U. Glaeser

45.4 Summary
Automatic test pattern generation yielding high fault coverage for CMOS circuits has received wide
attention in industry and academia for a long time. Mixed-level test pattern generation offers advantages,
since test generation from gate-level netlists has shortcomings regarding fault coverage in complex CMOS
gates. A switch-level approach relying on the transistor structure only is too slow and impractical for
larger circuits. The first part of this chapter describes automatic test pattern generation with a mixed
switch-level and gate-level approach. It combines acceptable performance for large networks with a high
fault coverage also for nontrivial transistor networks. Patterns generated this way are inherently capable
to detect stuck-open faults and transition faults as well as various other fault models on different
abstraction levels. In combination with local overcurrent detectors, also stuck-on and local bridging faults
can be identified. To increase the efficiency of mixed-level test generation, a reconvergency analysis is
performed and constraints are stored.
An original approach to test generation for synchronous sequential circuits was presented. Two levels
of hierarchy, the switch-level and the gate-level are supported. Inter-level backtracks between these two
hierarchies are implemented. The number of inter-level backtracks is minimized using simple heuristics
for constraint identification, which is a promising method for hierarchical test generation also on higher
levels (RT or behavior level). A new efficient algorithm called FOGBUSTER for the forward propagation
backward initialization technique handles synchronous sequential circuits. A 4-valued logic and a twostaged
backtracking mechanism are used to handle the over-specification problem and to achieve completeness.
Experimental results for the ISCAS ’85 and ISCAS ’89 benchmark circuits are encouraging. In
comparison to the BACK-algorithm and to the HITEC approach, FOGBUSTER on the average has a
significantly better performance.
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© 2002 by CRC Press LLC