A 0.011-mm² 27.5-GHz VCO with Transformer-Coupled Bandpass Filter Achieving -191dBc/Hz FoM in 16-nm FinFET CMOS

We present a new approach to improve the phase noise of a conventional transformer-coupled voltage-controlled oscillator (TC-VCO) for 5G mmWave application. Coupling capacitors are added to a single center-tapped transformer to introduce bandpass filtering that suppresses nonlinear conversion of second- and third-harmonic distortion to phase noise around the VCO fundamental. The resulting TC-VCO exhibits phase noise measured at -108.1 dBc/Hz at an offset of 1-MHz which is 4.3 dB better than a conventional TC-VCO. The proposed VCO is implemented in 16-nm finFET CMOS with a core area of only 0.011 mm². It tunes over a measured frequency range of 27.2 to 27.7 GHz while consuming only 4 mW of dc power. The phase noise performance corresponds to a figure-of-merit (FoM) of -191 dBc/Hz which, to our knowledge, is the best reported FoM with the smallest core area among nanoscale CMOS VCOs operating near 27 GHz.