A comparative study of MOS VCOs for low voltage high performance operation

Six 10GHz MOS VCOs were designed and fabricated in the IBM 6RF 0.25um CMOS process. Their oscillation frequency, output amplitude and phase noise performance are measured and compared, and the results confirm that replacing shielded-ground inductors with high-resistivity substrate inductors improves phase noise performance. Capacitive source degeneration has also been identified as a performance limiting mechanism in MOS based VCOs rather than performance enhancing as in BJT based VCOs.