Cryogenic ultra-low-noise SiGe transistor amplifier

An ultra-low-noise one-stage SiGe heterojunction bipolar transistor amplifier was designed for cryogenic temperatures and a frequency range of 10 kHz-100 MHz. A noise temperature T(N) approximate to 1.4 K was measured at an ambient temperature of 4.2 K at frequencies between 100 kHz and 100 MHz for a source resistance of similar to 50 Omega. The voltage gain of the amplifier was 25 dB at a power consumption of 720 mu W. The input voltage noise spectral density of the amplifier is about 35 pV/root Hz. The low noise resistance and power consumption makes the amplifier suitable for readout of resistively shunted DC SQUID magnetometers and amplifiers. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3655448]