Ultra-low-noise, high-impedance preamp for cryogenic detectors

A preamplifier design is presented which is based on a common-drain JFET input. The midband noise performance is E_n = 0.42 nV/Hz^½, In = 2.8 fA/Hz^½. The circuit has considerably less input capacitance than comparably noisy common-source amplifiers. It is particularly useful for preamplification of 0.1 to 10 MHz signals from liquid-helium-cooled radiation detectors