Feb 20, 2008 E0-286@SERC 1

VLSI Testing Sequential ATPG - I

VLSI Testing Sequential ATPG - I

Virendra SinghIndian Institute of Science (IISc)

Bangalorevirendra@computer.org

E0-286: Testing and Verification of SoC Design

Lecture – 14

Feb 20, 2008 E0-286@SERC 2

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Static and Dynamic Compaction of Sequences

Static and Dynamic Compaction of Sequences

Static compactionATPG should leave unassigned inputs as XTwo patterns compatible – if no conflicting values for any PICombine two tests ta and tb into one testtab = ta tb using D-intersection Detects union of faults detected by ta & tb

Dynamic compactionProcess every partially-done ATPG vector immediatelyAssign 0 or 1 to PIs to test additional faults

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Compaction ExampleCompaction Example

t1 = 0 1 X t2 = 0 X 1t3 = 0 X 0 t4 = X 0 1

Combine t1 and t3 , then t2 and t4

Obtain:

t13 = 0 1 0 t24 = 0 0 1

Test Length shortened from 4 to 2

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ATPG based Formal Verification

ATPG based Formal Verification

A

B

C

C

A

B

Z

s-a-0

P

Q

R

S

T

Formal Equivalence Checking

Feb 20, 2008 E0-286@SERC 5

Formal Equivalence Checking

Formal Equivalence Checking

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Sequential CircuitsSequential CircuitsA sequential circuit has memory in addition to combinational logicTest for a fault in a sequential circuit is a sequence of vectors, which

Initializes the circuit to a known stateActivates the fault, andPropagates the fault effect to a PO

Methods of sequential circuit ATPGTime-frame expansion methodsSimulation-based methods

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Example: A Serial AdderExample: A Serial Adder

FF

An Bn

Cn Cn+1

Sn

s-a-0

11

1

1

1X

X

X

D

D

Combinational logic

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Time-Frame ExpansionTime-Frame Expansion

An Bn

FF

Cn Cn+11

X

X

Sn

s-a-011

1

1

D

D

Combinational logicSn-1

s-a-011

1

1 X

D

D

Combinational logic

Cn-1

1

1

D

D

X

An-1 Bn-1 Time-frame -1 Time-frame 0

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Concept of Time-FramesConcept of Time-FramesIf the test sequence for a single stuck-at fault contains n vectors,

Replicate combinational logic block n timesPlace fault in each blockGenerate a test for the multiple stuck-at fault

using combinational ATPG

Comb.block

Fault

Time-frame

0

Time-frame

-1

Time-frame-n+1

Unknownor given

Init. state

Vector 0Vector -1Vector -n+1

PO 0PO -1PO -n+1

Statevariables

Nextstate

Feb 20, 2008 E0-286@SERC 10

Thank YouThank You