Analysis of the 50 Ω-noise mismatch in microwave low-noise transistors

The noise parameters are the electrical representation of the noise performance of transistors most widely used in the design of low-noise microwave amplifiers. The noise parameters F₀-Γ₀ (complex) and r_n of a given transistor type exhibit typical properties over the microwave frequency range as we have observes from several packaged devices characterized and modeled in our lab. In this work we have focused our attention upon the noise performance of transistors having their input terminated on 50 Ω which is the standard value of the signal impedance in a microwave system. This paper presents the results of a comparative analysis on the noise performance observed in advanced BJT´s and HEMT´s when moving from the noise matching condition (minimum noise figure) to the 50 Ω source termination. The analysis has been performed on the basis of the noisy circuit models previously extracted from device measurements