Fault Modeling and ATPG (Automatic Test Pattern Generation) Quiz Quiz

Explore essential concepts in fault modeling and Automatic Test Pattern Generation (ATPG), including stuck-at faults, fault coverage, ATPG algorithms, and practical testing techniques. Ideal for anyone seeking to strengthen their understanding of digital circuit verification processes.

1. Types of Faults in Digital Circuit Testing

   In digital circuit fault modeling, which of the following best describes a stuck-at-1 fault affecting a logic gate's output?

   1. The output randomly toggles between high and low.
   2. The output is stuck at logic low under all input conditions.
   3. The input is always held at logic high.
   4. The output is always logic high, regardless of input values.

   Explanation: A stuck-at-1 fault in fault modeling assumes that a given node or output is permanently fixed at logic high, regardless of the actual circuit behavior or applied inputs. Option C incorrectly refers to the input, not the output. Choice D describes a stuck-at-0 fault, which is the inverse of stuck-at-1. Option B describes a random fault, not a stuck-at fault. Only the correct choice matches the stuck-at-1 definition.

2. Purpose of ATPG

   What is the primary goal of Automatic Test Pattern Generation (ATPG) in digital design verification?

   1. To reduce static power consumption in logic gates.
   2. To generate a sequence of test patterns that maximize fault detection coverage.
   3. To convert analog signals into digital signals within the system.
   4. To accelerate the clock frequency of the circuit.

   Explanation: ATPG's main objective is to automatically create test patterns that efficiently detect modeled faults, such as stuck-at or bridging faults. Option B relates to performance enhancement rather than testing. Choice C is concerned with power optimization, which is outside ATPG's scope. Option D describes data conversion, not test pattern generation. Thus, only the correct option addresses ATPG's true goal.

3. Fault Coverage Calculation

   Suppose an ATPG tool detects 150 faults out of 200 modeled faults in a circuit. What is the fault coverage percentage reported?

   1. 75%
   2. 80%
   3. 50%
   4. 85%

   Explanation: Fault coverage is calculated as the number of detected faults divided by the total modeled faults, multiplied by 100. In this case, 150 divided by 200 equals 0.75, or 75%. Option B incorrectly states 50%, which would require 100 faults detected. Choices C and D overestimate the coverage for the given values. Only 75% is accurate based on the scenario.

4. Classification of Fault Models

   Which of the following is considered a logical fault model commonly used in combinational ATPG?

   1. Dynamic power fault
   2. Stuck-at fault model
   3. Electromigration model
   4. Aging defect model

   Explanation: The stuck-at fault model, assuming a signal line is permanently fixed at logic 0 or 1, is a standard logical fault model for combinational ATPG. Options B and C relate to physical or aging-related failure mechanisms rather than logical modeling. Dynamic power fault in option D refers to a performance or power issue, not a logical fault. The correct answer is the only logical model listed.

5. ATPG Algorithm Types

   In ATPG, which type of algorithm is exemplified by the D-algorithm used for test generation?

   1. Probabilistic algorithm
   2. Heuristic algorithm
   3. Analog modeling algorithm
   4. Deterministic algorithm

   Explanation: The D-algorithm is a well-known deterministic approach to ATPG, systematically generating patterns that guarantee detection of specific faults. Probabilistic algorithms, option B, involve randomness, which is not characteristic of the D-algorithm. Heuristic algorithms, option C, rely on approximations and are not strictly deterministic. Option D refers to analog domains, which are irrelevant here. Hence, deterministic algorithm is correct.