High Power Measurements using the Agilent Nonlinear Vector ...

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

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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)

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Applications

• Mobile phones

• Base stations

• Satellite systems

• Radar

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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

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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

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Agenda

•Test Devices (problem)

•Nonlinear Measurements (solution)

•High-Power Modifications

•Example Setup

•Summary and Conclusion

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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

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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)

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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

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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)

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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

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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