A novel mmWave CMOS VCO with an AC-coupled LC tank

We propose the concept of AC-coupled LC tank for minimizing VCO pushing, as well as to enable multi-terminal tuning of the varactors, in the widely used cross-coupled CMOS VCOs. The proposed concept is demonstrated with a mmWave VCO (40GHz) in a foundry-based 65nm bulk CMOS. Measured data demonstrates >;3× lower pushing while achieving 16% wider tuning range (7.2GHz versus 6.1GHz) compared to a reference cross-coupled CMOS VCO. Phase noise and output power at 40GHz are comparable to the reference VCO. Finally, the proposed VCO can operate at ultra-low V_DD=0.5V while maintaining wide tuning range, P_out>;-10dBm, and power consumption <;10mW.