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TOPIC : Introduction to Fault Simulation

TOPIC : Introduction to Fault Simulation. UNIT 2 : Fault modeling. Module 2.4 Fault Simulation. Introduction. Definition: Simulating a faulty circuit is known as fault simulation.

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TOPIC : Introduction to Fault Simulation

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  1. TOPIC : Introduction to Fault Simulation UNIT 2 : Fault modeling Module 2.4 Fault Simulation

  2. Introduction • Definition: Simulating a faulty circuit is known as fault simulation. • Aim of fault simulation is to arrive a test (set of vectors) which can detect any possible fault in a given circuit. • We analyze the operation of the circuit under various fault conditions.

  3. Applications of Fault Simulation • Evaluate a test – How effective the test is? • Fault coverage • Defect level • Test generation – During test generation we simulate the circuit for the given test. • Used in constructing fault dictionaries • Analyzing the operation in the presence of faults

  4. Fault Dictionary • The outputs of the simulated circuits are stored in the form of fault dictionaries. • It is a database generated by a fault simulator for diagnosing of faults. • It gives the relation between the fault and the corresponding output that results because of the fault. • This information can be used to identify the fault from the measured output of a faulty circuit.

  5. Fault Simulation concept • To obtain information on different faults in a circuit, one simulates the healthy circuit and the faulty circuit. • If the outputs of both the circuits are different for the considered test pattern, then we say that the fault is detectable.

  6. How to arrive at a test set? • A test set is to be developed that can detect any possible fault in the given circuit. • There are two approaches: 1) Random Test Generation (RTG) 2) Fault-targeted Test Generation (FTG)

  7. Random Test Generation • Take a random vector as test vector. • Calculate the performance of the circuit with & without faults. • Identify all the faults that can effect the output for this test vector. • Remove the covered faults from the fault list. • If there are some more faults in the fault list, take another random vector and repeat the process until the fault list becomes empty.

  8. Flow diagram of RTG

  9. Fault-targeted Test Generation(FTG) • Here we start with a vector which can detect a specified fault.

  10. RTG & FTG • The fault targeted simulation is a slow process initially compared to RTG. • If the number of faults is high, then a random test vector can detect more faults. If we use FTG then we need to generate a test for each single fault. • If the number of faults still left to be tested is less, then FTG is used. • Hence one adopts RTG in the initial stage when the number of faults to be tested are very high and when the number gets reduced, FTG is used.

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