Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Japanese Journal of Applied Physics

Input–output characteristics of a 999-stage double-flux-quantum amplifier designed for 1000-fold voltage multiplication

Yoshinao Mizugaki, Yusuke Sato, Hiroshi Shimada, Masaaki Maezawa

Published Apr 22, 2014• 12 citations
Publisher

Abstract

We evaluate the input–output characteristics of a 1000-fold voltage multiplier designed for single-flux-quantum (SFQ) digital-to-analog converters. The voltage multiplication is based on the double-flux-quantum amplifier (DFQA) that was originally proposed by Herr in 2005. We have designed and fabricated a 999-stage DFQA using a Nb/AlO x /Nb integration technology. In experiments, we have used two methods of feeding the input SFQ pulse train. The one is an overbiasing method, i.e., the input SFQ pulse train is generated at an overbiased input junction. A 1000-fold voltage multiplication with errors less than ±1% has been confirmed for input voltages of up to 27 µV, of which the corresponding Josephson frequency is 13 GHz. In the other method, a dc/SFQ converter is used for feeding the input SFQ pulse train. A 1000-fold voltage multiplication with an error of −0.03% has been obtained for an input frequency of 600 MHz, of which the corresponding Josephson voltage is 1.2 µV. In experiments, errors in measured voltages are likely to limit the accuracy in evaluation of the multiplication factor.

DOI
10.7567/jjap.53.053101

Related papers

1000-Fold Double-Flux-Quantum Voltage Multiplier Employing Directional Propagation of Flux Quanta Through Asymmetrically Damped Junction Branches

Yoshinao Mizugaki, Yuma Arai, Tomoki Watanabe +1 more

Precise voltage generation is a unique feature of single-flux-quantum (SFQ) circuits, in addition to their high-speed digital signal processing with low power consumption. We investigated SFQ pulse-frequency modulation D/A converters for metrological applications. In our SFQ-based D/A converters, the maximum output voltage is determined by the maximum SFQ pulse-frequency at the pulse number multiplier, and by the voltage multiplication factor at the voltage multiplier. In this study, we present our new design for a double-flux-quantum amplifier (DFQA) that works as a quantum voltage multiplier. In the new parameter set, we tuned the damping parameters of the Josephson junctions to realize proper propagation of SFQ pulses. A 1000-fold DFQA designed with the new parameter set was fabricated using a 25-μ A/μ m2Nb/AlOx/Nb integration technology. A 1000-fold voltage multiplication was confirmed for the input voltage up to 43 μV, with a corresponding SFQ repetition frequency of 21 GHz. That is, the output voltage reached 43 mV.

IEEE Transactions on Applied Superconductivity•Feb 13, 2019•5 citations

Design and Operation of 1000-fold Voltage Multiplier based on Double-flux-quantum Amplifier

Yusuke Sato, Masataka Moriya, Hiroshi Shimada +2 more

Rapid-single-flux-quantum digital-to-analogue converters (RSFQ-DACs) are now under development for ac voltage standard applications. The voltage multiplier (VM), which precisely amplifies the input voltage, is a key component for RSFQ-DACs. Because the amount of bias current for a conventional VM increases in proportion to its multiplication factor, we have been looking for a VM device which is operated on a different principle. In this paper, we report our design of a 1000-fold VM comprising double flux quantum amplifiers (DFQAs) of which the amount of bias current is independent of its multiplication factor. Test circuits were fabricated using a 2.5 kA/cm2 Nb process. We confirm that the experimental results demonstrate the 1000-fold operation up to 13.2 GHz input SFQ pulse repetition frequency.

Physics Procedia•Jan 1, 2013•14 citations

Modified Double-Flux-Quantum Amplifier for Bipolar Voltage Multiplication

Tomoki Watanabe, Hiroshi Shimada, Yoshinao Mizugaki

Single-flux-quantum (SFQ) circuits can generate highly accurate average voltage. We have developed SFQ digital-to-analog converters (DACs) for application of new ac voltage standards. In this paper, we present a bipolar voltage amplifier (BVA) based on a double flux quantum amplifier (DFQA) for generation of intrinsic bipolar voltage in an SFQ-DAC. The BVA realizes the identical multiplication factors for the positive and negative output, whereas the conventional DFQA has different multiplication factors in the bipolar output. The BVA can be used for the output stage of the SFQ- DAC. We have designed a 19-fold BVA and confirmed that the 19-fold BVA operated for input frequency of up to 31.2 GHz in positive voltage output and 33.6 GHz in negative voltage output.

