An Inverse Class-F VCO with Reduced Third Harmonic Detriment Using a High Fundamental and Second Harmonic Q-Factor Resonator Achieving a 198.9 dBc/Hz Peak FoM

This paper presents a novel topology to design the inverse-class-F voltage-controlled oscillator (VCO). The proposed architecture employs a distributed dual-mode resonator (DMR) as the LC tank to replace the transformer (xfmr)-based tank in the conventional class-$\mathrm{F}^{-1}$ VCOs. The proposed DMR can achieve high Q-factors at both the fundamental and $2^{\text {nd }}$ harmonic frequencies by avoiding magnetic flux cancellation that is inevitable for the xfmr-based counterpart. Using this DMR to construct a class-$\mathrm{F}^{-1}$ VCO, the ratio of $2^{\text {nd }}$ harmonic to fundamental components in the output oscillation is considerably large. This results in a sufficiently wide duration of impulse sensitivity function (ISF)~0 within the output waveform period to suppress noise to PN conversion without introducing excessive drain to gate gain. In the class-$\mathrm{F}^{-1}$ VCOs, the misaligned third harmonics in the oscillating signal deteriorates the ISF. Thanks to the DMR’s dual high-Q characteristics, the proposed VCO considerably reduces the detrimental $3^{\text {rd }}$ harmonic components, further optimizing PN. The fabricated VCO prototype demonstrates a frequency tuning range (FTR) from 9.37 GHz to 10.86 GHz, with a best–in–class phase noise (PN) of $-143 \mathrm{dBc} / \mathrm{Hz}$ at a 10 MHz offset, corresponding to a peak figure of merit (FoM) of $198.9 \mathrm{dBc} / \mathrm{Hz}$.