VLSI Multiple Choice Questions on “Fault Models”.
1. Which are processing faults?
A. missing contact window
B. parasitic transistor
C. oxide breakdown
D. all of the mentioned
Answer: D
Clarification: Some of the real defects in chip such as processing faults are missing contact window, parasitic transistor and oxide breakdown.
2. Surface impurities occurs due to ion migration.
A. true
B. false
Answer: A
Clarification: Some of the material defects are bulk defects and surface impurities. Bulk defects are cracks and crystal imperfection and surface impurities occurs due to ion migration.
3. Electromigration is a
A. processing fault
B. material defects
C. time dependent failure
D. packaging fault
Answer: C
Clarification: Different types of real defects in chips are processing fault, material defects, time dependent failure and packaging fault. Time dependent failures are dielectric breakdown and electromigration.
4. Which relation is correct?
A. failure – error – fault
B. fault – error – failure
C. error – fault – failure
D. error – failure – fault
Answer: B
Clarification: The relation fault – error – failure is correct. Error is caused by faults and failure which is a deviation of the circuit is caused by error.
5. For a circuit with k lines __________ single stuck-at fault is possible.
A. k
B. 2k
C. k/2
D. k2
Answer: B
Clarification: For a circuit with k lines, 2k single stuck-at faults are possible and 3^k – 1 multiple stuck-at faults are possible.
6. Single stuck-at fault is technology independent.
A. true
B. false
Answer: A
Clarification: Single stuck-at fault is technology independent. It can be applied to TTL, CMOS etc. It is also design style independent.
7. For a n signal lines circuit _____________ bridging faults are possible.
A. n
B. 2n
C. n2
D. n/2
Answer: C
Clarification: For circuit with n lines, n2 bridging faults are possible. Bridging fault occurs when two lines are connected when they should not be connected. It leads to wired AND or wired OR.
8. IDDQ fault occurs when there is
A. increased voltage
B. increased quiescent current
C. increased power supply
D. increased discharge
Answer: B
Clarification: When input is low, both P and N transistors are conducting causing increase in quiescent current which leads to IDDQ fault.
9. Which fault causes output floating?
A. stuck-open
B. stuck-at
C. stuck-on
D. IDDQ
Answer: A
Clarification: Transistor with stuck-open fault causes output floating. Stuck-open faults requires two vector tests.
10. Data retention time comes under __________ fault.
A. functional fault
B. memory fault
C. parametric fault
D. structural fault
Answer: C
Clarification: One of the memory faults is a parametric fault. Some of the parametric faults are noise margin, data retention time, power consumption, output levels, etc.
11. In PLA, missing cross point in OR-array leads to
A. OR fault
B. growth fault
C. missing fault
D. disappearance fault
Answer: D
Clarification: In PLA, missing cross point in AND array leads to growth fault and missing cross point in OR-array leads to disappearance fault.
12. In PLA, extra crosspoint in AND-array leads to
A. OR fault
B. growth fault
C. missing fault
D. disappearance fault