A 4 GHz cryogenic amplifier in 0.18 µm general purpose BiCMOS technology

Many specific SiGe processes have been well demonstrated with their excellent noise and gain performances at low temperature. However, general purpose BiCMOS processes may be the keys to cryogenic SoC for scientific instrumentation. To investigate the feasibility of a general BiCMOS process at low temperature, we have designed a 4 GHz amplifier in TSMC's 0.18 µm SiGe BiCMOS process. The amplifier had been tested on-wafer and in a box to distinguish the effect of housing. The results shows that while the gain is about 15 dB and the noise figure is 5.5 dB at 273 K temperature, the gain is 10 dB and the noise figure is 4.8 dB at 19 K. The noise performance is better indeed at the lower temperature regardless of that the gain decreases. We suggest the cryogenic amplifier is better biased with a constant current technique to minimize temperature variation effects on transistor cut-in voltages. As the result, it is possible to design cryogenic circuits in general purpose BiCMOS processes.