Modified T-Flip-Flop based scan cell for RAS

Testing using a random access scan (RAS) design-for-test approach is experiencing renewed interest because of the potential for lower test application time, low power dissipation, and low test data volume compared to standard serial scan. In this paper we propose a significant modification and enhancement to the T-Flip-Flop based cell design for Random Access Scan (RAS). Importantly, the new RAS cell can allow the overlap of the test response read out with the loading of the next test input patterns within the same memory addressing cycle, thereby masking out the need for a separate memory cycle to read the test response in many cases. This can greatly reduce test application time. Experimental results show that the Modified T-Flip-Flop based scan cell is able to mask about 33% to 76% of reads. Further, this new RAS cell also eliminates the need for clock gating and additionally achieves reduction in gate overhead as much as about 20% compared to the existing T-flip-flop based RAS cell design.