May 26, 2010
presented by:
Keith Anderson
Senior R&D Engineer/Scientist
Agilent Technologies
© Copyright 2010 Agilent Technologies, Inc.
High Power Measurements
using the
Agilent Nonlinear Vector Network Analyzer
April 2010Page 2
Agenda
•Test Devices (problem)
•Nonlinear Measurements (solution)
•High-Power Modifications
•Example Setup
•Summary and Conclusion
April 2010Page 3
High-Power Devices
•What qualifies as "high-power"?
• 1W to 1kW
• Operating at RF frequencies
•What is being measured?
• Transistors
• Amplifiers
• Subsystems (e.g. TR Modules)
April 2010Page 4
Applications
• Mobile phones
• Base stations
• Satellite systems
• Radar
April 2010Page 5
Nonlinearity
•Most high-power amplifiers are nonlinear
• Operate near compression to maximize power
• Measure near compression to properly characterize
• Nonlinear measurements include
• Gain Compression
• Distortion
• Load pull
April 2010Page 6
Problems
• Complete characterization of amp requires many
measurements
• Modeling nonlinear devices with linear measurements
results in incomplete characterization
• Circuit simulations of nonlinear devices are inaccurate
• Test equipment has power limitations
April 2010Page 7
Agenda
•Test Devices (problem)
•Nonlinear Measurements (solution)
•High-Power Modifications
•Example Setup
•Summary and Conclusion
April 2010Page 8
Measurement Solution
•Measure amplifier with Agilent Nonlinear Vector Network
Analyzer (NVNA)
•Modify NVNA to handle high power levels
•Measure X-parameters* of amplifier
•Use X-parameters for nonlinear circuit simulation
* "X-parameters" is a registered trademark of Agilent Technologies. The X-parameter format and underlying equations are open
and documented. For more information visit http://www.agilent.com/find/eesof-x-parameters-info
April 2010Page 9
NVNA Overview
•Stimulate amplifier input with Main Tone
•Stimulate amplifier input and output with Extraction Tone
•Vary frequency and power of tones
•Measure all waves
•Extract X-parameters
R1 A
R3 C
NVNA
Main Tone
Extraction Tone
Amp
Port 1
Port 3
Combiner ReferenceCoupler
TestCoupler
TestCoupler
ReferenceCoupler
TransferSwitch
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Agenda
•Test Devices (problem)
•Nonlinear Measurements (solution)
•High-Power Modifications
•Example Setup
•Summary and Conclusion
April 2010
Amplifier Considerations
•P1dB, Psat, Gain
•Match requirements
•Power supply sequencing
•Amp settling (heating effects)
Page 11April 2010
AmpP1dB & Psat
V1 V2
Gain
Load
MatchSource
Match
Power
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NVNA Considerations
•RF & DC damage levels
•Output power
•RF path losses
•Receivers (R1, A, R3, C)
• Distortion level
• Noise floor
• Direct receiver access
April 2010
R1 A
R3 C
NVNA
Main Tone
Extraction Tone
Amp
Port 1
Port 3
Combiner ReferenceCoupler
TestCoupler
TestCoupler
ReferenceCoupler
TransferSwitch
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NVNA Block Diagram
April 2010
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Adding Attenuator (1)
Attenuator at test port
•Improves match
•Protects components
•Degrades measurement stability
•Recommend: <10dB attenuation
•Recommend: Attenuator close to coupler
April 2010
R3
Port 3
C
Amp
Extraction
tone
Reference
coupler
Test
coupler
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Adding Attenuator (2)
Attenuator between couplers
•Improves match
•Protects components
•Recommend: Short cables
April 2010
R3 C
AmpPort 3
Extraction
tone
Reference
coupler
Test
coupler
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Adding Attenuator (3)
April 2010
Attenuator at receiver
•Protects receivers
•Improves distortion
•Recommend: Receiver power < -20dBm
•Recommend: Short cables
R3 C
AmpPort 3
Extraction
tone
Reference
coupler
Test
coupler
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Adding Pre-amplifier (1)
April 2010
Driving test amplifier input
•Provides power to drive test amplifier into compression
•Recommend: Pre-amp distortion < -20dBc
R1Pre-amp
A
AmpPort 1
Extraction
tone
Reference
coupler
Test
coupler
Main
tone
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Adding Pre-amplifier (2)
April 2010
Driving test amplifier output
•Pre-amp drives "extraction tone" into test amplifier output
•Recommend: Extraction tones between -20dBc and -40dBc
•Note 1: Test amplifier drives large signal into pre-amp output
•Note 2: Pre-amp distortion is not a problem
R3Pre-amp
C
AmpPort 3
Extraction
tone
Reference
coupler
Test
coupler
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Adding Coupler
April 2010
•Replace internal coupler with high-power coupler
•Requires direct receiver access
