Comparison of Dynamic Loadlines of CE and CB SiGe HBTs under Equivalent Bias Conditions

Large-signal dynamic loadlines of common-emitter (CE) and common-base (CB) SiGe power HBTs are measured and compared to reveal the different amplification mechanisms under the two configurations. Under equivalent junction voltage bias conditions for the two configurations, CB HBT can provide higher power gain and high power-added efficiency (PAE) than CE HBT at low input power. However, CE HBT can deliver more output power due to its later compression of power gain than CB HBT. Different input and output matching conditions affect the out-of-phase characteristics of output current and voltage and thus the power performance characteristics of both configurations