20GHz CMOS distributed voltage controlled oscillators with frequency tuning by MOS varactors

The feasibility of using standard 0.18 mum CMOS technology for low cost wideband monolithic microwave integrated circuits (MMICs) at ~20 GHz is demonstrated. Two monolithically integrated distributed oscillators with n-FET gain cells are designed having four and three stages respectively, Coplanar waveguides used as the on-chip inductive elements. MOS Varactors are employed to tune the frequency, a new study for distributed VCOs. Simulated results indicate that the 4-stage D-VCO is oscillating at 20.02 GHz and tuned up to 20.23 GHz (tuning of 210 MHz) where as the frequency of the 3-stage D-VCO is 20.46 GHz and tuned up to 21.03 GHz (tuning of 570 MHz). The change in output power level with tuning is ~1.5 dBm in 4-stage and ~2 dBm in 3-stage designs. These D-VCOs are also compared with measured results of previously reported D-VCOs.