Noise Measurement of Cryogenic Low Noise Amplifiers Using a Tunnel-Junction Shot-Noise Source

Cryogenic noise measurements are typically carried out using a variable-temperature load or a commercial noise diode in conjunction with a cryogenically-cooled attenuator. In both of these cases, thermal gradients can present a significant source of uncertainty. In the astronomy community, SIS mixers biased beyond their gap voltage are often used as shot-noise sources and employed to determine the noise of IF amplifiers. In this work, a tunnel junction with metal electrodes is used as noise source for characterization of cryogenic amplifiers. It is shown that this method is easily calibrated and can provide results that agree well with those obtained using the cold-attenuator method.