Cryogenic Differential Amplifier for NMR Applications

We have designed and characterized a cryogenic amplifier for use in [Formula: see text] He NMR spectrometry. The amplifier, with a power consumption of [Formula: see text] mW, works at temperatures down to 4 K. It has a high-impedance input for measuring a signal from NMR resonant circuit, and a 50 [Formula: see text] 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 [Formula: see text] and a 4.4 MHz bandwidth starting from DC. At 1 MHz, the voltage and current noise amount to 1.3 [Formula: see text] and 12 [Formula: see text] , respectively, which yields an optimal source impedance of [Formula: see text] k[Formula: see text] .