Abstract

This paper deals with modeling of a monolithic spiral transformer. The transformer is designed and fabricated as a symmetrical octagonal spiral structure using two-metal layer process on GaAs substrate for input balun applications of 2 GHz and 5 GHz push-pull power amplifiers. A distributed model of the transformer is developed to fit in wide frequency range with four ports. The model includes the skin effect which describes increase in series resistance with frequency. Six different sets of twoport s-parameters are measured to obtain full characteristics of the four-port transformer while the other two ports are shorted to ground. The model is validated with measurement results in 100 MHz to 6 GHz.