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Proceedings of the IEEE

Flux transfer devices

Y. Harada, W. Hioe, Eiichi Goto

Published Jan 1, 1989• 12 citations
Publisher

Abstract

Flux transfer device theory is reviewed. In such devices, generalized magnetic flux, defined as the time integral of voltage, is used to describe the device characteristics. The Josephson junction and inductor are the main circuit elements in flux transfer devices, because they maintain a constant value for the time integral of voltage. Flux transfer devices are based on either an RF SQUID (superconducting quantum interference device) or a fluxon device. Four devices, including the parametric quantron and the quantum flux parametron, are reviewed as applications of the RF SQUID. The fluxon feedback oscillator and a soliton device are also reviewed as applications of fluxon devices. The quantum flux parametron is then described. The parametron principle and the fundamental properties of the quantum flux parametron such as gain, switching speed, and power dissipation are discussed. Logic circuits and a memory cell are also reviewed. A novel analog-to-digital converter is proposed as an application of the quantum flux parametron.>

DOI
10.1109/5.34126

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Quantum flux parametron with magnetic flux regulator

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A magnetic flux regulator for a quantum flux parametron (QFP) is proposed. The regulator is formed with a parallel connection of a Josephson junction across activation inductors building an RF-SQUID (superconducting quantum interference device). This junction makes a nonlinear bypass channel for magnetic activation flux and contributes to regulation of applied flux and elimination of undesirable external noises. Using this flux regulator, the activation condition tolerance is not only improved, but also a higher speed transition from a nonactivated state to an activated state is expected. QFP operations with the regulators have been observed with integrated circuits.>

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A current amplifier design based on the principle of fluxon propagation in a multijunction exponential flux shuttle has been investigated. In this design, the critical current of the junctions is increased exponentially and the SQUID (superconducting quantum interference device) inductance is a Josephson-junction equivalent inductance. Current gain can be achieved by generating fluxons at the low end and dissipating them at the high end where the load is located. Advantages over other types of linear devices are discussed. Two parallel exponential flux shuttles can be used to duplicate flux from a high-inductance input coil to a low-inductance output. The device performance of the two circuits is evaluated by computer simulation, and noise performance is discussed.>

