A New Paradigm for Synthesis of Linear Decompressors

For more than two decades, the key objective for synthesis of linear decompressors has been maximizing encoding efficiency. For combinational decompressors, encoding satisfiability is dynamically checked for each specified care bit. By contrast, for sequential linear decompressors (e.g. PRPGs), encoding is performed for each test cube; the resultant static encoding considers that a test cube is encodable only if all of its care bits are encodable. The paper introduces a new class of sequential linear decompressors that provides a trade-off between the computational complexity and the encoding efficiency of linear encoding. As a result, it becomes feasible to dynamically encode care bits before a test cube has been completed, and derive decompressor-implied scan cell values during test generation. The resultant dynamic encoding enables an identification of encoding conflicts during branch-and-bound search and a reduction of search space for dynamic compaction. Experimental results demonstrate that dynamic encoding consistently outperforms static encoding in a wide range of compression ratios.