Design of On-Chip Self-Testing Signature Register

摘要

Over the last few years, scan test has turn out to be too expensive to implement for industry standard designs due to increasing test data volume and test time. The test cost of a chip is mainly governed by the resource utilization of Automatic Test Equipment (ATE). Also, it directly depends upon test time that includes time required to load test program, to apply test vectors and to analyze generated test response of the chip. An issue of test time and data volume is increasingly appealing designers to use on-chip test data compactors, either on input side or output side or both. Such techniques significantly address the former issues but have little hold over increasing number of input-outputs under test mode. Further, test pins on DUT are increasing over the generations. Thus, scan channels on test floor are falling short in number for placement of such ICs. To address issues discussed above, we introduce an on-chip self-testing signature register. It comprises a response compactor and a comparator. The compactor compacts large chunk of response data to a small test signature whereas the comparator compares this test signature with desired one. The overall test result for the design is generated on single output pin. Being no storage of test response is demanded, the considerable reduction in ATE memory can be observed. Also, with only single pin to be monitored for test result, the number of tester channels and compare edges on ATE side significantly reduce at the end of the test. This cuts down maintenance and usage cost of test floor and increases its life time. Furthermore reduction in test pins gives scope for DFT engineers to increase number of scan chains so as to further reduce test time.