RQL Phase-Mode D Flip-Flop With Built-In Logic Inversion
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Solution Overview
Problem
Conventional CMOS technology is nearing maturity, and there is a need for alternatives that can offer higher performance in terms of speed, power dissipation, computational density, and interconnect bandwidth, which is not effectively addressed by existing digital logic solutions.
Innovation Solution
The development of inverting reciprocal quantum logic (RQL) phase-mode D flip-flops using stacked Josephson junctions and comparators, which encode digital values as superconducting phases, allowing for efficient storage and inversion of logic states without the need for additional signal inversion stages, utilizing Josephson transmission lines and DC/AC biasing to propagate signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional CMOS technology is used for digital logic implementation, then manufacturing maturity and existing infrastructure are maintained, but performance in terms of speed, power dissipation, computational density, and interconnect bandwidth reaches maturity limits
Solution Approach 1:
The patent replaces conventional CMOS electronic switching mechanisms with superconducting Josephson junction-based phase-mode logic. This substitution enables higher computational density by utilizing quantum mechanical effects (Josephson effect) to create faster switching elements with lower power dissipation, directly addressing the performance limitations of mature CMOS technology while maintaining manufacturability through established superconducting fabrication processes
2Ease of operation
If separate inverter circuits are added to conventional flip-flops to achieve inversion, then the inversion function is provided, but component count and propagation delay increase
Solution Approach 1:
The patent merges the inversion function directly into the flip-flop circuit structure by utilizing the inherent phase-inversion characteristics of the superconducting phase-mode logic elements. The stacked Josephson junction configuration and comparator circuit naturally produce inverted output phases without requiring external inverter stages, thereby reducing component count and propagation delay while maintaining the inversion function
Solution Approach 2:
The flip-flop circuit is designed to simultaneously perform multiple functions: data storage, clocked operation, and logical inversion. The same core circuit elements (stacked Josephson junctions, comparators, and transmission lines) that enable flip-flop operation also inherently provide the inversion function through phase modulation, eliminating the need for separate dedicated inverter components
3Speed
If conventional flip-flop designs are used, then basic storage functionality is achieved, but propagation delay and component count prevent optimal performance in high-speed applications
Solution Approach 1:
The patent employs periodic AC clock signaling to control the flip-flop operation, where the superconducting phase-mode logic elements respond to alternating current cycles. This periodic action enables synchronized data capture and output transitions at specific clock phases, reducing propagation delay through predictable timing while maintaining signal stability through the regenerative nature of the superconducting oscillating circuits
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 highly efficient and fast inverting flip-flops with reduced component count and propagation delay, capable of storing logic states as superconducting phases, improving operating margins and eliminating the requirement for separate inverter circuits, leading to smaller and more cost-effective implementations.
Implementation Method 1
A stacked Josephson junction in the flip-flop is triggered to reverse the direction of DC bias current flowing through an output Josephson junction in the flip-flop
Implementation Method 2
Phase-mode logic allows digital values to be encoded as superconducting phases of one or more Josephson junctions. These values persist across RQL AC clock cycles because there is no requirement for a reciprocal pulse to reset the Josephson junction phase each AC clock cycle
Data Source
Figure 1~2
Figure 3A~3B
Figure 3C~3D
AI summary
An inverting reciprocal quantum logic (RQL) phase-mode D flip-flop (300) accepts a data input (Dl) and a logical clock input (LCLKI). The flip-flop includes a stacked Josephson junction (J3) and a comparator (J5, J4). The triggering or untriggering of the stacked Josephson junction (J3) by positive or negative single flux quantum (SFQ) pulses (Dl) can switch a direction of DC bias current through a component of the comparator (through J4), such as an output Josephson junction (J4), which can then either pass or suppress logical clock SFQ pulses (LCLKI). When so passed, the data input is captured to the output (QNO) upon clocking the flip-flop via the provision of the logical clock SFQ pulses, e.g., as reciprocal pulse pairs (pulse positive, pulse negative).