Cold Attenuator Noise Measurements on Cryogenic LNAs

ABSTRACT: In the quest to produce Low Noise Amplifiers (LNAs) with the lowest possible noise figures it is common to employ cryogenic techniques to cool the LNA to 20o kelvins (-253o C) or even lower. This has multiple beneficial effects: the minimum noise figure and noise resistance of the low noise transistors in the LNA are both substantially reduced, but also any ohmic losses in the LNA contribute far less thermal noise and indeed the losses themselves are usually substantially reduced as the conductivity of metals generally increases considerably at these low temperatures.