Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

117
Advanced Spectrum Analyzer measurements

description

Presented by Raul Sierra, Application Engineer at Rohde & Schwarz

Transcript of Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

Page 1: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

Advanced Spectrum Analyzer measurements

Page 2: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

Introduction

Applications Engineer

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Agenda

What is a spectrum analyzer?

Basic spectrum analyzer architecture

Dynamic Range

Spectrum analyzer features and usage

Advanced Spectrum Analyzer Architecture

Standard Measurements

Advanced Measurements

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Spectrum AnalyzerThe Swiss Army Knife of RF instruments

Before 1990: General spectrum measurements, harmonics, spurious, CW signal power (low accuracy)

1990’s: Phase noise, noise figure, frequency counter, some cellular standard measurements,

modulated signal power, ACPR, scalar network measurements (tracking generator)

2000’s: IQ analysis, precise analog demod, digital demod (VSA), high accuracy signal power

measurements, spur search, CCDF, wideband analysis, FFT mode sweeps, touch screen interface

2010’s: Pulsed signal analysis, group delay measurements, OFDM demod, digital pre-distortion

analysis, fast spur search

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Notable Milestones in Spectrum Analysis1940s: First sweep spectral analysis performed by MIT RAD LAB.1960s: Spectrum Analyzer market dominated by Polarad and Panoramic1964: HP makes the 1st LO tunable, revolutionizes the market1978: HP introduces the 8566/8568. First microprocessor based SA.1986: Rohde & Schwarz enters spectrum analyzer market with FSA and begins a tradition of

innovation– 1986: First SA with a color display– 1996: First RMS detector– 1999: FSP is fastest SA available– 2001: First SA with >8MHz resolution bandwidth (50MHz)– 2003: First SA with USB ports– 2003: First SA with power sensor reading function– 2006: First combination phase noise analyzer and SA– 2007: First SA to 67GHz without external mixer– 2008: FSV is again the fastest SA on the market– 2010: FSVR is first combination real-time analyzer and SA– 2011: FSW is the most advanced SA on the market

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Oscilloscope vs Spectrum Analyzer?

Time Domain Frequency Domain

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Oscilloscope vs Spectrum Analyzer?

Amplitude

Frequency

0 1 2 3 4 5 6 7-1

-0.8

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f1 f3 f5

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What is dBm?

dB Linear (unitless)

0 1

3 2

10 10

30 1000

40 10000

dBm Power

-20 0.01 mW

-3 0.5 mW

0 1 mW

3 2 mW

30 1 W

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Spectrum Analyzer ≠ Network Analyzer

Network Analyzers:• Measure response of components, devices, circuits, sub-assemblies to applied stimulus

• Contains sources and receivers

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

• Offers advanced error correction for high accuracy measurements

Spectrum Analyzers:• Measure signal amplitude characteristics, carrier level, sidebands, harmonics

• Can demodulate and measure complex signals

• Spectrum analyzers are receivers only (single channel)

• Can be used for scalar component test (amplitude only) with tracking gen. or ext. source

Measures signals Measures devices

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Agenda

What is a spectrum analyzer?

Basic spectrum analyzer architecture

Dynamic Range

Spectrum analyzer features and usage

Advanced Spectrum Analyzer Architecture

Standard Measurements

Advanced Measurements

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Simplified Swept Tuned Block Diagram

InputAtten

MixerEnvelopeDetector

Log Amp

LPFBPF

Display

Sawtooth

LocalOscillator

IFAmplifier

ResolutionBW Filter

y

x

VideoBW Filter

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Input Mixer

InputAtten

MixerEnvelopeDetector

Log Amp

LPFBPF

Display

Sawtooth

LocalOscillator

IFAmplifier

ResolutionBW Filter

y

x

VideoBW Filter

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Types of Mixing

Fixed RF, Swept LO and IF

Fixed LO, Swept RF and IF

Fixed IF, Swept LO and RF (used in spectrum analyzers)

Upconversion IF frequency is higher than RF and LO frequency

Downconversion IF frequency is lower that RF and LO frequency

RF

LO

IF

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RF

1 GHz

LO

1.1 GHz

Possible frequencies on IF port…to name a few:

LO-RF=100MHz

LO+RF= 2.1GHz

LO=1.1 GHz

RF=1 GHz

2LO-RF=1.2 GHz

2RF-LO= 900 MHz

IF

Mixer Example

{

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Resolution Bandwidth

InputAtten

MixerEnvelopeDetector

Log Amp

LPFBPF

Display

Sawtooth

LocalOscillator

IFAmplifier

ResolutionBW Filter

y

x

VideoBW Filter

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Sets IF Bandwidth of Spectrum Analyzer

