Signal Integrity Testing With a Vector Network Analyzer

Vector Network AnalysisIntroduction and Fundamentals

Fundamentals of Vector Network Analysis 2

• Introduction

• Transmission Lines

• S-Parameters

• Network Analyzer Architecture

• Calibration

• Other Measurements

Agenda


Rohde & Schwarz50 Years of Innovation in Network Analysis1950s: World’s First VNA

Z-g-Diagraph S-Parameter Analyzer

300 – 2400 MHz

1970s: ZPV Vector Analyzer

ZPV-Z5 Test Set

SWP Signal Generator

PCA5 Process Controller

1990s: ZVM / ZVK / ZVR / ZVC

World’s First Fundamental Mixing

Automatic VNA’s

9kHz – 40GHz

2000s: ZVA / ZVB / ZVT

High-Speed Multi-Port VNA’s

300kHz – 500GHz

• First Embedding/De-embedding (R&S Patent)• First Multisource Network Analyzer (ZVB)• First True Differential Capability (ZVA)• First One-Box VNA Supporting Hot S22 (ZVA)

• First VNA Supporting TOI Meas. (ZVA)• First Two-Tone Frequency Converter Group Delay

(ZVA)

Recent R&S Innovations


Spectrum Analyzers vs. Network Analyzers

Network Analyzers:• Measure components, devices, circuits, sub-

assemblies

• Contains sources and receivers

• Display ratioed amplitude and phase (frequency, power or time sweeps)

• Offers advanced error correction.

Spectrum Analyzers:• Measure signal amplitude characteristics,

carrier level, sidebands, harmonics..

• Can demodulate (+ measure) complex signals

• Spec Ans are receivers only (single channel)

• Can be used for scalar component test (no phase) with tracking gen. or external source

Measures Signals Measures Devices


Filters

RF Switches

Couplers

Cables

Amplifiers

Antennas

Isolators

Mixers

…

Most 2 (or more) port devices (and some 1 port devices)

What Devices do Network Analyzers Test?


Optical Analogy to RF Transmission

RF

Incident

Reflected Optical

DUT

• Network analyzers measure transmitted and reflected signals relative to the incident signal

• Scalar analyzers measure magnitude only, vector analyzers measure magnitude and phase of these signals

Transmitted


• Introduction


• S-Parameters


• Calibration


Agenda


Parallel LinesCoax Cable

Microstrip Line

Waveguide

Transmission Lines


Transmission Line Terminated with Short, Open

Zs = Zo

Vrefl

Vinc

A transmission line terminated in a short or open reflects all power back to source

OPEN: In-phase (0o) SHORT: Out-of-phase (180o)

Standing Wave(sum of incident and reflected waves)


Transmission Line Terminated with Zo

A transmission line terminated in Zo behaves like an infinitely long transmission line

Zs = Zo

Zo

Vrefl = 0 (all the incident power is absorbed in the load)

Vinc

Zo = characteristic impedance of transmission line


Transmission Line Terminated with 25

Vrefl

Standing wave pattern does not go to zero as with short or open

Zs = Zo

ZL = 25

Vinc

Standing Wave(sum of incident and reflected waves)


Agenda

• Introduction


• S-Parameters


• Calibration



High-Frequency Device Characterization

TransmittedIncident

TRANSMISSION

Gain / Loss

S-ParametersS21, S12

GroupDelay

TransmissionCoefficient

Insertion

Phase

ReflectedIncident

REFLECTION

SWR

S-ParametersS11, S22

ReflectionCoefficient

Impedance, Admittance R+jX

, G+jB

Return

Loss

Incident(“a1” receiver)

Reflected(“b1”

receiver)

Transmitted(“b2”

receiver)

b1

a1=

b2

a1=

Port 1 Port 2


S-Parameters• Basic DUT quantities measured by a VNA• Describe how DUT modifies a signal incident on any port

• 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)

Pin-refl

PoutPin

Prev-refl

Prev


Smith Chart• Published by Phillip H.

Smith of Bell Labs in 1939• Any impedance (resistive

or reactive) can be plotted on a Smith chart

• Used extensively in impedance matching

Short Match Open

Capacitive

Inductive


ρlog Loss Return 20

1

1

Vmin

Vmax VSWR

dB

No reflection(ZL = Z0)

RL

VSWR

0 1

Full reflection(ZL = open, short)

0 dB

1

Reflection Parameters

0

0

ZZ

ZZΦρ

V

V

L

L

incident

reflected

Reflection

Coefficient

• Return Loss, VSWR, Impedance, and Scalar Reflection Coefficient are calculated from measured Vector Reflection Coefficient ()


Criteria for Distortionless TransmissionConstant amplitude over bandwidth of interest

Mag

nit

ud

e

Phase

Frequency

Frequency

Linear phase over bandwidth of interest

Distortion is indicated by:• Deviation from constant amplitude

• Deviation from linear phase (or stated another way...)