IEEE International Superconductive Electronics Conference (ISEC)•Jul 1, 2015•4 citations

Enhanced operation frequencies of bipolar double-flux-quantum amplifiers fabricated using 10 kA cm −2 Nb/AlO x /Nb integration process

Yuta Somei, Hiroshi Shimada, Yoshinao Mizugaki

Abstract We have demonstrated digital-to-analog (D/A) operations using single-flux-quantum (SFQ) pulse-frequency modulation (PFM) D/A converters for future AC voltage standards. In this paper, for the improvement of SFQ-PFM D/A converters, we investigated a double-flux-quantum amplifier (DFQA) and a magnetically-coupling SFQ driver/receiver circuit (MC-SFQ-DR) fabricated using a 10 kA cm −2 Nb/AlO x /Nb integration process. The critical current density J c of 10 kA cm −2 was four times larger than that of the integration process we had used. A DFQA and an MC-SFQ-DR included unshunted Josephson junctions, and therefore, it was unclear if the high- J c process improved their performances. We measured test chips cooled in a liquid helium bath. The maximum input voltages for a +20 fold and a −20 fold DFQA were 147 and 126 μ V, for which the corresponding Josephson frequencies were 70.9 and 61.1 GHz. It was confirmed that the operation frequencies of the DFQAs and MC-SFQ-DR were improved approximately two-fold.

Japanese Journal of Applied Physics•May 24, 2021•6 citations

A double-flux-quantum amplifier with a single flux-biasing line

Yuma Arai, Yoshiaki Urai, Tomoki Watanabe +3 more

A Double-Flux-Quantum (DFQ) amplifier can multiply its input voltage with quantum accuracy using DFQ generation at under-damped Josephson junctions. We conducted research on digital-to-analogue converters that were implemented using DFQ amplifiers for metrological applications. Conventional DFQ amplifiers were usually operated using two flux-biasing lines. In this study, we redesigned the circuit layout to realize operation using a single flux-biasing line. We designed a new layout of a 20-fold DFQ amplifier and fabricated it using a 2.5-kA/cm 2 Nb/AlO x /Nb process. The measurement was performed in liquid He. The Single-Flux-Quantum (SFQ) pulse train was fed using an over-biasing method, and the input-output characteristics are acquired using an oscilloscope. When the magnetic flux bias current I fb1 was not supplied, the maximum input voltage V inmax was 68 μV, which was 4.2 times larger than the value of 17 μV that was observed in our previous study. V inmax was enhanced to 120 μV when we supplied an I fb1 of 1.00 mA.

Journal of Physics Conference Series•Jul 1, 2018•2 citations

Thermally-fluctuated single-flux-quantum pulse intervals reflected in input-output characteristics of a double-flux-quantum amplifier

Yoshinao Mizugaki, Yoshiaki Urai, Hiroshi Shimada

A double-flux-quantum amplifier (DFQA) is a voltage multiplier of quantum accuracy, which we have employed at the final stage of a single-flux-quantum (SFQ) digital-to-analog converter (DAC). We recently found that experimental input–output (IO) characteristics of DFQAs were always slightly different from numerical results assuming ideally-periodic SFQ pulse trains. That is, experimental IO characteristics obtained using an over-biasing method were gradually deteriorated near their maximum operation voltages. Numerical simulation including the over-biasing method at a finite temperature suggested that the difference was likely to be attributed to thermally-fluctuated intervals of input SFQ pulses.

