Ultra-low phase noise 7.2–8.7 Ghz clip-and-restore oscillator with 191 dBc/Hz FoM

In this paper we investigate benefits of a recently introduced clip-and-restore (C&R) oscillator for ultra-low phase noise RF applications and reconsider the original choices in light of further insight into the oscillator behavior. We also tackle undesired resonance frequencies and exploit them to facilitate clipping with proper choices of tuning capacitances. Based on the new theory, the proposed oscillator was implemented in 65-nm CMOS and verified to achieve 4 dB better phase noise and 1.8 dB better FoM than the original C&R oscillator, thus making it the lowest phase noise CMOS oscillator ever published. The measured phase noise is -145 dBc/Hz at a 3 MHz offset from a 4.2 GHz carrier. The resulting average FoM is 191 dBc/Hz and varies less than 2 dB across the tuning range. It covers the 7.28.7 GHz frequency band for a 19% tuning range, drawing 32 mA from a 1.3 V power supply.