Characterization of a cryogenically cooled Silicon Germanium HBT amplifier

In this paper, the gain and noise performances of a DC-6 GHz microwave amplifier using commercial Silicon Germanium Heterostructure Bipolar Transistor (SiGe HBT) are investigated at different bath temperatures. At room temperature, the two-stage amplifier has a gain of 21 dB and a noise figure of 3.7 dB at 2.62 GHz. When cooled to 70 K, it demonstrates 27 dB gain and 1.5 dB noise figure at the same frequency. The gain and noise figure of another three-stage amplifier at room temperature are 34.5 dB, 3.7 dB at 2.64 GHz, respectively. When cooled to 130 K, the gain goes up to 37.5 dB; when cooled to 170 K, the noise figure goes down to 2.4 dB. The higher gain and better noise figure of this amplifier are obtained when the ambient temperature decreases.