Highly linear, varactor-less, 24GHz IQ oscillator

This paper presents a varactor-less, quadrature oscillator with high linearity. It is based on two identical sections comprising a differential Colpitts part and a coupling part. Tuning of the common-mode current and/or differentially changing the tail currents of the coupling and Colpitts parts can achieve the variation of the oscillation frequency. The oscillation frequency can be changed from 23 GHz to 24.4 GHz (10%) for a variation in bias current from 1 mA to 2.25 mA. The linearity in the whole tuning range is better than ±1.5%. The measured phase-noise @1 MHz is about -94 dBc/Hz. At a nominal supply voltage of 3.3 V±10%, the supply pushing is better than 250 MHz/V. The IQ VCO has been realized in a BiCMOS process (QUBIC4) with 38 GHz f_T and 3 μm thick top metal layer for inductors. The occupied area is 0.23 mm² and the power consumption is 22 mW. Possible applications for this oscillator are IQ downconverters, transceivers for mm-wave and FMCW radar sensors where the linearity of the VCO is an important design specification.