Commdrunton r&w08

7/30/2019 Commdrunton r&w08

1/17

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


2/17

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


3/17

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


4/17

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


5/17

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


6/17

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


7/17


8/17

Design a 200W GaN Doherty Amplif ier

Page 8

Loadpull Data at the Drain Reference PlaneModel of device package/wires

Peak Efficiency

Peak Power


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Design for Load Modulation

Page 9

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)


10/17

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)


11/17

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

-40

-30

-20

-10Low Frequency Probe Results 2.1 GHz 2 X 90 Doherty

Frequency (MHz)

ResponseMagnitude(dB)

VBW > 70MHz


12/17

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

-45

-40

-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!!


14/17

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


15/17

Page 15

Backup Slides

Detailed Performance Graphs


16/17

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





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

Page 17

RF3933 Doherty Perform ance - ACP-l vs. Pout

3GPP TM1 PAR=7.5dB

-50

-45

-40

-35

-30

-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

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