A Q-band SiGe-HBT Cryogenic Colpitts VCO for Frequency-Division Multiplexed Quantum Computing

A Q-band (33-50 GHz) Colpitts voltage-controlled oscillator (VCO) operating from 300K to 4K is presented. To validate hardware-to-model correlation, the compact model HICUM/L2 has been extended, and the corresponding model parameters were extracted at cryogenic temperatures (CTs). At 1 MHz/10MHz offset, the VCO achieves a phase noise of -94/-120 dBc/Hz at 46 GHz (CT) and -92.6/-115 dBc/Hz at 43.5 GHz (RT) while consuming a PDC of 45mW from a 2.5-V supply voltage. The measured tuning range is 39.5 to 45 GHz (13%) at 300K and 43.9 to 46.5 GHz (5.8%) at 4 K. With the cascode buffer in the Colpitts topology, the measured single-ended output power at CT and RT is 5.8dBm and 4.5 dBm, respectively. To the best of authors’ knowledge, this is the highest reported oscillation frequency and output power for a VCO that can operate under cryogenic conditions for quantum computing.