FAULT-DETECTION IN CVS PARITY TREES WITH APPLICATION TO STRONGLY SELF-CHECKING PARITY AND 2-RAIL CHECKERS

In this paper 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 parity tree consists of only differential cascode voltage switch (DCVS) EX-OR gates then we show that the test set consists of at most only five vectors (in some cases only four vectors are required) for detecting all detectable 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, then the final gate will be a single-ended cascode voltage switch (SCVS) EX-OR gate. For such a tree we show that the test set has only eight vectors. We have already introduced the concept of a strongly self-checking (SSC) property for checkers. We show that for an SSC CVS parity checker, the size of a test set consisting of only codewords is nine, whereas for an SSC CVS two-rail checker the size of a test set consisting of only codewords is at most five.