Journal of Physics Conference Series•Jul 1, 2017•3 citations
We evaluate the input–output characteristics of a 1000-fold voltage multiplier designed for single-flux-quantum (SFQ) digital-to-analog converters. The voltage multiplication is based on the double-flux-quantum amplifier (DFQA) that was originally proposed by Herr in 2005. We have designed and fabricated a 999-stage DFQA using a Nb/AlO x /Nb integration technology. In experiments, we have used two methods of feeding the input SFQ pulse train. The one is an overbiasing method, i.e., the input SFQ pulse train is generated at an overbiased input junction. A 1000-fold voltage multiplication with errors less than ±1% has been confirmed for input voltages of up to 27 µV, of which the corresponding Josephson frequency is 13 GHz. In the other method, a dc/SFQ converter is used for feeding the input SFQ pulse train. A 1000-fold voltage multiplication with an error of −0.03% has been obtained for an input frequency of 600 MHz, of which the corresponding Josephson voltage is 1.2 µV. In experiments, errors in measured voltages are likely to limit the accuracy in evaluation of the multiplication factor.
Precise voltage generation is a unique feature of single-flux-quantum (SFQ) circuits, in addition to their high-speed digital signal processing with low power consumption. We investigated SFQ pulse-frequency modulation D/A converters for metrological applications. In our SFQ-based D/A converters, the maximum output voltage is determined by the maximum SFQ pulse-frequency at the pulse number multiplier, and by the voltage multiplication factor at the voltage multiplier. In this study, we present our new design for a double-flux-quantum amplifier (DFQA) that works as a quantum voltage multiplier. In the new parameter set, we tuned the damping parameters of the Josephson junctions to realize proper propagation of SFQ pulses. A 1000-fold DFQA designed with the new parameter set was fabricated using a 25-μ A/μ m2Nb/AlOx/Nb integration technology. A 1000-fold voltage multiplication was confirmed for the input voltage up to 43 μV, with a corresponding SFQ repetition frequency of 21 GHz. That is, the output voltage reached 43 mV.
Rapid-single-flux-quantum digital-to-analogue converters (RSFQ-DACs) are now under development for ac voltage standard applications. The voltage multiplier (VM), which precisely amplifies the input voltage, is a key component for RSFQ-DACs. Because the amount of bias current for a conventional VM increases in proportion to its multiplication factor, we have been looking for a VM device which is operated on a different principle. In this paper, we report our design of a 1000-fold VM comprising double flux quantum amplifiers (DFQAs) of which the amount of bias current is independent of its multiplication factor. Test circuits were fabricated using a 2.5 kA/cm2 Nb process. We confirm that the experimental results demonstrate the 1000-fold operation up to 13.2 GHz input SFQ pulse repetition frequency.
Single-flux-quantum (SFQ) circuits can generate highly accurate average voltage. We have developed SFQ digital-to-analog converters (DACs) for application of new ac voltage standards. In this paper, we present a bipolar voltage amplifier (BVA) based on a double flux quantum amplifier (DFQA) for generation of intrinsic bipolar voltage in an SFQ-DAC. The BVA realizes the identical multiplication factors for the positive and negative output, whereas the conventional DFQA has different multiplication factors in the bipolar output. The BVA can be used for the output stage of the SFQ- DAC. We have designed a 19-fold BVA and confirmed that the 19-fold BVA operated for input frequency of up to 31.2 GHz in positive voltage output and 33.6 GHz in negative voltage output.
Abstract We have demonstrated digital-to-analog (D/A) operations using single-flux-quantum (SFQ) pulse-frequency modulation (PFM) D/A converters for future AC voltage standards. In this paper, for the improvement of SFQ-PFM D/A converters, we investigated a double-flux-quantum amplifier (DFQA) and a magnetically-coupling SFQ driver/receiver circuit (MC-SFQ-DR) fabricated using a 10 kA cm −2 Nb/AlO x /Nb integration process. The critical current density J c of 10 kA cm −2 was four times larger than that of the integration process we had used. A DFQA and an MC-SFQ-DR included unshunted Josephson junctions, and therefore, it was unclear if the high- J c process improved their performances. We measured test chips cooled in a liquid helium bath. The maximum input voltages for a +20 fold and a −20 fold DFQA were 147 and 126 μ V, for which the corresponding Josephson frequencies were 70.9 and 61.1 GHz. It was confirmed that the operation frequencies of the DFQAs and MC-SFQ-DR were improved approximately two-fold.
A Double-Flux-Quantum (DFQ) amplifier can multiply its input voltage with quantum accuracy using DFQ generation at under-damped Josephson junctions. We conducted research on digital-to-analogue converters that were implemented using DFQ amplifiers for metrological applications. Conventional DFQ amplifiers were usually operated using two flux-biasing lines. In this study, we redesigned the circuit layout to realize operation using a single flux-biasing line. We designed a new layout of a 20-fold DFQ amplifier and fabricated it using a 2.5-kA/cm 2 Nb/AlO x /Nb process. The measurement was performed in liquid He. The Single-Flux-Quantum (SFQ) pulse train was fed using an over-biasing method, and the input-output characteristics are acquired using an oscilloscope. When the magnetic flux bias current I fb1 was not supplied, the maximum input voltage V inmax was 68 μV, which was 4.2 times larger than the value of 17 μV that was observed in our previous study. V inmax was enhanced to 120 μV when we supplied an I fb1 of 1.00 mA.
A double-flux-quantum amplifier (DFQA) is a voltage multiplier of quantum accuracy, which we have employed at the final stage of a single-flux-quantum (SFQ) digital-to-analog converter (DAC). We recently found that experimental input–output (IO) characteristics of DFQAs were always slightly different from numerical results assuming ideally-periodic SFQ pulse trains. That is, experimental IO characteristics obtained using an over-biasing method were gradually deteriorated near their maximum operation voltages. Numerical simulation including the over-biasing method at a finite temperature suggested that the difference was likely to be attributed to thermally-fluctuated intervals of input SFQ pulses.