Quantum-referenced voltage waveform synthesiser

A synthesiser of low-frequency voltage waveforms with absolute voltage accuracy is described, optimised for the calibration of measurement devices near power-line frequencies. The synthesis of a low-pass-filtered piecewise waveform from a conventional digital-to-analogue converter is controlled using the comparison with a second piecewise waveform, synthesised using the Josephson effect. A specially constructed amplifier is described, together with the controlling algorithm. The measurement of the ac/dc difference and direct ac calibration of a voltmeter is reported together with the level of agreement with the thermal transfer traceability route at the μV/V level.