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

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_b and emitter resistance r_e, which act as both noise sources and resistance. Correlation and roles of r_b and r_e as resistance have opposite effects on minimum noise figure NF_min, which explains why a widely used NF_min model that neglects correlation and roles of r_b and re as resistance sometimes agreed with measurements. The agreement, however, does not hold for noise matching source resistance R_opt, an important parameter for LNAs. With correlation, noise matching condition is better met for impedance matched LNAs.