A K-Band low-noise bipolar Class-C VCO For 5G backhaul systems in 55nm BiCMOS technology

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Abstract
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 -117dBc/Hz at 1MHz offset from f=20GHz. 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 ~2dB 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. To further minimize phase noise, emphasis is on the minimization of L/Q inductor versus quality factor ratio. Prototypes in a 55nm BiCMOS technology were operated at 2.5V supply with the largest amplitude allowed by reliability constraints. Measurements show a phase noise as low as -119dBc/Hz at 1MHz from a 20GHz carrier offset with a tuning range (TR) of 19% and FoM=-187dBc/Hz. Power consumption is 56mW. 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%.

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