SFQ Buffer Circuit Using High-Impedance PTLs for Low-Delay Routing

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Solution Overview

Problem

In single flux quantum (SFQ) technology, the use of Josephson transmission lines (JTLs) for interconnecting logic gates in very-large-scale integration (VLSI) environments leads to significant delay and delay variation, and existing design tools are inadequate for routing, while passive transmission lines (PTLs) face challenges such as limited wiring density, spurious pulse generation, and sensitivity issues due to impedance matching problems.

Innovation Solution

The implementation of a Josephson junction (JJ)-based current source (JCS) circuit design that uses higher impedance PTLs without loss of transmission integrity, allowing for denser routing and eliminating resonance issues by matching back termination resistance, and enabling direct connection of SFQ circuit outputs and inputs to PTLs without drivers and receivers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If Josephson transmission lines (JTLs) are used for interconnecting logic gates, then signal transmission is achieved, but significant delay and delay variation occur

Engineering Contradiction:

Improvesignal transmission speedVSAvoidtransmission delay

Core Design Contradiction:

SpeedVSLoss of time

Solution Approach 1:

The patent changes the impedance parameter of the transmission line from low impedance (JTL) to high impedance (PTL), which fundamentally alters the transmission characteristics and reduces delay while maintaining signal integrity through proper termination

Inventive Principle:

Principle #35Parameter changes

2Productivity

If passive transmission lines (PTLs) are used with lower impedance, then routing density is improved, but spurious pulse generation and sensitivity issues occur due to impedance matching problems

Engineering Contradiction:

Improverouting densityVSAvoidsignal integrity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent increases the impedance parameter of the PTL to a higher value, which reduces spurious pulse generation and improves signal integrity while maintaining adequate routing density through optimized line dimensions

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements termination resistance at the end of the PTL that matches the line impedance, creating a feedback mechanism that prevents signal reflections and eliminates spurious pulse generation

Inventive Principle:

Principle #23Feedback

3Ease of operation

If JTLs are used for interconnection, then signal transmission is achieved, but design tools are inadequate for routing

Engineering Contradiction:

Improverouting capabilityVSAvoiddesign tool complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent replaces the complex, difficult-to-route JTL structure with simpler PTL segments that can be routed using conventional EDA tools, effectively disposing of the complex routing requirement in favor of a simpler alternative

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Reliability

If PTLs with higher impedance are used, then wiring density is reduced, but sensitivity to turns and vias is improved

Engineering Contradiction:

Improvesensitivity to turns and viasVSAvoidwiring density

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent optimizes the impedance parameter to a higher value that naturally reduces sensitivity to geometric variations like turns and vias, while compensating for the reduced wiring density through efficient layout strategies

Inventive Principle:

Principle #35Parameter changes

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 results in more efficient and energy-efficient SFQ-based integrated circuits with improved sensitivity and reduced complexity, enabling higher impedance lines that are less sensitive to turns and vias, and eliminating data errors caused by spurious pulses, thus enhancing chip flexibility and routing density.

Implementation Method 1

SFQ technology uses JJs. A JJ can include two superconducting electrodes separated, for example, by a thin insulating tunnel barrier, which can support a current that can flow indefinitely without any voltage applied. Though SFQ technology itself has numerous variations, all make use of flux storage and transmission, which is affected by pulses emitted by JJs.

Methodology Applied

Scientific EffectJosephson effect: Josephson Effect

Implementation Method 2

SFQ technology, which relies on the quantum mechanical quantization of magnetic flux, is a technology that can help meet future computing and storage demands.

Methodology Applied

Scientific EffectMagnetic flux quantization: Magnetic Field

Implementation Method 3

Methodology Applied

Scientific EffectImpedance matching: Electrical Resistance

Data Source

PatentUS11342921B1Single flux quantum buffer circuit

Publication Date: 2022.05.24 SYNOPSYS INC

AI summary

A circuit can include a first Josephson junction (JJ), a second JJ, and a third JJ coupled in parallel using superconducting inductors. The first JJ, the second JJ, and the third JJ can be biased using one or more JJ-based current sources.