A Broadband Tunable On-Chip Transformer Based on Magnetic Coupling Technique

The growing demand for miniaturization and reconfigurability in mobile devices drives the need for tunable, highly integrated passive components in radio frequency integrated circuits (RFICs). As a critical component in RFICs, transformers have attracted significant attention for their tuning ability. This article introduces a broadband tunable on-chip transformer based on magnetic coupling by controlling both the amplitude ($r$) and the phase ($\theta $) of the currents in an auxiliary inductor. A comprehensive theoretical analysis details the amplitude and phase tuning technique. Simulations show a maximum inductor tuning ratio of 87.86%, and a reduction in inherent loss represented by a negative parasitic resistance of$- 1.37~\Omega $. Measurement results demonstrate favorable return loss and insertion loss across a 40GHz band. With continuous tuning capability, broad bandwidth, and simple control, the proposed transformer serves as an attractive building block for advanced reconfigurable RFICs.