Test coverage optimization in LBIST

The major disadvantage with LBIST is the test coverage in many cases is about 25% less compared to that of ATPG test coverage. The paper focuses on study of various coverage limitations of LBIST and provides solutions to overcome these coverage limitations to make the test coverage of LBIST closer to ATPG. Resolving the X sources by different X bounding techniques leads the interfacing logic of the core untested by LBIST. The X sources between cores/partitions can be solved by introducing an additional LBIST for wrapper chains of cores there by achieving an additional test coverage of 22.96% on untested paths in EXTEST mode of top level LBIST.