spectrum analyzer fundamentals/advanced spectrum analysis
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Advanced Spectrum Analyzer measurements
Introduction
Applications Engineer
February 2013| Spectrum Analyzer Fundamentals - Advanced | 3
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 | 4
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 5
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 6
Oscilloscope vs Spectrum Analyzer?
Time Domain Frequency Domain
February 2013| Spectrum Analyzer Fundamentals - Advanced | 7
Oscilloscope vs Spectrum Analyzer?
Amplitude
Frequency
0 1 2 3 4 5 6 7-1
-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 7-1
-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 7-1
-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 7-1
-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 7-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
f1 f3 f5
February 2013| Spectrum Analyzer Fundamentals - Advanced | 8
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 9
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 10
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 | 11
Simplified Swept Tuned Block Diagram
InputAtten
MixerEnvelopeDetector
Log Amp
LPFBPF
Display
Sawtooth
LocalOscillator
IFAmplifier
ResolutionBW Filter
y
x
VideoBW Filter
February 2013| Spectrum Analyzer Fundamentals - Advanced | 12
Input Mixer
InputAtten
MixerEnvelopeDetector
Log Amp
LPFBPF
Display
Sawtooth
LocalOscillator
IFAmplifier
ResolutionBW Filter
y
x
VideoBW Filter
February 2013| Spectrum Analyzer Fundamentals - Advanced | 13
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 14
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
{
February 2013| Spectrum Analyzer Fundamentals - Advanced | 15
Resolution Bandwidth
InputAtten
MixerEnvelopeDetector
Log Amp
LPFBPF
Display
Sawtooth
LocalOscillator
IFAmplifier
ResolutionBW Filter
y
x
VideoBW Filter
February 2013| Spectrum Analyzer Fundamentals - Advanced | 16
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 17
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
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
Date: 7.NOV.2006 12:16:17
Ref -20 dBm Att 5 dB
CLRWR
A
Center 1 GHz Span 100 kHz10 kHz/
1 AP
* RBW 20 kHz
VBW 50 kHz
SWT 2.5 ms
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
Date: 7.NOV.2006 12:15:43
Ref -20 dBm Att 5 dB
CLRWR
A
Center 1 GHz Span 100 kHz10 kHz/
*
1 AP
RBW 20 kHz
SWT 2.5 ms
VBW 50 kHz
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
Date: 7.NOV.2006 12:17:44
Ref -20 dBm Att 5 dB
CLRWR
A
Center 1 GHz Span 100 kHz10 kHz/
*
1 PK
RBW 20 kHz
AQT 2.5 ms
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
Date: 7.NOV.2006 12:17:11
Normal (Gaussian)
FFT
Ref -20 dBm Att 5 dB
CLRWR
A
Center 1 GHz Span 100 kHz10 kHz/
1 AP
* RBW 20 kHz
VBW 50 kHz
SWT 50 ms
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
Date: 7.NOV.2006 12:16:44
Channel
RRC5 Pole
Default Setting for standard spectrum analyzing tasks
IF Filter Types
February 2013| Spectrum Analyzer Fundamentals - Advanced | 18
Resolution Bandwidth
2 kHz
200 Hz
Signals separated by 1kHz can’t be resolved
by 2kHz RBW
February 2013| Spectrum Analyzer Fundamentals - Advanced | 19
Resolution Bandwidth and DANL*
100 kHz
300 kHz
1 MHz
RBW
*DANL: Displayed Average Noise Level
February 2013| Spectrum Analyzer Fundamentals - Advanced | 20
Envelope Detector
InputAtten
MixerEnvelopeDetector
Log Amp
LPFBPF
Display
Sawtooth
LocalOscillator
IFAmplifier
ResolutionBW Filter
y
x
VideoBW Filter
February 2013| Spectrum Analyzer Fundamentals - Advanced | 21
• 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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 22
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/
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
Date: 3.MAR.2009 16:33:15
Detector and averaging DON’T affect measured level
Detector and averaging DO affect measured level
February 2013| Spectrum Analyzer Fundamentals - Advanced | 23
• 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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 24
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 25
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/
-100
-99
-98
-97
-96
-95
-94
-93
-92
-91
-90
Date: 13.MAR.2009 15:06:16
Delta: 1.05 dB
RMSdetector
(true level)
Averagedetector
Measuring Noise
February 2013| Spectrum Analyzer Fundamentals - Advanced | 26
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 27
• 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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 28
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/
-100
-99
-98
-97
-96
-95
-94
-93
-92
-91
-90
Date: 13.MAR.2009 15:06:16
Delta: 1.05 dB
Delta: 2.51 dB
RMSdetector
Averagedetector
Sample detector
w/log avg
Measuring Noise
February 2013| Spectrum Analyzer Fundamentals - Advanced | 29
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/
-100
-99
-98
-97
-96
-95
-94
-93
-92
-91
-90
Date: 13.MAR.2009 17:29:46
Measuring Noise: RMS Detector
February 2013| Spectrum Analyzer Fundamentals - Advanced | 30
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/
-100
-99
-98
-97
-96
-95
-94
-93
-92
-91
-90
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 31
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/
-100
-99
-98
-97
-96
-95
-94
-93
-92
-91
-90
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 32
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 33
Video Filter
InputAtten
MixerEnvelopeDetector
Log Amp
LPFBPF
Display
Sawtooth
LocalOscillator
IFAmplifier
ResolutionBW Filter
y
x
VideoBW Filter
