Copyright © 2014 Wild River Technology LLC Slide 1 Wild River Technology LLC Alfred P. Neves phone A VNA Manifesto: A Primer for Practical Mastery Day 4: Application Topics of S-Parameters

Copyright © 2014 Wild River Technology LLC Slide 2 De-embedding with T-matrix approach TRL calibration Passivity and Causality – practical tests S-parameter work flow Rational Compact Modeling To fix or not to fix a bungled S-parameter

Copyright © 2014 Wild River Technology LLC Slide 3 T-matrix Create S-parameter from scaled T-line Port Extension

Copyright © 2014 Wild River Technology LLC Slide 4 © H. Heck 2008

Copyright © 2014 Wild River Technology LLC Slide 5 Measure a de-embedding structure and get s- parameter Model something and get S-parameter Use VNA firmware to de-embed with file from active measurement using T-matrix de-embedding Matlab is another option for T-matrix approach

Copyright © 2014 Wild River Technology LLC Slide 6 TRL Calibration, On-Board Lines 1,2,3 THRU Open

Copyright © 2014 Wild River Technology LLC Slide 7 TRL Calibration is finicky Launch must be decent (low S11, no resonance) – good launch design Launch Connector Repeatability from SMA to SMA – TDR must be very good Line lengths accurate – layout, etch Impedance variation across board low – etch, fiber- weave, etc., can wreak havoc We measure the LINE standards group delay, then use those group delays in Cal Kit, also verify impedance

Copyright © 2014 Wild River Technology LLC Slide 8 Establish a Concerted Calibration Verification Ideal TRL THRU S11=S22=0, S12=S21=1

Copyright © 2014 Wild River Technology LLC Slide 9 Verification of Group Delay of THRU includes noise and moving average, perfect group delay=0psec

Copyright © 2014 Wild River Technology LLC Slide 10 Without delving into all the details, I don’t use TRL calibration for general signal integrity work. There are better calibrations to get reference plane near DUT, especially for multi-port 4,6,.. 12 port structures

Copyright © 2014 Wild River Technology LLC Slide 11 Verification includes –THRU or Insertion Response using insertable adapter –return loss using wideband terminators –symmetry, S11=S22 –Reciprocity, S21=S12 –Group Delay

Copyright © 2014 Wild River Technology LLC Slide 12 Again, use validation structure features to your advantage

Copyright © 2014 Wild River Technology LLC Slide 13

Copyright © 2014 Wild River Technology LLC Slide 14 Start with Simple Cal Verification: Simple adapter THRU for non-insertable and flush THRU with insertable Cal. KF-KF adapter has approximately 0.1dB insertion loss and 50psec delay.

Copyright © 2014 Wild River Technology LLC Slide 15 Verify Low-Frequency Calibration. Passivity issues!

Copyright © 2014 Wild River Technology LLC Slide 16 Another example using on-board THRU Example of Simple THRU for TRL: Simple check of obvious Passivity Violations. The check of |S21|>1 is NOT sufficient however!

Copyright © 2014 Wild River Technology LLC Slide 17 Analysis of Calibration Causality Using Polar Plot, Causal S-parameters should only rotate clockwise Quick Polar view of Insertion locates non- causal behavior

Copyright © 2014 Wild River Technology LLC Slide 18 Cal verification using precision airlines First, examine transmission aberrations, and return loss I may check this S21 with no calibration enabled

Copyright © 2014 Wild River Technology LLC Slide 19 Secondly, use Resonant structure like Beatty Standard. Why?

Copyright © 2014 Wild River Technology LLC Slide 20 Simple Matlab routine to analyze for Beatty - Symmetry issues

Copyright © 2014 Wild River Technology LLC Slide 21 For 4 Ports: After Cal Verification, Assess S-parameter of DUT Overall return loss Symmetry Group Delay Distortion Reciprocity Insertion Loss variation Quick Time Domain Transform

Copyright © 2014 Wild River Technology LLC Slide 22 Rational Compact Modeling of S-parameters

Copyright © 2014 Wild River Technology LLC Slide 23 Be definition it fixes passivity and causality Is very accurate, low residual MSE error Address DC operating point No interpolation issues, continuous functions Works in Spice engines directly Required intermediate step for Time Domain Simulation

Copyright © 2014 Wild River Technology LLC Slide 24

Copyright © 2014 Wild River Technology LLC Slide 25 Stripline Resonator, CMP-28

Copyright © 2014 Wild River Technology LLC Slide 26 Validate calibration based on DUT Make measurement of external NIST standard, such as stepped impedance or 50ohm airline Try to predict what DUT measurement will look like based on length, resonances, pathologies, etc., Make measurement on on board standard, such as Channel Modeling Platform Analyze measurement Import measurement into SI Tool, obtain quality metrics – quality, passivity, causality RCM model

Copyright © 2014 Wild River Technology LLC Slide 27 Don’t fix S-parameters, the tools on the market don’t work very well. If a tool reports problems, check calibration Sometimes you have to live with and manage issues when using T-matrix, or partial calibration, or fancy de-embedding. See DesignCon2012 tutorial: High-confidence S- parameter Measurement Methodologies for Gbps, it is available WRT website.

Copyright © 2014 Wild River Technology LLC Slide 28 Questions, discussion? Alfred P. Neves