Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

Advanced Spectrum Analyzer
measurements

Introduction

Applications Engineer

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

February 2013| Spectrum Analyzer Fundamentals - Advanced | 3

Spectrum Analyzer
The 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


Notable Milestones in Spectrum Analysis
1940s: First sweep spectral analysis performed by MIT RAD LAB.
1960s: Spectrum Analyzer market dominated by Polarad and Panoramic
1964: HP makes the 1st LO tunable, revolutionizes the market
1978: 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


Oscilloscope vs Spectrum Analyzer?

Time Domain Frequency Domain


Oscilloscope vs Spectrum Analyzer?
1

0.8

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

-0.8

-1
0 1 2 3 4 5 6 7

Amplitude

f1 f3 f5 Frequency


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 1W


Spectrum Analyzer ≠ Network Analyzer


Measures signals Measures devices

Spectrum Analyzers: Network Analyzers:
• Measure signal amplitude characteristics, carrier • Measure response of components, devices,
level, sidebands, harmonics circuits, sub-assemblies to applied stimulus
• Can demodulate and measure complex signals • Contains sources and receivers
• Spectrum analyzers are receivers only (single • Display ratioed amplitude and phase
channel) (frequency, power or time sweeps)
• Can be used for scalar component test • Offers advanced error correction for high
(amplitude only) with tracking gen. or ext. source accuracy measurements


Agenda


 Dynamic Range






Simplified Swept Tuned Block Diagram
IF Resolution Video
Mixer BW Filter Log Amp BW Filter
Amplifier Envelope
Detector
BPF LPF

Input
Atten

Local y
Oscillator

x

Display

Sawtooth


Input Mixer
IF Resolution Video
Amplifier Envelope
Detector
BPF LPF

Input
Atten

Local y
Oscillator

x

Display

Sawtooth


Types of Mixing
RF IF
 Fixed RF, Swept LO and IF

 Fixed LO, Swept RF and IF LO

 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


Mixer Example
Possible frequencies on IF

{
port…to name a few:
LO-RF=100MHz
LO+RF= 2.1GHz
LO=1.1 GHz
RF IF
RF=1 GHz
1 GHz 2LO-RF=1.2 GHz
2RF-LO= 900 MHz
LO
1.1 GHz


