Christopher Burns - Keysight · 2013-03-12 · GaN-on-SiC RFMD High Power Doherty Design, Modeling...

Welcome

1

© 2013 Agilent Technologies, Inc.

Christopher Burns

RF Power Platform Development Manager /

Power Broadband Business Unit

RF Micro Devices

GaN-on-SiC RFMD High Power Doherty Design, Modeling & Measurement

Christopher T. Burns

RFMD, Chandler, AZ, [email protected]

Introduction

• Motivation

• Information-rich signals with high peak-to-average ratios

are standard in the commercial wireless infrastructure and

expanding in the military world

• Need to operate backed-off from peak power yet at the

same time maximize efficiency

• Doherty Configuration is mature technology

• PA suppliers are getting very nearly equal results

• Need a well-defined approach to arrive at best design

quickly!

Page 3

•GaN-on-SiC 48V FET technology features high impedance and

high power density to enable Doherty amplifiers with excellent

performance and bandwidth

Introduction

Doherty Design - Outline

Concept Introductions

Operational Fundamentals – Load Modulation

Doherty Design Procedure

Doherty Design Example & Results

Practical Doherty Circuit Implementation Hints

1

2

3

4

5

Page 5







1

2

3

4

5

Page 6

The Doherty Amplifier

• Carrier amp, biased class B or class AB, is always on

and handles signal at average power

• Peaking amp, biased class C, only handles signal peaks

• C and P’s operation is dependent on each other

C

P

Carrier Amp

Peaking Amp

Page 7

η

The Doherty Amplifier

Page 8

IV Curves & Class B load lines

10 20 30 40 50 600 70

4

8

12

16

20

0

24

VGS=-3.500VGS=-3.250VGS=-3.000VGS=-2.750VGS=-2.500VGS=-2.250VGS=-2.000VGS=-1.750VGS=-1.500VGS=-1.250VGS=-1.000VGS=-0.750VGS=-0.500VGS=-0.250VGS=0.000VGS=0.250VGS=0.500VGS=0.750VGS=1.000VGS=1.250VGS=1.500

VDS

IDS

RL

2xRL

Output Power

η

RL

2xRL

• Carrier mode:

• Carrier alone operates on 2xRL

load line

• ½ MaxPoutSingleDevice

• Peaking mode:

• Carrier and peaking each operate

on RL load line

• 2 x MaxPoutSingleDevice







1

2

3

4

5

Page 9

Textbook Load Modulation

• Doherty achieves Load

modulation by using the

principle of “load pulling”

using two devices*

0.5RL V

I1 I2

1

21 15.0

I

IRZ L

Page 10

RL

I1 I2

V1 RL V2

Textbook Load Modulation

LRZZ 21

0.5RL V

I1 I2

0.5RL V

I1

02I

LRZ 5.01

Case I

Both amplifiers contributing equally

Case II

Peaking amp off

Page 11

But we need Z1 = 2xRL for high

efficiency at lower power!

freq (1.000MHz to 1.000GHz)

ztos

(Zin

1)

indep(ztos(ZL)) (0.000 to 0.000)

ztos

(ZL)

indep(ztos(Z0)) (0.000 to 0.000)

ztos

(Z0)

indep(ztos(Zin)) (0.000 to 0.000)

ztos

(Zin

)

Quarter-wave Impedance Transformer

Page 12

Zin = Z02/ZL

Z0

Zin

ZL

Zin = 100Ω ZL = 25Ω

Z0 = 50Ω







1

2

3

4

5

Page 13

Doherty PA Concept and Practice

Simple ideal

Doherty PA

Carrier

Peak

λ/4 λ/4

RFOUT

RFIN

Implicit Assumptions: •Single Frequency

•Carrier and Peak amps are ideal current generators with no

reactive parasitics

•Carrier and Peak amps have same S21 magnitude and phase

regardless of biasing or drive level

•System Z = 0.5* optimum device RLoad

Car

Pk

CarrierIn

PeakingIn

CarrierOut

PeakingOut

Doherty PA Concept and Practice

Page 15

Output

Match

Input

Match

50Ω

•Parasitics, packaging and matching circuitry all have phase shift

•Peaking amp requires output offset line

•Carrier offset line– not necessarily 90 degrees

•Input offset lines to achieve in-phase output

•Output match to System Z0

•Impossible to achieve perfectly over frequency & power

Match

to 50Ω

Splitter

Complex in

Practice!

