Masking asymmetric line faults using semi-distance codes

The authors propose a masking method for asymmetric line faults in LSIs using semidistance codes, which are a class of nonlinear codes. Faults caused by open or short circuit defects in line areas of LSIs can be made asymmetric by controlling the bus driver and the bus terminal gates. The conditions required for codes to mask these faults are clarified, and the codes satisfying these conditions for random faults and adjacent faults caused by line bridging defects are constructed by using a novel concept of semidistance. This masking technique has the advantage that no additional circuits, such as error decoders, are needed. The codes have been applied to the bus lines in the address decoders of the 4-Mb ROMs to improve fabrication yield of the LSIs.<
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