Design of a novel type of on-chip transformer suitable for baluns in customary BICMOS/CMOS technologies

We present an on-chip transformer structure, side-coupling structure (SCS), suitable for baluns in the RF range of frequencies up to 5 GHz in customary BICMOS/CMOS technology. The novelty of the design lies in having identical spirals with symmetric layout (electrical center coincides with physical center) inter-wound in alternate pattern, primary surrounded by secondary and vice-versa, thereby achieving maximum coupling. A procedure to calculate the electrical characteristics, power-loss and the voltage-gain, from the S-parameters is presented. From the simulation results electrical characteristics of the structures is compared with other conventional identical spiral side-coupling structures having constant physical dimensions.