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0

Doherty Topology – Definitions

Page 16

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P

• At the current source plane we want RL→2xRL

• We don’t have access to the current source plane

• We need measured or reliably modeled load contours

Practical Circuit Load Modulation

High Power Low Power

Page 17

RL→2xRL ??

Carrier Device

Select Optimum Impedances from

measured or simulated load contours

• Identify maximum Pout load ZOPT,P

• Drive device well into compression

• Trade off a little, but not too much for

Gain, Efficiency

• Identify “carrier mode” target - ZOPT,C

• Obtain contours at Pout = Max Pout – 3dB

• Superimpose circle of VSWR = 2 centered

on ZOPT,P

• Find point of best Gain, Efficiency

Doherty Design Procedure 1

Page 18

indep(PAE_contours_p) (0.000 to 28.000)

PA

E_c

onto

urs_

p

indep(Pdel_contours_p) (0.000 to 51.000)

Pde

l_co

ntou

rs_p

Readout

ZOPTp

ZOPTp

indep(ZOPTp)=

Pdel_contours_p=0.006 / 2.590E-13

level=53.006379, number=1

impedance = 5.062 + j2.810E-16

8


Pde

l_co

ntou

rs_p


PA

E_c

onto

urs_

p

indep(circle_of_rhos1) (0.000 to 314.000)

circ

le_o

f_rh

os1

212

0.340 / 62.934

ZOPTc

ZOPTc

indep(ZOPTc)=

circle_of_rhos1=0.340 / 62.934

impedance = Z0 * (1.097 + j0.751)

212

POUT

PAE

Z0=5Ω

Pout compressed

Pout backed off

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0

Doherty Design Procedure - 2

Page 19

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P

•Select ZSUM (i.e., Z0/2)

•If ZSUM is 50Ω, then no need for ZMatch line

•But then Z0 becomes 100Ω!

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0


Page 20

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P

•Design Output Match to transform Z0 to ZOPT,P

•Identical for both Carrier and Peaking

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0


Page 21

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P

•Design Input Match

•Simplest if identical for both Carrier and Peaking

•May tweak Peaking side later

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0


Page 22

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P

•Carrier Z0 output delay line

•When terminated in Z0/2 (low power mode), must present

selected ZOPT,C to Carrier device.

•Not necessarily exactly 90 degrees!

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0


Page 23

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P

•Peaking Z0 output delay line

•When Peaking device is off (Low Power operation), ZOFF must

be very high impedance.

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0


Page 24

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P

•Peaking and carrier input delay lines and splitter selection

•Whatever delays are necessary to get carrier and peaking

outputs in-phase at summing node







1

2

3

4

5

Page 25

GaN Device used for Design Example

RF IN

VGQ

Pin 1 (CUT)

RF OUT

VDQ

Pin 2

GND

BASE

Features

Advanced GaN HEMT Technology

Peak Modulated Power > 240W

Single Circuit for 865 – 960MHz

48V Operation Typical Performance

o Pout 47dBm

o Gain 20dB

o Drain Efficiency 39%

o ACP -31.5dBc

o Linearizable to -55dBc with DPD

Optimized for video bandwidth and minimized

memory effects

RF tested for 3GPP performance

RF tested for peak power using IS95

Large signal models available

Page 26

Doherty Design Example - 1

Page 27


PA

E_c

onto

urs_

p


Pde

l_co

ntou

rs_p

Readout

ZOPTp

ZOPTp

indep(ZOPTp)=

Pdel_contours_p=0.006 / 2.590E-13

level=53.006379, number=1

impedance = 5.062 + j2.810E-16

8

ZOPT,P = 5.0 +j0 Ω

Pout = 53 dBm

PAE = 61%

Simulated Contours at Pin = 37 dBm


Pde

l_co

ntou

rs_p


PA

E_c

onto

urs_

p


circ

le_o

f_rh

os1

212

0.340 / 62.934

ZOPTc

ZOPTc

indep(ZOPTc)=


impedance = Z0 * (1.097 + j0.751)

