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

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 4: Application Topics of S-Parameters

2. Day 4 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

3. De-Embedding Approaches T-matrix Create S-parameter from scaled T-line Port Extension

4. T-matrix, Chaining ABCD matrix

5. VNA Approach to De-embedding 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

6. TRL Calibration, On-Board Lines 1,2,3 Open THRU

7. TRL Calibration is finicky • Launchmust 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

8. Establish a Concerted Calibration Verification Ideal TRL THRU S11=S22=0, S12=S21=1

9. Verification of Group Delay of THRU includes noise and moving average, perfect group delay=0psec

10. TRL- tip 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

11. Advanced Cal Verification • Verification includes • THRU or Insertion Response using insertable adapter • return loss using wideband terminators • symmetry, S11=S22 • Reciprocity, S21=S12 • Group Delay

12. Again, use validation structure features to your advantage

13. Calibration Verification 2-Port using KF-KF Adapter

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.

15. Verify Low-Frequency Calibration. Passivity issues!

16. Example of Simple THRU for TRL: Simple check of obvious Passivity Violations. The check of |S21|>1 is NOT sufficient however! Another example using on-board THRU

17. Analysis of Calibration Causality Using Polar Plot, Causal S-parameters should only rotate clockwise Quick Polar view of Insertion locates non-causal behavior

18. Cal verification using precision airlines First, examine transmission aberrations, and return loss I may check this S21 with no calibration enabled

19. Secondly, use Resonant structure like Beatty Standard. Why?

20. Simple Matlab routine to analyze for Beatty - Symmetry issues

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

22. Rational Compact Modeling of S-parameters

23. RCM 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

24. 1st Import S-parameters into Simbeor and evaluate quality, then RCM structure

25. Look Closely to S-parameter measured versus RCM simulation, CLOSE FIT! Stripline Resonator, CMP-28

26. S-parameter Work Flow 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

27. What to do with problem S-parameter 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 15-28 Gbps, it is available WRT website.

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