Castellanos-Beltran Manuel A, Olaya D I, Sirois A J, Donnelly C A, Dresselhaus P D, Benz S P, Hopkins P F
National Institute of Standards and Technology, Boulder, CO 80305 USA.
National Institute of Standards and Technology, Boulder, CO 80305 USA, and also with the University of Colorado Boulder, Boulder, CO 80309 USA.
IEEE Trans Appl Supercond. 2021 Apr;31(3). doi: 10.1109/tasc.2021.3057013.
We designed, simulated, and experimentally demonstrated components for a microwave-frequency digital-to-analog converter based on single flux quantum (SFQ) circuits and an amplifier based on superconducting-quantum-interference-device (SQUID) stacks. These are key components for a self-calibrated programmable waveform reference for communications metrology capable of synthesizing high-frequency signals with quantum-based output accuracy. The amplifier is an SFQ voltage multiplier circuit that consists of a network of SFQ-splitters and SQUID transformers that provides output signals consisting of quantized pulses. The circuits were fabricated using our Josephson-junction (JJ) fabrication process, which produces self-shunted JJs with Nb-doped silicon barriers. In order to demonstrate quantum-based reproducibility, stability and performance at 4 K, we synthesized single-tone and multitone waveforms at gigahertz frequencies and demonstrated their operation over a range of synthesizer output and experimental bias parameters. We also propose circuit designs for achieving higher synthesis frequencies and higher output power with improved power accuracy and spectral purity, and discuss the potential limitations of these circuits.
我们设计、模拟并通过实验展示了基于单磁通量子（SFQ）电路的微波频率数模转换器组件，以及基于超导量子干涉器件（SQUID）堆栈的放大器。这些是用于通信计量的自校准可编程波形基准的关键组件，能够以基于量子的输出精度合成高频信号。该放大器是一个SFQ电压倍增电路，由SFQ分路器和SQUID变压器网络组成，可提供由量化脉冲组成的输出信号。这些电路是使用我们的约瑟夫森结（JJ）制造工艺制造的，该工艺可生产具有铌掺杂硅势垒的自分流JJ。为了展示在4K温度下基于量子的可重复性、稳定性和性能，我们在千兆赫兹频率下合成了单音和多音波形，并展示了它们在一系列合成器输出和实验偏置参数下的运行情况。我们还提出了用于实现更高合成频率和更高输出功率以及提高功率精度和频谱纯度的电路设计，并讨论了这些电路的潜在局限性。
