We have designed and characterized a cryogenic amplifier for use in 3He NMR spectrometry. The amplifier, with a power consumption of ∼2.5 mW, works at temperatures down to 4~K. It has a hi-impedance input for measuring a signal from NMR resonant circuit, and a 50 Ω differential input which can be used for pick-up compensation and gain calibration. At 4.2 K, the amplifier has a voltage gain of 45, output resistance 146 Ω and a 4.4 MHz bandwidth starting from DC. At 1 MHz, the voltage and current noise amount to 1.3 \mboxnV/\mboxHz and 12 \mboxfA/\mboxHz, respectively, which yields an optimal source impedance of ∼100 kΩ.
@article{arxiv.1809.06649,
title = {Cryogenic differential amplifier for NMR applications},
author = {V. V. Zavjalov and A. M. Savin and P. J. Hakonen},
journal= {arXiv preprint arXiv:1809.06649},
year = {2019}
}