Review of Josephson Waveform Synthesis and Possibility of New Operation Method by Multibit Delta-Sigma Modulation and Thermometer Code for Its Further Advancement

摘要

A method of AC waveform synthesis with quantum-mechanical accuracy has been developed on the basis of the Josephson effect in national metrology institutes, not only for its scientific interest but its potential benefit to industries. In this paper, we review the development of Josephson arbitrary waveform synthesizers based on the two types of Josephson junction array and their distinctive driving methods. We also discuss a new operation technique with multibit delta-sigma modulation and a thermometer code, which possibly enables the generation of glitch-free waveforms with high voltage levels. A Josephson junction array for this method has equally weighted branches that are operated by thermometer-coded bias current sources with multibit delta-sigma conversion.