A Mirror Predistortion Linear Power Amplifier

Presented By: Khaled Fayed1

Co-Authors: Amir Zaghloul2,3 , Amin Ezzeddine1, and Ho Huang1

1. AMCOM Communications Inc., Gaithersburg, MD 2. Virginia Polytechnic Institute & State University3. U.S. Army Research Laboratory

A Mirror Predistortion Linear Power Amplifier

Khaled Fayed 2/29

Presentation Outline

Introduction Linearization Techniques Mirror Predistortion Technique

– What is it?– Implementation– Results

Conclusion

Khaled Fayed 3/29

Introduction

PA is the most Power Hungry component in wireless communication systems

WiMax, LTE and other new technologies use high data rates: Need higher linearity BO not recommended where Efficiency will suffer

Solution? Use Linearization Techniques

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Introduction (Cont…)

Power: 1 dB Compression Point (P1dB)

Efficiency:

Linearity:

.100%out

dc

PP

f1 f2

2f1-f2 2f2-f13f1-2f2 3f2-2f1

f2-f1f1+f2

2f1 2f23f1 3f2

3@3 10 log out

out

IM PIMDP

Khaled Fayed 5/29

Introduction (Cont…)

PA Linearity Characterization:AM-AM & AM-PM curves

AM

-AM

(dB

)

AM

-PM

(Deg

)

Pin (dBm)Pin (dBm)xi/p P1dB

1 dB

Khaled Fayed 6/29

Linearization Techniques

Three Major Categories– Feedback– Feedforward– Predistortion

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Linearization Techniques (Cont…)

Predistortion

PAPredistorter

AM

-AM

PinA

M-A

MPin

AM

-AM

Pin

+ à

AM

-PM

Pin

AM

-PM

Pin

AM

-PM

Pin

+ à

i/p Linearized o/p

Khaled Fayed 8/29


Predistortion (Diode PD)

RFC

Vd

Cp

Rd

DC Block DC Blocki/p o/p

RFC

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Predistortion (Diode PD)– Advantages

Simple Easy to be integrated with PA in a Chip

– Disadvantages Very limited linearization No tracking with Power or Temperature Requires Measurement of both PD and PA nonlinear

performance

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Predistortion (Cubic PD)

PAPredistorteri/p Linearized o/p

f f f

+ à

Fundamental tone

IM3 from Predistorter IM3 from PA IM3 free output

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Predistortion (Cubic PD)

Vector Modulator

DelayAtten

Cubic Predistorter

i/p o/p

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Predistortion (Cubic PD)– Advantages

Relatively simple Very good improvement in IMD3 reported (>20dB)

– Disadvantages IMD5 and higher degrades Vulnerable to Process & Temp variations No power tracking

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Predistortion (Modified Cubic PD)– Use one more CPD to cancel IM5 independently

i/p

Delay

o/p

IM3 Vector Modulator

IM5 Vector Modulator

IM3 Cancellation

Signal Cancellation

IM3 GeneratingAMP

IM5 GeneratingAMP

Khaled Fayed 14/29

Mirror PD Linearization

What is Mirror PD?– A new Linearization Technique!– Mitigates deficiencies of both Feedforward & PD by

using a PD that uses a smaller copy or mirror of the main PA

– This mirror feeds out of phase IM’s to PA input to get IM free output

Khaled Fayed 15/29

Mirror PD Linearization (Cont…)

Mirror Predistorter

Main PA

Mirror PAAtt1

Vector Modulator 1

EA

Delay1

Delay2

Pin PoutA

B

C

D

E

F

G

H I

J

K

Vector Modulator 2

Khaled Fayed 16/29


This leads to improvement in both IMD3 and IMD5 with:– Higher Efficiency than Feedforward (Note that EA

output power and gain requirements are reduced by the gain of the main PA)

– Generally has better power and temperature tracking than other PD technique (The mirror tracks the main PA)

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The copy is realized by using multiple cells of the mirror PA to build the main PA

For the shown case Power overhead is 25%

PA

PA

PA

PA

PA

Mirror PA

Main PA

Power Divider Power Combiner

Khaled Fayed 18/29


Implementation (Hybrid Module)

Mirror PA

Delay1

Delay2

Pin

PA

PA

PA

PA

PA

EAPout

PS_A

PS_B

Att_A

Att_BAtt_1 Att_3

Att_2

Cplr_1

Cplr_9

Cplr_10

Cplr_4

Cplr_5

Cplr_6

Cplr_7

Cplr_8

Cplr_2 Cplr_3

AMCOM Part # AM204437

AMCOM Part # AM304031

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Hybrid Module (Picture)

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Hybrid Module (Test Setup)

dBmPCV

I

PA

dBm

RF Generator 1 (f1)

RF Generator 2 (f1+Δf)

Input Power Meter (Pin) Output Power Meter (Pout)Power Supply Spectrum Analyzer

Attenuator

Attenuator

3dB Coupler

3dB Coupler

10dB Coupler

Driver Amplifier

Driver Amplifier

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Hybrid Module (Test Setup Picture)

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Hybrid Module Results (IMD3 vs. Pout)

Module Measurement

-80

-70

-60

-50

-40

-30

-20

26 28 30 32 34 36 38 40Pout (dBm)

IMD

3 (d

Bc)

Without linearization

With linearization

23 dB

5 dB

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Hybrid Module Results (IMD5 vs. Pout)

Module Measurement

-100

-90

-80

-70

-60

-50

-40

-30

26 28 30 32 34 36 38 40

Pout (dBm)

IMD

5 (d

Bc)


With linearization

5 dB

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Hybrid Module Results (Efficiency vs. IMD3)

Module Measurement

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

-80 -70 -60 -50 -40 -30 -20IMD3 (dBc)

Effi

cien

cy (%

)


With linearization

4.5 times

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Hybrid Module Results (Bandwidth)

Module Measurement

-80

-70

-60

-50

-40

-30

-20

26 28 30 32 34 36 38 40Pout (dBm)

IMD

3 (d

Bc)

Without LinearizationWIth Linearization @ 1 MHz spacingWIth Linearization @ 10 MHz spacingWIth Linearization @ 20 MHz spacing

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Hybrid Module Results (Temperature)

Module Measurement

-80

-70

-60

-50

-40

-30

-20

26 28 30 32 34 36 38 40Pout (dBm)

IMD

3 (d

Bc)

Without Linearization

With Linearization @ 38 Deg C

With Linearization @ 48 Deg C

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Conclusion

A new Linearization technique “Mirror PD” was presented

A Hybrid module was built with a P1dB of 41.5 dBm at 3.5 GHz

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Conclusion (Cont…)

Results Summary– IMD3 improved by 23 dB @ 7.5 dB BO– IMD3 improved by 5 dB @ 3.5 dB BO– IMD5 improved by 5 dB @ 8.5 dB BO– Efficiency Improved four times @ IMD3 of -60 dBc– BW > 20 MHz Sufficient for WiMax channel

Khaled Fayed 29/29

Questions?

[email protected]

mailto:[email protected]

A Mirror Predistortion Linear Power Amplifier

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