Identification of primitive faults in combinational and sequential circuits

Abstract

This paper presents a method of primitive fault identification and test generation for combinational and nonscan sequential circuits. It uses the concept of sensitizing cubes to obtain input vectors that statically sensitize primitive faults in combinational circuits. The same technique is used to identify combinationally primitive faults in the next-state and output logic of sequential circuits. Such faults are primitive if and only if the fault effects on paths to state variable flip-flops can be propagated to a primary output (PO). Test sequences, including initializing sequences from a reset state and sequences that propagate fault effects from flip-flops to POs, are generated for primitive faults, wherever possible. The proposed method has been implemented and used to derive tests for primitive faults in the ISCAS'89 and MCNC'91 benchmark circuits. It was able to find all primitive faults and also obtain robust tests for a large fraction of them when the circuits were treated as combinational. When the same circuits were treated as nonscan sequential circuits, all primitive faults could not be found because fault propagation had to be limited to a relatively small number of time frames.