RQL Josephson Logic Arrays for Fast Low-Power Superconducting FPGAs
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Solution Overview
Problem
Current CMOS-based field-programmable gate arrays (FPGAs) face limitations in terms of speed, power dissipation, computational density, and interconnect bandwidth, prompting the need for alternative technologies that can offer higher performance in digital logic applications.
Innovation Solution
The development of Josephson-transmission-line-based superconducting logic arrays (JTLBSLAs) and superconducting field-programmable gate arrays (FPGAs) that utilize reciprocal quantum logic (RQL) cells, including magnetic Josephson junctions and escape Josephson junctions, to enable efficient storage and readout of digital states, and implement complex logic operations with improved area efficiency and frequency capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If CMOS technology is used for FPGAs, then device complexity and adaptability are maintained, but speed and power dissipation performance deteriorate
Solution Approach 1:
The patent replaces CMOS electronic switches with superconducting Josephson junctions that operate based on quantum mechanical effects rather than classical semiconductor physics. The Josephson junctions utilize tunneling of Cooper pairs through a thin ins barrier, enabling lossless current flow and extremely fast switching speeds up to 20 Gbps or higher, while consuming only picowatt-scale power compared to CMOS nanowatt consumption.
Solution Approach 2:
The invention changes fundamental operating parameters by transitioning from room-temperature CMOS operation to cryogenic superconducting operation at approximately 4 Kelvin. This temperature parameter change enables zero electrical resistance in the superconducting interconnects and Josephson junctions, eliminating resistive power dissipation and enabling ultra-fast switching through quantum tunneling effects rather than classical charge carrier movement.
2Productivity
If CMOS FPGAs are used, then ease of manufacture is maintained, but computational density and interconnect bandwidth deteriorate
Solution Approach 1:
The patent segments the FPGA architecture into modular superconducting logic blocks, each containing multiple Josephson junctions arranged in specific configurations (such as RSFQ or ERSFQ cells). These modular blocks can be independently fabricated and then interconnected using superconducting transmission lines, allowing high computational density through efficient space utilization while maintaining manufacturing simplicity through standardized cell designs that repeat across the chip.
Solution Approach 2:
The invention creates universal superconducting logic cells that can perform multiple logic functions (AND, OR, NOT, XOR, etc.) by reconfiguring the same physical Josephson junction components. This multi-functionality increases computational density by allowing a single physical cell to replace what would traditionally require multiple dedicated circuits, while the standardized universal cell design actually simplifies the fabrication process compared to custom CMOS layouts.
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
JTLBSLAs and JTLBSFPGAs provide significant speed and energy-consumption advantages over CMOS FPGAs, enabling more efficient implementation of complex algorithms and achieving higher computational densities with increased area efficiency and frequency capabilities.
Implementation Method 1
The decision loop includes a magnetic Josephson junction (MJJ) configured to set the digital state as one of a first logic state and a second logic state based on write signals provided on write inputs
Implementation Method 2
The decision loop further includes an escape Josephson junction (JJ) configured to trigger or not to trigger so as to block the read data signal from propagating to an output JTL or to act as a superconducting short to pass the read data signal to the output JTL
Implementation Method 3
The decision loop further includes a secondary inductor of a selection input transformer through which the read selection signal is provided to the decision loop from a read selection Josephson transmission line (JTL)
Data Source
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AI summary
Superconducting logic arrays, SLAs, and field-programmable gate arrays, FPGAs that are based on Josephson transmission lines, JTLs, accommodate reciprocal quantum logic, RQL, compliant binary input signals and provide RQL-compliant output signals that are evaluations of generalized logic functions. Each JTL-based superconducting FPGA, JTLBSFPGA, incorporates multiple JTL-based SLAs, JTLBSLAs, connected together. Each JTLBSLA includes an array of software-programmable and/or mask-programmed logic cells that output products of inputs and cell states, such that the JTLBSLAs output evaluations of sum-of-products functions. New JTLBSLA logic cells are described, including some that provide programmable cell states via magnetic Josephson junctions (MJJ). JTLBSFPGAs provide area efficiency and clock speed advantages over CMOS FPGAs. Unlike SLAs based on Josephson magnetic random access memory, JMRAM, JTLBSLAs do not require word line drivers, flux pumps, or sense amplifiers. Because JTLBSLAs and JTLBSFPGAs are RQL-compliant, they can also include RQL gates connected within or between them, without signal conversion circuitry.