•Will typically also add attenuators or pre-amps
•May change frequency response
•Recommend: Short Cables
R3 C
(unused)
Port 3
Amp
Reference Coupler
TestCoupler
Extraction
tone
R3C
(unused)
Port 3
Amp
TestCoupler
Reference Coupler(unused)
Extraction
tone
R3 C
(unused)
Port 3
Amp
TestCoupler
Reference Coupler
Extraction
tone
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Agenda
•Test Devices (problem)
•Nonlinear Measurements (solution)
•High-Power Modifications
•Example Setup
•Summary and Conclusion
April 2010
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Goals
April 2010
•Measure 63W amplifier
• Frequency = 100M-500MHz
• Gain = +14dB
• P1dB = +48dBm
•Modify NVNA
• Provide high power to test
amplifier
• Protect NVNA from damage
• Avoid receiver distortion
• Avoid noise
R1 A
R3 C
NVNA
Main Tone
Extraction Tone
Amp
Port 1
Port 3
Combiner ReferenceCoupler
TestCoupler
TestCoupler
ReferenceCoupler
TransferSwitch
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Block Diagram Modifications
April 2010
Port 1
A Freq = 100M-500MHzP1dB = +48dBmGain = +14dB
Amp
R1
40dB40dB
Port 3
R3 C
10dB4dB
43dB40dB
Extractiontone
Maintone
NVNA
TestCoupler
Reference Coupler(unused)
Reference Coupler
TestCoupler
Reference Coupler(unused)
Reference Coupler
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Input side: Pre-amp
•Pre-amp drives test amplifier input at +34dBm
•Pre-amp Pout = +35dBm
•Pre-amp may operate into open or short-circuit
•Recommend: Ensure distortion < -20dBc
April 2010
Amp
P1dB = +48dBmGain = +14dB
Port 1
AR1
40dB40dB
+35dBm +34dBm +48dBmMaintone
Extractiontone
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Input side: Coupler
•Replace internal reference coupler
• NVNA reference coupler damage level = +30dBm
• External reference coupler Pmax > 41dBm
•Note: NVNA test coupler damage level = +43dBm
April 2010
Amp
P1dB = +48dBmGain = +14dB
Port 1
AR1
40dB40dB
+35dBm +34dBm +48dBmMaintone
Extractiontone
Testcoupler
Referencecoupler
(unused)
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Input side: Attenuators
•Receiver attenuators limit power level to -20dBm
•Minimizes distortion and protects receivers
April 2010
Amp
P1dB = +48dBmGain = +14dB
Port 1
AR1
40dB40dB
+35dBm +34dBm +48dBmMaintone
Extractiontone
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Output side: Pre-amp
•Provides +18dBm (= +48dBm - 30dBc) extraction tone
•Pre-amp Pout = +33dBm
•Reverse power may equal forward power
•Pre-amp may operate into open or short circuit
April 2010
+48dBm+18dBm
Port 3
R3 C
10dB
43dB40dB
+33dBm+33dBm
Amp
Extractiontone
4dB
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Output side: Coupler
•Replace internal reference coupler
• NVNA reference coupler damage level = +30dBm
• External reference coupler Pmax > 39dBm
•Note: NVNA test coupler damage level = +43dBm
April 2010
+48dBm+18dBm
Port 3
R3 C
10dB
43dB40dB
+33dBm+33dBm
Amp
Extractiontone
4dB
Testcoupler
Referencecoupler
(unused)
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Output side: Attenuators
• 10dB attenuator limits test coupler power to +40dBm
• Attenuators and couplers limit power incident on the pre-amp
to +33dBm
• Receiver attenuators limit receiver power to -20dBm to
minimize distortion and protect receivers
April 2010
+48dBm+18dBm
Port 3
R3 C
10dB43dB40dB
+33dBm+33dBm
Amp
Extractiontone 4dB Test
coupler
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Agenda
•Test Devices (problem)
•Nonlinear Measurements (solution)
•High-Power Modifications
•Example Setup
•Summary and Conclusion
April 2010
High-power Considerations
•Beware of RF and DC maximum levels
•Add voltages when calculating maximum signal levels
•Consider match requirements of test amplifier and pre-amps
•Consider power-on sequencing of test amplifier and pre-amps
•Use short, semi-rigid RF cables to optimize stability
•For NVNA, set "power limits" and define "user preset" to avoid
accidentally damaging test amplifier or system components
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Conclusion
•High-power amplifiers require nonlinear characterization
•Nonlinear Vector Network Analyzer (NVNA) characterizes
nonlinear devices by measuring X-Parameters
•NVNA is easily modified to test high-power devices
April 2010
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Information Sources
Agilent's high-power NVNA application note
www.agilent.com/find/pnaxapps
Agilent’s Nonlinear Vector Network Analyzer
www.agilent.com/find/nvna
Agilent’s PNA-X network analyzers
www.agilent.com/find/pnax
April 2010
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Are there any Questions?
April 2010