A 21GHz 20.5%-tuning range Colpitts VCO with −119 dBc/Hz phase noise at 1MHz offset

A SiGe BiCMOS Colpitts VCO with a transformer-coupled varactor operating from 18.8 to 23.1 GHz is presented. The Colpitts topology is leveraged to trade a slight degradation in the oscillator figure-of-merit for very low phase noise. The oscillator features a state-of-the-art phase noise of -119.4 dBc/Hz at 1 MHz offset from the carrier, while drawing 17.5 mA from the 4 V supply. The oscillator FoM is -188 dBc/Hz. The VCO also shows a wide 20.5% tuning range, which results in a FoMT = -194 dBc/Hz.