Test application time reduction for sequential circuits with scan

Scan designs alleviate the test generation problem for sequential circuits. However, scan operations substantially increase the total number of test clocks during test application stage. Classical methods used to solve this problem perform test compaction and obtain fewer test vectors. In this paper we show that such a strategy does not always reduce the test clocks or test application time. Our approach is to associate a scan strategy function with each test vector during test generation for circuits with full or partial scan. The paper presents two algorithms to generate test sequences that reduce the number of test clocks required to apply the test sequences. The algorithms are based on: (1) heuristics that determine the need for scan operations; and (2) controlling sequential test generation process by choosing an appropriate target fault. In this paper we define and investigate different scan strategies for full and partial scan designs. We propose approximate measures that can be used for selection of a target fault during sequential test generation. These concepts are integrated into the algorithms Test Application time Reduction for Full scan (TARF) and Test Application time Reduction for Partial scan (TARP). The algorithms are implemented, and their efficiencies are demonstrated by using them for a set of ISCAS sequential benchmark circuits. The experiments show that, in full scan designs, TARF generated vectors require 36% fewer test clocks compared to the vectors from COMPACTEST that produces near optimal test sets. Similarly for partial scan designs, TARP achieves over 30% cumulative test clock reduction compared to the results from FASTEST which produced generally fewer vectors than other ATPG systems.<
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