Filter types: Standard sweep filters: digital Gaussian filters Channel filters EMI filters (available with Quasipeak detector) FFT filters RRC

Determines frequency resolution and noise floor

Resolution Bandwidth

Sweep Time is function of Resolution Bandwidth and Span

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Ref -20 dBm Att 5 dB

CLRWR

A

Center 1 GHz Span 100 kHz10 kHz/

1 AP

* RBW 18 kHz

VBW 50 kHz

SWT 65 ms

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Date: 7.NOV.2006 12:16:17

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Center 1 GHz Span 100 kHz10 kHz/

1 AP

* RBW 20 kHz

VBW 50 kHz

SWT 2.5 ms

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Date: 7.NOV.2006 12:15:43

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CLRWR

A

Center 1 GHz Span 100 kHz10 kHz/

*

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RBW 20 kHz

SWT 2.5 ms

VBW 50 kHz

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Date: 7.NOV.2006 12:17:44

Ref -20 dBm Att 5 dB

CLRWR

A

Center 1 GHz Span 100 kHz10 kHz/

*

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RBW 20 kHz

AQT 2.5 ms

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Date: 7.NOV.2006 12:17:11

Normal (Gaussian)

FFT

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CLRWR

A

Center 1 GHz Span 100 kHz10 kHz/

1 AP

* RBW 20 kHz

VBW 50 kHz

SWT 50 ms

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Date: 7.NOV.2006 12:16:44

Channel

RRC5 Pole

Default Setting for standard spectrum analyzing tasks

IF Filter Types

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Resolution Bandwidth

2 kHz

200 Hz

Signals separated by 1kHz can’t be resolved

by 2kHz RBW

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Resolution Bandwidth and DANL*

100 kHz

300 kHz

1 MHz

RBW

*DANL: Displayed Average Noise Level

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Envelope Detector

InputAtten

MixerEnvelopeDetector

Log Amp

LPFBPF

Display

Sawtooth

LocalOscillator

IFAmplifier

ResolutionBW Filter

y

x

VideoBW Filter

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• Peak detector• Take only the highest sample

• Negative Peak detector• Take only the lowest sample

• Sample detector• Take the first sample• Effectively a random sample

• RMS detector (power average)

• Perform a power average of the results by squaring the samples, averaging the squares, then taking the square root.

• Average detector (voltage average)

• Perform a linear average of the results before they are converted to LOG scale for display on the screen

Detector Operation

pixel n(8 samples)

pixel n+1(8 samples)

s1 s2 s3 s4 s5 s6 s7 s8 s1 s2 s3 s4 s5 s6 s7 s8

Samples / pixel is determined by sweep time and sample rate

freq

A/D Samples

Positive peak

Sample

RMS

Average

Negative Peak

Displayed Pixels

N

iirms s

NV

1

21

N

iiavg s

NV

1

1

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Detectors and Trace Averaging

Signals with no amplitude dynamics (e.g. CW signals) are easy to measure with a spectrum analyzer

Measured amplitude is unaffected by detector type or trace averaging

Detector type and trace averaging do impact other types of signals such as noise or noise-like signals (e.g. digitally modulated signals)

Ref -20 dBm Att 5 dB

*

1 SA

AVG

2 SA

CLRWR

A

3DB

RBW 3 MHz

VBW 10 MHz

SWT 2.5 ms

Center 1.03025 GHz Span 625 MHz62.5 MHz/

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Date: 3.MAR.2009 16:33:15

Detector and averaging DON’T affect measured level

Detector and averaging DO affect measured level

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• Pos and Neg Peak detectors are not suitable for this type of signal – measure much too high or too low

• Sample detector w/Trace Averaging

• Best technique pre-1996• Averaging in log domain causes a -

2.51dB error (avg of logs < log of avgs)

• RMS detector (power average)• Measures true RMS noise level• Best technique (available since 1996)

• Average detector (voltage average)

• Averaging in voltage domain causes a-1.05dB error(square of avg < avg of squares)

Detector Operation: Noise-like Signal

pixel n(8 samples)

pixel n+1(8 samples)

s1 s2 s3 s4 s5 s6 s7 s8 s1 s2 s3 s4 s5 s6 s7 s8

Samples / pixel is determined by sweep time and sample rate

freq

A/D Samples

Positive peak

Sample

RMS

Average

Negative Peak

Displayed Pixels

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Measurement of noise with average detector

Gaussian noise (voltages) take on a Rayleigh distribution when envelope detected– (Negative voltages are converted to positive voltages.)

