improved measurements overcome high-speed interconnect challenges october 2013 bob buxton 1 eumw...

1EuMW Seminars 2013

Improved Measurements Overcome High-Speed Interconnect Challenges

October 2013

Bob Buxton

EuMW Seminars 2013

Agenda

• Background• S-parameter measurements - frequency range considerations• Eye Diagrams and low frequency measurement data issues• De-embedding• Correlation – measurements and simulation• Setting emphasis levels• Superposition vs. true mode stimulus for active device

measurement• Resources• Questions

2

EuMW Seminars 2013

Background – challenge for SI Engineers

• Compliance with higher data rate standards

• Cost/performance trade-offs

• Locating Defects

• Measurement – simulation correlation

• Dealing with test fixtures

3

EuMW Seminars 2013 4

8B/10B Encoder

SerializerEqualizer Driver

Clock/PLL

10B/8B Decoder

De-SerializerEqualizerData

Recovery

CR/PLL

ParallelData

ParallelData

SerialData

Jitter and Noise

Channel Issues

Challenges for SI Engineers


Types of Channel


Tx Rx

0 2 4 6 8 10 1205

101520253035404550

FR-4 Electrical Loss Function (1 m)

SkinDielectricTotal

Frequency (GHz)

Loss

(dB)

Channel Issues - Loss


Channel artifacts (vias, impedance changes, ground plane issues etc.)

Channel Issues - Structures


Backplane Transmission Measurement


Tx Rx

Tx Rx

TxRx

FEXT

NEXT

Channel Issues – Crosstalk


Harmonic Content of 28 Gbps NRZ clock signal

• Attenuating harmonics distorts signal

• Ideally measure to 5th harmonic

Importance of Maximum Frequency Range

EuMW Seminars 2013

High Frequency VNA impact – resolution

• Rule of thumb(air dielectric)

• Time = 1/BW

• Distance (reflect) = 150mm/BW (GHz)– 40 GHz = 3.7 mm– 110 GHz = 1.4 mm

• Non-air distance : divide by

11

TWO MISMATCHES SEPARATEDBy 2 mm (AIR)

span resolution1) 40 GHz 3.75

mm2) 50 GHz 3.0

mm3) 60 GHz 2.5

mm

EuMW Seminars 2013

High Frequency VNA impact - causality• Lack of causality

means output appears to occur prior to stimulus

• Can cause unstable simulations

• Higher frequency data improves causality

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Non-Causal Results

EuMW Seminars 2013

Need for Low Frequency Data – 2 Reasons

1. DC Extrapolation

2. Sampling in the frequency domain and aliasing*– Max unambiguous time domain result: Tmax = 1/(2fs)– Need to consider multiple reflections

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* A Reverse Nyquist Approach to Understanding the Importance of Low Frequency Information in Scattering Matrices Daniel Dvorscak and Michael Tsuk, ANSYSInc, DesignCon 2013

EuMW Seminars 2013

VNA performance and DC Extrapolation• Series of measurements

made on same 40 inch line

• VNA 1– 40 MHz to 40 GHz– Couplers for entire band

• VNA 2– 4 MHz to 40 GHz– Hybrid of bridges and couplers

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VNA performance and DC Extrapolation• DC extrapolation depends on

quality of S-parameter measurement

• Left trace from VNA limited low frequency performance– Coupler based– 92 dB DR at 40 MHz

• Right trace from VNA with better low frequency performance– Bridges at LF– 115 dB DR at 4 MHz

EuMW Seminars 2013

Impact on step response

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40 MHz to 40 GHz data VNA 1 4 MHz to 40 GHz data VNA 2

Slope due to poor DC extrapolation

Aliasing due to 40 MHz sampling

• Good low start frequency data improves DC extrapolation

• Low start frequency sets frequency domain sampling for low pass step response and hence alias free range

EuMW Seminars 2013

Stability at low frequency also critical

17

-40

-30

-20

-10

0

0 2 4

|S11

| (d

B)

Frequency (GHz)

Low frequency anomalies

nominal

major drift

minor drift

30

50

70

90

0.04 0.05 0.06 0.07 0.08

Impe

danc

e (o

hms)

Distance (m)

Low frequency drift impact

nominal

major drift

minor drift

-40

-30

-20

-10

0

0 20 40 60

|S11

| (d

B)

Frequency (GHz)

Low frequency anomalies

Low frequency data issues (drift/instability…) can have an out-sized effect on transformed data because of its criticality to large-distance-scale structure.

