SFQ-NRZ Interface Circuit Using Josephson Lines for High-Speed Conversion

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Solution Overview

Problem

There is a need for efficient interfacing between single flux quantum (SFQ) and non-return-to-zero (NRZ) data encodings in digital logic systems, as existing technologies struggle to effectively convert between these encoding formats, limiting transmission rates and computational performance.

Innovation Solution

The development of superconducting interface circuitry using three Josephson transmission lines to convert NRZ-encoded voltage signals to RQL-compliant SFQ pulse pairs and vice versa, utilizing inversion and delay circuitry and current-controlled voltage source circuitry to achieve seamless data encoding conversions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If conventional interfacing methods are used between SFQ and NRZ systems, then device complexity is reduced, but transmission rate is limited and cannot achieve high-speed operation

Engineering Contradiction:

Improvetransmission rateVSAvoidinterface circuit complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary interface circuit comprising Josephson transmission lines and latches that mediates between SFQ and NRZ systems. This intermediary converts NRZ voltage signals to SFQ flux signals and vice versa, enabling high-speed transmission without directly coupling the two disparate systems, thus resolving the contradiction between transmission rate and device complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The interface circuit exploits parameter changes in Josephson junctions, specifically the relationship between voltage, current, and flux in superconducting circuits. By utilizing the Josephson effect and changing operational parameters (voltage to flux conversion), the circuit achieves high-speed signal conversion while maintaining manageable complexity through physics-based transformation rather than complex logic circuits.

Inventive Principle:

Principle #35Parameter changes

2Speed

If high-speed signal conversion is implemented, then transmission rate increases, but power dissipation increases

Engineering Contradiction:

Improvedata rateVSAvoidpower dissipation

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

The patent utilizes phase transitions in superconducting materials, specifically the transition between superconducting and resistive states in Josephson junctions. This phase transition mechanism enables rapid signal conversion at high data rates while dissipating minimal power, as the superconducting state has zero electrical resistance. The interface circuit leverages this phase transition to achieve high-speed operation without proportional increases in power dissipation.

Inventive Principle:

Principle #36Phase transitions

Solution Approach 2:

The interface circuit employs periodic clocking signals to synchronize the conversion between NRZ and SFQ formats. By using periodic action rather than continuous operation, the circuit processes signals in discrete high-speed bursts, achieving high data rates while allowing the superconducting elements to return to low-power superconducting states between conversions, thereby limiting overall power dissipation.

Inventive Principle:

Principle #19Periodic action

3Productivity

If conventional encoding conversion is used, then device complexity is minimized, but computational density and interconnect bandwidth are limited

Engineering Contradiction:

Improvecomputational densityVSAvoidinterface circuit structure

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent replaces conventional electronic signal conversion mechanisms with superconducting quantum interference device (SQUID) based conversion. This substitution utilizes quantum mechanical effects in superconducting circuits to achieve rapid signal transformation, dramatically increasing computational density and interconnect bandwidth while keeping the physical interface structure relatively simple compared to traditional electronic conversion circuits.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solution enables increased transmission rates by a factor of two, allowing SFQ and NRZ systems to operate effectively together, with fabricated circuits achieving speeds between 2 and 12 gigabits per second, enhancing computational density and interconnect bandwidth.

Implementation Method 1

single flux quantum (SFQ) circuitry utilizes superconducting Josephson junctions (JJs)

Methodology Applied

Scientific EffectJosephson effect: Josephson Effect

Implementation Method 2

A reflecting JTL, connected to the input JTL, is configured to reflect and invert the SFQ pulse as an inverted SFQ pulse

Methodology Applied

Scientific EffectElectromagnetic reflection: Reflection

Data Source

PatentUS10243582B1Interfacing between SFQ and NRZ data encodings

Publication Date: 2019.03.26 NORTHROP GRUMMAN SYSTEMS CORP

AI summary

Superconducting interface circuits and methods convert between non-return-to-zero (NRZ) encoded voltage signals and reciprocal quantum logic (RQL) compliant signals of opposite-polarity single flux quantum (SFQ) pulse pairs, and vice-versa, so as to provide high-speed NRZ input to, and output from, RQL computing circuitry.