The average value of a Rayleigh distributed variable is:

The RMS value of the same distribution is:

The average value is 1.05dB lower than the true RMS value

2

2

2

2

R

eR

2value RMS

2

value Average

Rayleigh Distribution:

dB .

log

log

051

420

2220

RMS

Avg

Measuring Noise: Average Detector

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Ref -90 dBm Att 5 dB

*

*

1 RM

VIEW

2 AV

VIEW

3 SA

VIEW

* A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 13.MAR.2009 15:06:16

Delta: 1.05 dB

RMSdetector

(true level)

Averagedetector

Measuring Noise

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Graphical distribution of noise voltage on a linear scale2

= 6

8%

4 =

95

.45

%

6 =

99

.73

%

noise amplitude distribution

noise amplitude

Gaussian Noise

Measuring Noise: Gaussian Noise

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• Video (log) averaging (dBm) values causes a negative shift in the result.

• Positive peaks are compressed

• Negative peaks are enhanced

• The log of the average is not the same as the average of the log values

• The delta for a Gaussian distribution is -2.51 dB

• Linear averaging solves this problem, but was not available until relatively recently

dBxg .)(log E

1 0, withg(x) variable Gaussian a of value Avg

51220

Measuring Noise: Sample Detector w/Log Averaging

Noise on log (dB) scale Rayleigh Distribution

Amplitude

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Ref -90 dBm Att 5 dB

*

*

1 RM

VIEW

2 AV

VIEW

3 SA

VIEW

* A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 13.MAR.2009 15:06:16

Delta: 1.05 dB

Delta: 2.51 dB

RMSdetector

Averagedetector

Sample detector

w/log avg

Measuring Noise

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RMSdetector

RMS detector w/lin avg

RMS detector measures true noise power

We can apply linear trace averaging to an RMS detector

Ref -90 dBm Att 5 dB

*

*

1 RM

VIEW

2 RM

VIEW

* A

3DB

RBW 200 kHz

VBW 2 MHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 13.MAR.2009 17:29:46

Measuring Noise: RMS Detector

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Ref -90 dBm Att 5 dB

*1 RM

VIEW

2 SA

AVG

* A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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SWP 1000 of 1000

Date: 13.MAR.2009 15:13:07

RMSdetector

Sample detector w/lin avg

RMS detector measures true noise power

Sample detector with linear averaging can yield the same results

Measuring Noise: Sample Detector w/Lin Averaging

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Ref -90 dBm Att 5 dB

*

*

*

1 RM

VIEW

2 AV

VIEW

3 AV

VIEW

* A

3DB

RBW 200 kHz

VBW 2 MHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 13.MAR.2009 18:01:57

RMSdetector

Average detector w/lin avg

How about Average detector with linear averaging?

Average detector with any trace averaging does not yield accurate results

Don’t use average detector to measure noise power

Delta: 1.05 dBAveragedetector

Measuring Noise: Average Detector w/Lin Averaging

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Detectors, Averaging, and Noise Measuring Noise with the RMS Detector

To get a smoother trace use a slower sweep time – more samples/pixel

– 500ms sweep, 32MHz A/D sample rate, 625 pixels over 25,000 samples per pixel

Or apply linear (power) trace averaging to average multiple traces

Measuring Noise with the Sample Detector Only one sample per pixel is used so no advantage to slow sweep To get a smoother trace use Linear or Power average Log averaging will result in a -2.51dB measurement error

Measuring noise with the Pos Peak, Neg Peak, or Average Detector Not recommended for measuring level of noise or noise-like signals

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Video Filter

InputAtten

MixerEnvelopeDetector

Log Amp

LPFBPF

Display

Sawtooth

LocalOscillator

IFAmplifier

ResolutionBW Filter

y

x

VideoBW Filter

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Video Filter

500kHz

500Hz

• Display filter• Similar to trace smoothing in other instruments

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Local Oscillator

InputAtten

MixerEnvelopeDetector

Log Amp

LPFBPF

Display

Sawtooth

LocalOscillator

IFAmplifier

ResolutionBW Filter

y

x

VideoBW Filter

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Tunable

Sweeps across measurement Span

Linear sawtooth drives LO and X-position on Display

Repetition rate (sweep time) determined by RBW

Sweep time can be manually adjusted (for certain measurements)

Not perfect, introduces Phase Noise

Local Oscillator

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Agenda

What is a spectrum analyzer?

