Phase-Mode RQL Logic Gate with Integrated SFQ Inversion
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Solution Overview
Problem
Conventional digital logic circuits, such as CMOS technology, face limitations in performance, power dissipation, computational density, and interconnect bandwidth, prompting the need for alternative technologies like superconducting Josephson junction-based circuits for enhanced speed and efficiency.
Innovation Solution
The development of a reciprocal quantum logic (RQL) gate circuit with a phase mode logic (PML) inverter, which integrates a Josephson transmission line for amplification and combines input logic and output inversion into a single cell, using storage loops and bias signals to determine logic values and propagate signals efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional CMOS technology is used, then manufacturing maturity is maintained, but performance in speed, power dissipation, and computational density is limited
Solution Approach 1:
The patent combines the input logic function and output inversion function into a single integrated cell structure. The Josephson transmission line serves dual purposes as both input signal pathway and output signal pathway, eliminating the need for separate inverter components and reducing overall circuit complexity while maintaining high-speed operation
Solution Approach 2:
The Josephson transmission line is designed to perform multiple functions: it serves as an input signal transmission medium, an output signal transmission medium, and participates in the logic decision-making process through its interaction with the storage loops and bias signals, thereby reducing the total number of components required
2Productivity
If fan-in is increased to reduce logic circuit depth, then circuit efficiency is improved, but device complexity increases
Solution Approach 1:
The patent segments the input signals into separate storage loops, with each storage loop independently capturing and holding one input signal. This segmentation allows multiple inputs to be processed in parallel without increasing the complexity of the core logic decision mechanism, as each input is independently managed in its own storage loop
Solution Approach 2:
The storage loops act as intermediary elements between the multiple input signals and the single logical decision Josephson junction. Each storage loop mediates its corresponding input signal, converting temporal signal arrivals into persistent current states that can be simultaneously evaluated by the logical decision junction without signal interference or timing conflicts
3Adaptability or versatility
If separate inverter circuitry is added to achieve inverting logic, then logic function completeness is improved, but number of components increases
Solution Approach 1:
The patent merges the inverting function into the core logic cell by utilizing the natural phase relationship between the bias signals applied to the input and output Josephson transmission lines. The 180-degree phase difference in bias signals inherently provides the inversion function, eliminating the need for separate inverter circuitry while maintaining complete logic function capability
Solution Approach 2:
The logical decision Josephson junction and associated storage loops automatically generate the inverted output signal through their inherent superconducting quantum interference properties. The circuit self-services the inversion function through the quantum mechanical phase relationships established by the bias signals, without requiring external or additional inverter components
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 reduces the number of circuit components, enhances circuit efficiency, and improves performance by allowing a single Josephson transmission line to act as both input and output, thereby increasing speed and reducing complexity and cost.
Implementation Method 1
The logical decision JJ is configured to trigger based on biasing provided by one or more currents stored in the storage loops and an AC component of a first bias signal provided to the input stage
Implementation Method 2
at least one positive single flux quantum (SFQ) pulse input to assert one or more logical inputs
Data Source
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AI summary
An inverting reciprocal quantum logic, RQL, gate circuit (100) has an input stage (104) having a logical input asserted based on receiving a positive single flux quantum, SFQ, pulse and an output stage (102) comprising phase mode logic inverter circuitry. The input stage (104) includes one or more storage loops, at least one being associated with each logical input, each comprising an input Josephson junction, JJ, a storage inductor, and a logical decision JJ, the logical decision JJ being common to all the storage loops associated with the logical inputs and being configured to trigger based on biasing provided by one or more currents stored in the storage loops and a first bias signal provided to the input stage. The output stage (102) de-asserts an output and is provided with a second bias signal having a second state opposite of a first state of the first bias signal.