Elimination of the feed-through effect in vortex flow transistors

Ketkar, M.A.; Beyer, J.B.; Nordman, J.E.; Hohenwarter, G.K.G.

doi:10.1109/20.133916

Cited by 4 publications

(6 citation statements)

References 6 publications

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“…The remaining ends of both the input line and output line are properly terminated. This arrangement yields a larger gain bandwith product than a cascade amplifier with the same number of devices without saturating any device (Ketkar et al 1991, McGinnis et al 1989). …”

Section: Superconducting Vft Distributed Amplifiermentioning

confidence: 99%

“…The capacitive feedthrough effect in a VFT has been identified as a major limiting factor for high frequency distributed amplifiers. In order to eliminate this effect, a balanced controlled VFT technique has been proposed by Ketkar et al (1991), which utilizes a pair of Josephson junctions connected in series and driven by a balanced control line which is excited in a push-pull manner. Figure I also illustrates the principle of the balanced controlled VFT.…”

Section: Superconducting Vft Distributed Amplifiermentioning

confidence: 99%

“…The FET is a high impedance voltage controlled current source; the VFT can be modelled as a low impedance current controlled voltage source. Likewise, the role of charge carriers (electrons) in the FET is replaced by fluxons in the VFT (Ketkar et al 1991, McGinnnis et al 1988b). The equivalent circuit for the VFT is shown in Fig.…”

Section: Output Characteristicmentioning

confidence: 99%

“…if the phase progression between devices is made equal in both lines, a wave on the input line excites a growing wave on the output line. The waves travelling in the Downloaded by [RMIT University] at 05:55 15 March 2015 (3.1) reverse direction are not in phase, and any uncancelled signal is absorbed by another termination of the output transmission line (Ketkar et al 1991).…”

Section: Output Characteristicmentioning

confidence: 99%

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Review of microwave distributed superconducting vortex-flow transistor amplifiers

Yalamanchili

Qiu

1992

International Journal of Electronics

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The dynamics of fluxons in the vortex flow transistor (VFT) has been much studied. The fluxon transit time determines the fundamental speed limit of operation. Since fluxons can travel at the velocity of electromagnetic waves in the junction, the VFT has the potential for operating in high frequency systems ('" 100 GHz). However, owing to the low input and output impedance of the VFT, use of the device in a conventional circuit would be quite limited. A distributed amplifier configuration consisting of many VFTs has been proposed to remedy the problems of low impedance levels. However, the realization of such an amplifier circuit at microwave or millimetre wave frequencies depends on obtaining a circuit model. In this paper, microwave superconducting VFT distributed amplifiers using the balanced control technique is reviewed. This kind of amplifier has the advantage that the capacitive feedthrough effect is decreased to a negligible extent. This is the major limiting factor for high frequency applications. The self-field effect which makes the current step inclined is reduced by injecting bias current only around the region of one end of the junction thus obtaining steeper 1-V characteristics. With the asymmetric geometry, the slope of the current step is about one hundred times steeper than those obtained with the conventional overlap geometry. Owing to the diamagnetic behaviour of the Josephson junction, a little of the magnetic field induced by the current in the control line is allowed to penetrate the junction. Thus, the transresistance rm of a VFT is very small. Some methods for maximizing r., and minimizing the output impedance r., also appear in this review. The feasibility of fabricating VFT distributed amplifiers using low-1;, superconducting material has been demonstrated. The power gain of the amplifier can be as high as 15dB with a flat frequency response. NotationI length of the junction c electromagnetic wave velocity in the junction v velocity of fluxon <1>0 flux quantum 4> phase difference between the two electrodes <1> magnetic flux J 0 maximum Josephson current (critical current) density 1 0 maximum Josephson current (critical current) I b bias current J b bias current density I m maximum microwave signal current I total tunnelling current Ie current in control line

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Section: Superconducting Vft Distributed Amplifiermentioning

confidence: 99%

Section: Superconducting Vft Distributed Amplifiermentioning

confidence: 99%

Section: Output Characteristicmentioning

confidence: 99%

Section: Output Characteristicmentioning

confidence: 99%

See 2 more Smart Citations

Review of microwave distributed superconducting vortex-flow transistor amplifiers

Yalamanchili

Qiu

1992

International Journal of Electronics

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“…This output resistance is extremely voltage dependent and the device has a very small useable voltage range. Consequently, we did not pursue the fabrication of an amplifier using this device A preliminary study was made by Ketkar of a second approach for overcoming feed-thru capacitance by use of a balanced device with push-pull excitation 5 . The equivalent circuit of such a device consists of a pair of VFT's in series driven by a balanced control line.…”

Section: B Modified Devices and The Distributed Amplifier Using Nb Tmentioning

confidence: 99%

Vortices in Long Josephson Junctions

Nordman¹,

Beyer²

1989

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Approved AD-A253 230 4JTATION PAGE0MB No 0704-0188 ( J ,I-.. te h t:ir-tcYn Of 'nirmj)on '.nj ccrm,',s a'r -,q I, -.rt, jrd-.', l C' 1v 't'er spe't Z;1 ! ABSTRACT (Maximum 200 words)This research involved the study of quantized flux lines or vortices in long, Josephson junction structures and in superconductive films in the context ofi: electronic device possibilities suggested by these structures. The work encompassed fabrication and low frequency electrical measurement of thin film device configuration coupled with physical device modeling. This was followed byl! high frequency parameter measurement and creation of circuit models for the' devices.In some cases these circuit models were used to model and optimize i specific circuits such as amplifiers or oscillators and, when warranted, prototypes' were frabicated and tested. The primary structures studied were the long Josephson I junction transistors, including the vortex flow transistor (VFT) and the superCIT., In addition, initial success with an exploratnry device using a single high Tc superconducting film, the SFFT, led to some concentration on circuit realizations,' with this device.Comparisons were made of these three devices which were i fabricated using a variety of thin film superconductors. SUBJECT TERMS NUMBER OF PAGES PRICE CODE SECURITY CLASSIFICATION SECURITY CLASSIFICATIC*" SECURITY CLASSIFICATION LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT UlL (UNLIMITED)NSN 7540-0'-280-5500 Standard Form 298 (Rev 2-89)P-1,cDen by ANfSI 'id Z31.-i

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Superconductive amplifying devices using fluxon dynamics

Nordman

1995

Supercond. Sci. Technol.

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Elimination of the feed-through effect in vortex flow transistors

Cited by 4 publications

References 6 publications

Review of microwave distributed superconducting vortex-flow transistor amplifiers

Review of microwave distributed superconducting vortex-flow transistor amplifiers

Vortices in Long Josephson Junctions

Superconductive amplifying devices using fluxon dynamics

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