Fault detection in CVS parity trees: application in SSC CVS parity and two-rail checkers

Abstract

The problem of single stuck-at, stuck-open, and stuck-on fault detection in cascode voltage switch (CVS) parity trees is considered. The results are also applied to parity and two-rail checkers. CVS circuits are dynamic CMOS circuits which can implement both inverting and noninverting functions. If the CVS parity tree consists of only differential cascode voltage switch (DCVS) EX-OR gates, then it is shown that at most only five tests are needed for detecting all single stuck-at, stuck-open, and stuck-on faults, independent of the number of primary inputs and the number of inputs to any EX-OR gate in the tree. If, however, only a single-ended output is desired from the tree, than the final gate will be a single-ended cascode voltage switch (SCVS) EX-OR gate. For such a tree it is shown that only eight tests are enough. For a strongly self-checking (SSC) CVS parity checker the number of required tests is nine, whereas for an SSC CVS two-rail checker the size of the test set is at most five.<>