Test response compaction using multiplexed parity trees

Built-in self-testing requires test response streams from many observation points to be merged (space compaction) and compressed (time compaction) into a short signature. The compaction circuits should be transparent to error propagation in order to minimize aliasing, which occurs when a faulty response maps to the fault-free signature. We investigate the use of multiplexed parity trees (MPTs) for zero-aliasing space compaction. MPTs combine the error propagation properties of multiplexers and parity trees, and ensure zero aliasing via multistep compaction. We present two design techniques based on MPTs-output selection and fanout insertion-that eliminate aliasing for both deterministic and pseudorandom test sets. Our experiments with the ISCAS benchmark circuits show that zero aliasing can be achieved with small test sets and moderate hardware overhead. We also demonstrate that a very high percentage of single stuck-line faults in the compaction circuit are detected by the test patterns applied to the circuit under test.