Design-for-test strategies for analogue and mixed-signal integrated circuits

Recent advances in technology are leading to increases in the complexity and applications of analogue and mixed-signal integrated circuits. This trend has been accompanied by an increase in the complexity of associated test specifications. Furthermore, the use of functional and specification based test programs for the analogue circuitry is being questioned due to high implementation costs, the difficulties associated with quantifying the effectiveness of the tests and in many cases difficulties in accessing embedded analogue macros. In addition quality levels expected by integrated circuit (IC) users are increasing, with typical targets currently being better than 40 ppm defect levels. New test solutions are therefore required for these circuit types. Design-for-Test (DfT) strategies are well established for digital circuits, whilst for analogue and mixed signal circuits, few techniques have been proposed and implementation of custom approaches is rare. This paper presents a summary of a number of possible approaches for improving test access by increasing both controllability and observability of internal functional blocks in analogue and mixed-signal ICs, evaluating both their effectiveness and their impact on circuit performance.