February 2013| Spectrum Analyzer Fundamentals - Advanced | 34
Video Filter
500kHz
500Hz
• Display filter• Similar to trace smoothing in other instruments
February 2013| Spectrum Analyzer Fundamentals - Advanced | 35
Local Oscillator
InputAtten
MixerEnvelopeDetector
Log Amp
LPFBPF
Display
Sawtooth
LocalOscillator
IFAmplifier
ResolutionBW Filter
y
x
VideoBW Filter
February 2013| Spectrum Analyzer Fundamentals - Advanced | 36
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 37
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 | 38
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 39
Dynamic Range: Internal Distortion
frequency
leve
l
f1 2f1 3f1
Example: Carrier at 0dBm
February 2013| Spectrum Analyzer Fundamentals - Advanced | 40
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 41
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 42
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 43
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 | 44
Basic settings
Center Frequency
Span
Reference level
Resolution Bandwidth (RBW)
Video Bandwidth (VBW)
Detector
Sweep Time
Trigger
Display
Signal
Acquisition
February 2013| Spectrum Analyzer Fundamentals - Advanced | 45
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 46
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 47
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
Default settings, span = 10 MHz
Noise is 55 to 60 dBc
February 2013| Spectrum Analyzer Fundamentals - Advanced | 48
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
Narrow up the RBW to 30 KHz Span is 10 MHz
February 2013| Spectrum Analyzer Fundamentals - Advanced | 49
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
Change Attenuation to 0 dB RBW is 30 KHz Span is 10 MHz
February 2013| Spectrum Analyzer Fundamentals - Advanced | 50
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
Turn on the pre-amp Attenuation is 0 dB RBW is 30 KHz
Span is 10 MHz
February 2013| Spectrum Analyzer Fundamentals - Advanced | 51
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
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
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
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
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
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
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
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 60
Modern Spectrum Analyzer Architecture FSW Block Diagram
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
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 64
Zero Span Mode
February 2013| Spectrum Analyzer Fundamentals - Advanced | 65
Zero Span measurement
Demo
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
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 69
Channel Power and Adjacent Channel PowerChannel spacing
(center to center) AlternateChannel
Channel BWAdjacentChannel
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 72
Fast Spur Search – Getting Started
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)
February 2013| Spectrum Analyzer Fundamentals - Advanced | 74
Fast Spur Search – Peak Evaluation Screen
Specify how measured peaks are handled
February 2013| Spectrum Analyzer Fundamentals - Advanced | 75
Fast Spur Search
100MHz – 26GHz Sweep, 2603 points, < -120dBm Noise Floor
39 sec
February 2013| Spectrum Analyzer Fundamentals - Advanced | 76
Fast Spur Search
100MHz – 26GHz Sweep, 2603 points, ~ -110dBm Noise Floor
< 2 sec
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 80
CCDF Measurement
Demo
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 82
Third Order Intercept Measurement (TOI)
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 85
TOI Measurement
Demo
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
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
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
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
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
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)
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
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
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 96
Phase Noise Measurement
Demo
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)
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
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
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.
February 2013| Spectrum Analyzer Fundamentals - Advanced | 101
VSA Measurements
Demo
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 104
FSW Pulse Analysis – Getting Started
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 106
FSW Pulse AnalysisModulation on Pulse
Pulse Frequency Pulse Amplitude Pulse Phase
Capture BufferNumerical Results
February 2013| Spectrum Analyzer Fundamentals - Advanced | 109
FSW Pulse Analysis
Demo
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
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 115
FSW Multicarrier Group Delay
Based on the measurement of phase shift of carriers across frequency
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
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
February 2013| Spectrum Analyzer Fundamentals - Advanced | 118
FSW MC Group Delay – Getting Started
February 2013| Spectrum Analyzer Fundamentals - Advanced | 120
Marker Table
FSW MC Group Delay Display
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
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
Thank you!
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