Collaborative Research: High Quality Tests for Scan Circuits

Purdue University, West Lafayette IN

Investigators

Abstract

The goal of this research is to develop scalable procedures for the derivation of high-quality tests specifically designed for digital logic circuits that contain scan to enhance testability. Such procedures are needed since scan (either full or partial scan) is currently used in most electronic chips, and is expected to continue to be the prevalent design-for-testability technique for design paradigms such as core-based design. The investigators develop procedures for test generation, test compaction, identification of undetectable faults, built-in test generation and delay fault testing specifically targeting scan circuits. In the test application scheme used in this research, a sequence of one or more primary input vectors is applied between every two scan operations. In all the procedures developed, the goal is to use sequences of primary input vectors that are as long as possible. The reasons are that long sequences of primary input vectors contribute to at-speed testing of the circuit, which is important for detecting delay defects, and they allow the number of tests to be kept low, which reduces the test application time. In addition, the circuit operates in its normal mode of operation, potentially resulting in average power consumption which is typical of normal operation. Several commercial tools use the test application scheme adopted in this research, justifying its consideration. However, only a small number of studies have been reported in the literature of effective solutions to the various testing problems under this scheme. This research develops tools that may be used together to provide a comprehensive and scalable solution to the special problems associated with testing of scan circuits under this test application scheme.