RF Power Amplifier Design - ePanorama.net Power Amplifier Design.pdf · RF Power Amplifier Design...

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RF Power Amplifier Design Markus Mayer & Holger Arthaber Department of Electrical Measurements and Circuit Design Vienna University of Technology June 11, 2001 2 Contents / Basic Amplifier Concepts l Class A, B, C, F, hHCA l Linearity Aspects l Amplifier Example / Enhanced Amplifier Concepts l Feedback, Feedforward, ... l Predistortion l LINC, Doherty, EER, ...

Transcript of RF Power Amplifier Design - ePanorama.net Power Amplifier Design.pdf · RF Power Amplifier Design...

Page 1: RF Power Amplifier Design - ePanorama.net Power Amplifier Design.pdf · RF Power Amplifier Design June 11, 2001 Markus Mayer & Holger Arthaber, EMST 1 RF Power Amplifier Design Markus

RF Power Amplifier Design June 11, 2001

Markus Mayer & Holger Arthaber, EMST 1

RF Power Amplifier Design

Markus Mayer & Holger ArthaberDepartment of Electrical Measurements and Circuit Design

Vienna University of Technology

June 11, 2001

2

Contents

¤ Basic Amplifier Concepts

lClass A, B, C, F, hHCA

l Linearity Aspects

lAmplifier Example

¤ Enhanced Amplifier Concepts

l Feedback, Feedforward, ...

lPredistortion

l LINC, Doherty, EER, ...

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Efficiency Definitions

¤ Drain Efficiency:

¤ Power Added Efficiency:

DC

OUTD P

P=η

−⋅=

−=

GPPP

DDC

INOUTPA

11ηη

4

Ideal FET Input and Output Characteristics

DD

KDD

VVV −

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0V =VGS P

V =0GS

Ohmic Saturation Breakdown

gm

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Maximum Output Power Match

m

KDSOPT I

VVR

−= max

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0V =VGS P

V =0GS

Ohmic Saturation Breakdown

gm

6

Class A

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0

VGS VDS

2p

p

Q

IDS

Im

0 2pp Q

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Class A – Circuit

VDD

RLDG

S

48%

dB) 14 (e.g.

50%

PA ⋅=

=

⋅=

κη

κη

A

D

GG

8

Class B

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0

VGS VDS

2p

p

Q

IDS

Im

0 2pp Q

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Class C

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0

VGS VDS

2p

p

Q

IDS

Im

0 2pp Q

10

Class B and C – Circuit

%65

dB) (8 6dB-

%78

PA ⋅=

=

⋅=

κη

κη

A

D

GG

%0

1

%100

PA →

η

η

G

D

VDD

RLDG

S

f0

Class B Class C

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Influence of Conduction Angle

12

Class F (HCA ... harmonic controlled amplifier)

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0

VGS VDS

2p

p

Q

IDS

Im

0 2pp Q

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hHCA (half sinusoidally driven HCA)

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0

VGS VDS

2p

p

Q

IDS

Im

0 2pp Q

14

Class F and hHCA – Circuit

VDD

RLVDS

ID Ze(n)

0, n=eveninf, n=even

Zo(n)

0, n=1inf, n=odd

%87

dB) (9 5dB-

0%10

PA ⋅=

=

⋅=

κη

κη

A

D

GG

Class F hHCA

%96

dB) (15 1dB

0%10

PA ⋅=

+=

⋅=

κη

κη

A

D

GG

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hHCA – Third Harmonic Peaking

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0

VGS VDS

2p

p

Q

IDS

Im

0 2pp Q

16

Third Harmonic Peaking – Circuit

VDD

RLDG

Sf0

3f0

%87

dB) (14.6 0.6dB

91%

PA ⋅=

+=

⋅=

κη

κη

A

D

GG

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Linearity Aspects

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Linearity Aspects

¤ Class A

¤ Class B

¤ Class AB

¤ Class C

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Linearity Aspects

¤ Ideal strongly nonlinear model ¤ Strong-weak nonlinear model

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Amplifier Design – An Example ¤ Balanced Amplifier Configuration

Port 1Z=50 Ohm Port 2

Z=50 Ohm

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Amplifier Design – Simulation ¤Gate & Drain Waveforms

0 500 1000 1300Time (ps)

Drain waveforms

-5

0

5

10

15

20

25

-1000

0

1000

2000

3000

4000

5000Inner Drain Voltage (L, V)

Amp

Inner Drain Current (R, mA)

Amp

0 500 1000 1300Time (ps)

