Impact of Correlated RF Noise on SiGe HBT Noise Parameters and LNA Design Implications

Abstract

This work presents analytical models of SiGe HBT and LNA noise parameters accounting for high frequency noise correlation. The models are verified using measurement data and circuit simulation. The impact of noise correlation is shown to be a strong function of base resistance rb which acts as both a noise source and an impedance. Correlation and rb as impedance have opposite effects on minimum noise figure NFmin, which explains why a widely used NFmin model that neglects correlation and rb as impedance agreed with measurements. The agreement, however, does not hold for noise matching source resistance Ropt, an important parameter for LNAs. With correlation, noise matching condition is better met for impedance matched LNAs.