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stuck_at_fault_6per_page - Stuck-At Fault: A Fault Model...

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Stuck-At Fault: A Fault Model for the next Millennium? Janak H. Patel Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign © 2005 Janak H. Patel 2 Stuck-At Fault “I tell you, I get no respect!” -Rodney Dangerfield, Comedian “The news of my death are highly exaggerated” -Mark Twain, Author 3 Stuck-At Fault a Defect Model? You can call it - ± Abstract ± Logical ± Boolean ± Functional ± Symbolic ± or Behavioral …. .. Fault Model But don’t call it a Defect Model! 4 Stuck-At Fault as a Logic Fault z Stuck-at Fault is a Functional Fault on a Boolean (Logic) Function Implementation z It is not a Physical Defect Model ± Stuck-at 1 does not mean line is shorted to V DD ± Stuck-at 0 does not mean line is grounded! z It is an abstract fault model ± A logic stuck-at 1 means when the line is applied a logic 0, it produces a logical error ± A logic error means 0 becomes 1 or vice versa 5 Activates the fault s-a-0 on line G by applying a logic value 1 in line G B 1 G s - a - 0 F 1 C H E x D 0 A Fault Excitation 1 0 Y 6 Y B A F 0 C H E X D 0 0 G 1/0 1/0 0 Propagate Error To Primary Output Y ERROR Test Vector A,B,C = 1,0,0 detects fault G s-a-0 1 ERROR
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7 Y B F 0 C H E D 0 0 G 0 G I ERROR Unmodeled Defect Detection 1 Other Logic Defect ERROR ERROR 8 Defect Sites z Internal to a Logic Gate or Cell ± Transistor Defects – Stuck-On, Stuck-Open, Leakage, Shorts between treminals z External to a Gate or Cell ± Interconnect Defects – Shorts and Opens 9 Defects in Physical Cells ± Physical Cells such as NAND, NOR, XNOR, AOI, OAI, MUX2, etc. ± For primitive gates such as NOT, NAND and NOR, stuck-at tests are derived for faults on the pins. ± For complex cells such as XOR, XNOR, AOI, OAI, and MUX2 etc, Stuck-at Tests are assumed to be derived on faults on gate equivalent models. ± How good are these test vectors for a variety of defects? z Do we need additional vectors? z Do we need transistor level details? 10 z Physical VDD ± ± GND ± ± A B ± Fault Modeling z Electrical Z A B Z is Stuck-At-0 X z Logical Z A B Z 11 Non-Logical Values A B open 1 0 ? Indeterminate Value - N 12 Non-Logical Values A B open 1 0 Floating Node - Z
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13 Defect Detection in a NAND Gate z For a 2-input NAND gate, the complete stuck-at test set is: AB = 01, 10 and 11 z With a defect in the NAND cell, the gate may produce any combinations of 0, 1, N, Z ±
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stuck_at_fault_6per_page - Stuck-At Fault: A Fault Model...

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