wild river technology llc wildrivertech alfred p. neves al@wildrivertech

Copyright © 2014 Wild River Technology LLC

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Wild River Technology LLCwww.wildrivertech.com

Alfred P. [email protected]

phone 503 679 2429

A VNA Manifesto: A Primer for Practical Mastery

Day 1: What Is an S-Parameter?


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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


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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


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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


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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


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Usually narrow bandWide dynamic RangeRequires sliding load cal kit or coaxial TRLTime Domain not importantPassivity/causalityReciprocity/causalityTDR/VNA/BERT correspondenceEye Diagrams

RF SIYes No, DC to FstopYes NoSometimes Not often

Not often YesNot often YesNot often YesNot often Yes

Not often Yes


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… among others

• Loss Modeling – Surface Roughness, • Improved Measurements for 3D EM solver

correspondence• Package Design Verification• Channel Models for Simulation • S-Parameters Models for Simulation• System Design (Capitol Equipment

example)• Component

Evaluation/Characterization (SERDES, TIA, Limiting Amps, Clocks, etc.,)


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nx

Gaussian Noise

S-Parameter Model of Channel

• Insertion Loss• Return Loss• Impedance Variations• Resonance• Crosstalk

TX RX


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We demonstrate a

method of opening eye with higher

integrity


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Cost vs. performanceStackup/Via designASIC/IP vendor selectionConnector selectionEqualization settingsSpeed vs. LengthExtending backplane EOLStandards compliance

Increasing Equalization

Incre

asin

g C

han

nel Loss


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Line card Line cardBackplane

Traces(Wline model)

Traces(Wline model)

Backplane(S-parameters)

Backplane(S-parameters)Package Model

(S-parameters)Package Model(S-parameters)

SerDes(IBIS-AMI Model)

SerDes(IBIS-AMI Model)


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Full system (multi-board) model

Channels meet compliance specs?

How much margin?

Which channel is best? Worst? Why?

Isolate & debug failing channelsEye Height vs. Eye WidthRed: Send, Blue: Receive

Eye Height vs. Backplane layerEye Height vs. Connector row


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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


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THRU SHORT OPEN MATCHED

PORT 1

PORT 3PORT 2

PORT 4

Z relies on open, Y relies on short, S- parameter relies on matched impedance


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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)


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Sij = is the reflection coefficient of the ith port if i=j with all other ports matched

Sij = is the forward transmission coefficient of the ith port if I>j with all other portsmatched

Sij = is the reverse transmission coefficient of the ith port if I<j with all other portsmatched


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S11 (b1/a1)Forward reflection coefficient (input match, return loss, VSWR)

S21 (b2/a1)Forward transmission coefficient (gain or loss)

S12 (b1/a2) Reverse transmission coefficient (reverse isolation)

S22 (b2/a2)Reverse reflection coefficient (output match, return loss, VSWR)


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PORT 1

PORT 3

PORT 2

PORT 4

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

DUT


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2

11,1

1 0a

bS

a

2

22,1

1 0a

bS

a


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• .csv• .snp• Formatted and unformatted

proprietary• bit map images


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2 2

, , ,Re Imi j i j i jS S S

, ,20 logi j i jdBS S

magnitude

magnitude in dB

, , ,arctan Im Rei j i j i jS S S phase

TIP: We use Real/Imaginary Format exclusively, versus Mag/phase, Polar, etc.,


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Ratio% dB100 070 -350 -610 -205 -261 -40


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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


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• 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


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Questions, discussion?

Alfred P. [email protected] 679 2429

wild river technology llc wildrivertech alfred p. neves al@wildrivertech

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