2009 pb dws_multigigabit_models_of_lossy_coupled_lines

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A new modeling method of coupled transmission lines is shown. It is based on a simple one-port TDR characterization of an actual sample of the TL. A BTM (Behavioral Time Domain )S.parameter model is then obtained from this simple measurement. These models are supported by the SWAN/DWS simulation environment: https://www.ischematics.com/

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2009 pb dws_multigigabit_models_of_lossy_coupled_lines

  1. 1. MULTIGIGABIT MODELS FOR COUPLED LINES by Piero Belforte dec. 2009 Method for quick and accurate multigigabit model extraction of coupled line pairs using TDR measures and DWS simulations20/12/2009 Copyright Piero Belforte 1
  2. 2. TARGETS:• Mininum experimental setup effort• Fast measurements using TDR only• Minumum number of required measurements• Maximum efficiency of extracted models• No numerical stability problems• Possibly Time-Domain only20/12/2009 Copyright Piero Belforte 2
  3. 3. CHOSEN SOLUTIONSONE-PORT only TDR measurementsOTHER PORTS LEFT OPENMODEL BEHAVIORAL DESCRIPTIONPWL S-PARAMETERS DESCRIPTIONMAXIMUM 3-POINT PWLDWS for MODEL SIMULATION2D SOLVER to get STARTING LOSSLESS MODELMODEL PARAMETERS FOUND AS OPTIMUM MATCH WITH MEASURES OF the WHOLE SETUP20/12/2009 Copyright Piero Belforte 3
  4. 4. TEST VEHICULE• COUPLED MICROSTRIP PAIR• FR4 SUBSTRATE H=1.4mm• Length=136mm W=140um S=394um (Center)• ACCESS THROUGH VIA HOLES and 60um PADS20/12/2009 Copyright Piero Belforte 4
  5. 5. VIA HOLES and PADS• 60 mils (1520 um)square pad• 50 mils (1270 um) via diameter• Dielectric (FR4) height H=1400um• Very large compared to coupled pair20/12/2009 Copyright Piero Belforte 5
  6. 6. Full Ideal Setup• No Vias, No TDR parasitics, Ideal lossless lines• Mode data from 2D Field Solver• COMMON MODE: TD=891.4 ps• DIFFERENTIAL MODE: TD=710.9 ps20/12/2009 Copyright Piero Belforte 6
  7. 7. Ideal (Lossless model) from 2D Field Solver (DWS description)ModalAdaptors Lossless Modal Transmission Lines Voltage EigenVectors Matrix (2X2) This model is inserted as first order approximation in the DWS TDR setup description . 20/12/2009 Copyright Piero Belforte 7
  8. 8. PSEUDO-DIFFERENTIAL SETUP• TDR connected at port #1• Remaining ports left open 1 3 4 220/12/2009 Copyright Piero Belforte 8
  9. 9. COMMON MODE SETUPPorts #1 and #2 connected togetherPorts #3 and #4 left openTDR at ports #1 and #2 1 3 220/12/2009 Copyright Piero Belforte 9
  10. 10. Full Ideal Setup:Simulation Results Common mode setup Pseudo- differential setup 2xDeltaTD=360ps20/12/2009 Copyright Piero Belforte 10
  11. 11. Ideal Pseudo-diff vs Measure20/12/2009 Copyright Piero Belforte 11
  12. 12. Ideal Common mode vs Measure (Window 6ns)20/12/2009 Copyright Piero Belforte 12
  13. 13. Common mode TDR Lossless Model Actual measure The differences between the actual measure and the lossless model20/12/2009 Copyright Piero Belforte 13 are outlined in yellow
  14. 14. Ideal Near-end Xtalk vs Measure (Window 5ns)20/12/2009 Copyright Piero Belforte 14
  15. 15. Adding Vias and parasitics• Models of Vias and setup parasitics (Launch cable tip and common mode connection) are extracted by means of TDR measures.• The extracted models are the inserted in the setup simulation model to evaluate their effect on overall DUT response20/12/2009 Copyright Piero Belforte 15
  16. 16. TDR cable tip model• The effects of TDR semi-rigid launch cable are not negligible and have to be taken into account• The unshielded tip of the cable has a major discontinuity contribution on TDR response• An accurate model can be derived from an actual TDR measure of a grounded tip Semi-rigid coax. 1.8mm Outer Diameter. Unshielded PTFE dielectric Center conductor (diameter= .3mm) Via and pad Microstrip end 20/12/2009 Copyright Piero Belforte 16
