A design-for-test technique for multistage analog circuits

This paper concerns the test of mixed-signal circuits. A novel DFT approach for analog parts constituted of several op-amp-based modules is presented. The idea is to bring the testability resources (controllability and observability) on the frontier of each embedded module by creating transparent paths between external and local I/O´s. The key point of this transformation is to permit each analog stage to have a test mode for which it is converted into a follower stage. Adaptative solutions are proposed depending of the availability of on-chip digital resources eventually re-usable to manage analog test. The testability cost is shown to be very low in terms of additional circuitry, number of extra pins, analog response penalty and test management. A case study is presented that demonstrates the applicability of the method