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PCBD-Oct2014

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October 2014 • The PCB Design Magazine 23 feature SINk OR SWIM AT 28 GBPS continues much faster than the direct convolution. Thus, we will naturally use rational approximation for all time-domain computations here. After all modeling decisions on what to com- pare and how to compare are made, we run the post-layout analysis for all 27 structures on the CMP-28 platform and compare the magnitudes of S-parameters, phase and group delays (and optionally phases), TDR computed with Gauss- ian step with 20 ps 10–90% rise time and eye diagrams computed with PRBS signal with 25 ps rise and fall time generated with LFSR with order 32. Two examples of the validation are shown in Figure 5 and Figure 6. Results for microstrip line link with two ca- pacitive vias (Figure 1, structure 1) are shown in Figure 5. It contains connectors with adapters on both ends, microstrip launches with through- hole vias, two segments of microstrip line with about 50 ohm impedance, two vias and one segment of wide microstrip line in the middle. The link is not optimal by design and represents highly reflective structure. We can conclude that the correlation is very good in this case and all discrepancies may be explained by the manufac - turing and material properties variations. Results of validation for a relatively low-re- flective structure are shown in Figure 6. It is a simple 8-inch segment of single-ended stripline with launches, connectors and adapters on both ends (Figure 1, structure 2). The launches in this case are back-drilled with the goal to have less than 10-mil via stubs. Though, the manufac- turer specified that the stubs may have +- 5 mil variation. 10-mil stubs were used in the model. Considering this and other types of variations, the correlation is acceptable. See all details of the analysis and analysis-to-measurement cor- relation for all 27 structures on CMP-28 plat- form in Reference [5] . Conclusion A systematic process of the analysis-to- measurement validation up to 50 GHz is in- troduced here. The process is illustrated in this article with the CMP-28/32 validation platform and Simbeor software. Note that the validation problems can fall into three categories: manu- facturing, measurement, and analysis, and only measurement quality and the interconnect analysis parts are covered here. Following the procedure, you can easily qualify or reveal prob- lems in your signal integrity software of choice. Just try to do the analysis of all 27 test structures on CMP-28/32 validation platform and swim at 28 Gbps and beyond. Do not forget to compare the productivity and cost of the tools. Finally, is your software qualified for the analysis of PCB interconnects running at 50 Gbps? The question is rhetorical so far. PCBDESIGN References 1. Y. Shlepnev, Measuring correlation to 50 GHz and beyond, The PCB Design Magazine, February 2013, p. 10-21. 2. CMP-28/32 Channel Modeling Platform with Simbeor EDA Kit, Wild River Technology. 3. Simbeor Electromagnetic Signal Integrity Software, Simberian Electromagnetic Solutions. 4. Y. Shlepnev, A. Neves, T. Dagostino, S. McMorrow, Measurement-Assisted Electromag- netic Extraction of Interconnect Parameters on Low-Cost FR-4 boards for 6-20 Gb/sec Applica- tions, DesignCon 2009 5. Guide to CMP-28/32 Simbeor Kit, 2014. 6. Y. Shlepnev, Reflections on S-parameter Quality, IBIS Summit at DesignCon 2011, 7. Y. Shlepnev, PCB and package design up to 50 GHz: Identifying dielectric and conductor roughness models, The PCB Design Magazine, February 2014, p. 12-28. 8. Y. Shlepnev, System and method for iden- tification of complex permittivity of transmis- sion line dielectric, US Patent #8577632, Nov. 5, 2013, Provisional App. #61/296237 filed on Jan. 19, 2010. 9. Y. Shlepnev, System and method for iden- tification of conductor surface roughness mod- el for transmission lines, Patent Pending, App. #14/045,392 filed on Oct. 3, 2013. Yuriy Shlepnev, Ph.D., is found- er and president of Simberian Inc. He previously served as principal engineer at Men- tor Graphics and director of the Electromagnetic Group at Eagleware Corporation.

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