Diagnosis of Multiple Scan-Chain Faults in the Presence of System Logic Defects

We present a combined hardware-software based approach to scan-chain diagnosis, when the outcome of a test may be affected by system faults occurring in the logic out-side of the scan chain. For the hardware component we adopt the double-tree scan (DTS) chain architecture, which has previously been shown to be effective in reducing power, volume, and application time of tests for stuck-at and delay faults. We develop a version of flush test which can resolve a multiple fault in a DTS chain to a small number of suspect candidates. Further resolution to a unique multiple fault is enabled by the software component comprising of fault simulation and analysis of the response of the circuit to test patterns produced by ATPG. Experimental results on benchmark circuits show that near-perfect scan-chain diagnosis for multiple faults is possible even when a large number of random system faults are injected in the circuit.