• Non-constant group delay


Distortion from Magnitude Variation vs. Frequency

Time

Linear Network

Frequency Frequency Frequency

Mag

nit

ud

e

Time

F(t) = sin t + 1/3 sin 3t + 1/5 sin 5t


Distortion from Non-Linear Phase

Frequency

Mag

nit

ud

e

Linear Network

Frequency

Frequency

Time

0

-180

-360

°

°

°

Time

F(t) = sin t + 1/3 sin 3t + 1/5 sin 5t


Group Delay

Group Delay =

Frequency

Group delay ripple

Average delay

to

tg

Phase

Frequency

VNAs calculate group delay from phase measurement across frequency

Group-delay ripple indicates phase distortion (deviation from linear phase)

Average delay indicates electrical length of DUT Aperture of group delay measurement is very

important

Deviation from linear phase

)2( Hertz in

degrees in

cradians/se in

radians in

*

ff

df

d

d

d

360

1


Agenda

• Introduction


• S-Parameters


• Calibration



Scalar Network Analysis• Basic scalar analyzer can be a signal generator and a power

meter

Signal Generator

Power Meter

LAN / GPIBLAN / GPIB


Scalar Network Analysis• Basic scalar analyzer can be a spectrum analyzer with a

tracking generator

Spectrum Analyzer


Generic VNA Block Diagram

a1

b1

a2

b2

Port 1 Port 2


ZVA 4-Port Test Set

PORT 3

Bias Tee

Meas. Receiver

Ref. Receiver

Bias Tee

Meas. Receiver

Ref. Receiver

Bias Tee

Meas. Receiver

Ref. Receiver

PORT 2

PORT 1

PORT 4

Meas. Receiver

Ref. Receiver

Reflectometer 3

Reflectometer 1

Reflectometer 4

Reflectometer 2

Bias Tee

• Four Ports

• Two Sources

• All ports can source signals simultaneously

• 8 Receivers

• Modern calibration techniques

• Some older VNAs shared receivers and could not do a TRL type calibration


ZVA 2-Port Block Diagram

• Direct Receiver/Generator Access option

• Used for high power devices, mixers, pulsed Measurements, etc.


Directional Coupler (Reflectometer)Directivity

Test port

(undesired leakage signal)

(desired reflected signal)

Directional Coupler

b a

• Directivity is a measure of how well a coupler can separate signals moving in opposite directions

• A termination at the test port should result in no signal at the b receiver

• The difference between the coupled signal and the leakage signal is the directivity of the coupler (typical values: 15-25dB)


Agenda

• Introduction


• S-Parameters


• Calibration



cannot be removed – only minimized

Random Errors• Caused by instrument noise, switch and connector

repeatability• Not repeatable• Minimized by high quality equipment and good

measurement practices

Drift Errors• Caused by changes in environment after calibration

(temperature, humidity)• Minimized by controlling test environment

Systematic Errors• Due to non-ideal components in the VNA and test

setup• Assumed to be repeatable• Calibration is used to correct for these errors• Residual error limited by quality of calibration

standards

Measurement Errors

DUT

removed (nearly) with calibration


Systematic Measurement Errors

Port 1

DUT

Source

a1 b1 b2

CrosstalkDirectivity

SourceMismatch

LoadMismatch

Frequency Response• Reflection Tracking• Transmission Tracking

6 forward and 6 reverse error terms yields 12 error terms

for a 2 port device


DUT

ETT

1. Forward Transmission Loss

2. Mismatch-reflections DUT / Port 1

5. Crosstalk

3. Mismatch-reflections DUT / Port 2

4.Multiport mismatch-reflections

a'1 b'2

a1

a2

b2

b1

T2T'1

ER1

ER3

EX

ER2

Transmission Measurement Errors


Types of Error CorrectionResponse (normalization)

simple to perform only corrects for tracking errors stores reference trace in memory,

then does data divided by memory

Vector requires more standards requires an analyzer that can measure

phase accounts for all major sources of systematic

error

S11 m

SHORT

OPEN

MATCH

thru

thru

S11 a


Vector Error Correction Process of characterizing systematic error terms

Measure known standards Remove effects from subsequent measurements

1-port calibration (reflection measurements) Only 3 systematic error terms measured Directivity, source match, and reflection tracking

Full 2-port calibration (reflection and transmission measurements) 10 systematic error terms measured (crosstalk assumed to be

zero) Usually requires 7 measurements on four known standards

(TOSM) Thru need not be characterized (unknown thru calibration)

