Test Point Insertion with Control Points Driven by Existing Functional Flip-Flops

Abstract

Abstract-This paper presents a novel test point insertion method for pseudorandom built-in self-test (BIST) to reduce the area overhead. The proposed method replaces dedicated flip-flops for driving control points by existing functional flip-flops. For each control point, candidate functional flip-flops are identified by using logic cone analysis that investigates the path inversion parity, logical distance, and reconvergence from each control point. Four types of new control point structures are introduced based on the logic cone analysis results to avoid degrading the testability. Experimental results indicate that the proposed method significantly reduces test point area overhead by replacing the dedicated flip-flops and achieves essentially the same fault coverage as conventional test point implementations using dedicated flip-flops driving the control points.

Test Point Insertion with Control Point by Greater Use of Existing Functional Flip-Flops

“…This is the first replacement rule used in [29]. Reference [30] relaxed this rule to replace more dedicated flip-flops. Section III-2-A gives a detailed explanation and an example.…”

“…As a second replacement rule, [29] and [30] check the illegal re-convergence. Illegal re-convergence is defined as a path reconvergence blocking the fault propagation.…”

“…In this paper, we propose a novel TPI method that replaces dedicated flip-flops for control points with functional flip-flops to further reduce the area overhead. Reference [30] introduces a way to replace non-replaceable flip-flops by relaxing the replacement rules in [29]. This paper proposes a different TPI method.…”

“…This paper proposes a different TPI method. Unlike in [30], the proposed method replaces dedicated flip-flops via logic cone analysis without relaxing any replacement rules. It is able to replace more test dedicated flip-flops and achieves significant area reduction.…”

Test-point insertion efficiency analysis for LBIST applications

“…Over the past couple of decades, various research has focused on reducing the number of test points. [20] proposes to reuse the existing flip-flops to drive control points instead of using dedicated flip-flops. In [21], a method is presented to avoid adding extra registers by using pre-existing logic as test points.…”