Fault Models Flashcards
What is a fault model?
A fault model is an abstraction of a defect occurring during manufacture or in the field.
They differ in the kinds of defects that can be modelled and in their accuracy.
What is a fault.
Is an structural change caused by a defect.
What is defect analysis? And why is it used?
Maps defects to faulty behaviours. It is used to generate the set of faults for which tests are generated.
It typically analyses the critical areas of a chip(areas where a defect changes the behaviour of a system).
What is a test vector.
Is an input pattern which causes the faulty and the faulty free circuit to produce different values.
What is structural testing?
Is to use fault models based on the structural information of the circuit for testing.
What is Fault coverage.
And the difference to effective fault coverage.
Given the set of test vectors, we can give a quantitative measure of its quality w.r.t. the fault model.
Some faults cannot be detected by any test vector. Effective fault coverage takes them into account.
Detected Faults Fault Coverage = --------------------------------------------------
Total Faults - Undetected Faults
What are the single stuck at fault assumptions
The defects modelled are assumed to tie a gate‐level signal to a constant value
Only a single fault occurs in the circuit.
On the switch level, stuck at fault model cannot model accurately faulty behaviour.
Which fault models are used in CMOS transistors?
stuck open
stuck short
What is required to test a stuck open fault?
Sequence of vectors to trigger changes in the circuit to test them.
What is a transition delay fault?
A delay fault results in a delayed arrive of a transition at a flip flop or primary output of a circuit.
What is a path delay fault? Which paths are considered?
A path from input to the output propagates a transition with additional delay.
Not possible to consider all paths.
Normally only long path or time critical paths are considered.
How are bridging faults modelled?
It is modelled as a new element which ties the two wires together, causing oscillation, asynchronous or undefined behavior.
