commdrunton r&w08
TRANSCRIPT
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200W GaN Broadband, Quick-turnDoherty Amplifier
David W. Runton
GaN Basestation Products Design Team Manager
Michael LeFevre
RF Systems/Design Engineer
RF Micro DevicesChandler, AZ
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Outline
Page 2
Introduction
The Textbook vs. Practical Doherty Amplifier
Design of a 200W GaN Doherty Amplif ier
2 x RF3933 90W GaN Power Amplifier
Performance
Conclusions
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Introduction
Page 3
What can be said that hasnt been said before?
Doherty is old news!
PA suppliers are getting very nearly equal results
Optimizations/tweaks are simply exploiting tradeoffs
How do we put it all together?
And most importantly, do it quickly
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Doherty Topology Definitions
Page 4
Car
Pk
4,
lengthZZ ODoherty
Carrier
Peaking Carrier
Peaking
4
length
4,
2
lengthZZ Oxfmr
Create a splitter Wilkinson Gysel Hybrid
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Textbook Load Modulation
Page 5
Doherty achieves Loadmodulation by using the
principle of load pulling
using two devices*RL+-
+-V
I1 I2
1
2
11
I
IRZ L
*For more information see: Steve Cripps, RF Power Amplifiers for Wireless Communications and Advanced Techniques in RFPower Amplifier Design
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Textbook Load Modulation
Page 6
LRZZ 221
RL+-
+-V
I1 I2
*For more information see: Steve Cripps, RF Power Amplifiers for Wireless Communications and Advanced Techniques in RFPower Amplifier Design
RL+
-V
I1
02I
LRZ 1
Case I
Both amplifiers contributing equallyCase II
Peaking amp off
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Design a 200W GaN Doherty Amplif ier
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Loadpull Data at the Drain Reference PlaneModel of device package/wires
Peak Efficiency
Peak Power
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Design for Load Modulation
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2.0-2.2GHz Impedance presented at the drain reference planeBlue Peak Power Condition / Pink Peak Efficiency Condition
Not adjust properly not the desired load modulationCarrier
Peak Efficiency
Peak Power
Pout Contours (0.2dB per contour)
Contours (2% per contour)
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Design for Load Modulation
Page 10
Now adjust properly desired load modulationCarrier
2.0-2.2GHz Impedance presented at the drain reference planeBlue Peak Power Condition / Pink Peak Efficiency Condition
Peak Efficiency
Peak Power
Pout Contours (0.2dB per contour)
Contours (2% per contour)
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Tuned Doherty PCB
Page 11
Circuit Features
Tunable
Tunable Low memory bias lines*
Carrier
Peaking
*Runton, LeFevre, Kinney, Wood, Fernez, The Implications of Video Bandwidth Performance on DPD of a High PowerLDMOS Doherty Amplifier, RF Power Amplifier, IEEE Topical Conference on Power Amplifiers, J anuary 2007
0.1 1.0 10.0 100.0 1000.0-70
-60
-50
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-20
-10Low Frequency Probe Results 2.1 GHz 2 X 90 Doherty
Frequency (MHz)
ResponseMagnitude(dB)
VBW > 70MHz
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Modulated Performance vs Frequency
Page 12
Over 140 MHz bandwidth:
0.5 dB Gain Flatness>38% Efficiency
Across UMTS band:0.2 dB Gain Flatness
>40% Efficiency
PAR Variation < 1 dB Output PAR is arepresentation of Peakpower capability
RF3933 Doherty Performance vs Freq3GPP TM1 PAR=7.5dB, Pout = 46dBm (Idq_car = 0.35A @ Vg_car = -3.98V, Vg_pk=-6.5V)
5
6
7
8
9
10
11
12
13
2000 2050 2100 2150 2200 2250 2300
Frequency (MHz)
Gain
/OutputPA
R
(dB)
20
25
30
35
40
45
50
55
60
Drain
Efficiency(%
)
Gain
PAR
Eff
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DPD Linearized Performance - Doherty
Page 13
Over 20 dB linearityimprovement
( 2 Carrier 3GPP )
RF3933 Doherty Perform ance - ACP/Efficiency vs. Pout2 carrier 3GPP TM1 PAR=7.5dB (5th order polynomial - 0 memory term)
-55
-50
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-35
-30
-25
38 40 42 44 46 48
Pout (dBm )
A
djacentChannelPower(dB)
0
5
10
15
20
25
30
35
40
45
50
55
60
DrainEfficiency(%)
DPD - ACP-L DPD - ACP-HNo DPD - ACP-L No DPD - ACP-HEff
-20 -15 -10 -5 0 5 10 15 20-80
-70
-60
-50
-40
-30
-20
Normalized Frequency (MHz)
SpectralPower(dB)
5th order polynomial - No Memory mitigation necessary!!
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Conclusions
Page 14
The Doherty configuration is the current topology of choice
Given enough time, one can optimize and trade gain and bandwidth forefficiency
Sometimes, the quickest solution is the best
Solid/robust ampli fier design techniques combined with the illustratedtechnique results in a quick turn, Doherty amplifier
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Page 15
Backup Slides
Detailed Performance Graphs
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Modulated Efficiency Performance vs. Bias
Page 16
RF3933 Doherty Performance - Efficiency vs. Pout
3GPP TM1 PAR=7.5dB
0
10
20
30
40
50
25 30 35 40 45 50
Pout (dBm)
Efficiency
(%)
Idq_car = 300mA, Vg_pk = -5.0V
Idq_car = 300mA, Vg_pk = -5.5V
Idq_car = 300mA, Vg_pk = -6.0V
Idq_car = 300mA, Vg_pk = -6.5V
Idq_car = 300mA, Vg_pk = -7.0V
Balanced Idq = 300mA
Modulated data losesthe large peak that is
typically shown intextbooks forefficiency this is dueto the statistics of the
signal
Balanced ( Class AB )
Doherty Lite
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Modulated ACP vs Bias
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RF3933 Doherty Perform ance - ACP-l vs. Pout
3GPP TM1 PAR=7.5dB
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-45
-40
-35
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-25
25 30 35 40 45 50Pout (dBm)
AdjacentChannelPo
wer(dB)
Idq_car = 300mA, Vg_pk = -5.5V Idq_car = 300mA, Vg_pk = -6.0V
Idq_car = 300mA, Vg_pk = -6.5V Idq_car = 300mA, Vg_pk = -7.0V
Balanced Idq = 300mA
ACP performanceshows traditionalDoherty levelsreduces the linearity