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GA-Based Test Generation for Digitally-Assisted Adaptive Equalizers in High-Speed Serial Links

GA-Based Test Generation for Digitally-Assisted Adaptive Equalizers in High-Speed Serial Links. Mohamed Abbas 1 , Kwang-Ting (Tim) Cheng 1,2 , Yasuo Furukawa 3 , Satoshi Komatsu 1 and Kunihiro Asada 1. 1 VLSI Design & Education Center, The University of Tokyo

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GA-Based Test Generation for Digitally-Assisted Adaptive Equalizers in High-Speed Serial Links

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  1. GA-Based Test Generation for Digitally-Assisted Adaptive Equalizers in High-Speed Serial Links Mohamed Abbas1, Kwang-Ting (Tim) Cheng1,2, Yasuo Furukawa3, Satoshi Komatsu1 and Kunihiro Asada1 1VLSI Design & Education Center, The University of Tokyo 2 University of California, Santa Barbara 3ADVANTEST Corporation, Japan

  2. Outline • Background • Testability and Signature-Based Testing of the Digitally-Assisted Adaptive Systems • GA-Based Test Generation • Experimental Results • Quality of Manual vs. GA-Based Tests • Test Coverage of the Manual vs. GA-Based Stimuli • Conclusion and Future Work VDEC, ADVANTEST D2T Research Division

  3. Outline • Background • Testability and Signature-Based Testing of the Digitally-Assisted Adaptive Systems • GA-Based Test Generation • Experimental Results • Quality of Manual vs. GA-Based Tests • Test Coverage of the Manual vs. GA-Based Stimuli • Conclusion and Future Work VDEC, ADVANTEST D2T Research Division

  4. Background (1): Why HSSL? Block diagram of HSSL TX Data Clock Pre-emphasis Data from Core Serializer Equalizer Data to Core Deserializer CDRC RX High speed serial links (HSSL) have been introduced to support efficient communication between multiple chips in the high-performance systems. • Use serializer to reduce number of I/O pins • Use differential signaling to Improve SNR significantly • Use embedded clock to eliminate clock to data skew VDEC, ADVANTEST D2T Research Division

  5. High-Speed IO Trend [ITRS2008] Representation of ISI noise introduced by the communication channel Background (2): Trends and Consequences VDEC, ADVANTEST D2T Research Division

  6. Challenges in Testing Serial Links Test Cost: Multiple Gb/s IOs are deployed in a single chip Parallel testing requires very expensive ATE. Most applications require 10-12 or even lower BER Measuring <10-12 BER by comparing each captured bit for error detection is impractical for production testing. Test Quality: Loopback based testing is widely adopted The known fault-masking issues of loopback testing make it far from an optimal solution. • High-quality and cost-effective production test methods are still needed VDEC, ADVANTEST D2T Research Division

  7. TX Data Clock Pre-emphasis Data from Core Serializer Equalizer Data to Core Deserializer CDRC RX Block diagram of HSSL Testing of HSSL (Divide & Conquer!) • Challenges in Testing the EQ. • Driving the equalizer output signal off-chip and using a high bandwidth oscilloscope to measure the eye quality is inefficient. • The on-chip solution provides the self-test capability; however, the hardware overhead is high and may be unacceptable for some commercial applications. VDEC, ADVANTEST D2T Research Division

  8. Outline • Background • Testability and Signature-Based Testing of the Digitally-Assisted Adaptive Systems • GA-Based Test Generation • Experimental Results • Quality of Manual vs. GA-Based Tests • Test Coverage of the Manual vs. GA-Based Stimuli • Conclusion and Future Work VDEC, ADVANTEST D2T Research Division

  9. Block diagram of digitally-assisted adaptive FFE. Digitally-Assisted Adaptive Equalizers (1) Feed Forward Equalizer Adaptation Engine and LMS Algorithm VDEC, ADVANTEST D2T Research Division

  10. NT x(t) Analog Part y(t) S (t) Tester D/A d(t) A/D A/D Adapt. Engine W FF A/D Testability of the Digitally-Assisted Adaptive EQ. VDEC, ADVANTEST D2T Research Division

  11. Fault A Fault B Static vs. Dynamic Signature VDEC, ADVANTEST D2T Research Division

  12. Dynamic Signature Definition VDEC, ADVANTEST D2T Research Division

  13. Outline • Background • Testability and Signature-Based Testing of the Digitally-Assisted Adaptive Systems • GA-Based Test Generation • Experimental Results • Quality of Manual vs. GA-Based Tests • Test Coverage of the Manual vs. GA-Based Stimuli • Conclusion and Future Work VDEC, ADVANTEST D2T Research Division

  14. NT h1 h2 h3 h4 h5 T Input Space of GA x(t): 16 levels d(t): fixed T (Sampling time): fixed x(t) Example, for a 5-tap EQ, chromosome: 1001000001001001000 Corresponds to the stimulus h1-h5= [0.75 0.5 0.125 0.25 0.5]. d(t) Stimulus template for a 5-tap equalizer. VDEC, ADVANTEST D2T Research Division

  15. Implementation of GA • Randomly generate a large population of chromosomes. • Evaluate the fitness value of each chromosome. • Creating a new (offspring) generation: • Selection: The probability of an individual being selected is proportional to the chromosomes fitness.We usethe Roulette wheel method for the selection. • Crossover the selections . • Doing mutation. • Repeat step 3 until a new population has been created. • Replace the parent generation with the offspring generation • Repeat steps 2~5 until the stopping criteria has been reached. VDEC, ADVANTEST D2T Research Division

  16. Outline • Background • Testability and Signature-Based Testing of the Digitally-Assisted Adaptive Systems • GA-Based Test Generation • Experimental Results • Quality of Manual vs. GA-Based Tests • Test Coverage of the Manual vs. GA-Based Stimuli • Conclusion and Future Work VDEC, ADVANTEST D2T Research Division

  17. Faults and Fault Models VDEC, ADVANTEST D2T Research Division

  18. Quality of Manual vs. GA-Based Tests (a) (b) • two stuck-at faults, • two open faults • gain degradation fault. (c) VDEC, ADVANTEST D2T Research Division

  19. Outline • Background • Testability and Signature-Based Testing of the Digitally-Assisted Adaptive Systems • GA-Based Test Generation • Experimental Results • Quality of Manual vs. GA-Based Tests • Test Coverage of the Manual vs. GA-Based Stimuli • Conclusion and Future Work VDEC, ADVANTEST D2T Research Division

  20. Test Coverage of the Manual vs. GA-Based Stimuli (1) (b) (a) • the manual tests. • the GA tests. VDEC, ADVANTEST D2T Research Division

  21. Test Coverage of the Manual vs. GA-Based Stimuli (2) (b) (a) • (a) the manual tests. (b) the GA tests. VDEC, ADVANTEST D2T Research Division

  22. Test Coverage of the Manual vs. GA-Based Stimuli (3) VDEC, ADVANTEST D2T Research Division

  23. Conclusion and Future Work • An analog GA-based ATPG (AATPG) framework for generating high-quality analog test stimuli for equalizers has been proposed. • The results of applying our AATPG framework to a 5-tap digitally assisted adaptive equalizer demonstrate that: • The dynamic signatures reported by the GA-based tests can better differentiate between the faulty and fault-free devices. • In contrary, under the same conditions, the manual test stimuli have limited significantly lower fault coverage. • Our AATPG framework can take the rise/fall time limitations of the signal generator when considering the generation of high-frequency stimulus. • In future, we will consider the determination of pass/fail threshold based on more practical considerations taking into account the effect of process variations and signal noise. VDEC, ADVANTEST D2T Research Division

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