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Wild River Technology LLC wildrivertech Alfred P. Neves Al@wildrivertech

Wild River Technology LLC www.wildrivertech.com Alfred P. Neves Al@wildrivertech.com phone 503 679 2429. A VNA Manifesto: A Primer for Practical Mastery Day 1: What Is an S-Parameter?. Introduction.

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Wild River Technology LLC wildrivertech Alfred P. Neves Al@wildrivertech

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  1. Wild River Technology LLC www.wildrivertech.com Alfred P. Neves Al@wildrivertech.com phone 503 679 2429 A VNA Manifesto: A Primer for Practical Mastery Day 1: What Is an S-Parameter?

  2. Introduction • Al Neves – Chief Technologist for WRT, WRT has been in business 3 years, based in Portland Oregon area, was SI Consultant • WRT markets products for SI community • Signal Integrity Practitioner, Test/Measurement Track Chair DesignCon

  3. WRT Events • DesignCon • Presentation - 13-TH4: Managing S-parameter Data for 10 to 32 Gb/s Time-Domain Simulations. Thursday, 11:05am-11:45am • Presentation - 13-TH5: Cracking the Code of 32 Gbpsec Differential Vias with Advanced Time Domain Methods. Thursday, 2:00pm-2:40pm • Forum - VS-05: The Role of Improved Measurements and Tools in Assessing Simulation-Measurement Correspondence for 32 Gbps Systems. Wednesday, 3:45pm-5:15pm

  4. WRT Recent Papers Methods of Improving 3D EM Model Development and Associated Time/Frequency Domain Measurements, EDI Con, China, 2013 “Methods of Improving Time/Frequency Domain Measurements Suited for 3D-EM Simulation”, DesignCon 2013 “Robust Method for Addressing 12 Gbps Interoperability for High-Loss and Crosstalk-Aggressed Channels”DesignCon 2012 “Measurement-Assisted Electromagnetic Extraction of Interconnect Parameters on Low-Cost FR-4 boards for 6-20 Gb/sec Applications”, 2009 DesignCon “Practical identification of dispersive dielectric models with generalized modal S-parameters for analysis of interconnects in 6-100 Gb/s applications”, 2010 DesignCon “Developing Unified Methods of 3D Electromagnetic Extraction, System Level Channel Modeling, and Robust Jitter Decomposition in Crosstalk Stressed 10Gbpsec Serial Data Systems”, 2011 DesignCon

  5. Day 1 VNA Measurement Approaches: RF versus Signal Integrity Common Applications of S-parameters Basic S-Parameter format Relating S11 to S21 vectorial relationships Interpreting and getting feel for S-parameters

  6. RF/Microwave versus Signal Integrity RFSI Yes No, DC to Fstop Yes No Sometimes Not often Not often Yes Not often Yes Not often Yes Not often Yes Not often Yes Usually narrow band Wide dynamic Range Requires sliding load cal kit or coaxial TRL Time Domain not important Passivity/causality Reciprocity/causality TDR/VNA/BERT correspondence Eye Diagrams

  7. S-Parameter Applications for S.I. … among others

  8. S-Parameter Model of Channel RX TX nx • Insertion Loss • Return Loss • Impedance Variations • Resonance • Crosstalk Gaussian Noise S-parameter in a Typical Serial Data Channel

  9. S-parameter models play a critical role in close eye very high data rates We demonstrate a method of opening eye with higher integrity

  10. SiSofthas reported that a major fraction of S-parameter models are “junk”

  11. Pre-Silicon Channel Optimzation Using S-parameter Models • Cost vs. performance • Stackup/Via design • ASIC/IP vendor selection • Connector selection • Equalization settings • Speed vs. Length • Extending backplane EOL • Standards compliance Increasing Equalization Increasing Channel Loss

  12. IBIS AMI and Channel Model - Design Capture Traces (Wline model) Backplane (S-parameters) Package Model (S-parameters) SerDes (IBIS-AMI Model) Line card Backplane Line card

  13. Post-Route Validation • Full system (multi-board) model • Channels meet compliance specs? • How much margin? • Which channel is best? Worst? Why? • Isolate & debug failing channels Eye Height vs. Eye WidthRed: Send, Blue: Receive Eye Height vs. Backplane layer Eye Height vs. Connector row

  14. S-parameters fit into Generalized Network Theory • Linear networks can be completely characterized by parameters measured at the network ports without knowing the content of the networks. • Any number of ports. • The ports can be characterized with many parameters (Z, Y, S, ABDC). Each has a specific advantage. • Z relies on open, Y relies on short, S, relies on matched impedance • Each parameter set is related to 4 variables: • 2 independent variables for excitation • 2 dependent variables for response

  15. Termination of non-driving ports based on Network Parameter • Z relies on open, Y relies on short, S- parameter relies on matched impedance THRU SHORT OPEN MATCHED PORT 1 PORT 2 PORT 3 PORT 4

  16. S-parameter Application Scope • Circuit with lumped elements, rational polynomial and BB SPICE macro-models • Distributed circuits (models with delays) • Tabulated (discrete) Touchstone models • SPICE simulators • Electromagnetic analysis software • Measurements (VNA or TDNA)

  17. S-parameter Relation to Matched Load

  18. S-Parameter Basics

  19. S-parameter notation Sij = is the reflection coefficient of the ith port if i=j with all other ports matchedSij = is the forward transmission coefficient of the ith port if I>j with all other ports matchedSij = is the reverse transmission coefficient of the ith port if I<j with all other ports matched

  20. Large Multiport S-Parameter • S11 (b1/a1) • Forward reflectioncoefficient (inputmatch, returnloss, VSWR) • S21 (b2/a1) • Forward transmissioncoefficient (gainorloss) • S12 (b1/a2) • Reverse transmissioncoefficient (reverseisolation) • S22 (b2/a2) • Reverse reflectioncoefficient (outputmatch, returnloss, VSWR)

  21. How Would You Make this DUT Measurement with a 2-port VNA? PORT 1 PORT 2 PORT 3 PORT 4 DUT Tip: Getting port definitions consistent when for more than 2 ports is non-trivial, especially when the other members of the SI team are addressing 3D EM and system simulations

  22. Large 16 Port Example Mimics Backplane

  23. Flow Diagram Representation- [ref 1, Pozar]

  24. Common Signal Flow Relations

  25. Signal Flow Graph – Reference Plane

  26. Toucshtone S-parameter Format • .csv • .snp • Formatted and unformatted proprietary • bit map images

  27. S-parameter Complex Math magnitude phase magnitude in dB TIP: We use Real/Imaginary Format exclusively, versus Mag/phase, Polar, etc.,

  28. dB Ratio%dB 100 0 70 -3 50 -6 10 -20 5 -26 1 -40

  29. Common VNA setup for exercises – a good starting point IF BW 1kHz 4 port SOLT Calibration, THRU paths 1 to 2, 3 to 4 No averaging, no smoothing Fstart 25MHz, Fstop 40GHz, 1600 points

  30. Touchstone and S-parameter exercise • Display S-parameter Touchstone in text editor, Matlab, or some other tool of some measurement • Export and Save a .csv S-parameter and import into Excel. You can create a simple viewer using Complex Math slide. • Print out S2P file, examine frequency spacing, value of normalized impedance • Confirm format is Real/Imaginary and Not Mag/Phase, confirm this on VNA setting

  31. Thank You • Questions, discussion? • Alfred P. Neves • al@wildrivertech.com • 503 679 2429

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