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=l if at least m-out-of-n inputs 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 analyses 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.

Hardware Voters are bit voters computing a majority of n input bits. An m-out-of-nhardware bit voter is a circuit with n bit inputs, and I bitoutput y, such that y=l i f at least m-out-of-n inputs bits have the value I . A hardware voter can be constructed as two level AND-OR (equivalently OR-AND and other structures) using CMOS VLSI technology. The goal of the paper is to present Reliability Estimations, Failure Modes and Effects, Criticality Analysis (FMECA) of voting networks at the transistor level, in CMOS VLSI implementation.FMECA is performed using the functional tree of the system, representing the dataflow from the lowest level functional block up to the higher level functional blocks.The main idea of this research is to identifji the best designs of voting circuits in terms of reliability parameters and to identih their critical failures and effects.

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