Noise in Oscillators with Active Inductors

This talk examines phase-noise origins and mitigation in oscillators that replace bulky spiral inductors and noise-degrading varactors with tunable active inductors (TAIs) synthesized via gyrator networks. Building on and extending Leeson-type models, Dr. Rohde presents closed-form treatments that capture active-device noise (shot/flicker) and large-signal effects, then validates the analysis on a ~1.9 GHz Colpitts using high-ft SiGe HBTs. Practical circuits demonstrate that self-injection locking with a phase-shift network can improve phase noise by ~8–10 dB while preserving tunability. The results position TAI-based VCOs as compact, integrable, and cost-effective alternatives for RF/MW systems, with next steps aimed at wider tuning range, enhanced dynamic range, and monolithic integration for filters, resonators, and phase-agile modules.

Prof. Dr. Ing. habil. Ulrich L. Rohde, IEEE Life Fellow, is partner of Rohde & Schwarz, Germany and Chairman of Synergy Microwave Corp., Paterson, NJ. Dr. Rohde is a full professor of Radio & Microwave Theory & Techniques at the University of Oradea and honorary professor at several other universities worldwide: Prof. of Microwave Technology at IIT-Delhi, Chair Professor for Microwave Technology at IIT-Jammu, Professor of Microwave and RF at the BTU Cottbus-Senftenberg University of Technology, and professor at the German Armed Forces University Munich (Microwave Systems, Technical Informatics).