High Sensitivity Signatures for Test and Diagnosis of Analog, Mixed-Signal and Radio-Frequency Circuits by

The conventional approach, widely practiced in the industry today, for testing analog circuits is by ensuring the circuit conforms to data-sheet limits on all its specifications. However, such a specification based test methodology suffers from high levels of test cost stemming from long test-times on expensive test equipment. In recent years the situation has only worsened with the advent of mixed signal systems on chip (SoC), to a point where analog circuit test cost has been found to be as much as 50% of the total test cost in spite of analog portions occupying less than 5% of the chip area. To alleviate the analog circuit test cost problem, a number of techniques exist in the literature that can be broadly classified into (a) fault-model based testing and (b) alternate analog circuit testing. Fault model based test techniques direct their tests to identify faults in the circuit components much like their digital circuit test counterparts resulting in a test approach that can be easily automated and relies on readily available output measurements on inexpensive test equipment. On the other hand, alternate analog circuit test techniques seek to test the specifications of a circuit by building a regression model relating a few key observable parameters that serve as signatures of the circuit output to the actual circuit specification. Both these test paradigms for analog circuit test, however, have limited industry acceptance due to the lack of confidence in defect levels and yield loss that the test procedures can guarantee in the face of high manufacturing process variation, and low signal levels that are characteristic of modern analog circuits. An important reason for the (typically) high defect level and yield loss resulting from the use of either of these two test paradigms is due to the unavailability of easily obtainable circuit outputs that are (a) sufficiently sensitive to circuit component values and (b) have a high degree of correlation with all circuit specifications.