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Electronics Letters

Frequency down-conversion in self-pumped HTS R-SQUID mixer

Jia Du, J.C. Macfarlane

Published Jun 22, 2011• 16 citations
Publisher

Abstract

A pair of high-temperature-superconducting (HTS) step-edge Josephson junctions connected in the ‘resistive-SQUID’ (R-SQUID) configuration has been previously shown to generate a heterodyne oscillation which is frequency-tunable by a control current across the resistor. A method is described which enables the R-SQUID to act both as the local oscillator (LO) and simultaneously as a radio- frequency down-converter element. For the first time the autonomous Josephson mixer–local oscillator device for signal frequencies between 1–5 GHz, over a temperature range of 20–70 K, is demonstrated.

DOI
10.1049/el.2011.0404

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A pair of high-temperature-superconducting (HTS) step-edge Josephson junctions connected in the ‘resistive-SQUID’ (R-SQUID) configuration has been previously shown to generate a heterodyne oscillation which is frequency-tunable by a control current across the resistor. A method is described which enables the R-SQUID to act both as the local oscillator (LO) and simultaneously as a radio- frequency down-converter element. For the first time the autonomous Josephson mixer–local oscillator device for signal frequencies between 1–5 GHz, over a temperature range of 20–70 K, is demonstrated.
Experimental evaluation of a high-temperature superconducting Josephson heterodyne mixer based on a 'resistive-SQUID' configuration is reported. The device consists of two YBa 2 Cu 3 O 7− x step-edge Josephson junctions connected via a small resistor in an otherwise superconducting loop. It has been previously shown to generate a heterodyne oscillation, which is frequency-tunable by a control current through the resistor. Under certain conditions, this device can operate as a frequency-tunable heterodyne mixer (down-converter) in the presence of an RF signal. In this paper, we describe the operation of the autonomous Josephson mixer–local oscillator device and present the experimental results on the mixer performances in terms of the junction current–voltage characteristics, the frequency tunability, linearity, and dynamic range as well as their temperature dependence for signal frequencies from 1 to 5 GHz.
We have recently developed a high-temperature superconducting (HTS) Josephson self-pumped mixer with an on-chip heterodyne local oscillator. The device is based on HTS step-edge junction technology and a “resistive-superconducting quantum interference device” (RSQUID) configuration. The heterodyne local oscillator and mixer output are frequency-tunable from below 10 MHz to 5 GHz by a control current. The performance of the autonomous Josephson mixer–local oscillator has been experimentally evaluated in terms of the current-voltage characteristics, intermediate frequency (IF)-tunable bandwidth, operation range, linearity, bias current, and temperature dependence of the IF output (or mixer conversion efficiency). We find the results are in good overall agreement with numerical simulation.
We report continuing investigations into practical applications of the AC Josephson effect as the basis for a voltage-tunable radio-frequency oscillator. We have previously demonstrated experimentally that useful power levels (10 s of nW) and linewidths of a few kHz can be achieved in the heterodyne output from a high-temperature-superconducting resistive SQUID (HTS-RSQUID) operating in the frequency range 1-50 MHz. Those results were achieved with 2-junction R-SQUIDs incorporating current-biased shunt resistors of a few micro-ohms. We have now modified the fabrication procedures, and adjusted the shunt resistors and bias current values so that higher frequencies can be achieved. The Josephson junctions are of step-edge type, rather than the bi-crystal type used in our earlier work. The step-edge technique permits much more flexibility in the geometrical lay-out and utilizes the more cost-effective single-crystal MgO substrates. In the present paper, we report numerical simulations and experimental measurements on these devices in the frequency range up to 2 GHz.
We report the experimental evaluation of a high-temperature superconducting (HTS) Josephson mixer. The mixer is fabricated from a HTS step-edge junction on MgO substrate. The mixer device operates as a lower side-band down-converter from a radio frequency between 6 and 10 GHz to a 1-2 GHz intermediate frequency under the action of a local oscillator. The experimental results of the current-voltage characteristics, optimal bias conditions, dynamic range, linearity, conversion gain, and the temperature dependence of the mixer are presented.
A high-temperature superconducting (HTS) terahertz (THz) heterodyne mixer based on a thin-film antenna-coupled YBa2Cu3O7-xstep-edge Josephson junction is presented. The frequency down-conversion from 0.6 THz to an intermediate frequency (IF) of 2 GHz was achieved using high-order harmonic mixing of a local oscillator (LO), thus removing the need to use a second THz source as the LO pumping source. The DC and RF characteristics of the harmonic mixer as well as the relationship of the IF output power versus the harmonic number were experimentally studied and compared with simulated results. Most of our measurements were made at 40 K, but we also observed stable harmonic mixing at 77 K which we believe has not been reported previously in HTS junction mixers.
A high-temperature superconducting (HTS) terahertz (THz) frequency down-converter or mixer based on a thin-film ring-slot antenna coupled YBa 2 Cu 3 O 7– x (YBCO)/MgO step-edge Josephson junction is reported. The frequency down-conversion was achieved using higher order harmonics of an applied lower frequency (19–40 GHz) local oscillator signal in the Josephson junction mixing with a THz signal of over 600 GHz, producing a 1–3 GHz intermediate frequency signal. Up to 31st order of harmonic mixing was obtained and the mixer operated stably at temperatures up to 77 K. The design details of the antenna, HTS Josephson junction mixer, the matching and isolation circuits, and the DC and RF performance evaluation are described in this paper.