Boundary-Functional Broadside and Skewed-Load Tests

Abstract

Close-to-functional broadside tests are used for avoiding overtesting of delay faults that can result from non-functional operation conditions, while avoiding test escapes because of faults that cannot be detected under functional operation conditions. When a close-to-functional broadside test deviates from functional operation conditions, the deviation can affect the entire circuit. This article defines the concept of a boundary-functional broadside test where non-functional operation conditions are prevented from crossing a preselected boundary. Using the procedure described in this article, the boundary maintains the same values under a boundary-functional broadside test as under a functional broadside test from which it is derived. Indirectly, this ensures that the deviations from functional operation conditions throughout the entire circuit are limited. The concept of a boundary-functional broadside test is extended to skewed-load tests, and to partial-boundary-functional tests. Experimental results are presented for benchmark circuits to demonstrate the fault coverage improvements that can be achieved using boundary-functional broadside and skewed-load tests as well as partial-boundary-functional tests of both types.

LFSR‐based generation of boundary‐functional broadside tests

“…While partially invariant patterns ensure that the deviation from functional operation conditions does not increase with additional clock cycles of the test, boundary‐functional broadside tests address the fact that the deviations from functional operation conditions, which start with the scan‐in state, may affect the entire circuit at every clock cycle [17]. As they propagate through the circuit, the deviations are magnified relative to the deviations measured by the scan‐in state.…”

“…As a result, a fault-free circuit may fail a scan-based delay test, resulting in overtesting [1][2][3]. Overtesting is addressed by test generation procedures that create functional or close-to-functional operation conditions during their functional capture cycles [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. These clock cycles are important since delay faults are detected during these clock cycles.…”

“…The boundary-functional broadside tests considered in this paper address the fact that deviations from functional operation conditions may affect the entire circuit at every clock cycle [17]. As they propagate through the circuit, the deviations are magnified.…”