Test point insertion using functional flip-flops to drive control points

Abstract

This paper presents a novel method for reducing the area overhead introduced by test point insertion. Test point locations are calculated as usual using a commercial tool. However, the proposed method uses functional flip-flops to drive control test points instead of test-dedicated flip-flops. Logic cone analysis that considers the distance and path inversion parity from candidate functional flip-flops to each control point is used to select an appropriate functional flip-flop to drive the control point which avoids adding additional timing constraints. Reconvergence is also checked to avoid degrading the testability. Experimental results indicate that the proposed method significantly reduces test point area overhead and achieves essentially the same fault coverage as the implementations using dedicated flipflops driving the control points.

Comparison of two approaches to improve functional BIST fault coverage

“…A very efficient method to cope with RPR faults is test point insertion [9,10], used either to improve the controllability or observability of internal signals in the circuit [9,10,17]. Since test points add area and performance overhead, an important issue for test point insertion is where to place them in CUT in order to maximize the fault coverage at minimum number of test points.…”

Improving Small-Delay Fault Coverage of On-Chip Delay Measurement by Segmented Scan and Test Point Insertion

“…There are two types of TPI methods, namely observation point insertion and control point insertion [27]. As shown in Fig.…”

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

“…With a conservative replacement rule [36], if both inversion parities are found along paths from the control point to one flip-flop, that flipflop is discarded from the candidate list. This guarantees that paths are always testable by having the opposite parity along the Functional Path and TP_Driver Path.…”

“…Preliminary results were presented in [36]. A key feature of the proposed approach is that it significantly reduces the test point area overhead by removing the dedicated flip-flops used for driving the control points.…”