Structural constraints for circular self-test paths

Constraints on the structure of circular self-test paths in register transfer level (RTL) circuits with circular built-in self test (BIST) features are discussed. These constraints arise from the desire to avoid bit-level correlation, which can have a devastating effect on test quality. Two causes of bit-level correlation are examined, with examples demonstrating the resulting degradation in test quality. The first cause, register adjacency, is a byproduct of the ordering of the registers within the circular self test path. The second cause, a correlation inherent in circular BIST, stems from the shifting nature of the circular self-test path