17-05-2012, 10:36 AM
Stuck-At Fault: A Fault Model for the next Millennium?
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Stuck-At Fault as a Logic Fault
Stuck-at Fault is a Functional Fault on a Boolean
(Logic) Function Implementation
It is not a Physical Defect Model
Stuck-at 1 does not mean line is shorted to VDD
Stuck-at 0 does not mean line is grounded!
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
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?
Defect Detection in a NAND Gate
For a 2-input NAND gate, the complete stuck-at
test set is: AB = 01, 10 and 11
With a defect in the NAND cell, the gate may
produce any combinations of 0, 1, N, Z
N is an indeterminate logic value (active, driven)
Z is a floating node with unknown charge (passive)
Each of 4 possible input vectors can produce any
of the 4 possible output values
256 possible defective behaviors for 2-input NAND
Infinitely many delay and current behaviors
Is the stuck-at test set 01, 10 and 11 sufficient?