The article studies the current state and prospects for the development of broadband digital frequency synthesisers with low phase noise based on superconducting logic elements and arrays of Josephson junctions. It is shown that current developments are progressing along three complementary lines: large-amplitude metrological JAWS systems, microwave and VHF RF-JAWS with integrated cryogenic filters, and digital RSFQ/xSFQ/xeSFQ spectrum shaping systems. The main unresolved problems are highlighted: parasitic leakage of the control signal to the output, dispersion and non-uniform excitation of long arrays, the complexity of scaling the digital front-end, and the lack of built-in self-calibration of the quantum capture mode. A hybrid DDSJAWS architecture is proposed, combining a multiphase or clock-free SFQ front-end, a segmented JAWS output array, a differential mirror compensation path, and an embedded low-frequency QLR self-calibration. Mathematical models are presented for estimating the residual phase shift in the segmented array, the noise transfer function of a band-pass delta-sigma modulator, and the reduction of the quantum capture operating area.
Новак et al. (Tue,) studied this question.