AC Test Coverage Vs DC test coverage

[dft_learner]

hi,
can any one help me , why does AC test coverage is less than DC coverage .

thanks in advance

 

[Jennis]

can you please elaborate , what do you mean by AC test coverage and DC test coverage???

 

[dft_learner]

AC test - transition test
DC test - Stuck at test

 

[yadavvlsi]

Stuck at test is done at lower frequencies(10-50 MHz). It detects stuck at faults means a particular line is stuck to ground or VDD and opens and shorts in circuits. Transition test is done at speed (actual operating frequency of design). It detect transtion vilations. In lower technolgy node nets are sitting very close. This can lead to crosstalk in the design. Crosstalk increases signal delay, can causes transition violation that can't be detect at lower frequencies. Hence can not be detected in stuck at test.

Crosstalk in digital circuits