Josephson Memory Array with Quasi-Long Junction Interconnects
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Solution Overview
Problem
Current digital logic technologies, such as CMOS, face limitations in speed, power dissipation, computational density, and interconnect bandwidth, prompting the need for alternative solutions like superconducting Josephson junction-based circuits, particularly in non-destructive readout (NDRO) and reciprocal quantum logic (RQL) memory arrays.
Innovation Solution
The implementation of quasi-long-Josephson junction interconnects in Josephson memory arrays, which are faster, more power-efficient, and denser than traditional Josephson transmission lines, enabling efficient data transmission and storage while minimizing fan-out requirements and maintaining pulse integrity over short distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional Josephson transmission lines are used for interconnect, then signal transmission is achieved, but the circuit speed is limited and power dissipation is high
Solution Approach 1:
The patent changes the fundamental parameters of the interconnect by transitioning from traditional Josephson transmission lines to quasi-long Josephson junctions. This parameter change enables simultaneous achievement of high-speed operation and low power dissipation by exploiting the unique properties of quasi-long junctions that support faster signal propagation while maintaining lower energy consumption compared to conventional approaches.
Solution Approach 2:
The patent replaces the traditional Josephson transmission line mechanism with a quasi-long Josephson junction mechanism. This substitution fundamentally changes how signals are transmitted through the interconnect, enabling both higher speed and lower power dissipation by utilizing the different physical characteristics of quasi-long junctions versus conventional transmission lines.
2Productivity
If traditional Josephson transmission lines are used, then interconnect functionality is provided, but computational density and interconnect bandwidth are limited
Solution Approach 1:
The patent segments the interconnect structure into quasi-long Josephson junction units that can be densely packed and integrated with memory cells. This segmentation enables higher computational density by allowing more functional units to be placed in a given area while maintaining manageable complexity through modular design.
Solution Approach 2:
The patent utilizes a two-dimensional array architecture where quasi-long Josephson junctions are arranged in rows and columns, enabling efficient addressing and access patterns. This dimensional organization increases computational density by allowing parallel access to multiple memory locations while maintaining relatively simple control logic.
3Speed
If quasi-long-Josephson junction interconnects are used, then speed and power efficiency are improved, but fan-out requirements must be minimized
Solution Approach 1:
The patent applies local quality by designing the quasi-long Josephson junction interconnect to have specific characteristics optimized for point-to-point communication. The interconnect structure is tailored to provide high-speed transmission for directly addressed locations while using multiplexing techniques to handle the limited fan-out requirement, thereby maintaining high speed performance without needing high fan-out capability.
4Use of energy by moving object
If quasi-long-Josephson junction interconnects are used, then power consumption is reduced, but pulse integrity over longer distances may be compromised
Solution Approach 1:
The patent employs preliminary action by using refresh circuits that periodically restore and retransmit pulses along the quasi-long Josephson junction interconnect. This preliminary refresh action compensates for pulse degradation over distance, maintaining pulse integrity reliability while allowing the system to operate at lower power consumption levels than would be required for purely passive long-distance transmission.
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 a fast, low-power, and low-latency memory technology suitable for low-level caches and RQL processors, enhancing performance and efficiency in digital logic applications.
Implementation Method 1
superconducting Josephson junctions
Implementation Method 2
a logical '1' can be encoded as a positive single flux quantum (SFQ) pulse
Implementation Method 3
signal power of around 4 nanowatts (nW)
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A Josephson memory array and logic circuits use quasi-long-Josephson-junction interconnects to propagate signals at fast speeds and low energy expense, while permitting for memory arrays as dense fabrics of relatively simple unit cell sub-circuits, which include π Josephson junctions, connected together by the interconnects. Each of the unit cell sub-circuits can be configured as a looped or linear arrangement. The unit cell sub-circuits and interconnects provide a fast, dense memory technology for reciprocal quantum logic (RQL), suitable for low-level caches and other memories collocated with an RQL processor.