Reliability and failure analysis of voting circuits in hardware redundant design

This paper presents some aspects of fault-tolerant design using hardware redundancy. The voter is the key element in N-modular redundant design. Hardware voters are bit voters that compute a majority of n input bits. An m-out-of-n hardware bit voter is a circuit with n bit inputs, and 1 bit output y, such that y=1 if at least m-out-of-n input bits have the value 1. A hardware voter can be implemented with logic gates in CMOS VLSI technology. Designers are looking for optimal designs with respect to the following criteria: circuit complexity, number of logic levels, fan-in and fan-out, power dissipation, testability, or any combinations of the previous requirements in order to obtain high reliability for the voting circuits. A detailed reliability analysis, failure modes and effects analysis of voters at the transistor level, is performed using CARE tools. CARE (computer aided reliability engineering) is a powerful software tool that can be used concurrently in the phases of R&D for complex reliability analysis of electronic circuits. The main goal of these analyses is to identify the best designs of voting circuits, in terms of reliability parameters and to identify the possible technological failures that can affect them