EuMW Seminars 201318

Eye diagrams – 10 Gbit• 10 Gbit

– data from VNA 1– 40 MHz to 40 GHz

• 10 Gbit– Data from VNA 2– 4 MHz to 40 GHz

0 0.05 0.1 0.15 0.2 0.25Time (ns)

Veye of Bit Stream

-0.2

-0.1

0

0.1

0.2

0.3

Vo

ltag

e (

V)

Eye at Port 2 (V)

0 0.05 0.1 0.15 0.2 0.25Time (ns)

Veye of Bit Stream

0

0.1

0.2

0.3

0.4

0.5

Vo

ltag

e (

V)

Eye at Port 2 (V)

19EuMW Seminars 2013

Importance of Low Frequency Range

• VectorStar displays a flat 25 ohm section as expected

• Measured Data range from 25.11 to 25.28 ohms

(Composite picture of multiple screen captures showing measurements made on Beatty Standard)

• Low noise on low frequency data give rock-steady results from sweep to sweep


VectorStar Architecture: Two VNAs in One!

< 2.5 GHzLow Band

> 2.5 GHzHigh Band

Port 1 Port 2

a2a1

b1

b1

a1

b2

a2

b2

MS4640A Block Diagram(Fully Loaded Configuration)

optional

Bias 1 Bias 2

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Unique Hybrid VNA Architecture• Two VNAs in parallel: Almost the only way to get 6 decades of coverage

(from kHz to GHz frequencies)– Each receiver technology (sampler or mixer) used in its best range– Each coupling technology (coupler or bridge) used in its best range– Both share a common IF path and fully synthesized source


Method Standards complexity

Fundamental accuracy

Sensitivity to standards

Media preferences

Type A (adapter removal)

High High

High (refl.) Need good reflect and thru stds

Type B (Bauer-Penfield)

Medium High High (refl.) Only need reflect standards, not great for coupled lines

Type C (inner-outer)

High High Medium (refl.) More redundant than A so less sensitive but need good stds still

Type D(2-port lines)

Med

Low for low-loss or mismatched fixtures

Medium (line def’n.)

Only need decent lines; match relegated to lower dependence; can handle coupled lines

Type E(4 port inner-outer)

High High Medium (refl.) Somewhat redundant (like C) but need decent standards. Best for uncoupled multiport fixtures

Type F(4-port uncoupled)

Med



Only need decent lines; match relegated to lower dependence; can handle coupled lines

Type G(4-port coupled)

Med



Only need decent lines; match relegated to lower dependence; can handle coupled lines well

Backplanes

Best AccuracyRequires good repeatability

De-embeddingMethods available within VectorStar

EuMW Seminars 2013

Correlation - Measurement and Simulation

• Use Channel Modeling Platform

• Use time domain equipment to measure Eye and compare with simulated Eye

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EuMW Seminars 2013

Use of Channel Modeling Platform

• A set of known structures• Feed data into models• Make measurements• Make comparison

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Correlation – Measurement and Simulation

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Tx Rx

Simulated Using measured S-parameter data

Measured using Oscilloscope

Input waveform with no emphasis

Simulated Using measured S-parameter data

Measured using Oscilloscope

Input waveform with emphasis

- 80

- 60

- 40

- 20

0

0 10 20 30 40

Frequency [GHz]

Tra

nsm

issi

on C

hara

cter

istic

s [d

B]


• Challenge: Difficult to find the ideal emphasis settings from the many possibilities

• Problem: Searching for ideal settings while verifying the output waveform– takes an extremely long time– hard to explain why those settings are ideal.

• Solution: Use VNA-captured S-parameter data to apply inverse DUT characteristics to input waveform

Setting Ideal Emphasis

EuMW Seminars 2013

Time and Frequency Domain – a merged solution

27

DUT (27inch PCB)

- 80

- 60

- 40

- 20

0

0 10 20 30 40

Frequency [GHz]

Tran

smis

sion

Cha

ract

eris

tics

[dB

]

Tap Settings


MS4640B now with:• Option 031 Dual Source Architecture• Option 043 DifferentialViewTM


VectorStar PROVIDES

• Broadest frequency span: 70 kHz to 70/110 GHz• Best time domain analysis capability• Widest range of calibration & de-embedding methods• Upgradeable in frequency range, port count &

option additions• Choice of TMS or Superposition•

Good S-parameter DataPoor S-parameter Data


with DifferentialView and Dual Source

• True Mode Stimulus capability• Differential, common and mixed mode S-parameters• Adjust differential phase & amplitude• Instant view of results during parameter change

+

_

+ +

__

+ +

__

Differential Mode Common Mode Mixed Mode


Port 1 Port 2 Port 3 Port 4

Time-coherent in phase and amplitude

Port 1 Port 2 Port 3 Port 4

DUT DUT

Superposition and True Mode Stimulus


Applicability of the two methodsDevice to be measured: Superposition True Mode

Stimulus

Passive Balanced / Differential DUT

Transmission Lines X X

PCB X X

Lumped Components X X

Passive Filters X X

Unshielded and Shielded Twisted Pair, Quad Cables X X

Connectors / Interfaces X X

Linear Active Balanced / Differential DUT

Linear Amplifiers, Differential Amplifiers X X

Linear Active Filters X X

Input / Output Match ADC / DAC X X

Non Linear Active Balanced / Differential DUT

Devices in Compression / Saturation X

Log Amplifiers X


Trade OffsSuperposition True Mode Stimulus

Type of VNA Single source VNA Dual source required

Method of obtaining Differential and Mixed Mode Parameters

Calculated

Measured directly

Type of DUTs

Passive and active linear Necessary only for non-linear

Available Frequency Range 70 kHz to 110 GHz 70 kHz - 110 GHz (with VectorStar)

