RQL NDRO Circuit Topology for Simultaneous Write-Read
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Solution Overview
Problem
Current superconducting non-destructive readout circuits for quantum and classical digital logic face challenges in reducing device count, improving functionality, and allowing simultaneous writing and reading operations, while minimizing the use of large transformers and maintaining ultra-low power consumption.
Innovation Solution
The development of reciprocal quantum logic (RQL) non-destructive readout (NDRO) gates and demultiplexer circuits utilizing a body-tail topology with single flux quantum (SFQ) logical inputs and Josephson junctions, enabling non-destructive readout of stored logical states without affecting the stored information, and allowing for simultaneous writing and reading operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional superconducting readout circuits are used, then readout functionality is achieved, but device count is high and simultaneous write-read operations are not possible
Solution Approach 1:
The readout circuit is divided into separate tail circuits for each read port, with each tail containing dedicated Josephson junctions and inductors. This segmentation allows independent read operations from multiple ports while sharing a common body circuit for data storage, enabling simultaneous write and read operations without requiring a complete redesign of the entire memory cell.
Solution Approach 2:
The body circuit serves multiple functions: it stores data and provides the logical state for readout. The tail circuits are designed to be universally applicable for different read ports, with each tail able to independently read the same stored data without interfering with other tails or the body circuit. This multi-functionality reduces the need for separate dedicated circuits for each operation.
2Reliability
If traditional NDRO circuits are used, then non-destructive readout is achieved, but large transformers are required
Solution Approach 1:
The large transformer component is completely removed from the circuit topology. Instead of using transformers for magnetic coupling and signal transfer, the invention employs direct superconducting connections with Josephson junctions and inductors to achieve the same signal propagation and logical state transfer, thereby eliminating the area occupied by large transformers while maintaining non-destructive readout capability.
Solution Approach 2:
The magnetic coupling mechanism implemented by large transformers is replaced with a superconducting electronic mechanism using Josephson junctions and inductors. This substitution leverages quantum mechanical effects in superconducting materials to achieve signal transfer and logical state propagation without requiring bulky magnetic components, thus reducing circuit area while preserving the non-destructive readout function.
3Adaptability or versatility
If more read ports are added, then functionality is improved, but device count increases
Solution Approach 1:
Each additional read port is implemented by adding a separate tail circuit module, which contains the necessary Josephson junctions and inductors. This modular segmentation allows the circuit to scale to multiple read ports while keeping each port's implementation standardized and independent, thus improving versatility without proportionally increasing overall device complexity.
Solution Approach 2:
Multiple tail circuits share a common body circuit for data storage and control signals. This merging approach allows multiple read ports to access the same stored data simultaneously without requiring separate storage elements for each port, thereby improving multi-read functionality while minimizing the increase in total device count.
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 NDRO circuits achieve reduced device count, improved functionality, and the ability to write and read data within the same operation cycle, enhancing memory and computing performance while maintaining ultra-low power consumption.
Implementation Method 1
a tail Josephson junction connected between the body circuit and a circuit ground
Implementation Method 2
Each tail circuit in the NDRO gate includes an input inductor connected between an NDRO read-enable input port and the body circuit
Data Source
AI summary
Non-destructive read out (NDRO) circuits are provided for use in reciprocal quantum logic (RQL) superconducting systems. Each NDRO circuit includes a “body” circuit that provides a single or multi-state sub-critical bias current to one or many independent “tail” circuitries. Each “tail” has minimal effect on the “body” thereby preventing any interference or destruction to the state of the “body” circuitry. The circuits reduce device count and thereby increase circuit density, simplify and reduce the cost of fabrication, and provide functionality not available in existing designs, such as the ability to write a state and read it in the same operation cycle. The NDRO circuits provide more compact unit cells useful in memory or logic arrays, demanding fewer resources with increased functionality. The circuits also provide compact cells for AND, AND-OR, A-NOT-B, inverter, multiplexer, and demultiplexer gates.