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IEEE Transactions on Magnetics

Experimental implementation of analog-to-digital converter based on the reversible ripple counter

Lyudmila V. Filippenko, V. K. Kaplunenko, M. Khabipov, V. P. Koshelets, Konstantin K. Likharev, Oleg A. Mukhanov, Sergey V. Rylov, Vasili K. Semenov, Alexander N. Vystavkin

Published Mar 1, 1991• 31 citations
Publisher

Abstract

A new A/D converter which includes a comparator, and a reversible binary counter with DC outputs has been designed, fabricated, and tested. The comparator generates two trains of the single-flux-quantum (SFQ) pulses in response to increasing or decreasing input signal. The pulses are transferred through SFQ transmission lines to the adding and diminishing inputs of a reversible counter. The reversible counter has been realized by supplementing the usual counter with the SFQ transmission lines, splitters; and confluence elements for sending diminished pulses directly to each bit. Nondestructive read-out of the counter contents is carried out by SFQ/DC converters connected to each counter bit. The integrated circuit is fabricated using 5- mu m Nb-AlO/sub x/-Nb Josephson junction technology with a critical current density about 500 A/cm/sup 2/. External Mo shunts of the junctions provide the value of beta /sub c/<or=1 and I/sub c/R approximately=300 mu V. The A/D conversion is studied for low-frequency signals with an external clock. High-frequency performance of the reversible counter has been tested.

DOI
10.1109/20.133718

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A new A/D converter which includes a comparator, and a reversible binary counter with DC outputs has been designed, fabricated, and tested. The comparator generates two trains of the single-flux-quantum (SFQ) pulses in response to increasing or decreasing input signal. The pulses are transferred through SFQ transmission lines to the adding and diminishing inputs of a reversible counter. The reversible counter has been realized by supplementing the usual counter with the SFQ transmission lines, splitters; and confluence elements for sending diminished pulses directly to each bit. Nondestructive read-out of the counter contents is carried out by SFQ/DC converters connected to each counter bit. The integrated circuit is fabricated using 5- mu m Nb-AlO/sub x/-Nb Josephson junction technology with a critical current density about 500 A/cm/sup 2/. External Mo shunts of the junctions provide the value of beta /sub c/<or=1 and I/sub c/R approximately=300 mu V. The A/D conversion is studied for low-frequency signals with an external clock. High-frequency performance of the reversible counter has been tested.
A new generation of the Josephson digital circuits-rapid single flux quantum (RSFQ) devices-based on overdamped externally shunted high quality Nb-AlO x -Nb tunnel junctions have been designed, fabricated and experimentally investigated. All-refractory material 11-layer 5 mu m integrated technology has been successfully employed for the preparation of the RSFQ microcircuits. The T flip-flop has been demonstrated to operate properly up to clock frequencies of 100 GHz at 25% margins. The proper operation of the buffer stage for a one-directional SFQ pulse transmission at clock frequencies up to 125 GHz has been achieved. The possibilities to convert the information from the usual DC form to SFQ and vice versa have been demonstrated. An output signal in an SFQ/DC converter as high as 220 mu V has been measured. A new counter type A/D converter which includes a comparator and reversible binary counter with DC outputs has been fabricated and tested. The proposed ADC seems to be very promising for high-accuracy measurement of medium-bandwidth signals. The possibilities of creating a number of SFQ devices with outstanding parameters are discussed.
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We describe the design of an oversampling single-flux-counting analog-to-digital converter with the estimated bandwidth of a few tens of MHz, based on Rapid Single-Flux-Quantum (RSFQ) devices. It consists of an input analog circuit, high-speed quantizer with an original analog/digital negative feedback loop, decimation (comb) filter, and supporting subsystems including clock distribution circuits, quantization signal conditioner, and output drivers. We have applied a new approach, the 'symmetrizing' negative feedback, to free the quantizer from the intrinsic hysteresis without dynamic range sacrifice. The 16-bit version of the system comprises about 1,500 Josephson junctions and consumes 1.2 mW of DC power, when implemented using Nb-trilayer technology with 1 kA/cm/sup 2/, 3.5 /spl mu/m Josephson junctions. All subsystems of the converter have been successfully tested and testing of the system as a whole is in progress.>
High speed, single flux quantum (SFQ) binary scalers are important components in superconducting analog-to-digital converters (ADC). This paper reviews the concept for a SQUID ADC and the design of an SFQ binary ripple counter, and reports the simulation of key components, and fabrication and performance of non-latching SQUID scalers and SFQ binary ripple counters. The SQUIDs were fabricated with Nb/Nb2O5/PbIn junctions and interconnected by monolithic-superconducting transmission lines and isolation resistors. Each SQUID functioned as a bistable flip-flop with the input connected to the center of the device and the output across one junction. All junctions were critically damped to optimize the pulse response. Operation was verified by observing the do I-V curves of successive SQUIDs driven by a cw pulse train generated on the same chip. Each SQUID exhibited constant-voltage current steps at 1/2 the voltage of the preceding device as expected from the Josephson voltage-to-frequency relation. Steps were observed only for the same voltage polarity of successive devices and for proper phase bias of the SQUID. Binary frequency division was recorded up to 40GHz for devices designed to operate to 28GHz.
Abstract One of the unique applications of single-flux-quantum (SFQ) circuitry is a digital-to-analog converter (DAC) of which the output voltage is defined by the Josephson effect. Recently, we have designed and operated rapid single-flux-quantum (RSFQ) DACs with frequency modulation of SFQ pulse sequences. In this paper, we report our design and test results of a 4-bit RSFQ-DAC based on the configuration of the “sum of selected bits sequence (Σ-SBS)”. By adjusting the timing margins, in addition to the fabrication using the Nb integration process with the critical current density as high as 10 kA/cm2, the maximum output voltage up to 260 μV was demonstrated.