Zero-Compensation Method and Reduced Inductive Voltage Error for the AC Josephson Voltage Standard

In the pulse-driven ac Josephson voltage standard, the low frequency (LF) component of a drive signal increases the system complexity and induces unwanted voltages through on-chip inductances. A novel zero compensation (ZC) method for pulse-driven ac waveform synthesis is presented in this paper. A pulse train is obtained through a two-level Δ-Σ modulation and then reconstructed by replacing each pulse with three pulses of a negative-positive-negative pattern. The amplitudes of the reconstructed pulse train are carefully adjusted so that the positive pulses drive the Josephson junctions to the first quantum state, whereas the negative pulses keep the junctions on the zero quantum state and cancel the contribution of the positive pulses to the LF inductive voltage component. This new method eliminates the need for LF signal reinjection required by the conventional bias method and eliminates the need for a direct-current bias required by the recently proposed ZC method. An 8-kHz sinusoidal waveform with an amplitude of 1 mV rms is synthesized to demonstrate the feasibility of the approach. We also demonstrate that the inductive voltage error is significantly reduced for waveforms synthesized with the new method.