Impact of SiGe HBT parameters to the performance of LNAs for highly sensitive SKA receivers

Low-noise amplifiers (LNA) for highly sensitive applications such as radio astronomy have traditionally used Gallium Arsenide and Indium Phosphide transistor technologies coupled to cryogenic cooling to achieve sub-1 dB noise figure (NF) at high costs. For the Square Kilometre Array, the expected number of receivers is very large and a trade-off between performance and cost is required. Silicon-germanium heterojunction bipolar transistor technology is proposed for a cost-effective highly sensitive LNA at room temperature in the frequency range of 0.4 GHz to 1.4 GHz. An inductively degenerated cascode topology is recommended for simultaneous noise and impedance matching. The dependencies of the noise parameters of the two-port noise model of the LNA with the parameters of the transistors of the LNA are analysed. It is found that a low NF that is closer to the minimum achievable NF can be achieved with a low base resistance, a high direct current gain and unity gain frequency when the biasing and the sizing of the transistors as well as the value of the base and emitter inductors are optimum. A design methodology is derived from the analysis.