Class of undetectable stuck-open branches in CMOS memory elements

The authors consider a class of undetectable stuck-open faults in CMOS circuit branches and show that in basic static latch and flip-flop circuits some branches are of this class. Moreover, undetectable stuck-open faults in transistors reported in recent works pertain to this class. It is shown that, in the case of stuck-open faults in these branches, the static circuit becomes a dynamic one. Because most of the undetectable stuck-open faults in branches (or transistors) in sequential memory elements are of this class, a general approach for DFT (design for testability) for these faults is proposed, and examples of fully detectable circuits are presented