Modeling and Analysis of millimeter-wave Transformer Balun

This paper presents a modeling and analyzing methodology of millimeter-wave on-chip transformer balun based on the 90nm SiGe BiCMOS process. The physical parameters of transformer balun including turns ratio, coil geometry, tap grounding strategy, and geometric center misalignment, are investigated for adjusting balun’s electrical properties. Experiments show that increasing the turns ratio can improve its energy transmission efficiency, increases the coupling coefficient by a factor of +0.05 and +0.24 respectively. Adjusting the coil spacing can increase its coupling coefficient by a factor of 0.13. Shifting the centers of the primary and secondary coils can increase its amplitude and phase imbalance and deteriorate CMRR from 29.5dB to 24dB. These findings offer a systematic guidance for millimeter-wave balun design, enhancing high-frequency performance, interference resistance, and signal integrity.