Fully X-tolerant, Very High Scan Compression Scan Test Systems And Techniques
AssigneeSynopsys, Inc.
InventorsPeter Wohl, John A. Waicukauski, Frederic J. Neuveux
Life of this patent
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Abstract
Scan testing and scan compression are key to realizing cost reduction and shipped quality. New defect types in ever more complex designs require increased compression. However, increased density of unknown (X) values reduces effective compression. A scan compression method can achieve very high compression and full coverage for any density of unknown values. The described techniques can be fully integrated in the design-for-test (DFT) and automatic test pattern generation (ATPG) flows. Results from using these techniques on industrial designs demonstrate consistent and predictable advantages over other methods.
Claims17
A method for mapping care bits to a CARE pseudo-random pattern generator (PRPG), which uses the care bits to generate patterns for identifying faults of an integrated circuit design, the method comprising:
- determining a maximal window of shifts for which all care bits are mappable to a single seed;
- and
- using a scan test system, mapping the care bits to the CARE PRPG using the maximal window.
A method for mapping X-tolerance (XTOL) control bits to an XTOL pseudo-random pattern generator (PRPG), the XTOL control bits determining a level of observability of scan chains, the method comprising:
- determining a maximal window of shifts for which all XTOL control bits are mappable to a single seed;
- and
- using a scan test system, determining an optimal start for the maximal window
A method of selecting observability modes for a scan test, the method comprising:
- initializing mode merits associated with the observability modes;
- for each shift, eliminating any observability mode that lets an unknown value (X) through;
- for each shift, eliminating any observability mode that fails to detect a primary target of the scan test;
- increasing mode merits for secondary faults based on a number of secondary targets observed;
- for each shift, determining a best observability mode and a second best observability mode for a shift based on total mode merits;
- and
- using a scan test system, mapping resulting observability modes to X-tolerance (XTOL) seeds.
Dependencies are inferred from the claim text.