A Swing-Enhanced Class-D VCO Using a Periodically Time-Varying (PTV) Inductor

This letter reports the design and analysis of a swing-enhanced class-D voltage-controlled oscillator (VCO) utilizing a periodically time-varying (PTV) inductor to boost the output swing that effectively improves the phase noise (PN) in both
$1/f^{2}$
and
$1/f^{3}$
regions at a low supply voltage (
$V_{\mathrm{ DD}}$
). Without extra switches, the PTV inductor reuses the original cross-coupled transistors in the class-D oscillator that semiperiodically cancels the magnetic flux between two coupled inductors. Fabricated in 65-nm LP CMOS, the 3.67-to-4.43-GHz VCO prototype measures figure of merits of 192.4 ± 1.5 dBc/Hz at 1-MHz offset frequency and 194.4 ± 0.8 dBc/Hz at 10-MHz offset frequency when the
$V_{\mathrm{ DD}}$
varies from 0.3 to 0.4 V.