Cross-Coupled CMOS Series-Resonance VCO with 3rd-Harmonic Output and -142 dBc/Hz Phase Noise at 10 MHz Offset from 29.7GHz

A cross-coupled CMOS series-resonance VCO with efficient third-harmonic extraction is presented. Operation of the tank at series resonance enables low phase noise, while the N-type negative resistance of the active core shapes the tank voltage to enhance odd-harmonic content. The third harmonic is extracted using a doubly tuned series–parallel transformer that also provides consistent suppression of the fundamental component. Implemented in a 65-nm CMOS process, the VCO tunes from 8.45 to 9.91 GHz and delivers up to 9.3 dBm at 29.7 GHz with a phase noise of −142 dBc/Hz at 10 MHz offset. With a peak FoM of 187 dBc/Hz, the measured performance compares favorably with the state of the art.