A Periodically Time-Varying Inductor Applied to The Class-D VCO for Phase Noise Improvement

This paper proposes a periodically time-varying (PTV) inductor applied to a class-D oscillator resulting in a 4.7V
DD
output swing that effectively improves the phase noise in both 1/f
²
and 1/f
³
regions. Without extra switches, the PTV inductor is realized by reusing the original cross-coupled transistors in the class-D oscillator that semi-periodically cancel the magnetic flux between two coupled inductors. Fabricated in 65nm LP CMOS, the oscillator prototype operating at 0.35V measures FoMs of 192.5±1dBc/Hz at 1MHz offset frequency and 194.6±0.3dBc/Hz at 10MHz offset frequency, over a frequency tuning range from 3.67 to 4.43GHz.