Digital Phase Source for Josephson Junction Logic
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Solution Overview
Problem
Existing SuperConducting electronic (SCE) circuit technologies face challenges with low circuit density, reliability, and scalability due to analog biasing schemes, which lead to area inefficiencies, power losses, and complex fabrication processes.
Innovation Solution
The introduction of a digital phase source (DPS) that provides quantized energy replenishment to Josephson junction logic, allowing for the use of underdamped or unshunted junctions, which increases circuit density and reduces power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If analog biasing schemes are used in SCE circuits, then the circuits can operate with traditional Josephson junction technologies, but the circuit density is low and area efficiency is poor
Solution Approach 1:
The patent changes the biasing parameter from continuous analog values to discrete digital phases (0, π/2, π, 3π/2). This digital phase biasing enables the use of underdamped Josephson junctions without requiring large shunt resistors, thereby increasing circuit density and improving area efficiency by over an order of magnitude compared to traditional analog biasing schemes.
2Area of stationary object
If underdamped Josephson junctions are used, then circuit density increases and area is reduced, but traditional analog biasing causes excessive power dissipation
Solution Approach 1:
The patent employs periodic digital phase modulation of the bias signal at frequencies that are multiples of the Josephson junction's critical frequency. This periodic action enables energy-efficient operation by synchronizing the biasing with the natural oscillation characteristics of the underdamped junction, reducing continuous power dissipation while maintaining high circuit density.
3Reliability
If multi-phase power distribution is implemented, then AC-based approaches can be used, but area inefficiencies occur due to resonators and transformers
Solution Approach 1:
The patent extracts and eliminates the need for resonators and transformers from the multi-phase power distribution architecture. By using direct digital phase biasing through simple resistive dividers or current-limiting junctions, the system achieves AC-based operation without the area-consuming passive components, thereby reducing area overhead while maintaining high operational speed.
4Stability of the object's composition
If shunt resistors are added to damp Josephson junctions, then critical damping is achieved, but the junction area increases significantly
Solution Approach 1:
Instead of adding shunt resistors to damp the junction (traditional approach), the patent inverts the approach by using digital phase biasing to control the junction's effective damping. The underdamped junction is stabilized through feedback control mechanisms that adjust the bias phase, eliminating the need for large shunt resistors and significantly reducing the required junction area.
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 enhances circuit density by over an order of magnitude, improves reliability by reducing noise sensitivity and bias margin degradation, and achieves higher energy efficiency and faster operation.
Implementation Method 1
A Josephson junction ('JJ') consists of two layers of a superconductor, with an ultrathin (∼1 nm) layer of an insulator between them, acting as a weak link. The superconducting current between them is given by Is=Ic sin φ
Implementation Method 2
The phase difference φ is related to the voltage by V=(□/2e) dφ/dt. So the ideal Josephson junction acts like a nonlinear lossless inductance Lj=2e/(□Ic cos φ) between the two electrodes.
Data Source
AI summary
A superconducting integrated circuits (ICs) design based on Josephson junctions, wherein the junctions are biased using a digital phase source (DPS), rather than the standard DC or AC current bias. This DPS enables the use of underdamped junctions, which in turn leads to more compact, lower power, more reliable ICs applied to digital computing, digital signal processing, and readout and control for cryogenic sensor arrays and for quantum computers. This design approach, called Superconducting Sustainable Ballistic Fluxon (SSBF), can be integrated with all logic families based on single-flux-quanta (SFQ), synchronous and asynchronous clocking protocols, and both DC and AC power supplies. SSBF can also be incorporated in automated design tools for scaling superconducting ICs to millions of junctions.