Performance of the optimum noise source reflection coefficient (Γ0) vs. temperature in microwave HEMTs by model analysis

In the present paper we exploit the results of the characterization and modeling vs. frequency (2-18 GHz) and temperature (-50-20°C) of a series of pseudomorphic HEMTs to carry out an investigation on the noise parameter. We had previously observed from the characterization of several HEMT series at room temperature, that a close relationship exists between the optimum input termination reflection coefficient Γ₀ and the scattering parameter S₁₁ and it always occurred that |S₁₁|>|Γ ₀| over the frequency range given above. We here analyze the performance of |Γ₀| at lower temperatures and use the equivalent circuit model to explore the cause of its variations with respect to its behavior at 20°C