Dependence of noise temperature on physical temperature for cryogenic low-noise amplifiers

We present the results of noise-temperature measurements for four radio astronomy MMIC low-noise amplifiers (LNAs) at physical temperatures from 2 to 160 K. We observe and confirm recent reports that the noise temperature of an LNA exhibits a quadratic dependence with respect to the physical temperature. We are also able to confirm the prediction by Pospieszalski that below a certain physical temperature there is no further significant reduction in noise temperature. We then discuss these results in the context of both the Pospieszalski noise model and some recent Monte–Carlo simulations, which have implied that at very low temperatures, heating of the electron channel above ambient temperature may help to explain the behavior of the drain temperature parameter.