Outline

1. Test Wrapper Designs for the Detection of Signal Integrity Faults on Core External Interconnects of SOCs Qiang Xu and Yubin Zhang Krishnendu ChakrabartyTheChinese University of Hong Kong Duke University

2. Outline • Introduction • Prior work and motivation • Overshoot detector • Wrapper design for interconnect SI test • Experimental results • Conclusion

3. Signal Integrity

4. Impact of Technology Scaling Interconnect Crosstalk Serious crosstalk Shrinking feature size

5. Signal Integrity Problem Signal integrity is a major concern!

6. Testing SOC Interconnects

7. Typical WOC for Interconnect SI Test • Simultaneous aggressor transitions in test mode • Different from functional mode

8. Impact of Aggressor Alignment on Crosstalk • Transition timing of aggressors/victim significantly affects signal integrity • Need for skewed transitions to avoid under-testing

9. Prior Overshoot Detector • Cross-coupled differential amplifier • Test_Mode signal as control of source current • Hysteresis property • Input-dependent detection • Cannot detect overshoot in all cases! Source: M. Nourani and A. Attarha, TCAD’02

10. Motivation • Prior SI test techniques • simultaneous transitions in test mode may result in under-testing. • cannot detect overshoot in all cases. • We need • wrapper input cell that can detect overshoot and delay faults in all cases. • wrapper output cellthat can apply skewed transitions.

11. Proposed Overshoot Detector • Maintain hysteresis property • Self-biased amplifier, higher resolution • Reset mechanism • Can detect overshoot in all cases

12. Comparison of Overshoot Detectors

13. Comparison of Overshoot Detectors

14. Comparison of Overshoot Detectors

15. Wrapper Input Cell • Equipped with overshoot detector • One extra FF as delay detector (FF1).

16. Wrapper Input Cell • Equipped with overshoot detector • One extra FF as delay detector (FF1). • Save test data

17. Wrapper Input Cell • Equipped with overshoot detector • One extra FF as delay detector (FF1). • Save test data • Shift out result

18. Test Strategy I

19. Test Strategy I

20. Test Strategy I Functional path

21. Test Strategy II

22. Test Strategy II Test path

23. Controlled-Delay Element for Skewed-Transition

24. Proposed Wrapper Output Cell

25. Proposed Wrapper Output Cell

26. Experimental Setup • 90 nm technology with 1V power supply • 5 mm long victim with 5 aggressors, each coupling for a 1 mm length • On the eighth metal layer with typical parameter

27. Experimental Results with Previous WOC 0.556 ns

28. Experimental Results with Proposed WOC with 2 delay paths with 4 delay paths 0.614 ns 0.595 ns

29. Experimental Results with Proposed WOC – Cont. with 6 delay paths with 8 delay paths 0.622 ns 0.627 ns

30. Discussion • Benefits • Enhanced signal-integrity fault detection capability • Costs • DfT area overhead • test time • Possible over-testing

31. Conclusion • Signal integrity is a major concern for today’s SoC interconnects • We have proposed novel test wrappers that • Detect all kinds of overshoots • Apply skewed-transitions for aggressors/victim groups • Have moderate overhead

32. Q & A