Analog circuit observer blocks

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 circuit targeted. We present two ACOB schemes, one for the class of fully differential circuits, the second for pipelined analog-to-digital converters. In both cases, the ACOB schemes are shown to offer substantial benefits.