Basic spectrum analyzer architecture

Dynamic Range

Spectrum analyzer features and usage

Advanced Spectrum Analyzer Architecture

Standard Measurements

Advanced Measurements

Page 38: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

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Dynamic Range: Internal Distortion

The difference (in dB) between the Input Level that produces distortion products equal to the noise floor and the noise floor level (DANL)

But, what type of distortion? Compression Point Second Order Third order

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Dynamic Range: Internal Distortion

frequency

leve

l

f1 2f1 3f1

Example: Carrier at 0dBm

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f1 12f 3f1

harmonics

2nd order 3rd order

frequency

leve

l

f 3f2f2 2 2f -f 2f - f 2f - f2 1 1 2 12 f +f12

Intermod.intermod.3rd order

intermod.2nd order

Dynamic range:Intermodulation and Harmonics

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What is Spectrum Analyzer Dynamic Range?+30 dBm MAXIMUM INPUT POWER LEVEL

+13 dBm

-37 dBm

-42 dBm SECOND-ORDER DISTORTION

MIXER COMPRESSION

THIRD-ORDER DISTORTION

168 dB

185 dB

MINIMUM NOISE FLOOR (DANL)

113 dB

118 dB

-155 dBm

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Dynamic Range:WCDMA ACLR

• Often specified on Spectrum Analyzer (and Signal Generator) data sheets as a “figure of merit”

• Includes effects of noise and third-order distortion

Limited by Noise

Limited by DistortionOptimum

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Agenda

What is a spectrum analyzer?

Basic spectrum analyzer architecture

Dynamic Range

Spectrum analyzer features and usage

Advanced Spectrum Analyzer Architecture

Standard Measurements

Advanced Measurements

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Basic settings

Center Frequency

Span

Reference level

Resolution Bandwidth (RBW)

Video Bandwidth (VBW)

Detector

Sweep Time

Trigger

Display

Signal

Acquisition

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Triggering

Free run

External trigger Demodulation Pulsed measurements in zero span

IF level Instrument is triggered when IF level reaches defined level

Video Instrument is triggered when Video output reaches defined level

Gated trigger Defines measurement interval in time Typically used for viewing bursted signals in the frequency domain

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How to get most sensitivity?

Make frequency span very small

Set RBW to lowest value

Set Ref Level to low value

Set Attenuation to 0dB (must be done manually)

Turn on Preamp

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Spectrum Analyzers – How to reduce noise

Ref -20 dBm Att 5 dB

1 AP

CLRWR

A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 2.MAR.2009 20:06:32

Default settings, span = 10 MHz

Noise is 55 to 60 dBc

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Spectrum Analyzers – How to reduce noise

Ref -20 dBm Att 5 dB

1 AP

CLRWR

A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 2.MAR.2009 20:06:32

Ref -20 dBm Att 5 dB

*

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CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 2.MAR.2009 20:07:31

Narrow up the RBW to 30 KHz Span is 10 MHz

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Spectrum Analyzers – How to reduce noise

Ref -20 dBm Att 5 dB

1 AP

CLRWR

A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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-90

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Date: 2.MAR.2009 20:06:32

Ref -20 dBm Att 5 dB

*

1 AP

CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 2.MAR.2009 20:07:31

Ref -20 dBm Att 0 dB*

*

1 AP

CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 2.MAR.2009 20:08:51

Change Attenuation to 0 dB RBW is 30 KHz Span is 10 MHz

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Spectrum Analyzers – How to reduce noise

Ref -20 dBm Att 5 dB

1 AP

CLRWR

A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

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-90

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Date: 2.MAR.2009 20:06:32

Ref -20 dBm Att 5 dB

*

1 AP

CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 2.MAR.2009 20:07:31

Ref -20 dBm Att 0 dB*

*

1 AP

CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 2.MAR.2009 20:08:51

Ref -20 dBm Att 0 dB*

*

1 AP

CLRWR

A

PA

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

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Date: 2.MAR.2009 20:09:28

Turn on the pre-amp Attenuation is 0 dB RBW is 30 KHz

Span is 10 MHz

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Spectrum Analyzers – How to reduce noise

