ABSTRACT
This chapter extends the design methodology of complementary metal oxide semiconductors (CMOS) active inductors to CMOS active transformers. It shows that for each CMOS active inductor, there exists a set of corresponding CMOS active transformers. The characteristics of active inductors are inherited by active transformers. The chapter begins with a brief review of the fundamentals of active inductors. It is followed by the introduction of active transformers with a detailed mathematical treatment. The characterization of active transformers is presented. The nonidealities of transconductors synthesizing active transformers and their effect on the performance of the active transformers are investigated. CMOS implementation of four active transformers derived from the same CMOS active inductor is presented. The application of active transformers is exemplified using an active transformer quadrature oscillator. Active transformers have been used for applications where spiral transformers are usually employed to significantly reduce the silicon area requirement.
