SFQ Logic Gate Inversion Using a Cross-Coupled Transformer
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Solution Overview
Problem
Current digital logic technologies, such as CMOS, face limitations in performance efficiency, power consumption, and scalability, prompting the need for advanced superconducting logic gates that can efficiently process high-speed, low-power signals.
Innovation Solution
A single-flux-quantum logic gate circuit is designed with first and second input gates connected to Josephson junctions, featuring a cross-coupled transformer and offset coupling to divert or inhibit signal propagation based on input pulses, enabling efficient signal inversion and logic operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If CMOS technology is used for digital logic, then manufacturing maturity and ease of manufacture are improved, but performance efficiency, power consumption, and scalability deteriorate
Solution Approach 1:
The patent replaces conventional CMOS semiconductor devices with superconducting Josephson junction devices. This substitution transitions from standard semiconductor physics to superconducting quantum effects, enabling higher operating speeds (10-100 GHz vs. CMOS limits) and lower power consumption while maintaining scalability to VLSI circuits through established superconducting fabrication processes
Solution Approach 2:
The invention changes the operating parameters by utilizing superconducting states and Josephson effects instead of conventional semiconductor carrier transport. This enables operation at cryogenic temperatures (4°K) with signal powers around 4 nW and data processing rates exceeding 20 Gb/s, representing a fundamental parameter shift from room-temperature CMOS operation
2Speed
If superconducting Josephson junction devices are used, then speed and power consumption are improved, but device complexity and fabrication sophistication requirements worsen
Solution Approach 1:
The patent divides the logic gate functionality into distinct Josephson junction-based components (input gates, output gates, cross-coupled transformers) that can be independently fabricated and then assembled. This segmentation allows each component to be optimized separately while maintaining overall system performance at 10-100 GHz operating rates
Solution Approach 2:
The invention creates universal Josephson junction logic gate structures that can perform multiple logic functions (AND, OR, NOT, NAND, NOR) through configurable connections and biasing schemes. This multi-functionality reduces the need for separate specialized circuits, simplifying the overall fabrication process despite the advanced superconducting requirements
3Productivity
If advanced superconducting logic gates are developed, then productivity and performance efficiency are improved, but device complexity and fabrication difficulty worsen
Solution Approach 1:
The patent employs standardized, replicated Josephson junction cell designs that can be copied and assembled to create complex logic functions. This modular copying approach maintains high performance efficiency (20 Gb/s+) while reducing fabrication complexity through repetition of proven, optimized unit cells rather than designing each gate from scratch
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
The solution enables high-speed, low-power digital logic operations by effectively propagating or inhibiting signals based on input conditions, enhancing the performance and scalability of superconducting logic gates for quantum circuits.
Implementation Method 1
superconductor-based single flux quantum circuitry, utilizing superconducting Josephson junctions
Implementation Method 2
A cross-coupled transformer diverts the first pulse from the output gate if the second pulse is detected at the second input gate
Implementation Method 3
Such devices have operating temperatures of about 4°K
Data Source
Figure 1A~1B
Figure 1C
Figure 2A
AI summary
one embodiment, the disclosure relates to a single-flux quantum logic gate capable of providing output from one of the two inputs, which is also known as the A and NOT B gate. The logic gate includes a first input gate and a second input gate for respectively receiving a first input pulse and a second input pulse. An output gate is wired in parallel with the first input gate. A first Josephson junction and a second Josephson junction are connected to the first input gate and the second input gate, respectively. A cross-coupled transformer is also provided. The cross-coupled transformer diverts the first pulse from the output gate if the second pulse is detected at the second input gate. In an optional embodiment, the first Josephson junction has a first critical current which is selected to be less than the critical current of the second Josephson junction.