The Research On Delay Test Algorithm Based On Bounded Delay Model

Delay test is used to detect the defect that is arised from the too long propagationtime of the signal along a path. The path delay fault model(PDFM) is the commonlyused model for its accuracy. There are numerous paths in a circuit based on PDFMand we can’t test all the paths, so I select a subset of all paths as our test target toguarantee the correctness of our circuit. In addition,based on the transition faultmodel,there are some small delay defects(SDD) which can influence the timing actionof the circuit,we must select the longest path through the fault site to detect thedefect.Path selection is a important issue in delay test. I select thek (k1)longesttestable paths through each gate based on the bounded delay model(BDM).BDMdefine the upper and lower bounds of the path node delay and can describe thedistribution of the delay in the circuit more precisely compared to the unit delaymodel.The path we select must be also testable,only the testable paths can influencethe timing action of the circuit. Based on BDM,I select the non-robust testablepaths,the untestable path is recognized by the sensitization condition of that path.Idefine the u line and the b fpairs to record the untestable information and itspeeds up the process of paths selection.Some testabe paths in other delay model maybeacome untestable in BDM,so we can get more untestable information and select thereally testable paths in real circuit.The selected paths is used for the test generator as the propagation paths ofSDD,but the test vector set is too large and should be compacted.The sensitizationcondition of two paths don’t conflict can be detected by a single test vector.In order tocompact the test vector effectively in a proper time,before the process of compaction,I define the influence cone to analyse the conflict probability of two paths.The lessoverlap of two paths has less conflict probability and should be selected first forcompaction.The computation of influence cone of my method based on controllabilityjudge the conflict probability more precisely,and I use fault simulation in the processof compaction, these measures make the compact result more better. The experimenton the ISCAS’89and IWLS’05benchmark circuits demonstrate the effectiveness ofmy method.