In this module we will study automatic test pattern generation (ATPG) using sensitization–propagation -justification approach. We will first introduce the basics of. 1. VLSI Design Verification and Testing. Combinational ATPG Basics. Mohammad Tehranipoor. Electrical and Computer Engineering. University of Connecticut. Boolean level. • Classical ATPG algorithms reach their limits. ➢ There is a need for more efficient ATPG tools! 6. Circuits. • Basic gates. – AND, OR, EXOR, NOT.

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A fault model is a mathematical description of how a defect alters design behavior. The ATPG process for a targeted fault consists of two phases: Testing very-large-scale integrated circuits with a high fault coverage is a difficult task because atgp complexity.

Combinational ATPG Basics

Bridging to VDD or Vss is equivalent to stuck at fault model. In such a circuit, any single fault will be inherently undetectable.

For designs that are sensitive to area or performance overhead, the solution of using sequential-circuit ATPG and partial scan offers an attractive alternative to the popular full-scan solution, which is based on combinational-circuit ATPG. A short circuit between two signal lines is called bridging faults. These metrics generally indicate test quality higher with more fault detections basicw test application time higher with more patterns.

This allows using a relatively simple vector matrix to quickly test all the comprising FFs, as nasics as to trace failures absics specific FFs. Retrieved from ” https: If one driver dominates the other driver in a bridging situation, the dominant driver forces the logic to the other one, in such case a dominant bridging fault is used.

In the past several decades, the most popular fault model used in practice is the single stuck-at fault model.

NPTEL :: Computer Science and Engineering – VLSI Design Verification and Test

Views Read Edit View history. The combinational ATPG method allows testing the individual nodes or xtpg of the logic circuit without being concerned with the operation of the overall circuit.


Equivalent faults produce the same faulty behavior for all input patterns. By using this site, you agree to the Terms of Use and Privacy Policy.

Fault basicx establishes a signal value at the fault model site that is opposite of the value produced by the fault model. Also, due to the presence of memory elements, the controllability and observability of the internal signals in a sequential circuit are in general much more difficult than those in a combinational logic circuit.

Fault propagation moves the resulting signal value, or fault effect, forward by sensitizing a path from the fault site to a primary output. This observation implies that a test generator basocs include a comprehensive set of heuristics. It is also called a permanent fault model because the faulty effect is assumed to be bascs, in contrast to intermittent faults which occur seemingly at random and transient faults which occur sporadically, perhaps depending on operating conditions e.

A defect is an error caused in a device during the manufacturing process.

The logic values observed at the device’s primary outputs, while applying a test pattern to some device under test DUTare called the output of that test pattern. This tapg was last edited on 23 Novemberat Therefore, many different ATPG methods have been developed to address combinational and sequential circuits.

However, atpt to reported results, no single strategy or heuristic out-performs others for all applications or circuits. For nanometer technology, many current design validation problems are becoming manufacturing test problems as well, so new fault-modeling and ATPG techniques will be needed.

Automatic test pattern generation – Wikipedia

Second, it is possible that a detection pattern exists, but the algorithm cannot find one. The classic example of this is a redundant circuit, designed such that no single fault causes the output to change. Various search strategies and heuristics have been devised to find a at;g sequence, or to find a sequence faster. From Wikipedia, the free encyclopedia.


During design validation, engineers can no longer ignore the effects of crosstalk and power supply noise on reliability and performance. Historically, ATPG has bssics on a set of faults derived from a gate-level fault model. At transistor level, a transistor maybe stuck-short or stuck-open. Even a simple stuck-at fault requires a sequence of vectors for detection in a sequential circuit.

Automatic test pattern generation

During test, a so-called scan-mode is enabled forcing all flip-flops FFs to be connected in a simplified fashion, effectively bypassing their interconnections as intended during normal operation.

As design trends move toward nanometer technology, new manufacture testing problems are emerging. In this model, one of the signal lines in a circuit is assumed to be stuck at a fixed logic value, regardless of what inputs are supplied to the circuit. ATPG is a topic that is covered by several conferences throughout the year.

First, the fault may be intrinsically undetectable, such that no patterns exist that can detect that particular fault. The effectiveness of ATPG is measured by the number of modeled defects, or fault modelsdetectable and by the number of generated patterns.

ATPG efficiency is another important consideration that is influenced by the fault model under consideration, the type of circuit under test full scansynchronous sequential, or asynchronous sequentialthe level of abstraction used to represent the circuit under test gate, register-transfer, switchand the required test quality.