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

Abstract

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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1/f^{2}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1/f^{3}$ </tex-math></inline-formula> regions at a low supply voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm{ DD}}$ </tex-math></inline-formula> ). 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm{ DD}}$ </tex-math></inline-formula> varies from 0.3 to 0.4 V.