Superconducting Array Diagnostics via Time-Domain Multiplexed Readout
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Solution Overview
Problem
Diagnostic testing of superconducting integrated circuits with tens of thousands of elements requires efficient methods to assess reproducible and uniform behavior without excessive input and output contacts, which is challenging due to the high density and cryogenic operation requirements of ultrafast RSFQ circuits.
Innovation Solution
A time-domain multiplexed readout scheme using non-destructive-readout (NDRO) memory cells and analog-to-digital converters (ADCs) with SQUID quantizers allows for sequential selection and analysis of device outputs, reducing the number of contacts needed by using SFQ pulses to activate and measure devices, enabling efficient diagnostic testing of large arrays of nominally identical or varied elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual testing of each element is performed, then measurement precision is improved, but device complexity increases due to excessive input and output contacts required
Solution Approach 1:
Multiple device outputs are merged into a single shared output line through the use of a multiplexer. The multiplexer combines signals from many individual devices, allowing them to share a common output path and reducing the total number of output contacts required on the chip.
Solution Approach 2:
Devices in the array are tested sequentially rather than simultaneously. A multiplexer switches between different device outputs in a periodic manner, selecting one device at a time for measurement. This time-division multiplexing approach allows individual measurement precision while using far fewer physical contacts than would be needed for parallel testing of all devices.
2Quantity of substance
If sequential selection of devices is implemented, then the number of contact pads is reduced, but loss of time increases due to sequential measurement process
Solution Approach 1:
The multiplexer implements rapid periodic switching between device outputs, selecting each device in sequence at high speed. This periodic action allows the system to cycle through many devices quickly, reducing the time penalty of sequential measurement while maintaining the benefit of reduced contact pad requirements.
Solution Approach 2:
The system changes the timing parameters of measurement, using fast switching speeds and optimized pulse widths to minimize the total test time. By adjusting these temporal parameters, the sequential measurement process becomes efficient enough to be practical despite not testing all devices simultaneously.
3Device complexity
If multiplexer is used to reduce contacts, then device complexity is reduced, but measurement precision may deteriorate due to signal switching and selection overhead
Solution Approach 1:
The multiplexer acts as an intermediary device that manages signal routing between the device array and output contacts. By using a dedicated multiplexer designed for superconducting circuits, the system achieves clean signal switching with minimal noise and distortion, preserving measurement precision while enabling contact reduction.
Solution Approach 2:
The system optimizes electrical parameters such as switching speed, pulse width, and signal amplitude to minimize the impact of multiplexer switching on measurement precision. By carefully controlling these parameters, the overhead introduced by sequential selection is reduced to negligible levels.
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 enables efficient measurement of statistical variations and performance margins of superconducting devices, reducing the number of contact pads required and allowing for accurate analysis of large numbers of devices on a single chip, thereby advancing the scalability and reliability of superconducting VLSI circuits.
Implementation Method 1
analog-to-digital converters (ADCs) with SQUID quantizers
Data Source
AI summary
A superconducting circuit is disclosed for fast digital readout of on-chip diagnostics in an array of devices in an integrated circuit. The digital readout comprises a digital RSFQ multiplexer to select the readout channel. This permits a large number of devices to be tested with a minimum of input and output lines. The devices may comprise digital devices (such as elementary RSFQ cells), or analog devices (such as inductors, resistors, or Josephson junctions) with a SQUID quantizer to generate a digital signal. The diagnostic array and the digital multiplexer are preferably configured to operate as part of the same integrated circuit at cryogenic temperatures.