212

Simulated Contours at Pin = 32 dBm

ZOPT,C = 5.5 +j3.8 Ω

Pout = 50 dBm

PAE = 53%

POUT 0.2 dB steps

PAE 2% steps

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0


Page 28

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P

•Select ZSUM = 12.5Ω

•Z0 = 25Ω

Car

Pk

CarrierIn

PeakingIn

??4,0 CarrierOutZ

PeakingOutZ ,0


Page 29

Output

Match

Input

Match

POPTZ ,

COPTZ ,

HIGH POWER

LOW POWER

0Z

??2 0Z

HIGH POWER

LOW POWER

20ZZSUM

4/,50 SUMMatch ZZ

50Ω

0Z

OFFZLOW POWER

Splitter

• Wilkinson

• Gysel

• Hybrid

POPTZ , HIGH POWER

0Z2

0ZH

IGH

P

LO

W P


•Identical for both Carrier and Peaking


Page 30


freq (860.0MHz to 960.0MHz)

S(1

,1)

Readout

m3

S(2

,2)

m3

freq=

S(1,1)=0.007 / 85.104

impedance = 5.006 + j0.073

900.0MHz


Page 31

•Design Input Match

•Simplest if identical for both Carrier and Peaking


Page 32

•Check Class AB and Class C Response of input match

f req (700.0MHz to 1.100GHz)

S(1

,1)

0.75 0.80 0.85 0.90 0.95 1.00 1.050.70 1.10

-15

-10

-5

-20

0

14

15

16

17

18

13

19

freq, GHz

dB

(S(1

,1))

dB

(S(2

,1))

f req (700.0MHz to 1.100GHz)

S(1

,1)

0.75 0.80 0.85 0.90 0.95 1.00 1.050.70 1.10

-20

-15

-10

-5

-25

0

-1.0

-0.5

0.0

-1.5

0.5

freq, GHz

dB

(S(1

,1))

dB

(S(2

,1))

Class AB

VGG= -3.06V

IDQ = 600 mA

Class C

VGG= -5.06V

IDQ = 0 mA


Page 33

•Carrier Z0 output delay line

•When terminated in Z0/2 (low power mode), must present

selected ZOPT,C to Carrier device.

•Not necessarily exactly 90 degrees!

20ZZSUM


Page 34

•ZOPT,C is nearly perfectly nailed with ZERO δCarrierOut.

•This is not a general result

•This means no line is needed. How is this possible?


Pde

l_co

ntou

rs_p


PA

E_c

onto

urs_

p


circ

le_o

f_rh

os1

212

0.340 / 62.934

ZOPTc

ZOPTc

indep(ZOPTc)=


impedance = Z0 * (1.097 + j0.751)

212

ZOPT,C = 5.5 +j*3.8 Ω

Recall our loadpull:


S(1

,1)

Readout

m1

m1freq=S(1,1)=0.336 / 67.991E_len=0.000000impedance = 5.151 + j3.620

900.0MHz

ZL (12.500 to 25.000)

zto

s(Z

L,5

)


S(1

,1)


Page 35

•The PCB match itself provides the required impedance inversion from

ZOPT,P to ZOPT,C! •The combination of PCB match, package, bond wires, and CDS parasitics

constitutes the 90 degree shift that allows RL -> 2xRL at the current source

plane when summing node Z goes 25Ω -> 12.5Ω.

•The only reference planes that really matter are the

devices’ current generators and the summing node

ZOPT,C

ZOPT,P

12.5Ω 25Ω


Page 36

•Peaking Z0 output delay line

•When Peaking device is off (Low Power

operation), ZOFF must be very high

impedance.

•Required δPeakingOut is almost exactly

90 degrees

•Inverted Doherty?


S(2

,2)

Readout

m1

m1freq=S(2,2)=0.922 / 2.472E_len=90.000000impedance = 480.442 + j254.772

900.0MHz

Doherty Design example - 7

Page 37

•Select Peaking and carrier input delay

lines and splitter selection

•According to our design so far, there is

exactly 90 degree difference between

peaking and carrier path lengths on the

output side.

•An off-the-shelf, surface mount, 90

degree 3dB hybrid is a space efficient

option at 900 MHz

•Let’s use one, connect 0 deg to the

peaking and -90 deg to the carrier and

be done with it!