Standards defined in cal kit definition file Network analyzer contains standard cal kit definitions CAL KIT DEFINITION MUST MATCH ACTUAL CAL KIT USED! User-built standards must be characterized and entered into

user cal kit


Calibration KitsMechanical and Electronic

Type N 3.5mm 3.5mmw/sliding matches

Type N Calibration Unit

Connects to VNA via USB


Mechanical Calibration Types and Standards

Convenient Generally not

accurate, but can be useful for first-cut measurements

No errors removed

Easy to perform Use when highest

accuracy is not required

Removes frequencyresponse error

For reflection measurements

Need good termination for high accuracy with two-port devices

Removes these errors: Directivity Source Match Reflection Tracking

Highest accuracy Removes these errors:

Directivity Source & Load Match Reflection tracking Transmission Tracking

Uncorrected Response 1-Port Full 2-Port

DUT

DUT

DUT

DUT

thru

thru

One Path – Two Port Combines response and 1-port Corrects source match for

transmission measurements

SHORT

OPEN

MATCH

SHORT

OPEN

MATCH

SHORT

OPEN

MATCH


Automatic Calibration Units• Automatically performs a full calibration on

all connected ports• Connects to VNA via USB• Equivalent to TOSM mechanical

calibration• Available in 2, 4 and 8 Port versions• User definable port configurations


Improvement from a One-Port Calibration

uncalibrated

1-port cal

Measurement of match at the end of a 2ft cable


Two-Port Error Correction Each corrected S-parameter is a function of all four measured S-parameters VNA must make forward and reverse sweep to update any one S-parameter

Port 1 Port 2E

S11

S21

S12

S22

ESED

ERT

ETT

EL

a1

b1

A

A

A

A

X

a2

b2

= fwd directivity= fwd source match= fwd reflection tracking

= fwd load match= fwd transmission tracking= fwd isolation

ES

ED

ERT

ETT

EL

EX

= rev reflection tracking= rev transmission tracking

= rev directivity= rev source match

= rev load match

= rev isolationES'

ED'

ERT'

ETT'

EL'

EX'

Port 1 Port 2

S11

S

S12

S22 ES'ED'

ERT'

ETT'

EL'

a1

b1A

A

A

EX'

21A

a2

b2

S a

S m EDERT

S m EDERT

ES ELS m EXETT

S m EXETT

S m ED'ERT

ESS m EDERT

ES EL ELS m EXETT

S m EXETT

11

11 1 22 21 12

1 11 1 22 21 12

( )('

'' ) ( )(

'

')

( )('

'' ) ' ( )(

'

')

S a

S m EXETT

S m EDERT

ES EL

S m EDERT

ESS m EDERT

ES EL

21

21 22

1 11 1 22

1

( )('

'( ' ))

( )('

'' ) ' ( )(

'

')EL

S m EXETT

S m EXETT

21 12

'S E S E (

')( ( ' ))

( )('

'' ) ' ( )(

'

')

m XETT

m DERT

ES EL

S m EDERT

ESS m EDERT

ES EL ELS m EXETT

S m EXETT

S a

12 1 11

1 11 1 22 21 1212

('

')(

(

S m EDERT

S m EDERT

S a

22

1 1122

) ' ( )(

'

')

S m EDERT

ES ELS m EX

ETT

S m EXETT

11 21 12

ESS m EDERT

ES EL ELS m EXETT

S m EXETT

)('

'' ) ' ( )(

'

')1 22 21 12

1

Reverse Model

Forward Model


Modifications to Calibration• Port Extensions or Offsets

• Extends reference plane by mathematically adding ideal transmission line

• Many VNA’s can automatically set extension length by making a reflection measurement when the line is terminated with an open or short

• Some modern VNA’s can model loss into the extension

• Embedding / De-embedding• More sophisticated than simple port extensions

• Adds (embeds) or subtracts (de-embeds) an arbitrary network to the reference plane

• Network can be modeled from various RLC networks or S-parameter data (.s2p format)

• Examples:• Extract DUT measurements when embedded in a fixture with known S-

parameters

• Simulate adding a matching component or network to the input of a DUT


Agenda

• Introduction


• S-Parameters


• Calibration



Balanced DevicesIdeal device responds to differential input signals and rejects common-mode input signals

Differential-mode signal

Common-mode signal

(EMI or ground noise)

Differential-mode signal

Common-mode signal

(EMI or ground noise)

Balanced to single-ended

Fully balanced


7.5

8.0

8.5

9.0

9.5

10.0

10.5

11.0

11.5

9.5

5 of 16 (Max)

FreqFreq

2 GHz2 GHz

Ch1Ch2

StartStart

-25 dBm-25 dBm

— —

StopStop

-5 dBm-5 dBm

Trc5Trc21

Sdd21Sdd21

dB MagdB Mag

0.5 dB /0.5 dB /

Ref 9.5 dBRef 9.5 dB

Ch1Ch2

CalCal

Sdd21

1/19/2007, 11:53 PM

virtual differential

true differential

• Most VNA’s have a “Virtual Differential” mode• In “Virtual Differential” mode stimulus is applied to one port at

a time and superposition is used to calculate differential results

• ZVA provides an optional “True Differential” mode• In “True Differential” mode the dual sources are used to apply

differential in-phase and out-of-phase stimulus to the DUT

Balanced Device Measurement


Mixer Measurement (scalar)

