Very simple FET amplifier with a voltage noise floor less than 1   nV/sqrt(Hz)
  A field-effect transistor (FET) amplifier for small voltage signals is presented. Its design is elementary and the construction can be afforded by anyone. Despite its simplicity, with a voltage noise less than 1 nV/sqrt(Hz), it outperforms commercially available integrated FET amplifiers. The amplifier has a gain flatness better than 1 dB over 1 MHz bandwidth; it can be employed as a front-end for signal analyzers or signal recovery systems. 
Luca Callegaro, Marco Pisani, Alessio Pollarolo