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 inverse-class-F VCO. The proposed architecture employs a distributed dual-mode resonator (DMR) as the LC tank to replace the transformer-based tank in the conventional class-F-1 VCOs. The proposed DMR can achieve high Q-factors at both the fundamental and 2nd harmonic frequencies by avoiding magnetic flux cancellation. Using this DMR to construct a class-F-1 VCO, the ratio of 2nd harmonic to fundamental components is considerably large. This results in a sufficiently wide duration of ISF~0 within the output waveform period to suppress noise to PN conversion without introducing excessive drain to gate gain. Thanks to the DMR’s dual high-Q characteristics, the proposed VCO considerably reduces the detrimental 3rd harmonic components, further optimizing PN. The VCO prototype demonstrates a FTR from 9.37 GHz to 10.86 GHz, with a best PN of −143 dBc/Hz at 10 MHz offset, corresponding to a peak FoM of 198.9 dBc/Hz.