LAUSR

Differential sampling relative to a Josephson waveform, the ac quantum voltmeter (ac-QVM), has been established as the most accurate method for measuring signals below 1 kHz with an uncertainty of 1 part in 108 (k = 1) for 1 V at 250 Hz. Commercial ac-QVMs provide accuracies of about 1 part in 106 up to frequencies of 2 kHz. Here we present a new sub-sampling technique to extend the frequency range of an ac-QVM up to 100 kHz. The measurement results at 1 V RMS amplitude agree well within 5 µV V−1 (k = 1) with the nominal voltage values for all frequencies from 500 Hz to 100 kHz. Two different analogue-to-digital converters are compared, sampling techniques, error sources and corrections as well as detailed uncertainty estimations are discussed.