Analysis of generic spiral-coil RF transformers on silicon

This work demonstrates the effect of substrate loss, efficiency, and frequency response of the three generic spiral-coil transformers: stacked, bifilar and nested. The dependence of loss on the spacing of transformer coils from the oxide-silicon interface is confirmed experimentally. The high gains and better-than-expected bandwidths of the stacked transformers as compared to those of the bifilar and nested transformers are demonstrated. The effect of bulk silicon on transformer efficiency is investigated with the use of a substrate transfer technique.