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Superconductor Science and Technology

Design and operation of a series array of voltage doubler cells for rapid-single-flux-quantum digital-to-analog converters

Yoshinao Mizugaki, Yoko Namatame, Masaaki Maezawa

Published Oct 18, 2007• 8 citations
Publisher

Abstract

The output voltage of a rapid-single-flux-quantum digital-to-analog converter (RSFQ-DAC) is generated with a voltage multiplier (VM) that comprises multiple voltage mirror cells. We have demonstrated a new operation mode of a voltage mirror cell. It is a second-mode operation that doubles the input voltage, like the second-order Shapiro step. That is, a single cell works as a voltage doubler (VD). In this work, we propose a new parameter set of the VD (VD revision 1: VDr1) that improves the tolerance for multi-stage operation. Experimental results of a 16-stage VDr1 circuit are presented.

DOI
10.1088/0953-2048/20/11/s03

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IEEE Transactions on Applied Superconductivity•Nov 7, 2016•2 citations
The output voltage of a rapid-single-flux-quantum digital-to-analog converter (RSFQ-DAC) is generated with a voltage multiplier (VM) that comprises multiple voltage mirror cells. We have demonstrated a new operation mode of a voltage mirror cell. It is a second-mode operation that doubles the input voltage, like the second-order Shapiro step. That is, a single cell works as a voltage doubler (VD). In this work, we propose a new parameter set of the VD (VD revision 1: VDr1) that improves the tolerance for multi-stage operation. Experimental results of a 16-stage VDr1 circuit are presented.
Digital-to-analog converters based on rapid single flux quantum circuits (RSFQ-D/A converters) are candidates for the next generation of ac voltage standard. We re-optimized the device parameters of a voltage multiplier (VM) cell, one of the important components in the RSFQ-D/A converter, to implement a new voltage doubler (VD) cell. The output voltage of the VD cell was twice as high as that of the conventional VM cell. We fabricated VD cells using a Nb technology. We confirmed correct operation of the VD cells at input frequencies up to 30 GHz.
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.
We are developing a digital-to-analog (D/A) converter based on rapid single flux quantum (RSFQ) logic circuits. Since the RSFQ D/A converter operates according to the Josephson frequency–voltage relationship, arbitrary waveforms can be synthesized with an accuracy equivalent to that of the Josephson dc voltage standard. We have examined the characteristics of magnetically coupled voltage multipliers (VMs). The VM is a key component in the RSFQ D/A converter for use in metrological applications.
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.
Digital to analog converters based on the Josephson effect are promising for voltage standards, because they produce voltage steps with ultimate precision and stability. In this paper, we describe a project to develop a Josephson D/A converter designed for synthesizing a sinusoidal waveform with metrological accuracy. The D/A converter is based on RSFQ (Rapid Single Flux Quantum) logic circuits, and consists of a frequency multiplier (FM), a pulse distributor (PD), and a number of voltage multipliers (VMs). Each VM circuit, corresponding to the n-th bit digital code, multiplies the number of SFQ pulses by a factor of 2/sup n/. By gating the input SFQ pulses from the FM to the VMs using the PD circuits, a programmable output voltage is obtained. Possible sources of uncertainties in the measurement of the rms value of the synthesized sine wave are discussed.
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.