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
\(r_{\rm b}\)
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.