Optimum Biasing of SiGe-HBTs to Maximize the Gain Per Current for Power Efficient Amplification

Transistor biasing for RF-amplifiers typically is based on achieving the highest transistor speed given by the maximum oscillation frequency. However in low-power applications such as active tags achieving the maximum small-signal gain combined with minimum power consumption is desired. Therefore we analytically investigate the existence of a maximum of the realizable gain per collector current of SiGe-HBTs. The obtained observations are subsequently analyzed in simulations and proven in measurements of a differential cascode amplifier. When biasing for the proposed maximum the power consumption of amplifier chains can be decreased significantly without sacrificing small-signal gain therefore increasing efficiency and sustainability.