High CMRR in reduced-coupling monolithic baluns

Monolithic technologies (e.g. semiconductor-based passive components) have small dimensions and tight fabrication tolerances. For coupled-resonator baluns this results in superior amplitude and phase balance characteristics, which are directly related to the common-mode rejection. Achieving good CMRR becomes more difficult at higher frequencies because of the effects of capacitive coupling between the primary and secondary coils in the circuit. In this paper a modified physical design is presented that reduces the capacitive coupling and offers superior CMRR. These designs also have reduced inductive coupling, so they have a more narrow-band response. Measured performance characteristics of a practical example of one of these baluns are presented.