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

IEEE Transactions on Applied Superconductivity

Design and Operation of a Double-Flux-Quantum Amplifier Excluding Flux Bias Lines

Yoshinao Mizugaki, Tomoki Watanabe

Published May 10, 2016• 2 citations
Publisher

Abstract

In addition to their fast switching with low power dissipation, precise voltage generation is a unique feature of single-flux-quantum (SFQ) circuits. This feature is attractive for realizing ac voltage standards consisting of SFQ-based digital-to-analog converters (DACs). Among several key components in SFQ-based DACs, a double-flux-quantum amplifier (DFQA) is a potential candidate to amplify the output voltage. In this paper, we present a redesigned DFQA without flux bias lines. We found a parameter set that provided wide bias margins and zero-flux-bias operation. Improved bias regions were numerically demonstrated, whereas a ±20-fold DFQA excluding flux biases was fabricated using Nb integration technology and tested in a liquid helium bath.

DOI
10.1109/tasc.2016.2565602

Related papers

Single-Flux-Quantum Bipolar Digital-to-Analog Converter Comprising Polarity-Switchable Double-Flux-Quantum Amplifier

Yoshinao Mizugaki, Tomoki Watanabe, Hiroshi Shimada

We present a single-flux-quantum (SFQ)-based digital-to-analog converter (DAC) generating bipolar output voltages, in which the key component is a polarity-switchable double-flux-quantum amplifier (PS-DFQA). The DAC comprised a dc/SFQ converter, an 8-bit variable pulse-number multiplier (PNM), and a ±8-fold PS-DFQA integrated on a single chip. SFQ pulse-frequency modulation was employed to realize variable output voltage amplitude, for which the multiplication factor of the variable-PNM was controlled by a commercial data generator situated at room temperature. The variable-PNM realized 8-bit resolution with a multiplication factor between 0 and 255. Bias currents fed to the ±8-fold PS-DFQA were polarity switched in synchronization with the digital code for the variable-PNM. The whole circuits including I/O elements were designed using SFQ cell libraries, and fabricated using a niobium integration process. Sinusoidal bipolar voltage waveform of 0.38 mVpp was demonstrated using a reference signal source of 43.94 MHz.

IEEE Transactions on Applied Superconductivity•Nov 7, 2016•2 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

Superconducting bipolar digital-to-analog converter equipped with dual double-flux-quantum amplifier

Yoshinao Mizugaki, Tomoki Watanabe, Hiroshi Shimada

Precise voltage generation is a unique feature of superconducting single-flux-quantum (SFQ) circuits, and hence, several SFQ-based digital-to-analog converters (DACs) have been designed for metrological applications. In this letter, we propose a dual double-flux-quantum amplifier (dual-DFQA) that extends DAC output voltage from unipolar to bipolar. An SFQ-based DAC comprising a 4-bit variable pulse number multiplier and a ±20-fold dual-DFQA is fabricated using a niobium integration technology. A 1-kHz, ±0.29-mV sinusoidal voltage waveform is successfully synthesized.

IEICE Electronics Express•Jan 1, 2016•5 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

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

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
In addition to their fast switching with low power dissipation, precise voltage generation is a unique feature of single-flux-quantum (SFQ) circuits. This feature is attractive for realizing ac voltage standards consisting of SFQ-based digital-to-analog converters (DACs). Among several key components in SFQ-based DACs, a double-flux-quantum amplifier (DFQA) is a potential candidate to amplify the output voltage. In this paper, we present a redesigned DFQA without flux bias lines. We found a parameter set that provided wide bias margins and zero-flux-bias operation. Improved bias regions were numerically demonstrated, whereas a ±20-fold DFQA excluding flux biases was fabricated using Nb integration technology and tested in a liquid helium bath.
We present a single-flux-quantum (SFQ)-based digital-to-analog converter (DAC) generating bipolar output voltages, in which the key component is a polarity-switchable double-flux-quantum amplifier (PS-DFQA). The DAC comprised a dc/SFQ converter, an 8-bit variable pulse-number multiplier (PNM), and a ±8-fold PS-DFQA integrated on a single chip. SFQ pulse-frequency modulation was employed to realize variable output voltage amplitude, for which the multiplication factor of the variable-PNM was controlled by a commercial data generator situated at room temperature. The variable-PNM realized 8-bit resolution with a multiplication factor between 0 and 255. Bias currents fed to the ±8-fold PS-DFQA were polarity switched in synchronization with the digital code for the variable-PNM. The whole circuits including I/O elements were designed using SFQ cell libraries, and fabricated using a niobium integration process. Sinusoidal bipolar voltage waveform of 0.38 mVpp was demonstrated using a reference signal source of 43.94 MHz.
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.
Precise voltage generation is a unique feature of superconducting single-flux-quantum (SFQ) circuits, and hence, several SFQ-based digital-to-analog converters (DACs) have been designed for metrological applications. In this letter, we propose a dual double-flux-quantum amplifier (dual-DFQA) that extends DAC output voltage from unipolar to bipolar. An SFQ-based DAC comprising a 4-bit variable pulse number multiplier and a ±20-fold dual-DFQA is fabricated using a niobium integration technology. A 1-kHz, ±0.29-mV sinusoidal voltage waveform is successfully synthesized.
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.
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.
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.