SFQ Signal Conversion Circuit for Bilevel NRZ CMOS Interfaces
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Solution Overview
Problem
Superconducting digital systems face challenges in converting single flux quantum (SFQ) based return-to-zero (RZ) and non-return-to-zero (NRZ) signaling to bilevel voltage NRZ signaling, which is essential for interfacing with CMOS-based systems, due to limitations in transmission rates and interconnect bandwidth.
Innovation Solution
The development of superconducting circuitry that includes SET and RESET signal paths with escape Josephson junctions and output inductors, which convert SFQ-based RZ or NRZ signals to bilevel NRZ phase signals by triggering and resetting Josephson junctions to achieve phase transitions, enabling efficient conversion to CMOS NRZ encoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If SFQ-based RZ or NRZ signaling is used in superconducting systems, then data can be encoded and transmitted at high speeds (20 Gb/s or greater), but the systems cannot directly interface with CMOS-based systems that use bilevel voltage NRZ signaling
Solution Approach 1:
The patent employs an intermediary conversion circuit that translates between SFQ-based RZ/NRZ signaling and CMOS bilevel voltage NRZ signaling. This intermediary device includes Josephson junctions and associated circuitry that acts as a bridge, allowing superconducting systems to interface with conventional CMOS systems without requiring complete system redesign.
Solution Approach 2:
The conversion circuit utilizes parameter changes in Josephson junctions, specifically transitioning between superconducting and resistive states through controlled current application. By changing the electrical parameters (current, voltage, resistance) of the Josephson junctions in response to incoming SFQ signals, the circuit generates corresponding bilevel voltage outputs that match CMOS NRZ signaling standards.
2Productivity
If conventional CMOS bilevel voltage NRZ signaling is used, then interface compatibility with superconducting systems is achieved, but transmission rates and computational performance are limited compared to SFQ systems
Solution Approach 1:
The conversion circuit is designed with preliminary conditioning stages that prepare SFQ signals for accurate conversion. Escape Josephson junctions are configured to preemptively handle signal edge cases and timing variations, ensuring that the conversion to bilevel voltage NRZ signaling maintains signal integrity even at high transmission rates of 20 Gb/s or greater.
Solution Approach 2:
The circuit incorporates feedback mechanisms that monitor the conversion process and adjust operating parameters of the Josephson junctions in real-time. This feedback ensures that timing skew, phase boundary glitches, and other potential signal integrity issues are compensated for dynamically, maintaining high reliability during high-speed operation.
3Speed
If phase boundary glitches occur during SFQ to CMOS conversion, then signal integrity deteriorates, but increasing transmission rates exacerbate the glitch problem
Solution Approach 1:
The conversion circuit uses periodic clocking and timing reference signals to synchronize the conversion process. By establishing regular periodic action in the Josephson junction switching, the circuit maintains consistent phase boundaries and reduces timing skew that would otherwise cause glitches at high transmission rates.
Solution Approach 2:
The circuit design includes cushioning elements such as escape Josephson junctions and timing margin circuits that are positioned to preemptively protect against phase boundary glitches. These elements provide a buffer zone in the timing and voltage domains, absorbing potential glitches before they can propagate to the output, thereby maintaining signal integrity even at increased transmission rates.
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 solution allows for increased transmission rates, improved bit error rates, and reduced phase boundary glitches, effectively bridging the gap between SFQ-based systems and CMOS-based systems, enhancing the compatibility and performance of superconducting digital systems.
Implementation Method 1
superconducting Josephson junctions (JJs)
Implementation Method 2
single flux quantum (SFQ) circuitry utilizes superconducting Josephson junctions
Data Source
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AI summary
Edge-sensitive, state-based single flux quantum (SFQ) based circuitry and related methods convert return-to-zero (RZ) or non-return-to-zero (NRZ) encoded SFQ-pulse-based signals to bilevel NRZ phase signals that can subsequently be converted to bilevel voltage signals by an output amplifier (OA). The SFQ-based circuitry can be integrated with a current amplification stage of a driver that can be coupled to a stage of the OA. The SFQ-based circuitry can be made to be compatible with RQL-encoded input signals that can be either RZ or NRZ The SFQ-based circuitry can thus be compatible with both wave-pipelined (WPL) and phasemode (PML) RQL circuitry. Because the SFQ-based circuitry and related methods are edge-sensitive and state-based, they can function at system clock rates in excess of 1 GHz with reduced glitches and improved bit error rates as compared to other superconducting RZ-NRZ conversion circuitry and methods.