High-performance electronic circuits would incorporate self-checking features for detection of radiation-induced single-event latchups (SELs), according to a proposal. The basic SEL-detection scheme calls for redundant circuitry and a current-voting scheme similar to voting schemes that have been used to reveal malfunctions in other redundant systems. The redundancy and voting scheme could also be combined with other fault-tolerance features [e.g., for detection of single-event upsets (SEUs)].
As in some older schemes for detecting SEL and other anomalies, the proposed current-voting scheme would involve detection of operating current outside the normal range for a circuit to be protected. However, unlike in some older methods for detecting SEL, no attempt would be made to establish precise limits of normal operating current - limits that could be difficult if not impossible to establish for a complex circuit that normally operates over a wide dynamic range of current and/or is subject to radiation or to variations in temperature. Instead, one would build a duplicate of the circuit to be protected and would operate both circuits concurrently under the same nominal conditions, using comparator circuitry to detect differences between the currents drawn by the two circuits (see left side of figure). Each of the duplicate circuits would serve as a high-fidelity model of "normal" behavior for the other. "Normal" behavior would be defined ratiometrically; that is, in terms of a range, α , of allowable fractional difference between the currents (or corresponding voltages) in the two duplicate circuits. Any excursion from the allowable range would be detected by the comparator circuitry, which would respond by triggering an alarm, shutdown, reset, or other appropriate corrective signal.
The current-voting scheme could be implemented, for example, by the current-comparison and threshold-logic circuitry shown on the right side of the figure. Potentials V1 and V2 are voltages representative of the currents flowing from a power supply (at potential VCC) to each of two duplicate circuits. The values of R1 and R2 would be chosen so that R1/(R1+R2) = α . Thus, the left voltage divider (R1, R2) would provide comparison voltages V1 and V1(1 - α ), while the right voltage divider (R1, R2) would provide comparison voltages V2 and V2(1 - α ). Then the output of the upper comparator would go high if V2 were less than V1(1 - α ), whereas the output of the lower comparator would go high if V1 were less than V2(1 - α ). It is noted that in this scheme, it would not matter which voltage (V1 or V2) was the "normal" voltage; instead, if either voltage deviated from the other by a fraction > α , the behavior would be deemed to be abnormal, causing the circuit to generate an "out-of-bounds" signal.
A Duplicate of the Circuit To Be Protected would be operated concurrently, under the same conditions. The currents drawn by the protected circuit and its duplicate would be indicated by V1 and V2. If either of V1 or V 2 differed from the other by a fraction greater than R1/(R1+ R2) = α , then the circuit would generate an "out-of-bounds" signal.
This work was done by Douglas W. Caldwell of Caltech forNASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Electronic Components and Circuits category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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Refer to NPO-20143, volume and number of this NASA Tech Briefs issue, and the page number.
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Self-checking circuitry for detecting single-event latchups
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Overview
The document presents a technical support package from NASA's Jet Propulsion Laboratory, detailing a novel approach to detecting single-event latchup (SEL) in complex electronic circuits. Authored by Douglas W. Caldwell, the invention addresses the limitations of existing techniques that struggle to manage the wide dynamic variations in power consumption inherent in high-performance electronics, particularly in environments exposed to radiation.
The primary innovation described is a self-checking hardware system that employs a "current voting" technique. This method involves the use of duplicate circuits that operate concurrently under identical conditions. By comparing the currents drawn by these circuits, the system can flag errors if the currents deviate beyond a specified fractional limit. This approach is particularly beneficial in detecting SEL, which can occur due to radiation-induced events that traditional methods fail to identify.
The document outlines the challenges faced by current detection methods, which often rely on static thresholds that may not accommodate the dynamic nature of modern electronic devices. For instance, existing techniques may not effectively respond to variations caused by factors such as temperature changes, switching frequencies, or manufacturing discrepancies. The proposed self-checking circuitry aims to overcome these limitations by continuously monitoring circuit health and providing real-time feedback.
Additionally, the document discusses the potential for built-in test (BIT) functions to enhance circuit reliability. However, it notes that few commercial devices perform BIT functions at frequencies high enough to adequately protect against SEL. The proposed solution, therefore, not only improves detection capabilities but also enhances overall circuit robustness.
The technical disclosure emphasizes the importance of maintaining circuit integrity in critical applications, such as aerospace and defense, where reliability is paramount. By implementing a voting scheme that reveals anomalies in circuits with wide dynamic ranges, the invention promises to significantly improve the safety and performance of electronic systems in challenging environments.
In summary, this document outlines a significant advancement in the detection of single-event latchup through innovative self-checking circuitry, providing a reliable solution for ensuring the health and functionality of complex electronic circuits in radiation-prone settings.
