A mid-value select voter

Hardware redundancy may be used in a variety of manners to achieve fault tolerance. One of the most popular techniques is a triple modular redundancy (TMR) scheme. Such a scheme has also been referred to as masking redundancy because failures those affect only if one of the three modules is masked by the majority of the nonfailed modules. Most of the published works on TMR make one crucial assumption: In fault-free operation the outputs are equal. However it is well known that the output of redundant sensor elements in fault-tolerant data acquisition systems cannot be guaranteed to match even in fault-free operation. They are usually handled by a median-select or similar selection rule, so that redundant voter can pick a common value for processing by the rest of the system. This paper presents a VLSI fault-tolerant voter, with redundancy designed into the internal chip architecture. Instead of three we propose installation of four sensor elements. In order to insure that the voted value represents a correct consensus, we propose a mid-value hardware voting technique thanks to which we solve the problem of dissemination of each sensor element value to other ones. Finally, the effect of fault-tolerance on voter performance is discussed.