INVESTIGATION OF LOGIC CIRCUIT COMPLEXES. RELIABILITY AND FAULT-MASKING IN N-VARIABLE NOR TREES.

摘要

In the preceding final report the n-variable NOR tree was developed and some of its properties were studied. This tree will be referred to as the general n-variable tree. If any of the NORs are not operating correctly,then at least one of the logical functions will not be executed correctly for all assignments of values to the variables. The first part of this paper develops three methods for masking faults in the general tree by adding additional NORs. These yield restoring trees, quadded trees,and generalized majority trees. The next section discusses three different definitions of reliability:system reliability,function reliability and signal state reliability. Methods for computing these reliabilities as functions of the failure probabilities of the diodes and transistors which compose the NOR elements for restoring, quadded and general trees are presented. Since system reliability is the most important type of reliability to the circuit designer,this paper next considers the computation of system reliability for the general, quadded and restored trees. The computation is simple for the general tree. However,for the quadded and restored trees,compensating errors make the computation extremely difficult. In these cases upper and lower bounds for the system reliability are computed. The computations are carried out for n = 1, 2, 3, 4,and the curves provide comparisons between the two fault masking techniques being considered,as well as comparisons between the upper and lower bounds for the system reliabilities. Curves are also drawn for n = 1, 2, 3, 4of the system reliability for restored quadded and general trees as a function of the reliability of a NOR element. (Author)