Resolution Bandwidth
IF Resolution Video
Amplifier Envelope
Detector
BPF LPF

Input
Atten

Local y
Oscillator

x

Display

Sawtooth


 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

Sweep Time is function of Resolution Bandwidth and Span


IF Filter Types Ref -20 dBm Att 5 dB
* RBW
VBW
SWT
18
50
65
kHz
kHz
ms

-20

A
-30

1 AP
CLRWR
-40

* RBW 20 kHz -50
VBW 50 kHz
Ref -20 dBm Att 5 dB SWT 2.5 ms

-20 -60

A
-30
-70
1 AP
CLRWR
-40
-80

-50
* RBW 20 kHz -90
VBW 50 kHz
-60
-100
-70 -20
-110
-80 A
-30
-120

-90 1 AP Center 1 GHz 10 kHz/ Span 100 kHz
CLRWR
-40
-100

Channel
-110 -50 Date: 7.NOV.2006 12:16:17

-120

Center 1 GHz 10 kHz/ Span 100 kHz
-60

-70
Date: 7.NOV.2006 12:15:43

FFT -80

-90

-100

-110
* RBW 20 kHz
VBW 50 kHz
Ref -20 dBm Att 5 dB SWT 50 ms
-120
-20

Center 1 GHz 10 kHz/ Span 100 kHz A
-30

1 AP
CLRWR
-40
* RBW 20 kHz

Ref -20 dBm Att 5 dB AQT 2.5 ms -50

-20
Date: 7.NOV.2006 12:17:44
-60

Normal (Gaussian)
A
-30

1 PK
-70
CLRWR
-40

-80
-50

-90
-60

-100

Default Setting for standard
-70

-110
-80

-120

-90 Center 1 GHz 10 kHz/ Span 100 kHz

-100

-110

-120
spectrum analyzing tasks Date: 7.NOV.2006 12:16:44

5 Pole
Center 1 GHz 10 kHz/ Span 100 kHz

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

RRC



200 Hz

Signals separated by
2 kHz
1kHz can’t be resolved
by 2kHz RBW


Resolution Bandwidth and DANL*

RBW

1 MHz

300 kHz

100 kHz

*DANL: Displayed Average Noise Level


Envelope Detector
IF Resolution Video
Amplifier Envelope
Detector
BPF LPF

Input
Atten

Local y
Oscillator

x

Display

Sawtooth


Detector Operation
• Peak detector
• Take only the highest sample Samples / pixel is determined by sweep time and sample rate

pixel n pixel n+1
• Negative Peak detector (8 samples) (8 samples)
s1 s2 s3 s4 s5 s6 s7 s8 s1 s2 s3 s4 s5 s6 s7 s8
• Take only the lowest sample

• Sample detector
 A/D Samples
• Take the first sample
• Effectively a random sample

• RMS detector (power average)
N
1
Vrms =
N
∑s
i =1
2
i

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

Positive peak
• Average detector (voltage average) Sample
N
1 RMS
Vavg =
N
∑s
i =1
i
Average
freq
• Perform a linear average of the results Negative Peak
before they are converted to LOG scale
for display on the screen


Detectors and Trace Averaging
 Signals with no amplitude RBW
VBW
3
10
MHz
MHz

dynamics (e.g. CW signals) are

-20

easy to measure with a spectrum -30
A

analyzer 1 SA
AVG
-40

2 SA *
CLRWR Detector and averaging
-50
DON’T affect measured level
-60
 Measured amplitude is
unaffected by detector type or
-70

3DB

trace averaging -80

-90

-100

 Detector type and trace -110
Detector and averaging
DO affect measured level
averaging do impact other types -120

of signals such as noise or noise-
Center 1.03025 GHz 62.5 MHz/ Span 625 MHz

like signals (e.g. digitally
modulated signals) Date: 3.MAR.2009 16:33:15


Detector Operation: Noise-like Signal
• Pos and Neg Peak detectors are Samples / pixel is determined by sweep time and sample rate
not suitable for this type of signal
– measure much too high or too pixel n pixel n+1
(8 samples) (8 samples)
low
s1 s2 s3 s4 s5 s6 s7 s8 s1 s2 s3 s4 s5 s6 s7 s8

• Sample detector w/Trace
Averaging
• Best technique pre-1996
 A/D Samples
• 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)
 Displayed
• Average detector (voltage Pixels
average)
• Averaging in voltage domain causes a Positive peak
-1.05dB error Sample
(square of avg < avg of squares)
RMS
Average
freq
Negative Peak


Measuring Noise: Average Detector
 Measurement of noise with average detector

 Gaussian noise (voltages) take on a Rayleigh distribution when envelope detected
– (Negative voltages are converted to positive voltages.)
 R2 
− 2 
R  2σ 
 
Rayleigh Distribution: e
σ2
σ π 
Avg  2
= 20 log 
 The average value of a Rayleigh distributed variable is: RMS  σ 2 
π  
Average value = σ
2  π 
= 20 log
 4

 The RMS value of the same distribution is:  
RMS value = σ 2 = −1.05 dB

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


Measuring Noise
RBW 200 kHz
VBW 500 kHz

RMS -90
*
detector
A
-91

1 RM *

(true level)
VIEW
-92

2 AV *
VIEW
-93

Average Delta: 1.05 dB
3 SA
VIEW
-94

detector -95

3DB
-96

-97

-98

-99

-100

Center 1 GHz 1 MHz/ Span 10 MHz

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


Measuring Noise: Gaussian Noise

 Graphical distribution of noise voltage on a linear scale

noise amplitude

4σ = 95.45%
2σ = 68%

6σ =
%
99.73
noise amplitude
distribution
Gaussian
Noise


Measuring Noise: Sample Detector w/Log Averaging
• Video (log) averaging (dBm) values causes a negative shift in the result.
• Positive peaks are compressed Avg value of a Gaussian variable g(x) with µ = 0, σ = 1
• Negative peaks are enhanced → E [ 20 log( g ( x ) ) ] = −2.51 dB

