Low noise preamplifier for gravitational research

Abstract

The sensitivity of the new generation of gravitational wave antennas to be cooled to the temperature of liquid helium is limited by the noise performance of the preamplifier. Two circuits are described that have been realized to measure the Brownian motion of a small low temperature antenna. They use a parallel arrangement of four low noise FETs (2N6550) followed by an operational amplifier to obtain an input noise that is characterized by a voltage of 0.33 nV/√Hz and a current of 24 fA/√Hz plus a correlated current contribution of 8 fA/√Hz at 10 kHz.