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 model-to-hardware 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 (room temperature (RT)) while consuming a PDC of 45mW from a 2.5-V supply voltage. The measured tuning range is 39.5 to 45GHz (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 the authors’ knowledge, this is the highest reported oscillation frequency and output power for a VCO that can operate under cryogenic conditions for quantum computing.