A DC-4 GHz 270Ω differential SiGe low-noise amplifier for cryogenic applications

The design and measurement of a differential DC-4 GHz low-noise amplifier that is impedance matched to 270 Ω is presented in this paper. At room temperature, the amplifier has a measured gain of 29 dB with a 3 dB bandwidth of 4 GHz. To measure the noise temperature of the amplifier at cryogenic temperatures, an extension of the cold attenuator method was employed. The measured noise was found to be better than 10 K from 1-3 GHz at 24 K physical temperature. To the authors' knowledge, this is the lowest reported noise for a differential amplifier that is impedance matched to 270 Ω.