• 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
Amplitude

Noise on log (dB) scale Rayleigh Distribution


Measuring Noise
RBW 200 kHz
VBW 500 kHz

RMS -90
*
detector
A
-91

1 RM *
VIEW
-92

2 AV *
VIEW
-93

Average Delta: 1.05 dB
3 SA
VIEW -94

detector -95

-96
3DB Delta: 2.51 dB

Sample -97

detector -98

w/log avg -99

-100


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


Measuring Noise: RMS Detector
 RMS detector measures true noise power

 We can apply linear trace averaging to an RMS detector
RBW 200 kHz
VBW 2 MHz

RMS -90
*
A

detector
-91

1 RM *
VIEW
-92

2 RM *
VIEW
-93

RMS detector -94

w/lin avg -95

3DB
-96

-97

-98

-99

-100


FebruaryDate: 13.MAR.2009 Analyzer Fundamentals - Advanced | 29
2013| Spectrum 17:29:46

Measuring Noise: Sample Detector w/Lin Averaging
 RMS detector measures true noise power

 Sample detector with linear averaging can yield the same results
RBW 200 kHz
VBW 500 kHz

RMS -90
*
A

detector
-91

1 RM *
VIEW
-92

2 SA
AVG
-93

Sample -94

detector -95

SWP 1000 of 1000
3DB

w/lin avg -96

-97

-98

-99

-100


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

Measuring Noise: Average Detector w/Lin Averaging
 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
RBW 200 kHz
VBW 2 MHz

RMS -90
*
detector 1 RM *
-91
A

VIEW
-92

2 AV *
VIEW
-93

3 AV *

Average VIEW
-94 Delta: 1.05 dB
detector -95

3DB
-96

Average -97

detector -98

w/lin avg -99

-100


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

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


Video Filter
IF Resolution Video
Amplifier Envelope
Detector
BPF LPF

Input
Atten

Local y
Oscillator

x

Display

Sawtooth


Video Filter

500kHz

500Hz

• Display filter
• Similar to trace smoothing in other instruments


Local Oscillator
IF Resolution Video
Amplifier Envelope
Detector
BPF LPF

Input
Atten

Local y
Oscillator

x

Display

Sawtooth


Local Oscillator
 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


Agenda


 Dynamic Range






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


Dynamic Range: Internal Distortion
 Example: Carrier at 0dBm

level

f1 2f1 3f1
frequency


Dynamic range:
Intermodulation and Harmonics
intermod. intermod.
Intermod.
level

2nd order 3rd order harmonics

2nd order 3rd order

f2 -f
1 2f - f2
1 f1 f2 2f2 - f1 2f f2 +f1 2f2
1 3f
1 3f2 frequency


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

+13 dBm MIXER COMPRESSION

185 dB -37 dBm THIRD-ORDER DISTORTION

168 dB
-42 dBm SECOND-ORDER DISTORTION

118 dB
113 dB

-155 dBm MINIMUM NOISE FLOOR (DANL)


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 Limited by
Noise Optimum Distortion


Agenda


 Dynamic Range






Basic settings
 Center Frequency

 Span Display
 Reference level

 Resolution Bandwidth (RBW)

 Video Bandwidth (VBW) Signal
 Detector

 Sweep Time
Acquisition
 Trigger


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


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


Spectrum Analyzers – How to reduce noise
 Default settings, span = 10 MHz

RBW 200 kHz
VBW 500 kHz

-20

A
-30

1 AP
CLRWR
-40

Noise is 55 -50

to 60 dBc -60

-70

3DB
-80

-90

-100

-110

-120


February 2013| Spectrum Analyzer 2.MAR.2009 20:06:32
Date: Fundamentals - Advanced | 47

 Narrow up the RBW to 30 KHz
 Span is 10 MHz

* RBW 30 kHz RBW 200 kHz
VBW 100 kHz VBW 500 kHz
Ref -20 dBm Att 5 dB SWT 30 ms Ref -20 dBm Att 5 dB SWT 2.5 ms

