Hardware Reference
In-Depth Information
Tabl e 4. 4
Resistive bridging fault ATPG results (no compaction)
Procedure RBF ATPG
Stuck-at test sets
Undetect.
faults
Test
patterns
Undetect.
sections
Stuck-at
patterns
G- FC of
s-a patterns
Top-up
patterns
Circuit
Time (s)
c5315
6
384
480
641.63
127
99.37
144
c7552
10
357
704
1,579.12
184
99.47
171
cs15850
8
1,060
501
4,684.61
197
99.07
218
cs35932
148
516
3,213
101,045.79
56
98.75
129
cs38417
1
1,178
1,678
52,233.31
194
98.80
320
cs38584
93
1,822
1,147
89,227.03
209
97.72
487
The tool can fully classify moderate-size circuits. The run times are relatively
high. This is partly because the tool is not highly optimized for speed. For instance,
it employs interval-based simulation and not the faster sectioning-based simulation
(SUPERB was not available at the time the tool was developed) and does not use
state-of-the art speed-up techniques for SAT-based ATPG. On the other hand, the
number of undetectable sections is quite large. Each undetectable section translates
to an unsatisfiable SAT instance which often requires long SAT solving time. On the
other hand, some of these sections might be very small, so their impact on the fault
coverage is negligible. It would be possible to start the SAT solver with a time limit
and treat the sections which could neither be classified as testable or untestable as
coverage loss.
The rightmost three columns of Table 4.4 report the performance of stuck-at test
sets generated by a commercial tool in detecting resistive bridging faults. Their size,
coverage ( G-FC ) and the number of test patterns which procedure RBF AT P G gen-
erated to cover RBFs undetected by the stuck-at test sets to achieve G-FC of 100%
(top-up patterns) are reported. It can be seen that stuck-at test sets do not cover all
RBF. The smaller size of stuck-at test sets compared to RBF test sets is somewhat
misleading, because no static or dynamic compaction of any kind is included in
RBF AT P G while the commercial tool employs sophisticated techniques to opti-
mize the test set size.
We performed an investigation of the average number of faults covered by a test
pattern ( Engelke 2006a ) . It turned out that this number is higher for our tool than for
academic stuck-at tools (with compaction switched off) and resistive bridging fault
test generators published before Cusey ( 1997 ), Sar-Dessai ( 1999 ).
4.4.4
Summary
Resistive bridging fault ATPG can cover all possible bridge resistances by uti-
lizing the sectioning technique. Previously published approaches ( Cusey 1997 ;
Sar-Dessai 1999 ) could not guarantee detection of all possible defects. In its present
shape, our implementation can handle moderate-size circuits. Incorporating known
 
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