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

The feasibility of using standard 0.18 mu m CMOS technology for low cost wideband monolithic microwave integrated circuits (MMICs) at similar to 20GHz 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 20.02GHz and tuned up to 20.23GHz (tuning of 210MHz) where as the frequency of the 3-stage D-VCO is 20.46GHz and tuned up to 21.03GHz (tuning of 570MHz). The change in output power level with tuning is similar to 1.5dBm in 4-stage and similar to 2dBm in 3-stage designs. These D-VCOs are also compared with measured results of previously, reported D-VCOs