A “Strongly-Fail-Safe Majority Voted Output” Circuit used for Designing Dependable Computer Systems
Complexity of design in case of redundant solutions, done till now, which require conventional fail-safe circuits.
Necessity of off-line test sequences in case of non-redundant solutions involving “strongly-fail-safe” circuits.
This paper aims to provide a practical solution using “strongly-fail-safe” circuit for designing dependable computer systems aimed at critical processes. The goal is to make use of such systems easier, to avoid the drawbacks generated by off-line test phase and to obtain the best “cost-safety” compromise. First of all, we introduce the scheme of a “strongly-fail-safe” basic cell without any off-line test equipments. The advantage is to obtain a “strongly-fail-safe” circuit which requires few components. Then, we suggest an architecture of a “strongly-fail-safe majority voted output” circuit designed from the “strongly-fail-safe” basic cell. The reliability, the availability and the safety of this “majority voted output” mechanism is assessed. For information a triple modular redundancy computer system including this last mechanism is compared with well-known dependable computer systems. The good results obtained show that such a solution may meet a wide range of safe applications because of its low complexity and its fitness to be easily implemented. In conclusion a quantitative and a comparative study is performed. It involves two dependable redundant computer architectures suggested for an industrial refinery project need.
KeywordsCMOS Inverter Triple Modular Redundancy Full Duplex Combine Fault Functional Input
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