At-Speed Scan Test Method for the Timing Optimization and Calibration

An at-speed scan test methodology is proposed for the purpose of the timing optimization and calibration. The proposed method, called TOC-ATPG, addresses both undertesting and overtesting issues of the traditional at-speed scan-based structural test. A pseudo-random pattern-based circuit analysis is first applied to analyze the potential glitches and transitions due to the functional illegal states. A list of state elements to be constrained during ATPG to prevent the sensitization of the functional illegal transitions and glitches are derived. During ATPG the derived constraints are applied to prevent overtesting, and timing-aware transition fault approach is used simultaneously to detect the fault through the timing critical paths to overcome the undertesting issue. The proposed method demonstrates very high correlation to the purely sequential test in functional mode with bounded run time overhead and can be applied to very large design.