Automatic Window Repositioning Technique for Digital Window Comparator Used Within Mixed-Signal Design-for Testability Schemes

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The construction of digital window comparators for the on-chip evaluation of analogue signals within the mixed-signal integrated circuit is reviewed. One of the difficulties in their application is due to the lot-to-lot variation of the comparator window. A technique that allows the automatic window repositioning is described by which the window shift can be compensated. For this automatic compensation a so-called reference comparator is required. From the reference comparator the control signal are derived to select the actual configuration of the used evaluation comparators. It is shown, that this technique allows the automatic lot condition adjustment of the evaluation comparators by repositioning the windows of those comparators. As a synergy effect this technique provides lot specific information for an automated test equipment that can be documented in the test results for further diagnosis and traceability capabilities.