Configurable low noise amplifier for voltage noise measurements

The noise performances of monolithic operational amplifiers are generally insufficient for the realization of low noise amplifiers for applications in the field of low frequency voltage noise measurements. In order to obtain very low levels of equivalent input voltage and current noise, discrete JFETs input stages can be used, with the disadvantage of introducing a large input capacitance that can reduce the usable bandwidth in the case of large source impedances. In this work we propose to employ a modular design entirely based on monolithic operational amplifiers that allows, by paralleling and/or combining in a proper way a number of identical basic amplifier blocks, to reach different compromises in terms of background noise and input capacitance while enabling, at the same time, differential measurement configurations and/or cross correlation background noise reduction approaches.