Parametric faults are a significant cause of incorrect operation in analog circuits. Many design for test techniques for analog circuits are ineffective at detecting multiple parametric faults because either their accuracy is poor, or the circuit is not tested in the configuration in which it is used. We present a design for test (DFT) scheme that offers the accuracy needed to test high-quality circuits. The DFT scheme is based on a circuit that digitally measures the ratio of a pair of capacitors. The circuit is used to characterize the transfer function of a switched capacitor circuit, which is usually determined by capacitor ratios. In our DFT scheme, capacitor ratios can be measured to within 0.01% accuracy and filter parameters can be shown to be satisfied to within 0.1% accuracy. With this characterization process, a filter can be directly shown to satisfy all specifications that depend on capacitor ratios. We believe the accuracy of our approach is at least an order of magnitude...

Analog and mixed-signal integrated circuits (IC's) are rapidly becoming more complex. In addition to the traditional problems associated with testing IC's, such as limited controllability and observability, analog and mixed-signal test is vulnerable to measurement induced errors. Constraints on measuring analog signals significantly increase the complexity and cost of testers for such circuits. In this paper, we introduce a design for test technique for analog and mixed-signal circuits, analog circuit observer blocks (ACOB's). ACOB's are structures designed to reduce the need for precision in measuring analog signals during circuit test. The primary technique used is that of encoding the data in the circuit (only during the test phase). ACOB's potentially offer a number of advantages over conventional offchip test techniques such as reduced tester complexity, smaller measurement induced errors and increased observability. ACOB schemes will necessarily have to be tailored to the type of...