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Electronics and Communications in Japan (Part II Electronics)

IF output characteristics of Josephson mixer

Keiichi Yamaguchi, Akira Kawaji, Katsumi Suzuki, Yoichi Enomoto, Shoji Tanaka

Published Mar 1, 1997• 10 citations

Abstract

The Josephson junction device is promising as a mixer for regions from millimeter wave to infrared. It is important to analyze Josephson devices to determine the circuit parameters and operating points of the circuits. However, it is difficult to analyze the mixer operation because of the nonlinear characteristic of the Josephson junction device. Therefore, small signal analysis has been conducted in characterizing the Josephson junction device. In this study, a detailed characterization of the IF output characteristic was obtained by introducing the concept of IF Shapiro steps. That is, it was determined that the minima that are not present in the local-oscillator Shapiro steps are present in the Josephson junction mixer output. In addition the impedance of the Josephson junction device was discussed and illustrated using a Smith chart. In this paper, the theoretical result was proved by a mixing experiment on the step-edge junction. As a result, the minima points in the IF output were confirmed. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 2, 80(3): 69–79, 1997

DOI: 10.1002/(sici)1520-6432(199703)80:3<69::aid-ecjb8>3.0.co;2-2

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IEEE Transactions on Microwave Theory and Techniques•Jan 1, 1995•3 citations

The Josephson junction device is promising as a mixer for regions from millimeter wave to infrared. It is important to analyze Josephson devices to determine the circuit parameters and operating points of the circuits. However, it is difficult to analyze the mixer operation because of the nonlinear characteristic of the Josephson junction device. Therefore, small signal analysis has been conducted in characterizing the Josephson junction device. In this study, a detailed characterization of the IF output characteristic was obtained by introducing the concept of IF Shapiro steps. That is, it was determined that the minima that are not present in the local-oscillator Shapiro steps are present in the Josephson junction mixer output. In addition the impedance of the Josephson junction device was discussed and illustrated using a Smith chart. In this paper, the theoretical result was proved by a mixing experiment on the step-edge junction. As a result, the minima points in the IF output were confirmed. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 2, 80(3): 69–79, 1997

Microwave superconducting mixers operating at 10–13 GHz utilizing Josephson junctions have been investigated analytically and experimentally. Measurements on mixer sensitivity were carried out at 13 GHz using waveguide-mounted experimental point-contact Josephson junctions at 4.2 K. Results showed sensitivities of −90 dBm/MHz (10−18 W/Hz) which included mismatch losses encountered in the waveguide structure. The Josephson junction mixing mechanism was analyzed on the basis of small-signal modulation of the staircase like dc I-V characteristics. It was shown that a small-signal microwave excitation results in an ac lateral shift of the regions between steps, such that: (a) Optimum Josephson mixing occurs halfway between steps. (b) Mixing occurs between all steps with maximum conversion efficiency between the zero and first step. (c) Predicted low conversion loss and possibly internal gain for a matched mixer. The analytical model was simulated by a digital computer and the behavior of the Josephson mixer predicted for various conditions of excitation. The model chosen for the analysis and the computer simulation is based on the simplest assumptions concerning bulk-formed Josephson junctions. In the laboratory an external local oscillator set 60 MHz below the signal frequency was used to induce the well-known step structure in the dc I-V characteristic of the point-contact Josephson junction. Mixing of the Lo and signal was found to occur between constant voltage steps in agreement with both analysis and computer simulation. The correctness of the model is demonstrated by the agreement between the theory and experiment.

Characteristics of the K-band microwave mixing using a YBaCuO step-edge microbridge Josephson junction were systematically investigated, and the optimum bias conditions were experimentally determined. A large intermediate frequency (IF) output signal was observed at every midway between the Shapiro steps, and the maximum IF output was obtained between the 0th and 1st steps (0-1) for the local oscillation (LO) power level of I 0/I c=0.2-0.3 (absolute LO power of -49.9 dBm). The maximum conversion efficiency was estimated to be -26.6 dB. Although the IF output (0-1) was observed for a wide range of LO power, it vanished or decreased radically under some peculiar conditions (I 0/I c?0 and ?(I 0/I c)/?I LO?0). These characteristics were qualitatively accounted for by the basic Josephson-mixing theory.

Harmonic mixing characteristics in thin-film YBa2Cu3O7-x (YBCO) Josephson junctions fabricated using photolithography were examined at the liquid nitrogen temperature (77 K) using 94 GHz millimeter wave radiation. As a result, a mixing signal (IF output) was obtained up to the harmonic number of 55 in harmonic mixing using the local oscillation (LO) wave as the microwave. The output strongly depended on the power of the LO and signal waves, and on the Shapiro step spacing induced by the LO wave. The IF output decreased in proportion to N -2 in the lower harmonic number region. However, the rate of decrease increased with an increase in the harmonic number.

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.

Abstract The Josephson junction is an oscillator driven by constant current. Therefore, the integrated device of the weak‐link type Josephson junction for detecting electromagnetic waves using the junction as a local oscillator can be considered. The superconducting device proposed by Likharev based on this concept is the Josephson triode consisting of three Josephson junctions. This paper describes the analysis of the Josephson triode which is the superconducting device for the heterodyne detection. First, the static characteristics are analyzed by use of the equivalent circuit and the fundamental equations. The necessary conditions for the normal resistances are derived. It is shown by numerical analysis that the millimeter wave heterodyne detection characteristics of the triode are identical with the theory and experiment for a tunnel junction. Moreover, the results analyzed numerically can be explained by analytical considerations and the simplified equivalent circuit of the Josephson triode is derived. The relations between the intermediate frequency output power and the local oscillator power are represented analytically via the simplified equivalent circuit of the triode.