A new definition and a new class of sequential circuits with combinational test generation complexity

We introduce a new class of sequential circuits with combinational test generation complexity which we call internally balanced structures. It is shown that sequential circuits can be classified by their structure as follows: (sequential circuits of acyclic structure)⊃(sequential circuits of internally balanced structure)⊃(sequential circuits of balanced structure) and that internally balanced structures allow test generation with combinational test generation complexity. On the other hand, if finite state machines (FSMs) are classified by their realization possibility, it can be shown that (FSMs which can be realized as a sequential circuit of acyclic structure)=(FSMs which can be realized as a sequential circuit of internally balanced structure)⊃(FSMs which can be realized as a sequential circuit of balanced structure). In addition, we discuss the definition of test generation possibility with combinational test generation complexity and introduce a new definition which covers the previous narrow definition