Measuring mixed-signal test stimulus quality

The percentage of circuit elements stimulated by a test stimulus applied to a mixed-signal circuit is analogous to the toggle coverage of a test pattern applied to a digital circuit and can serve as an estimate of the quality of, or maximum test coverage achievable with, that stimulus. This paper proposes a novel definition for analog activity coverage and how to measure it in a defect-free circuit for any potential defects (shorts, opens, and parametric). Results are provided for the ITC'17 analog benchmark circuits and show that activity coverage is an approximate upper limit for defect coverage. Other uses for measuring test stimulus quality are discussed, such as assessing burn-in and over-voltage stress stimuli, and ensuring defect tolerance measured for ISO 26262 is accurate.