Wild River Technology LLC Alfred P. Neves [email protected]

Copyright © 2014 Wild River Technology LLCSlide 1

Wild River Technology LLCwww.wildrivertech.com

Alfred P. [email protected]

phone 503 679 2429

A VNA Manifesto: A Primer for Practical Mastery

Day 4: Application Topics of S-Parameters

http://www.wildrivertech.com/

mailto:[email protected]



Day 4

De-embedding with T-matrix approachTRL calibrationPassivity and Causality – practical testsS-parameter work flowRational Compact ModelingTo fix or not to fix a bungled S-parameter


De-Embedding Approaches

T-matrixCreate S-parameter from scaled T-linePort Extension


© H. Heck 2008

I1

+

-

V1

I2

V2

I1

I3

+

-

V3

T-matrix, Chaining ABCD matrix

2DCBA

1DCBA


VNA Approach to De-embedding

Measure a de-embedding structure and get s-parameterModel something and get S-parameterUse VNA firmware to de-embed with file from active measurement using T-matrix de-embeddingMatlab is another option for T-matrix approach


TRL Calibration, On-Board

Lines 1,2,3THRU

Open


TRL Calibration is finicky Launch must be decent (low S11, no resonance) – good launch designLaunch Connector Repeatability from SMA to SMA – TDR must be very goodLine lengths accurate – layout, etchImpedance variation across board low – etch, fiber- weave, etc., can wreak havocWe measure the LINE standards group delay, then use those group delays in Cal Kit, also verify impedance


2 4 6 8 10 12 14 16 180 20

-50

-40

-30

-20

-10

-60

0

freq, GHz

dB(S

(1,1

))dB

(S(2

,1))

THRU - SOLT calibration

2 4 6 8 10 12 14 16 180 20

-60

-40

-20

0

-80

20

freq, GHz

dB(S

(1,1

))dB

(S(2

,1))

TRL calibrated THRU

Establish a Concerted Calibration Verification

Ideal TRL THRU S11=S22=0, S12=S21=1


2 4 6 8 10 12 14 16 180 20

-1.0

-0.5

0.0

0.5

1.0

1.5

-1.5

2.0

freq, GHz

grou

p_de

lay_p

icose

cond

sav

ggro

upde

lay

Group Delay THRU in psec

Verification of Group Delay of THRU includes noise and moving average, perfect group

delay=0psec


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


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


Again, use validation structure features to your advantage


Calibration Verification 2-Port using KF-KF Adapter


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.


Verify Low-Frequency Calibration. Passivity issues!


Another example using on-board

THRU

Example of Simple THRUfor TRL:

Simple check of obvious Passivity Violations. The check of |S21|>1 is NOT

sufficient however!


Analysis of Calibration Causality Using Polar Plot,

Causal S-parameters should only rotate

clockwise

Quick Polar view of Insertion locates non-causal behavior


Cal verification using precision airlinesFirst, examine transmission aberrations, and return loss

I may check this S21 with no calibration

enabled


Secondly, use Resonant structure like Beatty Standard.Why?


Simple Matlab routine to analyze for Beatty - Symmetry issues


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


Rational Compact Modeling of S-parameters


RCM

Be definition it fixes passivity and causalityIs very accurate, low residual MSE errorAddress DC operating pointNo interpolation issues, continuous functionsWorks in Spice engines directlyRequired intermediate step for Time Domain Simulation


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


Look Closely to S-parameter measured versus RCM simulation, CLOSE FIT!

Stripline Resonator, CMP-28


S-parameter Work Flow

Validate calibration based on DUT Make measurement of external NIST standard, such as stepped impedance or 50ohm airlineTry to predict what DUT measurement will look like based on length, resonances, pathologies, etc.,Make measurement on on board standard, such as Channel Modeling PlatformAnalyze measurementImport measurement into SI Tool, obtain quality metrics – quality, passivity, causalityRCM model


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 calibrationSometimes 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.


Thank You

Questions, discussion?

Alfred P. [email protected] 679 2429


Wild River Technology LLC Alfred P. Neves [email protected]

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