An Efficient Segmented Random Access Scan Architecture with Test Compression

Abstract

Integrated circuit (IC) chip designs relying on Random Access Scan (RAS) architecture for post-production structural tests typically provide lower test power dissipation, test data volume, and test application time compared to the classical serial scan-based Design for Test (DFT) methodology. However, previous RAS schemes incur high signal routing and test area overheads relative to the serial scan way. Unlike serial scan schemes, previous RAS schemes have not been effectively combined with test compression to further reduce test application time and test data volume. Authors have already formally documented a locally addressed (segmented) and compressed Segmented RAS (SRAS) architecture with low area overhead and test application time. This paper describes the SRAS architecture in more detail and provides comparative experimental results. Area overhead is reduced using test access hierarchy (segmented), while adding compression to RAS lowers the test application time. Also presented is another enhancement to incorporate a scan channel multiplex block at hierarchy segments which helps drastically decrease the area and routing overhead of the original architecture to practically implementable levels on commercial circuits. The extra Segment Data Multiplexor (SDM) blocks reduce the area overhead of other components by the multiplexing factor, and the reduction in overall area is significant based on experimental data. Test data compression and auto addressing of segments are achieved by transmitting a seed address to select segments with auto-increment or auto-decrement capability followed by either single cell selection or entire leaf cell segment selection. To further reduce the area overhead and test power, this architecture is enhanced to contain multiple channels at a cost of increased overall test application time with no increase in test data volume. Results of applying the enhancements to a large circuit with one level of intermediate segments with each of them having 256 leaf segments are presented in the paper with and without multichannel multiplexing for comparison.