A novel built-in dynamic supply current monitor for mixed IC testing

The problem of successful testing of mixed-signal integrated circuits (MSIC) is extremely complex. An efficient fault detection methodology must consider problems related to the simultaneous operation of the analogue and digital parts. Power supply current (Idd) test methods are a valid approach to MSIC testing in so far as it would be possible to extract information with a minimal impact upon the performances of the circuit under test (CUT). An important characteristic of Idd testing is derived from its availability to implement a unified and simultaneous test of the analogue and digital parts in a MSIC. Different measurements can he carried out on the Idd; in particular, the analysis of the transient spikes that appear in the Idd (Iddt) would provide a great deal of information about the CUT, overcoming resolution problems in the analogue part due to its larger consumption of Idd. Because of the complexity of the measurement, for such an analysis type, it is necessary to provide some additional test circuitry. Due to parasitic effects, the reliability of any external circuitry is seriously compromised. Hence, a built-in current monitor (BICM) is required to implement an Iddt testing approach. In this paper a novel BICM is described, the circuit proposed provides a serially digital representation for the positive as well as the negative transient spikes that appear in the Idd. The BICM operation has a minimum impact on circuit performances, and its output signals can be post-processed by means of a conventional digital tester