Diagnosis of scan-chains by use of a configurable signature register and error-correcting codes

In this paper a new diagnosis method for scan designs with many scan-paths based on error correcting linear block codes with N information bits and K control bits is proposed, where N is the number of scan-paths. The new approach can be implemented on a modified STUMPS-architecture. In diagnosis mode the test has K times to be repeated. In the K repetitions of the test the outputs of the scan-paths are connected to a configurable signature register (with disconnected feedback logic) according to the coefficients of the K syndrome equations of the code. By monitoring the one-dimensional output sequence of the configurable signature register the failing scan-cells in the different scan-paths can be identified with the resolution of the selected error correcting code. Since for the relevant codes, e.g. (shortened) Hamming codes, T-error correcting BCH-code, the ratio K/N decreases very fast with an increasing number N the method is useful for a large number of scan-paths.