DC SQUID Bias-Level Sensing for RQL Clock Calibration
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Solution Overview
Problem
Reciprocal quantum logic (RQL) systems face challenges in maintaining optimal biasing parameters due to variations in fabrication processes and operating conditions, leading to malfunctions when bias signals are outside the operating margins, and direct probing of integrated circuits at cryogenic temperatures is impractical.
Innovation Solution
The implementation of a stack of direct current superconducting quantum interference devices (DC SQUIDs) coupled to Josephson transmission lines, which serve as bias-level sensors to measure and adjust AC and DC bias parameters, allowing for continuous operation and optimal biasing within the RQL system's margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct probing methods are used to measure bias parameters, then measurement capability is improved, but the system requires disruption of RQL circuitry and exposure to room temperature which is impractical
Solution Approach 1:
The patent introduces DC SQUID-based sensor circuits as intermediary elements that can measure bias parameters indirectly through magnetic flux coupling. These sensors act as mediators between the cryogenic RQL circuitry and measurement systems, enabling non-intrusive measurement without requiring physical probing or circuit disruption.
Solution Approach 2:
The patent replaces direct electrical probing (mechanical contact method) with magnetic flux-based measurement using DC SQUIDs. This substitution eliminates the need for physical connection to the circuit nodes, allowing measurement through magnetic coupling alone, thus avoiding circuit disruption and temperature exposure requirements.
2Reliability
If bias parameters drift outside operating margins, then system reliability deteriorates, but adjustment requires system shutdown and repatching
Solution Approach 1:
The patent implements continuous feedback measurement using DC SQUID sensors that monitor bias parameters in real-time. The measured values are fed back to control systems that can automatically adjust bias levels or alert operators, maintaining operation within margins without requiring system shutdown. This closed-loop feedback mechanism ensures reliability while maximizing productivity.
Solution Approach 2:
The patent employs preliminary measurement and adjustment capabilities that detect bias parameter drift before it causes malfunction. By continuously monitoring and making preemptive adjustments, the system prevents reliability degradation before it occurs, avoiding the need for shutdowns and repatching operations.
3Manufacturing precision
If fabrication process variations occur, then bias parameter consistency worsens, but reconfiguration is not feasible after assembly
Solution Approach 1:
The patent introduces dynamically adjustable bias parameters through programmable voltage sources and variable impedance elements. These dynamic components allow post-assembly reconfiguration of bias levels to compensate for fabrication variations. The system can be tuned and adapted after manufacturing, providing both manufacturing precision through initial design and adaptability through post-assembly adjustment capabilities.
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
Enables accurate measurement and adjustment of bias levels within the RQL system, ensuring reliable operation by maintaining bias parameters within the operating margins without disrupting the RQL circuitry, thus improving performance and stability.
Implementation Method 1
Each DC SQUID in the stack is transformer-coupled to a respective JTL to receive flux from an output of the respective JTL
Implementation Method 2
a stack of direct current superconducting quantum interference devices (DC SQUIDs)
Data Source
AI summary
An output-amplifier-based reciprocal quantum logic (RQL) bias-level sensor is used to measure and/or calibrate bias parameters of AC and/or DC bias signals provided to RQL circuitry. The bias signals can include an output amplifier output bias current. The bias-level sensor includes a stack of DC SQUIDs that are supplied their inputs from outputs of respective Josephson transmission lines (JTLs) to which the SQUIDs are transformer-coupled. Staging relative strengths of the bias taps of the JTLs, or the critical currents of the Josephson junctions in the DC SQUIDs, allows an output voltage signal of the bias-level sensor to be indicative of whether a provided bias value is an improvement or optimization of the bias value when varied over a range. The outputs of two such bias-level sensors driven by I and Q clocks can be compared to adjust AC bias amplitudes of the clocks. Relative clock phase can be similarly adjusted.