Ref -20 dBm Att 5 dB

1 AP

CLRWR

A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:06:32

Ref -20 dBm Att 5 dB

*

1 AP

CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:07:31

Ref -20 dBm Att 0 dB*

*

1 AP

CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:08:51

Ref -20 dBm Att 0 dB*

*

1 AP

CLRWR

A

PA

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:09:28

Ref -20 dBm Att 0 dB*

*

*1 RM

CLRWR

A

PA

3DB

RBW 30 kHz

VBW 300 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:11:02

Select RMS detector Pre-amp is on Attenuation is 0 dB

RBW is 30 KHz Span is 10 MHz

Page 52: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 52

Spectrum Analyzers – How to reduce noise

Ref -20 dBm Att 5 dB

1 AP

CLRWR

A

3DB

RBW 200 kHz

VBW 500 kHz

SWT 2.5 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:06:32

Ref -20 dBm Att 5 dB

*

1 AP

CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:07:31

Ref -20 dBm Att 0 dB*

*

1 AP

CLRWR

A

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:08:51

Ref -20 dBm Att 0 dB*

*

1 AP

CLRWR

A

PA

3DB

RBW 30 kHz

VBW 100 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:09:28

Ref -20 dBm Att 0 dB*

*

*1 RM

CLRWR

A

PA

3DB

RBW 30 kHz

VBW 300 kHz

SWT 30 ms

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:11:02

Ref -20 dBm Att 0 dB **

*

*1 RM

CLRWR

A

PA

3DB

RBW 30 kHz

VBW 300 kHz

SWT 10 s*

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:11:50

Set sweep time to 10 seconds RMS detector Pre-amp is on

Attenuation is 0 dB RBW is 30 KHz

Span is 10 MHz

Page 53: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 53

Spectrum Analyzers – How to reduce noise

Ref -20 dBm Att 0 dB **

*

*1 RM

CLRWR

A

PA

3DB

RBW 30 kHz

VBW 300 kHz

SWT 10 s*

Center 1 GHz Span 10 MHz1 MHz/

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

Date: 2.MAR.2009 20:11:50

Same noise, but looks different… Sweep time 10 seconds RMS detector

Pre-amp is on Attenuation is 0 dB

Span is 10 MHz RBW is 30 KHz

Noise is 83 dBc

Page 54: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 54

Agenda

What is a spectrum analyzer?

Basic spectrum analyzer architecture

Dynamic Range

Spectrum analyzer features and usage

Advanced Spectrum Analyzer Architecture

Standard Measurements

Advanced Measurements

Page 55: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 55

Swept Tuned Block Diagram (conceptual)

InputAtten

MixerEnvelopeDetector

Log Amp

LPFBPF

Display

Sawtooth

LocalOscillator

IFAmplifier

ResolutionBW Filter

y

x

VideoBW Filter

Page 56: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 56

Modern Spectrum Analyzer Architecture

NCO

I

QA

D sin

cos

DSP

Triple Conversion Superheterodyne

Digital IF – output of the 3rd stage is digitized for DSP processing

4.62

84 G

Hz

404.

4 M

Hz

20.4

MHz

Page 57: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 57

Modern Spectrum Analyzer Architecture Input Attenuation – Both mechanical (large step) and electrical (small step)

Pre-Amplifier – supports Noise Figure and low signal measurements

The first LO sweeps

NCO

I

QA

D sin

cos

DSP

4.62

84 G

Hz

404.

4 M

Hz

20.4

MHz

Page 58: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 58

Modern Spectrum Analyzer Architecture

NCO

I

QA

D sin

cos

DSP

Multiple conversion stages are used to remove unwanted signals created by mixing

Fixed LO – these are fixed IF frequencies

4.62

84 G

Hz

404.

4 M

Hz

20.4

MHz

Page 59: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 59

Modern Spectrum Analyzer Architecture

NCO

I

QA

D sin

cos

DSP

Digitized and converted to I (real) and Q (imaginary) values

Detector and Video filter done digitally

With digitized I and Q more sophisticated analysis can be conducted

4.62

84 G

Hz

404.

4 M

Hz

20.4

MHz

Page 60: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 60

Modern Spectrum Analyzer Architecture FSW Block Diagram

Page 61: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 61

Agenda

What is a spectrum analyzer?

Basic spectrum analyzer architecture

Dynamic Range

Spectrum analyzer features and usage

Advanced Spectrum Analyzer Architecture

Standard Measurements

Advanced Measurements

Page 62: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 62

Spectrum Analyzer Measurement Functions Standard Measurement Functions

Time domain power (zero span) Channel Power & Adjacent Channel

Power (CP & ACP) Occupied bandwidth Spurious search Noise marker Frequency counter Statistics (CCDF) TOI Harmonics

Page 63: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 63

Zero Span Mode

Frequency selective Oscilloscope Amplitude on Y axis and time on X axis

Measurement of pulsed signals such as GSM, EDGE, TDD, etc.

Key parameters Sweep time RBW

– Frequency selectivity

– Dynamic range

– Rise and fall time

Page 64: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 64

Zero Span Mode

Page 65: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 65

Zero Span measurement

Demo

Page 66: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 66

Measuring the Power Level of a Signal

What is the power level of this CW signal?

For unmodulated signal simply use a marker

Level matches closely to power meter (reference) measurement

Page 67: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 67

Measuring the Power Level of a Signal

What is the power level of this modulated signal?

