Occurrence frequency (%)
51 1 6
13 6 8 5 5 5
Ref.: J. Bateson, In-Circuit Testing, Van Nostrand Reinhold, 1985.
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3 Common Fault Models 公共的故障模型
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4.1 Fault Equivalence 故障等价性
Number of fault sites in a Boolean gate circuit = #PI + #gates + # (fanout branches).
Fault equivalence: Two faults in a boolean circuit are called equivalent iff they transform the circuit such that the two faulty circuits have identical output functions.
Single stuck-at faults Transistor open and short faults Memory faults PLA faults (stuck-at, cross-point, bridging) Functional faults (processors) Delay faults (transition, path) Analog faults For more examples, see Section 4.4 (p. 60-70) of
应用：When dominance fault collapsing is used, it is sufficient to consider only the input faults of Boolean gates. See the next example.
特例：In a tree circuit (without fanouts) PI faults form a dominance collapsed fault set.
Lecture 5 Fault Modeling 第五讲：故障模型
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2.1 Observed PCB Defects 可观察的PCB缺陷
Defect classes
Shorts Opens Missing components Wrong components Reversed components Bent leads Analog specifications Digital logic Performance (timing)
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4.2 Equivalence Rules 等价规则
sa0 sa1
AND
sa0 sa1
sa0 sa1 sa0 sa1
OR
sa0 sa1
sa0
sa0
sa1
sa1
WIRE sa0 sa1
sa0 NOT
sa1
sa1 sa0
sa0 sa1
NAND
sa0 sa1
the book.
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4 Single Stuck-at Fault 单固定故障
Three properties define a single stuck-at fault
➢Only one line is faulty ➢The faulty line is permanently set to 0 or 1 ➢The fault can be at an input or output of a gate
sa0 sa1
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sa0 sa1
sa0 sa1
Faults in green removed by equivalence sa0 sa1 collapsing
sa0 sa1
sa0 sa1
sa0 sa1
sa0 sa1
sa0 sa1
20 Collapse ratio = ----- = 0.625
Example: XOR circuit has 12 fault sites ( ) and 24
single stuck-at faults
Faulty circuit value Good circuit value
c ad
1
0b e
s-a-0
gh
1i
j
0(1) 1
1(0)
z
f
k
Test vector for h s-a-0 fault
32
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4.4 Fault Dominance 故障支配性
定义：If all tests of fault F1 detect another fault F2, then F2 is said to dominate F1.
规则：Dominance fault collapsing: If fault F2 dominates F1, then F2 is removed from the fault list.
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sa0 sa1 sa0 sa1
sa0 sa1
NOR
VLSI TesΒιβλιοθήκη : Lecture 5sa0 sa1
sa0
sa0
sa1
sa1
sa0
FANOUT sa1
9
4.3 Equivalence Example 等价实例
sa0 sa1
sa0 sa1 sa0 sa1
sa0 sa1 sa0 sa1 sa0 sa1 sa0 sa1
Fault collapsing: All single faults of a logic circuit can be divided into disjoint equivalence subsets, where all faults in a subset are mutually equivalent. A collapsed fault set contains one fault from each equivalence subset.