Built-in test sequence generation for synchronous sequential circuits based on loading and expansion of test subsequences

We describe an on-chip test generation scheme for synchronous sequential circuits that allows at-speed testing of such circuits. The proposed scheme is based on loading of (short) input sequences into an on-chip memory, and expansion of these sequences on-chip into test sequences. Complete coverage of modeled faults is achieved by basing the selection of the loaded sequences on a deterministic test sequence T₀, and ensuring that every fault detected by To is detected by the expanded version of at least one loaded sequence. Experimental results presented for benchmark circuits show that the length of the sequence that needs to be stored at any time is on the average 10% of the length of T₀, and that the total length of all the loaded sequences is on the average 46% of the length of T₀