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

Abstract

This paper presents analytical models of SiGe HBT and low-noise amplifier (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 \(r_{\rm b}\) and emitter resistance \(r_{\rm e}\) , which act as both noise sources and resistance. Correlation and roles of \(r_{\rm b}\) and \(r_{\rm e}\) as resistance have opposite effects on minimum noise figure \(N\!F_{\rm min}\) , which explains why a widely used \(N\!F_{\rm min}\) model that neglects correlation and roles of \(r_{\rm b}\) and \(r_{\rm e}\) as resistance sometimes agreed with measurements. The agreement, however, does not hold for noise matching source resistance \(R_{\rm opt}\) , an important parameter for LNAs. With correlation, noise matching condition is better met for impedance matched LNAs.