Inductor- and Transformer-based Integrated RF Oscillators: A Comparative Study

Prior publications claim that transformer-based resonators achieve improvements in quality factor (Q), which translates to better phase noise in oscillators. This paper combines rigorous analysis with on-chip practical considerations for various types of on-chip transformers to demonstrate the importance of the resonator topology for Q-enhancement. We show that for a fixed silicon chip area, transformer-based resonators do not exhibit superior performance compared to inductor-based designs. Prototype oscillators are implemented at 5GHz in a 0.18mum CMOS process to validate these claims