Digitally assisted coaxial bridge for automatic quantum Hall effect measurements at audio frequencies

This paper describes the principle of a new fully automatic digitally assisted coaxial bridge having a large bandwidth ranging from 100 Hz to 20 kHz. The bridge is characterized by making a 1:1 comparison between calculable ac resistors. The agreement between the calculated and the measured frequency dependence of the resistors is better than 10
^-7
over its entire bandwidth. Such a bridge is a perfect tool to start investigating the ac transport properties of graphene in the quantum Hall regime.