Calibration Complexity

Typical 4-port

Typical 4-port plus calibration of dual sources

Average Calibration Time

T (Time depends on number of points, IF BW, skill of operator)

Approx. 2T

Calibration stability considerations Normal measurement calibration intervals

Calibrate more frequently due to stability issues if VNA does not feature advanced correction algorithms

Overall Solution Cost $ $$

• VectorStar MS4640B has a second source option and DifferentialViewTM for true mode stimulus measurement

• Only recommended when device is non-linear


To Use or Not Use True Mode Stimulus?

• Amplifier in non-linear region

• Difference between superposition and TMS apparent

• Amplifier in linear region

• Difference between superposition and TMS not discernable


• Broadest frequency span: 70 kHz to 70/110 GHz• Best time domain analysis capability• 4-port test set upgrades 2 port VectorStar to 4-

port performance.• Widest range of calibration & de-embedding

methods• Choice of TMS or Superposition

Good S-parameter DataPoor S-parameter Data

DifferentialViewTM for Signal Integrity Measurements


DifferentialViewTM for Broadband and mmWave Measurements

• Compact size and high performance make the Anritsu mmWave modules ideal for broadband differential analysis


DifferentialViewTM True Mode Stimulus Interface

• DifferentialView offers easy configuration for differential and mixed mode measurements for thorough analysis


DifferentialViewTM TMS Setup and Editing

• DifferentialView menu provides real time display of measurement parameters

• Immediately observe DUT performance changes with changes in setup

• Example of modifying phase sweep parameters while observing effects


• Option 031 Dual Source eliminates the need for a transfer switch

• Provides up to 7 dB of additional power at 70 GHz

• MS4640B series improves noise floor specification as much as 9 dB

• Combined, results in improved dynamic range performance up to 16 dB at 70 GHz!

+ +

__

Dual Source VectorStar

a1 b1

a2 b2

xN

xN

VectorStarTM Dual Source Option


+ +

__

1800 Phase Offset at Test Port Non-1800 Phase Offset at DUT Input


a1 b1

a2 b2

xN

xN

No TMS correction applied.

• Characterizing differential devices with a 1800 offset is the goal of component designers• Nonlinear devices are sensitive to source mismatch• Source mismatch will shift stimulus signals to non-ideal offset• Without proper offset correction performance of device will vary• Anritsu white paper discusses this issue

Measurements of Nonlinear Differential Devices


+ +

__

1800 Phase Offset at Test Port 1800 Phase Offset at DUT Input

• Applying TMS correction within DifferentialView corrects offset shift

• Monitoring the applied signals (a3/a1) will provide an indication on the success of correction

Opt 043 DifferentialViewTM: Measure mismatch and apply correction during measurement


a1 b1

a3 b3

xN

xN

Measurements of Nonlinear Differential Devices


• Sweep to sweep phase variations from 1800 differential while driving nonlinear DUT at -12 dBm. 10 MHz to 50 GHz.

• Measured result showing < 1 degree sweep to sweep stability

DifferentialViewTM Phase Stability


Resource Materials• MS4640B Technical Data Sheet• Signal Integrity Application Brief• White Papers

– Overcoming High Speed Interconnect Challenges– Signal Integrity: Frequency Range Matters– High Data rates Require New De-embedding Techniques– Superposition vs. True balanced: What’s Required for Your Signal

Integrity Application– True Mode Stimulus and Stability

• Application Note: Ideal Pre-Emphasis Constant Settinghttp://www.anritsu.com/en-us/products-solutions/products/ms4640b-series.aspx

http://www.anritsu.com/en-US/Products-Solutions/Products/MP1800A.aspx

http://www.anritsu.com/en-us/products-solutions/products/ms4640b-series.aspx

http://www.anritsu.com/en-US/Products-Solutions/Products/MP1800A.aspx


• Solutions available to 20, 40, 50, 70 and 110 GHz

• 70 kHz start frequency and low frequency dynamic range of VectorStarTM critical to signal integrity application and to ensuring measurement-simulation correspondence

• MS4640B now offers DifferentialViewTM and 2nd internal source option for true mode stimulus measurements– Easy to use graphical set-up– Real-time view of measurement while making parameter changes– Advanced true mode stimulus corrections hold phase relationship at DUT

• Upgradeable in frequency, port count and options– E.g. can add second source and DifferentialView later

Summary

improved measurements overcome high-speed interconnect challenges october 2013 bob buxton 1 eumw...

Documents

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channel issues structures

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