RQL Phase-Mode D Flip-Flop Using Shared Josephson Junctions
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Solution Overview
Problem
Conventional CMOS technology is nearing maturity, and there is a need for alternative digital logic solutions that offer higher performance in terms of speed, power dissipation, computational density, and interconnect bandwidth, which is not adequately addressed by existing superconducting Josephson junction-based circuits.
Innovation Solution
A reciprocal quantum logic (RQL) phase-mode D flip-flop is developed, incorporating a storage loop, comparator, and output amplifying Josephson transmission line, utilizing shared Josephson junctions to encode and amplify data input signals as superconducting phases, enabling efficient storage and propagation of logic states without the need for reciprocal pulses to reset the phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional CMOS technology is used, then current digital logic performance is maintained, but speed and power dissipation performance deteriorate as technology approaches maturity
Solution Approach 1:
The patent replaces conventional CMOS electronic switching mechanisms with superconducting Josephson junction-based phase-mode logic. This substitution enables operation at higher speeds (20 Gb/s or greater) with lower power consumption by utilizing quantum mechanical effects in superconducting materials rather than traditional semiconductor switching.
Solution Approach 2:
The invention changes the fundamental operating parameters by using phase-encoded logic levels (0 and 2π phases) instead of voltage levels. This phase-mode operation allows for higher speed operation and reduced power dissipation while maintaining logical functionality, directly addressing the performance limitations of mature CMOS technology.
2Productivity
If superconducting Josephson junction circuits are implemented, then speed and power performance improve, but device complexity increases
Solution Approach 1:
The patent merges multiple functions into shared Josephson junctions that serve dual purposes in both the storage loop and comparator circuitry. This consolidation reduces the total number of required components and interconnections, thereby lowering device complexity while maintaining high computational density through efficient resource utilization.
Solution Approach 2:
The shared Josephson junction is designed to perform multiple functions: it acts as part of the storage loop for data retention and as part of the comparator for data retrieval and amplification. This multi-functionality reduces overall circuit complexity by eliminating redundant components and simplifying the circuit architecture.
3Duration of action of stationary object
If phase-mode encoding is used, then data persistence across clock cycles is achieved, but setup and hold time requirements are eliminated
Solution Approach 1:
The patent employs periodic AC clock cycles to read and amplify the phase-encoded data without requiring the data input to remain stable during the entire clock cycle. The phase information persists naturally through the superconducting loop, and only brief sampling moments are needed during each clock cycle, eliminating stringent setup and hold time requirements while maintaining data integrity.
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 RQL phase-mode D flip-flop enhances performance by allowing data encoding as superconducting phases, persisting across AC clock cycles, and efficiently capturing and propagating logic states, thereby improving speed and power efficiency in digital logic operations.
Implementation Method 1
superconducting Josephson junctions (JJs), with typical signal power of around 4 nanowatts (nW), at a typical data rate of 20 gigabits per second (Gb/s) or greater
Implementation Method 2
a storage loop (106, 206) configured to receive a data input signal on a data input line as a positive or a negative single flux quantum, SFQ, pulse and store the data input signal in the storage loop
Data Source
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AI summary
A reciprocal quantum logic (RQL) phase-mode D flip-flop accepts a data input and a logical clock input. A D flip-flop with an enable input further accepts enable input and further requires that the enable be asserted high to allow the data input to change the output on the logical clock pulse. The flip-flop includes a storage loop and a comparator, each of which includes Josephson junctions (JJs). The storage loop stores the data input, provided as a positive or negative single flux quantum (SFQ) pulse, is stored in the storage loop as positive or negative state, respectively, effectively biasing a JJ shared between the storage loop and the comparator. The data input is captured to the output upon clocking (or enabled clocking), when a clock pulse causes the shared JJ to preferentially trigger over an escape JJ in the comparator, the shared JJ having been biased by storage loop current.