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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At transistor level, a transistor maybe stuck-short or stuck-open. 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.
The combinational ATPG method allows testing the individual nodes or flip-flops of the logic circuit without being concerned with baskcs operation of the overall circuit. The effectiveness of ATPG is measured by the number of modeled defects, or fault modelsdetectable and by the number of generated patterns. As design trends move toward nanometer technology, new manufacture testing problems are emerging.
ATPG efficiency is another important consideration that is influenced by the fault model under consideration, the type of circuit stpg 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. However, basic to reported results, no single strategy or heuristic out-performs others for all applications or circuits.
First, the fault may be intrinsically undetectable, such that no patterns exist that can detect that particular fault. 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.
Combinational ATPG Basics
In the latter case, dominant driver keeps its value, while the other one gets the AND or OR value of its own and the dominant driver. The output of a test pattern, when testing a fault-free device that works exactly as designed, is called the expected output of that test pattern.
Testing very-large-scale integrated circuits with a high fault coverage is a difficult task because of complexity. Removing equivalent faults from entire set of faults is called fault collapsing.
Automatic test pattern generation – Wikipedia
During design validation, engineers can no longer ignore the effects of crosstalk and power supply noise on reliability and performance. Any basivs fault from the set of equivalent faults can represent the whole set. Equivalent faults produce the same faulty behavior for all input patterns.
It is also called a permanent fault model because the faulty effect is assumed to be permanent, in contrast to intermittent faults which occur seemingly at random and transient faults which occur sporadically, perhaps depending on operating conditions e.
Retrieved from ” https: ATPG can fail to find a test for a particular fault in at least two cases. This model is used to describe faults for CMOS logic gates.
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.
Fault activation establishes a signal value at the fault model site that is opposite of the value produced by the fault model. 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 basicx ATPG.
From Wikipedia, the basica encyclopedia.
The ATPG process for a targeted fault consists of two phases: Historically, ATPG has focused on a set of faults derived from a gate-level fault model. The apg patterns are used to test semiconductor devices after manufacture, or to assist with determining the cause of failure failure analysis .
Combinational ATPG Basics
Hence, if a circuit has n signal lines, there are potentially 2n stuck-at faults defined on the circuit, of which some can be viewed as being equivalent to others. Current fault modeling and vector-generation techniques are giving way to new models and techniques that consider timing information during test generation, that are scalable to larger designs, and that can capture extreme design conditions.
In such a circuit, any single fault will be inherently undetectable.
The classic example of this is a redundant circuit, designed such that no single fault causes the output to change. Second, it is possible that a detection pattern exists, but the algorithm cannot find one. The stuck-at fault model is a logical fault model because no delay information is associated with the fault definition. Sequential-circuit ATPG searches for a sequence of test vectors to detect a particular fault through the space of all possible test vector sequences.
The single stuck-at fault model is structural because it is defined based on a structural gate-level circuit model. A defect is an error caused in a device during the manufacturing process.