Characteristics of Integrated RF Transformers on GaAs Substrate

Stacked transformers, coupling stacked transformers, interleave transformers and symmetrical transformers on GaAs substrate are systematically studied in this paper. Two kinds stacked transformer are under study. One has the symmetrical electric property while the other one has a better quality factor for the primary port. The stack transformers have achieved the highest coupling coefficient (~0.9) at the cost of lower self-resonance frequency. The interleave transformers have the identical electric properties for the primary and the secondary ports. However, the layout is incompatible with the differential operation. On the other hand, the symmetrical transformer is compatible with the differential operation and can have the center-tapped biasing option. The data established here provide a useful design library for the GaAs RFIC.