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

A Q-band (33-50GHz) 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 1MHz/10MHz offset, the VCO achieves a phase noise of -94/-120dBc/Hz at 46GHz (CT) and -92.6/-115dBc/Hz at 43.5GHz (room temperature (RT)) while consuming a P DC 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 46.5GHz (5.8%) at 4K. With the cascode buffer in the Colpitts topology, the measured single-ended output power at CT and RT is 5.8dBm and 4.5dBm, 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.