  17. 17. Model of TDR Cable tip• A LCR DWS model of the tip is extracted from the measure of the grounded tip• The model parameters are optimized to get the best match between measure and simulation20/12/2009 Copyright Piero Belforte 17
  18. 18. Pad and via model• From the TDR response of an open via a circuital model is extracted by optimization of the model response The TDR launch cable tip is also taken into account20/12/2009 Copyright Piero Belforte 18
  19. 19. Optimized model response vs actual measure20/12/2009 Copyright Piero Belforte 19
  20. 20. Via and pad DWS optimized model description• The model is described as DWS subcircuit (stub TL with radiation losses and RC lumped load to gnd)20/12/2009 Copyright Piero Belforte 20
  21. 21. Adding Vias and parasitics• The previous models of Vias and setup parasitics (Launch cable tip and common mode connection) are added to the whole simulation model including the lossless modal description of the coupled pair.20/12/2009 Copyright Piero Belforte 21
  22. 22. Pseudo Differential TDR: results 3 4 2 Model Simulation Actual TDR 1 Measure Several differences can be still pointed out between this model20/12/2009 Copyright Piero Belforte 22 and the actual measure
  23. 23. Adding losses and adjusting DUT model parameters Losses are added to the DWS simulation model of the DUT. A simplified Behavioral model of both even and odd modes is used instead of lossless trasmission lines. A three point PWL description of S21 is used to model losses. The S11 is assumed ideal. The coordinates of S21 PWL description are optimized to match the measurement results . The mode impedances and propagation delay times are also optimized to match the actual measure. The optimization procedure is applied to both measurement setups (pseudo- differential and common configurations with all other ports left open). In this way a true de-embedding of coupled line parameters is performed because all other setup effects are taken into account in the DWS netlist. To check the results a near-end crosstalk simulation is performed and compared to the actual measure.20/12/2009 Copyright Piero Belforte 23
  24. 24. Coupled pair lossless DWS model using Bimodal adaptors20/12/2009 Copyright Piero Belforte 24
  25. 25. Adding setup effects and losses(1)20/12/2009 Copyright Piero Belforte 25
  26. 26. Adding setup effects and losses (2)20/12/2009 Copyright Piero Belforte 26
  27. 27. Coupled pair lossy DWS model: optimized results20/12/2009 Copyright Piero Belforte 27
  28. 28. Checking the near-end crosstalk: setup20/12/2009 Copyright Piero Belforte 28
  29. 29. Checking the Near-end crosstalk:model vs measure20/12/2009 Copyright Piero Belforte 29
  30. 30. TraceAnalyzer: input configuration20/12/2009 Copyright Piero Belforte 30
  31. 31. TraceAnalyzer: results20/12/2009 Copyright Piero Belforte 31
  32. 32. Results comparison Z0e (ohms) Z0o (ohms) TDe (ps) Tdo(ps)Trace AnalyzerFromcrossection 217 79.87 755 688dataDWS meas.based 190 64 725 675optimization20/12/2009 Copyright Piero Belforte 32
  33. 33. De-embedding setup and via effects21/12/2009 Copyright Piero Belforte 33
  34. 34. De-embedded model: effect of losses on reflected edge rise time21/12/2009 Copyright Piero Belforte 34
  35. 35. TLineSim results for a single line: effect of losses on the reflected edge21/12/2009 Copyright Piero Belforte 35

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