Marker only measures power within the RBW – this signal occupies a much larger bandwidth

Must use a different technique:

Channel Power

Page 68: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 68

Measuring the Power Level of a Signal

Channel Power function uses a small RBW and integrates (sums) power over the entire specified bandwidth

Channel Power function also selects the RMS detector for most accurate measurement of noise-like signal

Increasing sweep time improves repeatability. RMS detector collects more samples – similar to averaging

Level agrees with power meter

Page 69: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 69

Channel Power and Adjacent Channel PowerChannel spacing

(center to center) AlternateChannel

Channel BWAdjacentChannel

Page 70: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 70

Spur Searching

Need to scan over very broad frequency ranges to test for unwanted spurious emissions

Typically run on frequency synthesizersSpurious emissions may be required to be < –100dBm (or lower) Requires broad sweep on spectrum analyzer with low RBW to get low noise

floor – SLOW!Older analyzers used harmonic mixing and had “stair-step” noise floor

Required lower RBW at higher freqs

FSW has very fast spur search

Page 71: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 71

Spur Search using basic Spectrum Analyzer

Noise floor may change with frequency

Limited to 32001 frequency points May not be enough to get required resolution over broad frequency range

FSW Spur Search functionovercomes these limitations

Page 72: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 72

Fast Spur Search – Getting Started

Page 73: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 73

Fast Spur Search – Setup ScreenAllows flexible spur search configuration

Up to 20 ranges (segments) can be defined

Each has its own RBW, VBW, Atten, Sweep Points settings

Each range up to 32001 frequency points (>640,000 total)

Page 74: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 74

Fast Spur Search – Peak Evaluation Screen

Specify how measured peaks are handled

Page 75: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 75

Fast Spur Search

100MHz – 26GHz Sweep, 2603 points, < -120dBm Noise Floor

39 sec

Page 76: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 76

Fast Spur Search

100MHz – 26GHz Sweep, 2603 points, ~ -110dBm Noise Floor

< 2 sec

Page 77: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 78

CCDFComplementary Cumulative Distribution Function Statistical map of peak to average level characteristics

Calculated from histogram of amplitude samples

Page 78: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 79

CCDFComplementary Cumulative Distribution Function Statistical map of peak to average level characteristics

Calculated from histogram of amplitude samples

Power vs. TimeZero Span

CCDF

Page 79: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 80

CCDF Measurement

Demo

Page 80: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 81

Third Order Intercept Measurement (TOI) TOI is a measure of the two-tone IM distortion of a device

With two input tones at f1 and f2, distortion (non-linearity) in the DUT will

create tones at 2f1-f2 and 2f2-f1 (third order products)

Pin

Pout

ff1 f2 2f2-f12f1-f2f

Po Po

PIM3PIM3

f1 f2

DUT

Input tones

Amplified input tones

Distortion products created by DUT

Page 81: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 82

Third Order Intercept Measurement (TOI)

Page 82: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 83

Third Order Intercept Measurement (TOI) For every 1dB increase in the output level of the fundamental signals the third-order

distortion products increase 3dB The extrapolated level at which the distortion tones “intercept” the level of the

fundamental tones is called the Third Order Intercept point (TOI or IP3) TOI is calculated using the formula:

+5dBm

- 40dBm

+10dBm

- 25dBm

2)P(3PIPTOI 303

TOI = (3*5+40)/2 = 27.5dBm TOI = (3*10+25)/2 = 27.5dBm

Page 83: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 84

Third Order Intercept Measurement (TOI) TOI is a built-in measurement function on some spectrum analyzers Markers are automatically placed and TOI is calculated

Page 84: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 85

TOI Measurement

Demo

Page 85: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 86

Noise Floor Cancellation to achieve 1 dB NFPreamplifier and noise correction reduce DANL to -173 dBm

With preamp.

With preamp. + noise correction

Page 86: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 87

Spectrum Analyzer Measurement Functionsl Advanced Measurement Functions

l Measurement Probes

l Noise Figure

l Phase Noise

l Vector Signal analysis (VSA)

l Pulsed Signal analysis

l Multi-carrier Group Delay

l Digital Wireless Commsl LTE

l WCDMA (UMTS)

l GSM/EDGE

l CDMA2000/1xEV-DO

l 802.11(a/b/g/n/ac)

l WiMAX

Page 87: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 88

Probing

Simple RF Sniffer (semi-rigid coax)

• Provides a means to measure signals within a circuit where no connection point is available

• Usually used for troubleshooting, not accurate measurements• Also called an RF Sniffer• Simple, cheap, and easy to make• Loads circuit

