Typical Aspects of the Microwave Noise Performance of HEMTs at Decreasing Temperatures

Abstract
In analog signal processing at microwave frequencies the noise performance of active devices is of fundamental importance for the accurate design of low-noise amplifiers. To this aim, the determination of the four noise parameters F_o, Γ_o (complex variable) and R_n has to be accomplished together with the usual scattering parameter measurements vs. frequency. In addition, the dependence of the device performance vs. temperature is of interest for circuit applications characterized by harsh environmental conditions. In this work the noise behavior of high electron mobility transistors has been investigated by means of measurements and modeling in the 2-18 GHz frequency range and as a function of the decreasing temperature over the -50 - +20 °C range. The most interesting aspects of the observed variations occurred with temperature are explained on the basis of the device equivalent circuit.