Increasing PRPG-based compression by delayed justification

Scan testing and scan compression have become key components for reducing test cost, and most high-compression schemes are based on linear, sequential compressors e.g., pseudo-random pattern generators (PRPG). We present a novel technique to increase PRPG-based compression by modifying test generation so that justification of certain decision nodes is delayed and merged with PRPG seed computation. Our method does not affect test coverage or diagnosis, requires no hardware support, and can be applied to any linear compression scheme. Results on industrial designs demonstrate consistent increase in compression.