-20 -20

A A
-30 -30

1 AP 1 AP
CLRWR CLRWR
-40 -40

-50 -50

-60 -60

-70 -70

3DB 3DB
-80 -80

-90 -90

-100 -100

-110 -110

-120 -120

Center 1 GHz 1 MHz/ Center 1S p a n
GHz 10 MHz 1 MHz/ Span 10 MHz

Date: 2.MAR.2009 20:07:31 February 2013| Spectrum Analyzer 2.MAR.2009 20:06:32

 Change Attenuation to 0 dB
 RBW is 30 KHz
 Span is 10 MHz
* RBW 30 kHz * RBW 30 kHz RBW 200 kHz
VBW 100 kHz VBW 100 kHz VBW 500 kHz
Ref -20 dBm * Att 0 RdeBf -20 dBSWT
m 30 ms Att 5 dR e f
B -20 dSBWmT 30 ms Att 5 dB SWT 2.5 ms

-20 -20 -20

A A A
-30 -30 -30

1 AP 1 AP 1 AP
CLRWR CLRWR CLRWR
-40 -40 -40

-50 -50 -50

-60 -60 -60

-70 -70 -70

3DB 3DB 3DB
-80 -80 -80

-90 -90 -90

-100 -100 -100

-110 -110 -110

-120 -120 -120

Center 1 GHz C e n t e1r M H z / H z
1 G C e n t e r H z1/0 G H z z
1 M
Span MH S p a1n M H z / M H z
10 Span 10 MHz

Date: 2.MAR.2009 20:08:51 February 2013| Spectrum
Date: 2.MAR.2009 20:07:31 Analyzer 2.MAR.2009 20:06:32

 Turn on the pre-amp
 Attenuation is 0 dB  Span is 10 MHz
 RBW is 30 KHz
* RBW 30 kHz * RBW 30 kHz * RBW 30 kHz RBW 200 kHz
VBW 100 kHz VBW 100 kHz VBW 100 kHz VBW 500 kHz
Ref -20 dBm Ref * -20
Att d B0m d B R e *T A t3t0 0 m d B m B
S Wf - 2 s
0 d Ref
SWT A20 s
- t t m d B5m d B
30 S W T A t3t0 ms
5 dB SWT 2.5 ms

-20 -20 -20 -20

A A A A
-30 -30 -30 -30

1 AP 1 AP 1 AP 1 AP
CLRWR CLRWR CLRWR CLRWR
-40 -40 -40 -40

-50 -50 -50 -50
PA

-60 -60 -60 -60

-70 -70 -70 -70

3DB 3DB 3DB 3DB
-80 -80 -80 -80

-90 -90 -90 -90

-100 -100 -100 -100

-110 -110 -110 -110

-120 -120 -120 -120

Center 1 GHz Center 1 GHz 1 M H z /C e n t e r 1 GHz 1 M H z /C e n t e Sr p a 1 G1H0z M H z1
n MHz/ Span 10 M H z1 MHz/ Span 10 MHz Span 10 MHz

Date: 2.MAR.2009 20:09:28 2.MAR.2009 20:08:51 2.MAR.2009 Analyzer 2.MAR.2009 20:06:32
Date: FebruaryDate: Spectrum 20:07:31 Fundamentals - Advanced
2013| Date: | 50

 Select RMS detector
 Pre-amp is on  RBW is 30 KHz
 Attenuation is 0 dB  Span is 10 MHz
* RBW 30 kHz * RBW 30 kHz * RBW 30 kHz * RBW 30 kHz RBW 200 kHz
VBW 300 kHz VBW 100 kHz VBW 100 kHz VBW 100 kHz VBW 500 kHz
Ref -20 dBm R e* A t t 0
f -2 dBm B
0 d Ref S T* A 0 m s 0
- 2 0 W d B m3 t t R e f dB0
-2 * A SW0
dBm ttRefT d B 0 md B m t t S W 5 d B
30
-2 s A T 30 ms Att SW5
T dB
30 ms SWT 2.5 ms

