A Low Phase Noise All Cryogenic Microwave Oscillator Based on a Superconductor Resonator

A 1-GHz full cryogenic oscillator is presented. The oscillator is based on a planar superconductor resonator featuring a loaded ${Q}$ factor of 200 000 at low microwave input power (unloaded ${Q}$ of 400 000) and on amplifying parts realized with SiGe bipolar transistors. The circuit is designed with a harmonic balance software and realized on an alumina substrate. A nonlinear model is extracted at low temperature both for the transistor and the resonator. This double nonlinearity increases the difficulty of the oscillator design and implies a strategy to limit the power inside the resonator. The vibrations of the cryogenerator are also a serious issue to get high performance. Finally, the oscillator features a phase noise of 112 dBc/Hz at 100-Hz offset frequency and a phase noise floor of 170 dBc/Hz (100-kHz offset) at a temperature of 65 K.