On the configuration- and frequency-dependent linearity characteristics of SiGe HBTs under different impedance matching conditions

Linearity characteristics of common-emitter (CE) and common-base (CB) configuration SiGe HBTs are analyzed and compared under different matching, bias and frequency conditions. Impedance matching is demonstrated to have significant effect on the configuration-dependent linearity characteristics. Moreover, with source and load impedance matched for maximum output power, CE and CB configurations not only show different power gain relation but also different linearity characteristics dependence on frequency. Theoretical expressions show good agreement of the RF linearity property for simulation and experimental results. Further dc bias study reveals that both higher power-gain and better linearity can be obtained from the CB than the CE configuration under certain bias and operation conditions. A potential tradeoff between the two configurations in terms of linearity and power gain is also demonstrated.