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Superconductor Science and Technology

Integrated microwave circuits for digital-to-analogue converters based on high-temperature superconducting Josephson junction arrays

Alexander M. Klushin, C. Weber, M. Siegel, S. I. Borovitskii, R.K. Starodubrovskii, K. Yu. Platov, M. Yu. Kupriyanov, R. Semerad

Published Nov 1, 1999• 2 citations
Publisher

Abstract

A digital-to-analogue converter based on series arrays of high-temperature superconducting Josephson junctions can work properly when the microwave bias current distribution in large arrays is uniform. Unfortunately, the considerable microwave attenuation per overdamped junction with normal resistances RN0.1 results in a strong total attenuation of the microwave signal in a traditional layout. Also, the meander geometry of the array, necessary when using bicrystal junctions, disturbs the uniformity of the rf current, especially in the millimetre waveband. To overcome these drawbacks we coupled the meander array inductively to a parallel transmission line. The mechanism of microwave coupling in which both external and mutual frequency locking takes place was studied numerically. A circuit with a coplanar waveguide feed line was fabricated and successfully tested at an operating frequency of 30 GHz. A microstrip line with a small attenuation for pumping of junction arrays at frequencies up to 120 GHz was demonstrated.

DOI
10.1088/0953-2048/12/11/304

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A digital-to-analogue converter based on series arrays of high-temperature superconducting Josephson junctions can work properly when the microwave bias current distribution in large arrays is uniform. Unfortunately, the considerable microwave attenuation per overdamped junction with normal resistances RN0.1 results in a strong total attenuation of the microwave signal in a traditional layout. Also, the meander geometry of the array, necessary when using bicrystal junctions, disturbs the uniformity of the rf current, especially in the millimetre waveband. To overcome these drawbacks we coupled the meander array inductively to a parallel transmission line. The mechanism of microwave coupling in which both external and mutual frequency locking takes place was studied numerically. A circuit with a coplanar waveguide feed line was fabricated and successfully tested at an operating frequency of 30 GHz. A microstrip line with a small attenuation for pumping of junction arrays at frequencies up to 120 GHz was demonstrated.
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High-Tc Josephson junction arrays with coupling by superconducting short- circuited (5 µm wide and 0.1 µm thick) coupled microstrip lines, provided dc bias in parallel, were fabricated on bicrystal sapphire substrates for experimental investigation of the phase- locking phenomenon. Josephson self radiation, emitted by the array was measured by an external 90 GHz receiver for different applied dc magnetic fields. The numerical simulation of array shows that strong interaction between Josephson junctions and the standing waves within structure require small enough damping α≤ 10 -3 per coupling section for reduction of Josephson oscillation linewidth.