Transcript Generation and Conditioning of Multitone Test Signals

Generation and Conditioning
of Multitone Test Signals
December 2002
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
Linear versus nonlinear behavior
A * Sin 360o * f (t - to)
A
Linear behavior:

Time
to
Sin 360o * f * t
A
Time
f
1
DUT
Input

phase shift =
to * 360o * f
input and output frequencies are
the same (no additional
frequencies created)
output frequency only undergoes
magnitude and phase change
Frequency
Output
Nonlinear behavior:
f
1

Frequency
Time

f
1
Frequency
output frequency may undergo
frequency shift (e.g. with mixers)
additional frequencies created
(harmonics, intermodulation)
Nonlinear distortion
A
Vin = Vacos(wat)
2nd
harmonic
A
Amplifier
[A]
Vout = AVin
3rd
harmonic
Linear behavior
Vs.
Non-linear behavior
A
Vin = Vacos(wat)
A
Amplifier
[A]
2A
3A
Vout = AVin + A1(Vin)2 + A2(Vin)3 +…
harmonic distortion
Nonlinear distortion
In
Out
Amplifier
AB
Intermodulation
distortion
AB
typical
channel
bandwidth
3rd order
IMD
5th order
IMD
2nd order
IMD
3rd order
IMD
5th order
IMD
2nd
harmonics
(2A-B)
3rd
harmonics
(2B-A)
(3A-2B)
(3B-2A)
(B-A)
f
AB
2A 2B
3A 3B
Methods to characterize nonlinear distortion
Two-tone
Multitone
NPR
AM - AM
AM - PM
ACPR
Two-tone measurements
PSA performance
spectrum analyzer
Isolator AMP
LPF
Combiner
PSG
CW signal generators
Attenuator
DUT
2nd & 3rd
harmonics
IMD
products
• Power source cannot
Two-tone IMD
IDS
supply current
IOutput
POutput
• “Clipped” sine waves
Fourier transform
Q
PInput
VGS
• 1st, 2rd, 3th, etc.
harmonics mix together
forming IMD
VInput
• Rate of compression
2nd
determines harmonic
amplitude & IMD Tones
3rd
f
Amplifier linearity behavior & common metrics
•
•
Power
In
Linear amplification
AB
Power
Out
Amplifier
AB
IP3 or TOI
Saturated power
POutput
•
Gain compression
•
Power at 1 dB of compression
•
•
Two-tone intermodulation (IMD)
Third order intercept point (TOI)
Psat.
P1dB
P3rd
P5th
PInput
Multitone IMD
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 ratio
PSG CCDF
Plots
63-tone
signal
Equal phase set
peak-to-average
17.88 dB
Random phase set
peak-to-average
6.70 dB
Effect of phase relationships…on IMD performance
Random phase set #1
3rd order IMD
-60.22 dB
Random phase set #2
3rd order IMD
-48.65 dB
Equal phase set
3rd order IMD
-52.89 dB
Conventional analog test stimulus
PSA performance
spectrum analyzer
PSG
CW signal generators
Isolator AMP
+
LPF
Combiner
DUT
+
+
Conventional analog test stimulus
Advantages of analog test approach
• Well established test procedure
• Common test equipment
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
Vector test stimulus
Internal
Baseband
Generator
I
Q
Isolator
DUT
E8267C PSG
Vector Signal
Generator
E8267C PSG vector signal generator personalities
Two-tone
Vary tone spacing: 100 Hz to 80 MHz
Multitone
Number of tones: 2 to 64
Vary tone spacing: 100 Hz to 80 MHz
(2-tone)
Tone power: 0 to –40 dB
Initial phase: fixed or random
E8267C PSG vector signal generator personalities
…and After
Before…
Signal Studio
for
Enhanced Multitone
(opt. 408)
• Up to 64 tones
• Vary tone power
• Change phase
settings
LAN/GPI
B
• Improved IMD
suppression
• 80 MHz correction
BW
• CCDF plot
• COM-based API
PSG
PSA
• Correct with additional
devices in the loop
Enhanced Multitone Measurements

Tone
correction
Minimize test stimulus IMD …
even at the output of an
external power amplifier!
Low IMD
reduces test
uncertainty
E8267C PSG
DUT
IMD
products
from DUT
E4440A PSA

Non-linear distortion
measurement
Vector test stimulus
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
•
•
•
•
Available output power
Carrier feed through
Images
Relative tone spacing
Traditional NPR test methods
PSA performance
spectrum analyzer
Band Stop
Filter
Up converter
Noise Source
IF
RF
DUT
LO
Measurement Bandwidth
Noise Stimulus
PSG
CW signal generators
Noise generated
By DUT
NPR
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
E8267C PSG Vector Signal Generator personalities
wideband
component
and
satellite test
Signal Studio
NPR
for
NPR
Coming
Soon
Features
LAN/GPI
B
•Vary tone spacing and notch depth
•Distortion correction
PSG
PSA
Value
•Simplified test setup
•Repeatable test results
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