-20 -20 -20 -20 -20

A A A A A
-30 -30 -30 -30 -30

1 RM * 1 AP 1 AP 1 AP 1 AP
CLRWR CLRWR CLRWR CLRWR CLRWR
-40 -40 -40 -40 -40

-50 -50 -50 -50 -50
PA PA

-60 -60 -60 -60 -60

-70 -70 -70 -70 -70

3DB 3DB 3DB 3DB 3DB
-80 -80 -80 -80 -80

-90 -90 -90 -90 -90

-100 -100 -100 -100 -100

-110 -110 -110 -110 -110

-120 -120 -120 -120 -120

Center 1 GHz Center 1 GHz C1 nM H z / 1
e ter GHz Center 1 1 G M H z /C e n tSepra n 1 11 G MH HMzH/z
Hz 0 z 1 MS p a n
Hz/ 10 M H z1 M SH p a n
z/ 10 MHz Span 10 MHz Span 10 MHz

Date: 2.MAR.2009 February 2013| Spectrum Analyzer 2.MAR.2009 20:06:32
Date: 2.MAR.2009 20:08:51 Date: Fundamentals - Advanced
20:11:02 2.MAR.2009 20:09:28 Date: 2.MAR.2009 20:07:31
Date: | 51

 Set sweep time to 10 seconds
 RMS detector  Attenuation is 0 dB  Span is 10 MHz
 Pre-amp is on  RBW is 30 KHz
* RBW 30 kHz * RBW 30 kHz * RBW 30 kHz * RBW 30 kHz * RBW 30 kHz RBW 200 kHz
VBW 300 kHz VBW 300 kHz VBW 100 kHz VBW 100 kHz VBW 100 kHz VBW 500 kHz
Ref -20 dBm Ref -20 dBm tt
* A R e f d B- 2 0 * B m t S R e f d B- 2 s
0 dAt * W0 10 0
T * A SWT 0 020
dBm ttRef 3dBmsdBm ttRef
- * A SW0T d B 0 md B m t t S W 5 d B
30
-2 s A T 30 ms Att SW5
T dB
30 ms SWT 2.5 ms

-20 -20 -20 -20 -20 -20

A A A A A A
-30 -30 -30 -30 -30 -30

1 RM * 1 RM * 1 AP 1 AP 1 AP 1 AP
CLRWR CLRWR CLRWR CLRWR CLRWR CLRWR
-40 -40 -40 -40 -40 -40

-50 -50 -50 -50 -50 -50
PA PA PA

-60 -60 -60 -60 -60 -60

-70 -70 -70 -70 -70 -70

3DB 3DB 3DB 3DB 3DB 3DB
-80 -80 -80 -80 -80 -80

-90 -90 -90 -90 -90 -90

-100 -100 -100 -100 -100 -100

-110 -110 -110 -110 -110 -110

-120 -120 -120 -120 -120 -120

Center 1 GHz Center 1 GHz Center 11 MGHHzz/ C e n t e r 11 MGHHzz/ C e n t e r 1 1 G MpHazn/C e1n0t eMrH z 1 1 G MH Hazn/ 1 0
SHz Spz MHz 1 MS p a n
Hz/ 10 M H z1 M SH p a n
z/ 10 MHz Span 10 MHz Span 10 MHz

Date: 2.MAR.2009 20:11:02 February 2013| Date: 2.MAR.2009 20:07:31
Date: 2.MAR.2009 20:11:50 Date: 2.MAR.2009 20:09:28 Spectrum Analyzer 2.MAR.2009 20:06:32
Date: 2.MAR.2009 20:08:51 Date: Fundamentals - Advanced | 52

 Same noise, but looks different…
 Sweep time 10 seconds  Pre-amp is on  Span is 10 MHz
 RMS detector  Attenuation is 0 dB  RBW is 30 KHz
* RBW 30 kHz
VBW 300 kHz
Ref -20 dBm * Att 0 dB * SWT 10 s

-20

A
-30

1 RM *
CLRWR
-40

-50
PA

-60

Noise is -70

83 dBc -80
3DB

-90

-100

-110

-120


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

Agenda


 Dynamic Range






Swept Tuned Block Diagram (conceptual)
IF Resolution Video
Amplifier Envelope
Detector
BPF LPF

Input
Atten

Local y
Oscillator

x

Display

Sawtooth


Modern Spectrum Analyzer Architecture
 Triple Conversion Superheterodyne

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

Hz

Hz

Hz
G

M

M
84

4

.4
4.
62

20
I

40
4.

