Redundancy by Coding Versus Redundancy by Replication for Failure-Tolerant Sequential Circuits

A synthesis procedure for failure-tolerant sequential circuits using error-correcting codes is presented. Coding redundancy is then compared with replication as to circuit complexity and reliability improvement. Using appropriate assumptions, it is shown that for a specified ability to tolerate failures, replication yields better circuit reliability than coding redundancy. When circuit complexity as well as reliability are taken into consideration, it is shown that schemes based on orthogonizable codes generally provide a greater improvement in reliability for a given complexity than replication. As in any redundant scheme, these results presuppose reasonably good reliabilities for irredundant circuits.