Path Sensitisation

Path sensitisation is a 4-step algorithmic process, applied per fault:

1. Select a path from the fault site to a primary output.
2. Activate the fault — force the faulty line to the opposite value from its stuck value (so the fault actually causes a difference).
3. Sensitise the path — set every other input along the chosen path so that the path is the only active route to the output.
4. Backward trace to determine what primary inputs produce the required internal values. If steps 2/3 conflict, backtrack and try a different assignment.

Sensitised Paths

For an AND or NAND gate, set all other inputs to 1.

For an OR or NOR gate, set all other inputs to 0.

Thus, the output would depend entirely on the fault line.

In the example above, we get the test vector 110 for fault 1/0.

Comment bq

You can have multiple possible test vectors, as seen below.

Single vs Multiple Paths

When there are multiple paths from the fault site to the output, you can try sensitising either path or both together. However, ALL of the different choices only work sometimes; there is always a risk of failure.

Reconvergent fan-out can prevent us from propagating the fault to the output. If one method doesn’t work, try a different path or method.

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