A DSP
D sin
Q

cos

NCO


 Input Attenuation – Both mechanical (large step) and electrical (small step)

 Pre-Amplifier – supports Noise Figure and low signal measurements

 The first LO sweeps

Hz

Hz

Hz
G

M

M
4

4
28

.4
4.

20
I
6

40
4.

A DSP
D sin
Q

cos

NCO


 Multiple conversion stages are used to remove unwanted signals created by mixing
 Fixed LO – these are fixed IF frequencies

Hz

Hz

Hz
G

M

M
4

4
28

.4
4.

20
I
6

40
4.

A DSP
D sin
Q

cos

NCO


 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

Hz

Hz

Hz
G

M

M
4

4
28

.4
4.

20
I
6

40
4.

A DSP
D sin
Q

cos

NCO


 FSW Block Diagram


Agenda


 Dynamic Range






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


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


Zero Span Mode


Zero Span measurement

Demo


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


 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


 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


Channel Power and Adjacent Channel Power
Channel spacing Adjacent Alternate
Channel BW (center to center)
Channel Channel


Spur Searching
Need to scan over very broad frequency ranges to test for unwanted spurious
emissions
Typically run on frequency synthesizers
Spurious 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


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 function
overcomes these limitations


Fast Spur Search – Getting Started


Fast Spur Search – Setup Screen
Allows 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)


Fast Spur Search – Peak Evaluation
Screen

Specify how measured peaks are handled


Fast Spur Search

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

Fast Spur Search

100MHz – 26GHz Sweep, 2603 points, ~ -110dBm Noise Floor
< 2 sec

CCDF
Complementary Cumulative Distribution Function
 Statistical map of peak to average level characteristics
 Calculated from histogram of amplitude samples


CCDF
Complementary Cumulative Distribution Function
 Statistical map of peak to average level characteristics
 Calculated from histogram of amplitude samples

Power vs. Time
Zero Span

CCDF


CCDF Measurement

Demo


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)

Amplified
input tones

Input tones Pout Po Po
Pin
PIM3 PIM3

DUT
f1 f2 2f1-f2 f1 f2 2f2-f1 f
f

Distortion products created
by DUT


 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:

TOI = IP3 = (3P0 − P3 ) 2

+10dBm
+5dBm

- 25dBm

- 40dBm

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


 TOI is a built-in measurement function on some spectrum analyzers
 Markers are automatically placed and TOI is calculated


TOI Measurement

Demo


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

With preamp. + noise correction

With preamp.


Spectrum Analyzer Measurement Functions
l 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 Comms
l LTE
l WCDMA (UMTS)
l GSM/EDGE
l CDMA2000/1xEV-DO
l 802.11(a/b/g/n/ac)
l WiMAX


Probing
• 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

Simple RF Sniffer
(semi-rigid coax)


Probing
• 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

+ 

RT-ZS30 Active RTO-ZA9 Probe
Scope Probe Adapter


Noise Figure
l Ratio of Input S/N to Output S/N
l Degradation of S/N through device
(key point: only input noise is thermal, or kTB noise)

Sin Sout SinG
G =
Nin Nout Nout

l Noise Factor (linear ratio):
Sin Nin Sin Nin N
l F= = = out
Sout Nout SinG Nout NinG

l Nout = NinG + Na(Na is noise added by DUT)

Na
l F= +1
NinG

l Noise Figure is Noise Factor expressed in dB (FdB = 10 log F)


Noise Figure
l 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
Non (W) Non
(kTonBG + Na ) Y= (Y-factor)
Noff
Slope = kBG

