An ultralow noise amplifier for superconductive detectors

Abstract

The design and construction of an AC-coupled, ultralow noise amplifier (equivalent input noise voltage En=0.33 nV/ square root Hz, optimum source impedance 1 k Omega at 100 kHz) is presented. The amplifier employs nine Sony 2SK 152-4 JFETS in parallel to yield the low noise result. Measurements were taken to characterize the amplifier's bandwidth, the additive voltage noise versus frequency, and the current noise versus frequency. SPICE modelling parameters for the JFETs used will also be discussed. Finally, the authors will review the performance of the amplifier in a flux-locked SQUID application.