Characterization of a high-resolution analog-to-digital converter with a Josephson AC voltage source

A Josephson AC voltage source was employed to characterize the dynamic behavior of a high-resolution 28-bit (8.5-digit) integrating analog-to-digital converter of a digital sampling voltmeter (DSV), which is widely used in AC metrology at the Physikalisch-Technische Bundesanstalt. Extensive measurements were carried out to validate previous mathematical models of the DSV when sampling AC signals. The characterization method is based on the discrete Fourier transform applied on sampled data of the ADC and on the known Josephson plateau values for quantifying the ratio of AC quantities and the nonlinearities of the DSV. The method shown allows considerable improvement of the accuracy of sampling techniques at low frequencies (DC up to some kilohertz) to be attained.