december 2002 generation and conditioning of multitone test signals
TRANSCRIPT
December 2002December 2002
Generation and Conditioning of Multitone Test Signals
Generation & Conditioning of Multitone Test Signals
Agenda
• Linear vs. nonlinear behavior
• Nonlinear distortion
• Methods to characterize nonlinear distortion
• Two-tone measurements
• Multitone measurements
• Noise power ratio (NPR) measurements
• Summary
Output
Linear versus nonlinear behavior
Linear behavior: input and output frequencies are
the same (no additional frequencies created)
output frequency only undergoes magnitude and phase change
Frequencyf
1
Time
Sin 360o * f * t
Frequency
A phase shift = to * 360o
* f
1f
DUT
Time
A
to
A * Sin 360o * f (t - to)
Input Output
Time
Nonlinear behavior: output frequency may undergo
frequency shift (e.g. with mixers) additional frequencies created
(harmonics, intermodulation)
Frequencyf
1
Nonlinear distortion
Linear behavior
Vin = Vacos(wat)Amplifier
[A]Vout = AVin
A A
Linear behaviorVs.
Non-linear behavior
Vin = Vacos(wat)Amplifier
[A]Vout = AVin + A1(Vin)2 + A2(Vin)3 +…
harmonic distortion
A A 2A 3A
2nd
harmonic
3rd
harmonic
5th orderIMD
Nonlinear distortion
Amplifier
In Out
(3A-2B)
(2A-B)
(3B-2A)
2nd
harmonics
3rd
harmonics
2B2Af
A B
3rd orderIMDtypical
channelbandwidth
(2B-A)
3A 3B
A B
2nd orderIMD
A B
(B-A)
Intermodulationdistortion
3rd orderIMD
5th orderIMD
Methods to characterize nonlinear distortion
ACPR
AM - AMAM - PM
NPR
Multitone
Two-tone
PSA performance spectrum analyzerPSA performance spectrum analyzer
PSG CW signal generators
PSG CW signal generators
Two-tone measurements
DUT
LPF
Combiner
Isolator AMP
Attenuator
2nd & 3rd
harmonicsIMD
products
2nd
3rd
f
Q
VGS
IDS
VInput
• 1st, 2rd, 3th, etc. harmonics mix together forming IMD
• Power source cannot supply current
IOutput
• “Clipped” sine waves Fourier transform
• Rate of compression determines harmonic amplitude & IMD Tones
POutput
PInput
Two-tone IMD
Amplifier linearity behavior & common metrics
IP3 or TOI
POutput
PInput
“linea
r”
• Linear amplification
• Saturated power
• Gain compression
• Power at 1 dB of compression
• Two-tone intermodulation (IMD)
• Third order intercept point (TOI)
Psat.
P1dB
P3rd P5th
Amplifier
PowerIn
AB AB
PowerOut
Multitone IMD
Why use multitone test signals? Why use multitone test signals?