IEEE Transactions on Magnetics•Mar 1, 1989•1 citation
Flux transfer device theory is reviewed. In such devices, generalized magnetic flux, defined as the time integral of voltage, is used to describe the device characteristics. The Josephson junction and inductor are the main circuit elements in flux transfer devices, because they maintain a constant value for the time integral of voltage. Flux transfer devices are based on either an RF SQUID (superconducting quantum interference device) or a fluxon device. Four devices, including the parametric quantron and the quantum flux parametron, are reviewed as applications of the RF SQUID. The fluxon feedback oscillator and a soliton device are also reviewed as applications of fluxon devices. The quantum flux parametron is then described. The parametron principle and the fundamental properties of the quantum flux parametron such as gain, switching speed, and power dissipation are discussed. Logic circuits and a memory cell are also reviewed. A novel analog-to-digital converter is proposed as an application of the quantum flux parametron.>
A magnetic flux regulator for a quantum flux parametron (QFP) is proposed. The regulator is formed with a parallel connection of a Josephson junction across activation inductors building an RF-SQUID (superconducting quantum interference device). This junction makes a nonlinear bypass channel for magnetic activation flux and contributes to regulation of applied flux and elimination of undesirable external noises. Using this flux regulator, the activation condition tolerance is not only improved, but also a higher speed transition from a nonactivated state to an activated state is expected. QFP operations with the regulators have been observed with integrated circuits.>
Superconducting quantum interference devices (SQUIDs), single flux-quantum (SFQ) logic circuits, and quantum Josephson junction circuits have been developed into a family of superconductor integrated circuit, and are widely applied for subtle magnetic-field measurements, energy-efficient computing, and quantum computing, respectively. They are Josephson junction networks composed of Josephson junctions and normal resistor-inductor-capacitor (RLC) components, working with the fluxoid-quantization principle and Josephson effects to achieve unique flux-modulated dynamics and characteristics; they react to the vector potential of magnetic fields rather than the electric potential. However, the conventional circuit diagrams and nodal analysis methods focus on the electric charges flowing though branches and nodes, ignoring dynamics of the magnetic fluxes flowing from loop to loop. This article introduces a general flux-based circuit theory to unify the analyses of Josephson junction circuits and normal RLC circuits. This theory presents a magnetic-flux-generator (MFG) concept to unify Josephson junctions and normal circuit elements, and abstract both Josephson junction circuits and normal RLC circuits as MFG network; it derives a general network equation to describe dynamics of Josephson junction circuits, and invents a kind of magnetic-flux flow (MFF) diagram to depict the working principles of magnetic-flux flows inside Josephson junction circuits. The flux-based theory is complementary to the conventional circuit theories in the design and analysis of superconductor integrated circuits.
The dc and ac Josephson effects and the behavior of the current‐voltage characteristics of Josephson junctions are briefly reviewed. The Josephson junction cryotron is described. Two cryotrons have been incorporated into a NDRO memory cell with a switching time of 80ps, a power‐delay product of 10−16J, and an area of 900μm2. DRO memory cells involving the storage of a single flux quantum have estimated switching speeds of 50ps and a dissipation in continuous operation of 40nW. Latching logic elements with a switching time of 200ps and a power‐delay product of 5fJ have been built. Non‐latching devices and the flux shuttle are described. The use of dc and rf SQUIDS in conjunction with flux transformers for magnetic measurements is discussed. Presently achieved sensitivities are: magnetic field, 10−15THz−1/2, magnetic field gradient, 10−13Tm−1Hz−1/2; magnetic susceptibility, 2×10−11 e.m.u. for 1cm3 at 10−1T; voltage, 10−15VHz−1/2. The highest energy resolution reported for a SQUID‐transformer combination is 8×10−30 JHz−1 in a frequency range from 2×10−2Hz to 1kHz. At lower frequencies the noise power spectrum is 1/f. The performance of the computer and measuring devices is compared with that of conventional (non‐superconducting) devices.
Josephson junction circuits, such as superconducting quantum interference devices (SQUIDs) and single-flux-quantum circuits, have been successfully applied in both the analog and digital domains. Due to phase-based working principles, their analyses are not well supported by charge-based analysis methods and conventional circuit diagrams. This article introduces a type of magnetic-flux-flow (MFF) diagrams to simplify the design and analysis of Josephson junction circuits. MFF diagrams are the graphical expression of circuit equations derived by loop analysis methods. They vividly depict the functions of Josephson junctions and superconducting loops and visualize how Josephson junctions transfer flux quanta among superconducting loops. The applications of MFF diagrams in the design and analysis of typical Josephson junction circuits are demonstrated case by case; it is shown that MFF diagrams are complementary to conventional circuit diagrams for both Josephson junction circuits and normal electric circuits.
A flash-type superconducting A/D (analog/digital) converter is proposed. The basis low-frequency operation of this converter, which compromises a quantum flux parametron (QFP) and an RF SQUID (superconducting quantum interference device), has been observed. The RF SQUID consists of a Josephson junction and a load inductor which is part of the QFP. It converts an analog signal to period digital signals of one quantum flux (2.07*10/sup -5/ W-b) per cycle. The QFP works as both an amplifier and a comparator of the periodic digital signals, by adding an exciting signal. This A/D converter is expected to achieve high-speed operation of 20 GHz. Several 4-bit A/D converter circuits were fabricated, using the conventional Nb-Pb alloy process, with a junction size of 5 mu m*5 mu m and supercurrent density of 200 A/cm/sup 2/. Basic operation at 100 KHz was confirmed experimentally.>
A current amplifier design based on the principle of fluxon propagation in a multijunction exponential flux shuttle has been investigated. In this design, the critical current of the junctions is increased exponentially and the SQUID (superconducting quantum interference device) inductance is a Josephson-junction equivalent inductance. Current gain can be achieved by generating fluxons at the low end and dissipating them at the high end where the load is located. Advantages over other types of linear devices are discussed. Two parallel exponential flux shuttles can be used to duplicate flux from a high-inductance input coil to a low-inductance output. The device performance of the two circuits is evaluated by computer simulation, and noise performance is discussed.>