ZVA 24 VECTOR NETWORK ANALYZER 10 MHz … 24 GHzROHDE&SCHWARZ

1

4

3

2

RF IF

LO


1

4

3

2

RF IF

LO

IEEE Bus

LAN / GPIB

• Use second source as LO• Use additional (3rd) source for mixer TOI measurement


• Uses phase coherent internal sources

• ZVA receivers can measure two tones simultaneously

• Tolerates large LO drift

• Works very well with DUTs containing multiple conversion stages

• No mismatch error correction – must use pads


SOURCE REF MEAS PORT SOURCE REF MEAS PORTSOURCE REF MEAS PORTSOURCE REF MEAS PORT

OUT

IN IN

OUTOUT

IN IN

OUT OUT

IN IN

OUT OUT

IN IN

OUT 2413GND

IF

LO

RF

attenuators

cables to use ZVA’scoupler as combiner

)))(((cos 11 LOLO outtff

)))(((cos 22 LOLO outtff IF

LO

RF

))((cos 11 intf

))((cos 22 intf

Mixer Delay – No LO Access Two-Tone Technique


Vector Mixer Measurements

• Traditionally difficult measurement for VNA

• Modern VNA architecture and calibration techniques full frequency converter characterization

–S11, S22 and absolute phase and delay

RF IF

LO

RF IF

LO

RF IF

LO

LOSplitter

LP-FilterMUT

LO from ZVAor external

Source

Measurementand

Calibrationplane


Power Sweep – Gain Compression

Saturated output power

Outp

ut

Pow

er

(dB

m)

Input Power (dBm)

Compression region

Linear region (slope = small-signal gain)


Power Sweep - Gain Compression

1 dB Compression

Point: output (or input)

power resulting in 1dB drop in gain


TOI Measurement

Fixed TOITwo sources set to fixed frequencies while receiver sweeps(like spectrum analyzer measurement)

Swept TOISources sweep with fixed offset while receiver track at the IM3 frequency(very difficult with spectrum analyzer)


Hot S22 Measurement• Normal (cold) S22 is measured with no signal on input of DUT

• Hot S22 is measured with DUT (amp) in active state

• Signal from Port 1 puts amplifier in operating mode (f2)

• S22 is measured at different frequency (f1)

• Measures amplifier under realistic operating conditions


1 43

2

f1

f2 f2


DC Current & Power Added Efficiency

U=

DCmeas +/-1VDCmeas +/-10V

P1 P2

P=

Rmeas

P 3 P 1 P 4 P 2

• Makes use of ZVA‘s built-in voltmeters


Amplifier Measurements Many results on one display

• S11 and S21

• Hot and Cold S22

• DC Current vs. Frequency

• 1dB Compression Point at Low, Mid, and High Freqs

• DC Current vs. Input Power

• 2nd Harmonic Suppression vs. Frequency

• 2nd Harmonic Suppression vs. Input Power

• TOI


Programming emulation of some VNA‘s you may have heard of...


R&S Network Analyzer Family

GeneralPurpose

Top Class

Multiport & Production

50 G

Hz

20 G

Hz

8 G

Hz

6 G

Hz

4 G

Hz

3 G

Hz

10 M

Hz

300

kHz

9 k

Hz

ZVA24 [2 & 4 ports , 3.5mm(m)]

ZVB20 [2 & 4 ports , 3.5mm(m)]

ZVT8 [2 to 8 ports, N(f)]

ZVB8 [2 & 4 ports, N(f)]

ZVB4 [2 & 4 ports, N(f)]

ZVA8 [2 & 4 ports, N(f)]

ZVA40 [2 & 4 ports, , 2.92mm(m), or 2.4mm(m)]

ZVL6 [2 ports, N(f)]


Compact & Flexible

ZVA67 [2 & 4 ports, 1.85mm(m)]

40 G

Hz

ZVT20 [2 to 6 ports , 3.5mm(m)]

ZVB14 [2 & 4 ports, 3.5mm(m)]

14 G

Hz

24 G

Hz

15

0 k

Hz

(uns

pe

cifie

d)

ZVA / ZVT with External Converters ZV-Zxxx

500

GH

z

80 G

Hz

ZVA50 [2 & 4 ports, 2.4mm(m)]

ZVA80 [2 & 4 ports, 1.00mm(m)]

67 G

Hz


Signal Integrity Testing With a Vector Network Analyzer

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Transcript of Signal Integrity Testing With a Vector Network Analyzer