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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
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Presentation Outline
Introduction Linearization Techniques Mirror Predistortion Technique
– What is it?– Implementation– Results
Conclusion
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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
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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
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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
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Linearization Techniques (Cont…)
Predistortion (Diode PD)
RFC
Vd
Cp
Rd
DC Block DC Blocki/p o/p
RFC
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Linearization Techniques (Cont…)
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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Linearization Techniques (Cont…)
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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Linearization Techniques (Cont…)
Predistortion (Cubic PD)
Vector Modulator
DelayAtten
Cubic Predistorter
i/p o/p
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Linearization Techniques (Cont…)
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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Linearization Techniques (Cont…)
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
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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
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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
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Mirror PD Linearization (Cont…)
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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Mirror PD Linearization (Cont…)
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
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Mirror PD Linearization (Cont…)
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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Mirror PD Linearization (Cont…)
Hybrid Module (Picture)
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Mirror PD Linearization (Cont…)
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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Mirror PD Linearization (Cont…)
Hybrid Module (Test Setup Picture)
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Mirror PD Linearization (Cont…)
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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Mirror PD Linearization (Cont…)
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)
Without linearization
With linearization
5 dB
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Mirror PD Linearization (Cont…)
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 (%
)
Without linearization
With linearization
4.5 times
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Mirror PD Linearization (Cont…)
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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Mirror PD Linearization (Cont…)
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