Self-Positioning Digital Window Comparators for Mixed-Signal DfT

The use of simple digital window comparators for the on-chip evaluation of analogue signals is described. It is shown that a window can be created by choosing different gate input configurations. The potential problem of lot-to-lot variation of the comparator window position can be compensated by an on-chip repositioning technique. The components for the implementation comprise of a reference comparator and the evaluation comparators that are described along with the implementation of the technique. It is shown, that this technique allows the automatic lot condition adjustment for the evaluation comparator windows. The technique can optionally provide lot condition diagnostics for the test record as well as diagnosis of the actual window selection of the evaluation comparator.