyzed for their effectiveness in extending inductance tuning, quality factor, frequency range, and power efficiency. At the end, synergistic integration of these techniques to implement High-Q, wideband, and low-loss inductors suitable for RF and microwave applications is emphasized.