Fault dictionary based scan chain failure diagnosis

• US 9,110,138 B2
• Filed: 12/23/2013
• Issued: 08/18/2015
• Est. Priority Date: 04/04/2007
• Status: Expired due to Fees

• Current Assignee: Mentor Graphics Corporation (Siemens AG)
• Original Assignee: Mentor Graphics Corporation (Siemens AG)
• Inventors: Guo, Ruifeng, Huang, Yu, Cheng, Wu-Tung
• Primary Examiner(s): MCMAHON, DANIEL F
• Application Number:
  US14/139,480
• Publication Number:
  US 20140115413A1
• Time in Patent Office: 603 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G01R 31/3177 Testing of logic operation, e.g. by logic analysers
• CPC Class Codes: G01R 31/318525 Test of flip-flops or latches
• CPC Class Codes: G01R 31/318541 Scan latches or cell details

Abstract

A dictionary-based scan chain fault detector includes a dictionary with fault signatures computed for scan cells in the scan chain. Entries in the fault dictionary are compared with failures in the failure log to identify a faulty scan cell. In one embodiment a single fault in a scan chain is identified. In another embodiment, a last fault and a first fault in a scan chain are identified.

Claims

1. A method of generating a fault dictionary to determine faulty scan cells in a scan chain, comprising:

by a computer;

receiving a description of an integrated circuit that includes combinational and sequential logic that can be tested by applying test patterns to the sequential logic and reading scan chain outputs;

for one or more scan cells in scan chains, determining respective lists of failures that will be observed at the scan chain outputs when each of the one or more scan cells has a defined fault; and

storing a fault dictionary representative of the respective lists of failures for each of the one or more scan cells.

2. The method of claim 1, further comprising:

determining a difference between failures for a first scan cell in a scan chain versus failures for a second scan cell in the scan chain; and

storing the difference in failures as a fault signature for the first scan cell in the fault dictionary.

3. The method of claim 2, wherein the first scan cell and the second scan cell are adjacent to one another in a respective scan chain.

4. The method of claim 1, further comprising storing a complete list of failures as a fault signature for at least one scan cell in a respective scan chain in the fault dictionary.

5. The method of claim 1, wherein the storing a fault dictionary representative of the respective lists of failures for each of the one or more scan cells comprises:

storing a complete fault signature for a first scan cell; and

storing an incomplete differential fault signature for a second scan cell from which a complete fault signature for the second scan cell can be recreated.

6. The method of claim 1, wherein the storing a fault dictionary representative of the respective lists of failures for each of the one or more scan cells comprises:

determining a differential fault signature from which a complete fault signature can be determined with reference to a base fault signature; and

storing the differential fault signature.

7. One or more non-transitory computer-readable media storing a sequence of instructions that are executable by a computer to perform a method, the method comprising:

receiving a description of an integrated circuit that includes combinational and sequential logic that can be tested by applying test patterns to the sequential logic and reading scan chain outputs;

for one or more scan cells in scan chains, determining respective lists of failures that will be observed at the scan chain outputs when each of the one or more scan cells has a defined fault; and

generating a fault dictionary representative of the respective lists of failures for each of the one or more scan cells.

8. The one or more non-transitory computer-readable media of claim 7, wherein the method further comprises:

determining a difference between failures for a first scan cell in a scan chain versus failures for a second scan cell in the scan chain; and

storing the difference in failures as a fault signature for the first scan cell in the fault dictionary.

9. The one or more non-transitory computer-readable media of claim 8, wherein the first scan cell and the second scan cell are adjacent to one another in a respective scan chain.

10. The one or more non-transitory computer-readable media of claim 7, wherein the method further comprises storing a complete list of failures as a fault signature for at least one scan cell in a respective scan chain in the fault dictionary.

11. The one or more non-transitory computer-readable media of claim 7, wherein the generating a fault dictionary representative of the respective lists of failures for each of the one or more scan cells comprises:

generating a complete fault signature for a first scan cell; and

generating an incomplete differential fault signature for a second scan cell from which a complete fault signature for the second scan cell can be recreated.

12. The one or more non-transitory computer-readable media of claim 7, wherein the generating a fault dictionary representative of the respective lists of failures for each of the one or more scan cells comprises generating a differential fault signature from which a complete fault signature can be determined with reference to a base fault signature.

13. A system, comprising:

a processor; and

a memory storing instructions which when executed by the processor cause the processor perform a method, the method comprising;

receiving a description of an integrated circuit that includes combinational and sequential logic that can be tested by applying test patterns to the sequential logic and reading scan chain outputs;

for one or more scan cells in scan chains, determining respective lists of failures that will be observed at the scan chain outputs when each of the one or more scan cells has a defined fault; and

storing a fault dictionary representative of the respective lists of failures for each of the one or more scan cells.

14. The system of claim 13, wherein the method further comprises:

determining a difference between failures for a first scan cell in a scan chain versus the failures for a second scan cell in the scan chain; and

storing the difference in failures as a fault signature for the first scan cell in the fault dictionary.

15. The system of claim 14, wherein the first scan cell and the second scan cell are adjacent to one another in a respective scan chain.

16. The system of claim 13, wherein the method further comprises storing a complete list of failures as a fault signature for at least one scan cell in a respective scan chain in the fault dictionary.

17. The system of claim 13, wherein the storing a fault dictionary representative of the respective lists of failures for each of the one or more scan cells comprises:

storing a complete fault signature for a first scan cell; and

storing an incomplete differential fault signature for a second scan cell from which a complete fault signature for the second scan cell can be recreated.

18. The system of claim 13, wherein the storing a fault dictionary representative of the respective lists of failures for each of the one or more scan cells comprises:

determining a differential fault signature from which a complete fault signature can be determined with reference to a base fault signature; and

storing the differential fault signature.