A method of generating tests for marginal delays and delay faults in combinational circuits

In this paper, we propose an algorithmic method for generating a test for marginal delays and gate delay faults, called an MD test. The time at which the MD test activates the latest transition at the primary output changes linearly with the size of the target delay. (1) The MD tests determine at a given clock rate (observation time) whether a circuit tender test is marginal chip or not. (2) The MD tests determine the maximum circuit clock speeds. (3) The MD test detects the target gate delay fault regardless of the size of the fault by comparing the latest transition time at the primary output of the fault-free circuit and that of the faulty circuit. In order to determine the detectable size of gate delay faults the proposed method introduces a new extended timed calculus which calculates both the latest transition time at the line in the fault-free circuit and the transition time at the same line affected by a gate delay fault of maximum fault size. We also demonstrate experimental results for gate delay faults on ISCAS benchmark circuits to show the performance of our method.