Design of delta-sigma feedback loop for quantum voltage digitizer

A system utilizing a delta-sigma (DS) feedback loop to digitize an arbitrary voltage waveform in terms of the quantum-accurate output of a Josephson junction array (JJA) has been designed. Using commercially available components, a first order DS loop has been constructed and tested with direct feedback. At a sample rate of 20 MHz a signal to noise ratio of <; 10
⁴
was demonstrated.