Page 88: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 89

Probing

+

RT-ZS30 Active Scope Probe

RTO-ZA9 Probe Adapter

• Active scope probe with Probe Adapter

• Probe/Adapter powered by USB cable

• Adapter stores factory probe calibration and provides offset info to spectrum analyzer (via USB)

• Much less loading effect than simple RF Sniffer

• Useful to 3GHz

Page 89: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 90

Noise Figure

Gin

in

N

S

out

in

out

out

N

GS

N

S

l Ratio of Input S/N to Output S/Nl Degradation of S/N through device

(key point: only input noise is thermal, or kTB noise)

l Noise Factor (linear ratio):

l

l (Na is noise added by DUT)

l

l Noise Figure is Noise Factor expressed in dB

GN

N

NGS

NS

NS

NSF

in

out

outin

inin

outout

inin

ainout NGNN

1GN

NF

in

a

)Flog10F( dB

Page 90: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 91

Noise Figurel Use calibrated noise source to generate Ton and Toff

l Ton generated when biased with 28V, Toff when not biased

l Ton known from calibrated ENR (Excess Noise Ratio)

l R&S analyzers work with noise sources from NoiseCom, Micronetics, and Agilent

– R&S does NOT make noise sources

l Noise Figure calculated using Y-factor technique

Noise Power (W)

Noise Temperature (˚K)

Slope = kBG

)NBGkT(N

aon

on

)NBGkT(N

aoff

off

offTonTK0

aN}

)1Ylog(10ENRFdB

off

on

N

NY

Where:Toff is actual temp of noise sourceT0 is 290K

(Y-factor)

Page 91: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 92

Noise Figure

• Guidelines for repeatable measurements

• Noise Source ENR should be at least 3dB higher than Spectrum Analyzer NF

(ENR) – (NFSA) > 3 dB

• Noise Source ENR should be at least 5dB higher than DUT NF

(ENR) – (NFDUT) > 5 dB

• Gain+NF of DUT should be at least 1dB higher than Spectrum Analyzer NF

(NFDUT) + (GainDUT) – (NFSA) > 1 dB

• Advantages of Measurement Mode• Fast and Easy• Plots of Gain and NF vs. frequency• Takes care of calibration• Tabular results also available

Page 92: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 93

Phase Noise

• Ideal Signal (noiseless)

V(t) = A sin(2t)

where A = nominal amplitude = nominal frequency

• Real Signal

V(t) = [A + E(t)] sin(2t + (t))

whereE(t) = amplitude

fluctuations(t)= phase fluctuations

Phase Noise is unintentional phase modulation on a carrier

Level

f

Level

f

t

t

• Radom (short term) fluctuation in the phase of a waveform

Page 93: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 94

Phase Noise

• In the frequency domain phase noise is represented by L(f) in units of dBc/Hz• Terms that can be calculated from L(f)

• Integrated Phase Noise• Residual PM• Residual FM• Jitter Plot

Offset from Carrier

Page 94: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 95

Phase Noise

• Phase noise is measured over a user specified offset range.

• Residual PM and FM, and RMS Jitter are calculated from the phase noise data.

• This is very convenient and provides a plot, but is still limited by the phase noise of the analyzer

• For improved measurements use FSUP which uses the more sensitive phase detector method

Page 95: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 96

Phase Noise Measurement

Demo

Page 96: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 97

EVM is probably the single most measured quantity on a digitally modulated signal.

Start by defining an ideal symbol location in the IQ plane

Then define a reference vector that points from the origin to the ideal location.

Ideal symbol location

I

Q

Refer

ence

Vec

tor

Vector Signal Analysis (VSA)

Page 97: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 98

Vector Signal Analysis (VSA)

EVM is 20 log ( | error / ref | )

The reference vector is (usually) the length from the origin to the ideal point that is the farthest away from the origin.

Therefore, changing the modulation from QPSK to 64-QAM does not have an impact on the EVM result.

This means higher order modulations require better EVM values.

Ideal symbol location

I

Q

Refer

ence

Vec

tor

Errorvector

Measuredsymbol location

ErrorVectormag

Page 98: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 99

Vector Signal Analysis (VSA)

Ideal symbol location

I

Q

Refer

ence

Vec

tor

Errorvector Measured

symbol location

ErrorVectormag

Quadrature component

Phase error

In phasecomponent

Phase oferror vector

Measured V

ector

Amplitudeerror

Page 99: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 100

Vector Signal Analysis (VSA)

User enters: Modulation type, Symbol rate, and Filter type

The signal is demodulated into a series of detected symbols. From these symbols a mathematically perfect model of the signal (reference signal) is created internally and then compared to the measured signal.

