Reducing Test Data Volume Using Random-Testable and Periodic-Testable Scan Chains in Circuits with Multiple Scan Chains

For a scan design with multiple scan chains, we say that a scan chain is random-testable if it is possible to achieve complete fault coverage for the circuit (i.e., detect all the detectable circuit faults) when the scan chain is driven from a source of pseudo-random values for the complete test application process. Similarly, a periodic-testable scan chain can be driven from a source that produces a periodic sequence for the complete test application process. Both pseudo-random and periodic sources are simple to implement on-chip. By identifying scan chains that can be driven from pseudo-random and periodic sources and driving them from the appropriate on-chip sources, we reduce the number of scan chains that need to be driven from an external tester. In this way, we reduce the number of scan inputs that a tester needs to control and the amount of test data that the external tester needs to store and apply to the circuit. Existing test data compression techniques can be used to further reduce the test data volume.