Design for test of analog and mixed-signal circuits

Rapid advances in VLSI technology have led to a significant increase in device density. Even today over 5 million transistors can be accommodated on a single integrated circuit. Test times now form a large fraction of the total design cost and is likely to dominate in the future. This is more pronounced for analog and mixed-signal integrated circuits. The primary purpose of manufacture-time test is to verify performance and detect faults caused by local and global parameter variations and spot defects. Traditional analog test technique verify correct operation by checking functionality, i.e., all performance parameters are checked to see if they meet specifications. Defect based test techniques target faults resulting from specific defect occurrences. A design for test (DFT) method redesigns a circuit to improve the fault coverage and/or reduce the total test cost. In this tutorial we discuss the various approaches for on- and off-line test. We present DFT techniques for a variety of analog and mixed-signal circuits. We address specific design concerns and present simulation and measurement results from a number of fabricated designs.