Compact Set of Functional Broadside Tests with Fault Detection on Primary Outputs

Abstract

When a broadside (launch-on-capture) test is extracted from a functional test sequence, the test addresses the need to avoid overtesting the circuit by exercising it under functional operation conditions. A broadside test t is extracted from a functional test sequence A by duplicating two or more functional capture cycles from A between the scan-in and scan-out operations of t. The functional capture cycles in t detect a fault f if it is activated and propagated to an observable output. This is typically a next-state variable whose value is observed during the scan-out operation of t. This article considers the added requirement that an extracted broadside test would propagate fault effects to the primary outputs. This reduces overtesting further by eliminating the detection of effects that cannot be propagated to the primary outputs during functional operation. The article makes several observations about the use of sequential fault simulation for the efficient extraction of a compact set of broadside tests that detect transition faults on the primary outputs. Experimental results for transition faults in benchmark circuits demonstrate an improved fault coverage and a reduced number of clock cycles for test application.