FdB = ENR − 10 log( Y − 1)
Noff
(kToff BG + Na )
Where:
} Na Toff is actual temp of noise source
T0 is 290K
0°K Toff Ton
Noise Temperature (˚K)


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


Phase Noise
• Radom (short term) fluctuation in the phase of a waveform
Level
• Ideal Signal (noiseless)

V(t) = A sin(2πνt)
f

where
A = nominal amplitude t
ν = nominal frequency

• Real Signal Level

V(t) = [A + E(t)] sin(2πνt + φ(t))
f
where
E(t) = amplitude fluctuations t
φ(t) = phase fluctuations

Phase Noise is unintentional phase modulation on a carrier


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


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


Phase Noise Measurement

Demo


Vector Signal Analysis (VSA)

 EVM is probably the single most
Ideal symbol location measured quantity on a digitally
modulated signal.
Q

 Start by defining an ideal symbol
or

location in the IQ plane
ct
Ve
ce
en
er

 Then define a reference vector that
f
Re

points from the origin to the ideal
location.

I


Error
Vector
 EVM is 20 log ( | error / ref | ) mag

Error
Q Ideal symbol location
 The reference vector is (usually) the vector
length from the origin to the ideal
point that is the farthest away from
Measured

r
to
the origin. symbol location

c
Ve
ce
en
er
 Therefore, changing the modulation

f
Re
from QPSK to 64-QAM does not have
an impact on the EVM result.

 This means higher order modulations I
require better EVM values.


Error
Vector
mag

Ideal symbol location Error
Q Measured
vector
symbol location
Quadrature

or
component

ct
Ve
ce
Amplitude
n
re r
ct o error
fe

Ve
Re

d
ure
eas
Phase M
error

I
Phase of In phase
error vector component



 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.


VSA Measurements

Demo


FSW Pulse Analysis
l Timing
l Timestamp
l Pulse Width
l Rise / Fall / Settling Time
l Duty Cycle / Ration

l Power / Amplitude
l Peak and Average Power
l Overshoot
l Droop, Ripple
l Pulse to Pulse Magnitude
Difference

l Phase
l Phase, Frequency
l Phase/Freq. Error


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


FSW Pulse Analysis – Getting Started


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

 Configurable pulse result table shows measured pulse parameters


FSW Pulse Analysis
Modulation on Pulse

Numerical Results
Capture Buffer

Pulse Frequency Pulse Amplitude Pulse Phase


FSW Pulse Analysis

Demo


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 response
Linear phase response represents a constant Group Delay


What is Group Delay?

A linear Phase response is a sloping line
Phase distortion is measured as deviation from the straight Phase
response line
The slope of the line represents the Group Delay
Slope = group delay Ripple = phase distortion

phase

frequency


Spectrum Analyzer Solution for Measuring
Group Delay – FSW-K17
Introduced in May 2012
Utilizes multicarrier CW method
Supports frequency translating devices (mixers)
Can measure relative and absolute Group Delay
Calibration only requires a “thru” (or reference mixer)
Requires vector signal generator


FSW Multicarrier Group Delay

Based on the measurement of phase shift of carriers across frequency


FSW Multicarrier Group Delay

Requires a generator to generate known multicarrier signal
Measurement bandwidth limited to generator BW and FSW digitizer
option (up to 160 MHz)

SMx FSW
Meas
Signal Generator DUT Spectrum Analyzer
(MCCW opt) (Group Delay opt)
Cal

Trigger


Multicarrier Group Delay
Aperture
Aperture is defined as ∆f – corresponds to carrier spacing
Carrier spacing is user defined
Aperture should be set based on DUT characteristics
Small aperture  noisy trace
Large aperture  low resolution
In VNAs aperture defined by 2-tone
separation and sweep points


FSW MC Group Delay – Getting Started


FSW MC Group Delay Display

Marker Table


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


FSW MC Group Delay Calibration
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


Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

More Related Content

What's hot

Viewers also liked

Similar to Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

More from Rohde & Schwarz North America

Spectrum Analyzer Fundamentals/Advanced Spectrum Analysis

Editor's Notes