Pulse-Conserving SFQ Logic Gates for Efficient Inversion

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Solution Overview

Problem

The efficiency of logic gate implementations in superconducting digital systems, particularly for inversion operations, remains a challenge compared to CMOS technologies.

Innovation Solution

The development of Josephson junction based logic devices that utilize pulse-conserving gates and dual-rail data encoding to recreate the functions of standard CMOS gate libraries, including the implementation of D-latch devices and single-ended to dual-rail data conversion without transformers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If traditional SFQ logic gate implementations are used, then inversion operations can be performed, but the efficiency is low and the process is costly compared to CMOS technology

Engineering Contradiction:

Improveinversion operation efficiencyVSAvoidenergy cost of inversion

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent implements inversion operations efficiently by using pulse-conserving gates where the inversion is achieved through the natural behavior of the SFQ pulse transmission in the gate structure, rather than through expensive auxiliary components. The OA2 and OMA3 gates are designed so that inversion is a direct consequence of the pulse routing logic, making it as efficient as forward operations.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The OA2 and OMA3 gates are designed as universal building blocks that can perform multiple logic functions (AND, OR, NOT, NAND, NOR, XOR, XNOR) depending on how they are configured and connected. This multi-functionality eliminates the need for separate dedicated inversion circuits, reducing overall system complexity and energy consumption while maintaining high inversion efficiency.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If transformers and auxiliary inductors are used in SFQ logic gates, then logic functions can be implemented, but the device size becomes large and scalability is limited

Engineering Contradiction:

Improvelogic function implementation capabilityVSAvoidgate device area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent extracts and eliminates the need for transformers and auxiliary inductors from the SFQ logic gate structure. The pulse-conserving OA2 and OMA3 gates achieve logic function implementation using only the essential Josephson junctions and interconnect inductors, removing bulky components that limited scalability while preserving full logic functionality.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the functions of multiple components into a unified gate structure. The OA2 gate combines two input paths with a single output path using a minimal set of Josephson junctions and inductors, while the OMA3 gate extends this to three inputs. This merging eliminates the need for separate transformers and auxiliary inductors that would be required in traditional implementations, significantly reducing device area.

Inventive Principle:

Principle #5Merging (Combining)

3Speed

If SFQ logic gates operate at high clock rates, then computational speed improves, but maintaining efficiency and avoiding signal degradation becomes challenging

Engineering Contradiction:

Improveclock rateVSAvoidsignal integrity

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent replaces traditional magnetic coupling mechanisms (transformers) with a direct inductive coupling scheme using interconnect inductors that are integral to the gate structure. This substitution enables faster signal transmission at high clock rates while maintaining signal integrity through the conservative pulse transmission design, where each SFQ pulse is faithfully transmitted without degradation.

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 approach effectively addresses the inversion problem in SFQ logic, achieving computational density comparable to leading-node CMOS systems while eliminating the need for physically large components like transformers.

Implementation Method 1

Josephson junction based logic devices... single-flux-quantum (SFQ) pulses... Josephson junctions

Methodology Applied

Scientific EffectJosephson effect: Josephson Effect

Implementation Method 2

first input node inductively coupled to a first input source... first plurality of inductors coupled between the first input node

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS12206413B2SFQ-based pulse-conserving logic gates

Publication Date: 2025.01.21 INTERUNIVERSITAIR MICRO ELECTRONICS CENT (IMEC VZW)

AI summary

Josephson junction based logic devices and methods for their use are described. An example Josephson junction based logic device includes a two-input OR/AND (OA2) gate. The OA2 gate includes a first input node inductively coupled to a first input source and a second input node inductively coupled to a second input source. The first and second input sources are configured to provide single-flux-quantum (SFQ) pulses. The OA2 gate also includes first plurality of inductors coupled between the first input node and one of: a first output node or a second output node. The OA2 gate additionally includes a second plurality of inductors coupled between the second input node and one of: the first or the second output nodes. The OA2 gate also includes Josephson junctions coupled between a common node and one of: the first or the second input node, or the first or the second output node.