This paper describes an input reduction design framework for delay testing. This design framework can be used to construct efficient test pattern generators (TPGs) for built-in self-test (BIST), to order scan cells in a scan chain to eliminate unnecessary dummy flip-flops, and to generate compact test sets for delay testing.

A new technique called input reduction is proposed for built-in self test (BIST) test pattern generator (TPG) design and test set compaction. This technique analyzes the circuit function and identifies sets of compatible and inversely compatible inputs; inputs in each set can be combined into a test signal in the test mode without sacrificing fault coverage, even if they belong to the same circuit cone. The test signals are used to design BIST TPGs that guarantee the detection of all detectable stuck-at faults in practical test lengths. A deterministic test set generated for the reduced circuit obtained by combining inputs into test signals is usually more compact than that generated for the original circuit. Experimental results show that BIST TPGs based on input reduction achieve complete stuck-at fault coverage in practical test lengths (/spl les/2/sup 30/) for many benchmark circuits. These are achieved with low area overhead and performance penalty to the circuit under test. Results also show that the memory storage and test application time for external testing using deterministic test sets can be reduced by as much as 85%.

This paper describes a new formulation to generate robust tests for path delay faults in combinational circuits based on Boolean satisfiability. Conditions to detect a target path delay fault are represented by a Boolean formula. Unlike the technique described in [16], which extracts the formula for each path delay fault, the proposed formulation needs to extract the formula only once for each circuit cone. Experimental results show tremendous time saving on formula extraction compared to other satisfiability-based ATPG algorithms. This also leads to low test generation time, especially for circuits that have many paths but few outputs. The proposed for-mulation has also been modied to generate other types of tests for path delay faults.

Testing for delay and CMOS stuck-open faults requires two-pattern tests, and typically a large number of two pattern tests are needed. Built-in self-test (BIST) schemes are attractive for comprehensive testing of such faults. BIST test pattern generators (TPGs) for two-pattern testing, should be designed to ensure high transition coverage. In this paper, necessary and sufficient conditions to ensure complete/maximal transition coverage for linear feedback shift register (LFSR) and cellular automata (CA) have been derived. The theory developed here identifies all LFSR/CA TPGs that maximize transition coverage under any given TPG size constraint. It is shown that LFSRs with primitive feedback polynomials with large number of terms are better for two-pattern testing. Also, CA are shown to be better TPGs than LFSRs for two pattern testing, independent of their feedback rules. Based on the necessary sufficient conditions, efficient algorithms to design optimal TPGs for two-pattern testing have been developed. Experiments on benchmark circuits indicate that TPGs designed using the procedures outlined in this paper obtain high robust path delay fault coverage in short test lengths.

Conventional built-in self-test (BIST) test pattern generators (TPGs) are designed to maximize stuck-at fault coverage in combinational circuits. Such TPGs often provide inadequate coverage of two-pattern tests which are required for the detection of delay faults. In this paper, theoretical results and procedures are presented to design efficient TPGs that ensure high two-pattern coverage for comprehensive delay testing of a circuit under test (CUT). First, new concepts particular to delay testing are identified and exploited to design efficient TPGs based on interleaved cyclic codes. A new concept of test cones is then introduced to further reduce the test length. Finally, the proposed procedures are used to design TPGs for delay testing of ISCAS'89 benchmark circuits and the results demonstrate their effectiveness.

This paper describes a new technique to design efficient test pattern generators (TPGs) for built-in self-test (BIST). The proposed technique identifies compatible circuit inputs that can be connected to the same TPG stage in the test mode. Compatibility between circuit inputs is determined by analyzing the circuit function to guarantee coverage of all faults in a given target fault set. Unlike pseudo-exhaustive testing, circuit inputs that fanout to the same output can be compatible, provided that connecting them to the same TPG stage does not cause any loss of fault coverage. Experimental results show that TPGs designed by the proposed technique achieve 100% stuck-at fault coverage in practical test length (/spl les/2/sup 28/) with low hardware overhead and performance penalty for a wide range of benchmark circuits.