A K-band low-noise bipolar class-C VCO for 5G backhaul systems in 55 nm BiCMOS technology

The development of 5G communication systems is underway. When employing 64 QAM, very low phase noise levels are required to limit EVM - i.e. less than −117 dBc/Hz at 1 MHz offset from f = 20 GHz. In this paper, the challenges of achieving such a low phase noise are discussed in detail. The choice between CMOS vs BJT devices is investigated and the impact of the base resistance intrinsic in BJT-based VCOs is addressed. BJT-based VCO shows ∼2 dB better phase noise when compared to CMOS-based VCO and low supply is employed. When higher supply is leveraged, BJT-based VCO advantage is kept while CMOS-based VCO is not able to reach the targeted tuning range due to thick-oxide devices parasitics. Emphasis is on the minimization of L/Q inductor versus quality factor ratio, to further minimize phase noise. Prototypes in a 55 nm BiCMOS technology were operated at 2.5 V supply with the largest amplitude allowed by reliability constraints. Measurements show a phase noise as low as −119 dBc/Hz at 1 MHz from a 20 GHz carrier offset with a tuning range (TR) of 19% and FoM = −187 dBc/Hz. Power consumption is 56 mW. To the best of authors' knowledge, the presented VCO shows the lowest reported phase noise among state-of-the-art BiCMOS VCOs with TR>10%.