A Class-F23 CMOS Oscillator With Second and Third Harmonic Resonances Expansion

This paper presents a class-F₂₃ voltage-controlled oscillator (VCO) designed to improve phase noise performance through harmonic shaping while suppressing the flicker and white noise upconversion without manual 2nd or 3rd harmonic tuning. By leveraging a three-coil transformer-based resonator, the design achieves differential-mode (DM) resonance expansion at the 3rd harmonic frequency while maintaining the class-F operation. This approach eliminates the need for a low-quality (Q) factor switched-capacitor array (SCA) for 1st-to-3rd harmonic alignment, thereby improving the tank’s Q. Additionally, a two-coil transformer-based resonator is employed for tail filtering, enabling wideband common-mode (CM) resonance at the 2nd harmonic frequency, which helps to nullify flicker noise and prevent tank Q degradation due to the differential pair operating in the triode region. Implemented in a 65-nm CMOS process, the proposed prototype achieves a frequency tuning range from 18.5 to 22.4 GHz, phase noise from −110.7 to −106.1 dBc/Hz at 1-MHz offset, while consuming 5 mW and occupying a compact core area of 0.061 mm², corresponding to a peak figure-of-merit (FoM) of 189.1 dBc/Hz and FoM_T of 194.7 dBc/Hz.