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IEEE Transactions on Magnetics

Proposal of unilateral single-flux-quantum logic gate

Hidetaka MIYAKE, N. Fukaya, Yoji Okabe, T. Sugano

Published Mar 1, 1985• 4 citations
Publisher

Abstract

A new type of single flux quantum logic gate is proposed, which can perform unilateral propagation of signal without using three-phase clock. This gate is designed to be built with bridge-type Josephson junctions. A basic logic gate consists of two one-junction interferometers coupled by superconducting interconnecting lines, and the logical states are represented by zero or one quantized fluxoid in one of one-junction interferometers. The bias current of the unequal magnitude to each of the two one-junction interferometers results in unilateral signal flow. By adjusting design parameters such as the ratio of the critical current of Josephson junctions and the inductances, circuits with the noise immunity of greater than 50% with respect to the bias current have been designed. Three cascaded gates were modeled and simulated on a computer, and the unilateral signal flow was confirmed. The simulation also shows that a switching delay about 2 picoseconds is feasible.

DOI
10.1109/tmag.1985.1063827

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A new type of single flux quantum logic gate is proposed, which can perform unilateral propagation of signal without using three-phase clock. This gate is designed to be built with bridge-type Josephson junctions. A basic logic gate consists of two one-junction interferometers coupled by superconducting interconnecting lines, and the logical states are represented by zero or one quantized fluxoid in one of one-junction interferometers. The bias current of the unequal magnitude to each of the two one-junction interferometers results in unilateral signal flow. By adjusting design parameters such as the ratio of the critical current of Josephson junctions and the inductances, circuits with the noise immunity of greater than 50% with respect to the bias current have been designed. Three cascaded gates were modeled and simulated on a computer, and the unilateral signal flow was confirmed. The simulation also shows that a switching delay about 2 picoseconds is feasible.
A new type of logic gate that can be designed using a nonhysteretic Josephson weak link is proposed. The basic component of the proposed device is a one-junction interferometer, and a logic state is represented by either a zero or a single-flux-quantum. In contrast to the "Parametric Quantron," this device is designed to operate without a three-phase clock and the dependence of the junction critical current on magnetic field is not used. The switching behavior of the device was simulated by computer and an analytical expression for the switching delay has been obtained.
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We designed several single flux quantum (SFQ) flip-flops and logic gates composed of Josephson junctions (JJs) and π-shifted JJs (π-JJs) to quantitatively evaluate effectiveness of introduction of π-JJs into the SFQ logic circuit. One-output flip-flops and logic gates were designed on the basis of the circuit design methodology we built for the SFQ circuit containing π-JJs. The designed flip-flops and logic gates have wide operating margins, the dc-bias margins of larger than ±30%, and device parameter margins of ±18%, though the static power consumption are reduced compared to conventional ones composed of JJs. We found that the difference in the critical current density between JJs and π-JJs does not affect the operating margins of the SFQ flip-flop composed of JJs and π-JJs. We devised a circuit structure of the delay flip-flop with complementary outputs composed of JJs and π-JJs (π-DFFC). The analog circuit simulation shows the dc-bias margin of the π-DFFC is larger than ±33%. These results indicate that the large-scale SFQ logic circuit system can be implemented using the flip-flops and logic gates containing π-JJs.
A quantum-flux-type logic circuit is proposed which is composed of Josephson junction transmission lines, along which localized magnetic flux can propagate. By choosing bias current properly, the duplication of magnetic flux and a variety of logical functions can be obtained without changing the circuit topology. Computer simulation results are presented on AND and OR operations with two and three inputs for the same circuit topology, confirming that these circuits can be used as logic circuits. The simulations demonstrate the high-speed operation and low power consumption of this circuit.>
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We report on a voltage-state logic family based on shunted Josephson junctions and on the Rapid Single Flux Quantum (RSFQ) concept. Storing information in a voltage-state form makes this Multi-Flux-Quantum Logic (MFQL) easier to match to complementary metal-oxide semiconductor (CMOS) circuits. The switching of MFQL element between the voltage and zero-voltage states takes a minimum of two SFQ pulses, and the switching time of this logic is comparable to that of RSFQ logic. The key logic element is an inverter in the form of an asymmetric interferometer, and the underlying idea is to use a separate superconducting wire to supply a standard dc output voltage for the elements. The asymmetric interferometer, directly coupled to the other elements, is actually a Josephson junction based three-terminal device or transistor. Elements such as NOT, OR, NOR, XOR, XNOR, a toggle flip-flop, and an RS trigger have been simulated, and show margins better than /spl plusmn/24%. The performance of this logic with current circuit fabrication technologies is also discussed.