Automatic repositioning technique for digital cell based window comparators and implementation within mixed-signal DfT schemes

The possibility of using window comparators for the on-chip evaluation of signals in the analogue circuit part has been demonstrated and is shortly summarized. One of the problems is the lot-to-lot variation of the comparator window. An automatic window repositioning technique is detailed that allows to compensate the window shift. The components for the implementation comprising a reference comparator and the evaluation comparators are described along with the implementation of the technique. It is shown, that this technique allows the automatic lot condition adjustment of the evaluation comparators. Furthermore the technique can provide lot specific information to an automated test equipment that can be documented in the test results due to its diagnosis capability.