•For wideband components two-tone measurement results vary depending on tone spacing
•Simulate real-world operating conditions
•Stress device with higher peak-to-average ratio
•Test with multiple phase sets
Effect of phase relationships…on peak-to-average ratioPSG CCDF PlotsPSG CCDF Plots
Equal phase set peak-to-average
17.88 dB
Random phase set peak-to-average
6.70 dB
63-tone signal63-tone signal
Effect of phase relationships…on IMD performance
Random phase set #13rd order IMD
-60.22 dBRandom phase set #2
3rd order IMD -48.65 dB Equal phase set
3rd order IMD -52.89 dB
Conventional analog test stimulus
DUT
LPF
Combiner+
+
+
Isolator AMP
PSG CW signal generators
PSG CW signal generators
PSA performance spectrum analyzerPSA performance spectrum analyzer
Advantages of analog test approach Advantages of analog test approach
•Well established test procedure
•Common test equipment
Disadvantages of analog test approach Disadvantages of analog test approach
•Complicated test setup
•Signal parameters are not easily modified
•Manual tuning
•Difficult to generate random phase sets
•Equipment and capital intensive
Conventional analog test stimulus
Vector test stimulus
I Q
Internal Baseband Generator
Internal Baseband Generator
E8267C PSG Vector Signal
Generator
E8267C PSG Vector Signal
Generator
DUT
Isolator
Multitone Number of tones: 2 to 64Vary tone spacing: 100 Hz to 80
MHz (2-tone)Tone power: 0 to –40 dBInitial phase: fixed or random
E8267C PSG vector signal generator personalities
Two-tone Vary tone spacing: 100 Hz to 80 MHz
Two-tone Vary tone spacing: 100 Hz to 80 MHz
•Up to 64 tones
•Vary tone power
•Change phase settings
•80 MHz correction BW
•CCDF plot
•COM-based API
LAN/GPIB
PSG PSA
E8267C PSG vector signal generator personalities…and After
• Improved IMD suppression
•Correct with additional devices in the loop
Before…Signal Studio
for Enhanced Multitone
(opt. 408)
IMD products from DUT
Low IMD reduces test uncertainty
Tone correction Minimize test stimulus IMD …
even at the output of an external power amplifier!
Non-linear distortion measurement
E8267C PSG
E4440A PSA
Enhanced Multitone Measurements
DUT
Vector test stimulus
Advantages of vector test approach Advantages of vector test approach
•Simple test setup and procedure
•Easily modify signal parameters
•Apply pre-distortion to improve signal quality
•Repeatable and accurate test results
•Save time and capital equipment cost
Disadvantages of vector test approach Disadvantages of vector test approach
•Available output power
•Carrier feed through
•Images
•Relative tone spacing
Traditional NPR test methods
LO
RFIF
Up converter
Noise Source
Band StopFilter
Noise generatedBy DUT
NPR
Noise Stimulus
Measurement Bandwidth
DUT
PSA performance spectrum analyzerPSA performance spectrum analyzer
PSG CW signal generators
PSG CW signal generators
NPR challenges and alternatives
• CHALLENGES:
• Need signal generator + AWGN
source + band stop filter
TIME & COST
• AWGN is constant only if measured
in a long period
REPEATABILITY
• ALTERNATIVE:
• Use multiple tones with a large tone
density to simulate noise signal
Features
•Vary tone spacing and notch depth
•Distortion correction
Value •Simplified test setup•Repeatable test results
Features
•Vary tone spacing and notch depth
•Distortion correction
Value •Simplified test setup•Repeatable test results
NPR
wideband component
and satellite test
wideband component
and satellite test
ComingSoon
Signal Studio for
NPR
E8267C PSG Vector Signal Generator personalities
LAN/GPIB
PSG PSA
Summary
• Nonlinear behavior must be characterized and addressed to minimize in-band and out-of-band interference
• Distortion Measurements are typically performed using CW signals
• Common test signals include two-tone, multitone, and NPR signals
• Digital multi-tone generation approach provides repeatability and cost advantages over analog generation approaches
• Digital generation approach uses pre-distortion to improve dynamic range, which can minimize cost and setup time
Where to find additional information…
[1] Kent K. Johnson, Agilent Technologies, “Predicting BER II –Measurements for Lowering Radio Cost”, http://www.agilent.com/find/BroadbandSymp/
[2] “Characterizing Digitally Modulated Signals with CCDF curves”, Agilent Technologies Application Note, literature number 5968-6875E
[3] “Spectrum Analysis Basics”, Agilent Technologies Application Note 150, literature number 5952-0292
[4] “Optimizing Dynamic Range for Distortion Measurements”, Agilent PSA series Product Note, literature number 5980-3079EN
[5] www.agilent.com/find/psg
[6] www.agilent.com/find/signalstudio
[7] www.agilent.com/find/psa