Trading Off Test Coverage and False Reject Risk of Self-Calibrating Self-Test Systems

Self-calibrating systems are becoming more popular as increasing variability in shrinking geometries demands compensating techniques. Comparator based self-calibration is the most common base for self-compensating circuits due to its minimum overhead. If a self-test feature is added, care must be taken that the tails of the calibrated distribution are not causing false rejects. This paper presents the implementation and verification of an ultra-low current reference which is self-calibrated and self-tested. By introducing two independent unit test elements, instead of one fixed test element of 1.5 LSB, more headroom for distribution tails is gained. Using a simple fault model of the trim DAC, the paper investigates the trade-off between test coverage and the risk of false rejects.