If the signal is poor enough in quality an incorrect symbol may be detected which will cause an error in the internal reference signal. If this occurs the reported EVM will be less than the actual EVM.

Page 100: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 101

VSA Measurements

Demo

Page 101: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 102

FSW Pulse Analysisl Timing

l Timestampl Pulse Widthl Rise / Fall / Settling Timel Duty Cycle / Ration

l Power / Amplitudel Peak and Average Powerl Overshootl Droop, Ripplel Pulse to Pulse Magnitude

Difference

l Phasel Phase, Frequencyl Phase/Freq. Error

-0.5 0 0.5 1 1.5 2 2.5-20

0

20

40

60

80

100

120

Time (s/T)

Am

plitu

de (

% o

f P

uls

e T

op)

Pulse Signal

On Time Off Time

Low (e.g. 10% Ampl.)

Mid (e.g. 50% Ampl.)

High (e.g. 90% Ampl.)

Rise Time Fall Time

Pulse Top (100%)

Pulse Bottom (0%)

Settling Time

Upper Top Boundary

Lower Top Boundary

Overshoot

Undershoot

Page 102: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 103

Pulse Definition

Width: level is above 50%

Rise: 10 – 90 %

Fall: 90 – 10 %

Off: below 50 %

Top level: level within top boundary

Droop and non-Droop models

-0.5 0 0.5 1 1.5 2 2.5-20

0

20

40

60

80

100

120

Time (s/T)

Am

plit

ud

e (%

of P

ulse

To

p)

Pulse Signal

On Time Off Time

Low (e.g. 10% Ampl.)

Mid (e.g. 50% Ampl.)

High (e.g. 90% Ampl.)

Rise Time Fall Time

Pulse Top (100%)

Pulse Bottom (0%)

Settling Time

Upper Top Boundary

Lower Top Boundary

Overshoot

Undershoot

Page 103: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 104

FSW Pulse Analysis – Getting Started

Page 104: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 105

FSW Pulse Measurement Results Capture Buffer indicates detected pulses (green bars)

Configurable pulse result table shows measured pulse parameters

Page 105: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 106

FSW Pulse AnalysisModulation on Pulse

Pulse Frequency Pulse Amplitude Pulse Phase

Capture BufferNumerical Results

Page 106: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 109

FSW Pulse Analysis

Demo

Page 107: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 110

What is Group Delay?

Group Delay represents the propagation time of a wave as it goes through a device

Group Delay is calculated from measurement of the Phase distortion of the wave at the output of the device

A non-dispersive device has a linear phase responseLinear phase response represents a constant Group Delay

Page 108: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 111

What is Group Delay?

A linear Phase response is a sloping linePhase distortion is measured as deviation from the straight Phase

response lineThe slope of the line represents the Group Delay

phase

frequency

Ripple = phase distortionSlope = group delay

Page 109: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 114

Spectrum Analyzer Solution for Measuring Group Delay – FSW-K17Introduced in May 2012Utilizes multicarrier CW methodSupports frequency translating devices (mixers)Can measure relative and absolute Group DelayCalibration only requires a “thru” (or reference mixer)Requires vector signal generator

Page 110: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 115

FSW Multicarrier Group Delay

Based on the measurement of phase shift of carriers across frequency

Page 111: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 116

FSW Multicarrier Group Delay

Requires a generator to generate known multicarrier signalMeasurement bandwidth limited to generator BW and FSW digitizer

option (up to 160 MHz)

SMxSignal Generator

(MCCW opt)

FSWSpectrum Analyzer(Group Delay opt)

DUT

Cal

Meas

Trigger

Page 112: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 117

Multicarrier Group DelayApertureAperture is defined as ∆f – corresponds to carrier spacingCarrier spacing is user defined Aperture should be set based on DUT characteristicsSmall aperture noisy traceLarge aperture low resolutionIn VNAs aperture defined by 2-tone

separation and sweep points

Page 113: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 118

FSW MC Group Delay – Getting Started

Page 114: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 120

Marker Table

FSW MC Group Delay Display

Page 115: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 121

FSW MC Group Delay Measurement Setup

Span defined by the no. of carriers and spacing

Span can only be defined as multiple of ∆f

Sample rate/BW determined automatically

Page 116: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

February 2013| Spectrum Analyzer Fundamentals - Advanced | 124

Must perform calibration to perform measurement

For non-frequency translating devices (amps, filters) Only requires a “thru” connection

For frequency translating devices (mixers) Calibrate using raw mixer with known delay (usually <400ps) for absolute delay

measurements Use reference mixer and measure relative delay (normalize) Use gold mixer and import calibration data

FSW MC Group Delay Calibration

Page 117: Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

Thank you!