We examine a silicon-germanium heterojunction bipolar transistor (HBT) forcryogenic pre-amplification of a single electron transistor (SET). The SETcurrent modulates the base current of the HBT directly. The HBT-SET circuit isimmersed in liquid helium, and its frequency response from low frequency toseveral MHz is measured. The current gain and the noise spectrum with the HBTresult in a signal-to-noise-ratio (SNR) that is a factor of 10-100 larger thanwithout the HBT at lower frequencies. The transition frequency defined by SNR =1 has been extended by as much as a factor of 10 compared to without the HBTamplification. The power dissipated by the HBT cryogenic pre-amplifier isapproximately 5 nW to 5 {\mu}W for the investigated range of operation. Thecircuit is also operated in a single electron charge read-out configuration inthe time-domain as a proof-of-principle demonstration of the amplificationapproach for single spin read-out.
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