Design of Two Novel Impedance-Transforming Baluns Based on Transformer and Autotransformer for RF Integrated Circuits

This article presents the analysis and validation of a novel impedance-transforming balun featuring an autotransformer and a countermagnetic coupling transformer. By separately generating positive and negative signals through two different broadband transformers, the design offers flexible impedance matching. The balun demonstrates excellent performance in return loss, insertion loss, and minimal amplitude and phase imbalances across a broad frequency range. Theoretical analysis further shows that integrating series capacitors can optimize return loss, effectively extending the bandwidth. Simulation and measurement results under the 45-nm CMOS process exhibit strong agreement, highlighting the balun’s superior performance and potential for radio frequency integrated circuit (RFIC) applications.