Page 38

38 40 42 44 46 48 50 52 54 5636 58

14

16

18

12

20

VGG_DIFF=0.000VGG_DIFF=0.750VGG_DIFF=1.500VGG_DIFF=2.250

VGG_DIFF=3.000VGG_DIFF=3.750

Fund. Output Power, dBm

Transducer Power Gain, dB

38 40 42 44 46 48 50 52 54 5636 58

20

40

60

0

80

VGG_DIFF=0.000VGG_DIFF=0.750VGG_DIFF=1.500VGG_DIFF=2.250VGG_DIFF=3.000VGG_DIFF=3.750

Fund. Output Power, dBm

PAE, %

• Put it all together!

• HB 1-tone

simulation results • Vdd = 48V

• Freq = 910 MHz

• Delta VGC – VGP swept

from 0V to -3.75V


Page 39

Ideal TLINE,

MLINE, etc.

Verify with Momentum

Simulation

Fabricate Circuit

Measured CW Efficiency, Gain

Freq = 895 MHz

Vdd = 48V

Power limited by

current capability

of lab VDD supply

800-1000 MHz Broadband WCDMA Performance

•No DPD correction

•Peak Output Power

measured at 0.01%

probability on CCDF

•Vdd = 48V

•Carrier Idq = 650 mA

•Peaking-Carrier delta

VGG = -3V

•Avg Pout = 50 dBm







1

2

3

4

5

Page 42

Practical Implementation hints

Page 43

• RF Tuning

• Phase adjustment Give yourself options!

Practical Implementation hints

Page 44

• Move coupling

capacitors to

bypass splitter /

summing node

• Test carrier and

peaking halves

independently

Summary

• The Doherty Amplifier topology can provide efficiency

benefits

• GaN-on-SiC technology has significant benefits

• Ideal theory requires numerous extensions and

adjustments to work in practice

• Understanding basics and following correct procedure

leads to functional solution

Page 45

Do You Have

Any Questions?

Page 46

Further Reading

Cripps, S., RF Power Amplifiers for Wireless

Communications, Artech House, 1999, pp. 225-235

Grebennikov, A., Bulja, S.,“High-Efficiency Doherty Power

Amplifiers: Historical Aspect and modern Trends” Proc

of IEEE, Vol. 100, No. 12, Dec. 2012, pp. 3190-3219

Page 47

Acknowledgements

David Runton

Michael LeFevre

Matt Mellor

Rod Miller

Bob Davidson

Basim Noori

Page 48

Appendix: Measured WCDMA Performance with DPD

3GPP WCDMA signal

with 7.5 dB Peak-to-

Average ratio

Digital Pre-distortion

algorithm:

7th order polynomial

with 3 memory taps

Vdd = 48V

Carrier Idq = 650 mA

Freq = 895 GHz

NO DPD

DPD ON

•DPD ON

•Peak Output Power measured

at 0.01% probability on CCDF

•Vdd = 48V

•Carrier Idq = 650 mA

•Freq = 895 GHz

Appendix: Measured WCDMA Performance with DPD

Appendix: Load modulation in simulation captured dynamically

Create an ideal directional

coupler

Use it to probe dynamic

impedances at various points

in circuit in HB simulations

RFpower (20.000 to 42.500)

zto

s(P

kZ

su

m.Z

L,2

5)

zto

s(C

arZ

su

m.Z

L,2

5)

RFpower (20.000 to 42.500)

zto

s(P

kZ

pkg

.ZL

,Zre

f1)

zto

s(C

arZ

pkg

.ZL

,Zre

f1)

Appendix: Load modulation in simulation captured dynamically

Z0=25Ω

Z0=5Ω

Carrier and

Peaking

impedances vs.

VGS,PK and Pin

You are invited

You can find more webcasts

www.agilent.com/find/eesof-innovations-in-eda

www.agilent.com/find/eesof-webcasts-recorded

David Leiss

Senior Application Engineer

Agilent EEsof EDA

Dingqing Lu

Senior Application Engineer

Agilent EEsof EDA

http://www.agilent.com/find/eesof-innovations-in-eda







http://www.agilent.com/find/eesof-webcasts-recorded





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Christopher Burns - Keysight · 2013-03-12 · GaN-on-SiC RFMD High Power Doherty Design, Modeling...

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