Gate waveforms

-3

-2

-1

0

1

-1000

-500

0

500

1000

Inner Gate Voltage (L, V)

Amp

Inner Gate Current (R, mA)

Amp

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Amplifier Design – Simulation ¤ Dynamic Load Line & Power Sweep

0 3 6 9 12 15Voltage (V)

Dynamic load line

-2000

0

2000

4000

6000

8000IVCurve (mA)

IV_Curve

Dynamic Load Line (mA)

Amp

0 5 10 15 20 24Power (dBm)

Power Sweep 1 Tone

0

10

20

30

40

0

10

20

30

40

50

60

70

80Output Power (L, dBm)

Amp

PAE (R)Amp

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Amplifier Design – Measurements¤ Single Tone & Two Tone

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35

P in [dBm]

P o

ut [

dBm

], G

ain

[dB

]

0

10

20

30

40

50

60

70

80PAE [%]

P outGain

Gamma In

PAE

1dB CP

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35

P in [dBm]

P o

ut [d

Bm

], IM

DD

[dB

c], G

ain

[dB

]

0

10

20

30

40

50

60 PAE [%]

P out

IMDD

Gain

PAE

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Amplifier Nonlinearity¤Gain and Phase depends on Input Signal

¤ 3rd Order Gain-Nonlinearities:

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Amplifier Nonlinearity¤ Higher Output Level (close to Saturation) results

in more Distortion/Nonlinearity

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Nonlinearity leads to?¤Generation of Harmonics

¤ Intermodulation Distortion / Spectral Regrowth

¤ SNR (NPR) Degradation

¤ Constellation Deformation

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Intermodulation and Harmonics

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Spectral Regrowth

¤ Energy in adjacent Channels

¤ ACPR (Adjacent Channel Leakage Power Ratio) increases

-15 -10 -5 0 5 10 15-60

-50

-40

-30

-20

-10

0

10

rela

tive

po

we

r /

dB

relative frequency / MHz

ACPR1>60dB

ACPR2>60dB

ACPR1=16dB

ACPR2=43dB

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Reduced NPR (Noise Power Ratio)

¤ Input Signal

¤ Degradation of Inband SNR

¤ „Noisy“ Constellation

¤ Output Signal of Nonlinear Amplifier

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Constellation Deformation¤ Input Signal ¤ Output Signal of

Nonlinear Amplifier(with Gain- and Phase-Distortion)

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Modeling of Nonlinearities¤ with Memory-Effects

lVolterra Series (=„Taylor Series with Memory“)

¤ without Memory-Effects

lSaleh Model

l Taylor Series

lBlum and Jeruchim Model

lAM/AM- and AM/PM-conversion

2

2

2 1)(

1)(

rr

rgr

rrf

a

a

Θ

Θ

+=

+=

βα

βα

bette

rpe

rfor

man

ce

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AM/AM- and AM/PM-Conversion¤GaAs-PA

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AM/AM- and AM/PM-Conversion¤ LDMOS-PA

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How to preserve Linearity?¤ Backed-Off Operation of PA

lSimplest Way to achieve Linearity

¤ Linearity improving Concepts

lPredistortion

l Feedforward

l ...

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How to preserve Efficiency?¤ Efficiency improving Concepts

lDoherty

lEnvelope Elimination and Restoration

l ...

¤ Linearity improving Concepts

lHigher Linearity at constant Efficiencyà Higher Efficiency at constant Linearity

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Direct (RF) Feedback

¤ Classical Method

¤ Decrease of Gain à Low Efficiency

¤ Feedback needs more Bandwidth than Signal

¤ Stability Problems at high Bandwidths

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Distortion Feedback

¤ Feedback of outband Products only

¤ Higher Gain than RF feedback

¤ Stability Problems due to Reverse Loop

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Feedforward

¤ Overcomes Stability Problem by forward-only Loops

¤ Critical to Gain/Phase-Imbalances0.5dB Gain Error à -31dB Cancellation2.5° Phase Error à -27dB Cancellation

¤ Well suited for narrowband application

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-30 -20 -10 0 10 20 30-60

-50

-40

-30

-20

-10

0

10

rela

tive

po

we

r /

dB

relative frequency / MHz

original signal predistorted signal

Cartesian Feedback

¤ AM/AM- and AM/PM-correction

¤ High Feedback-Bandwidth

¤ Stability Problems

I

Q

I

Q

I

Q

modulator

demodulator

OPAs

main amp.

localoscillator

RF-output

bas

eba

nd in

put

UMTS example:

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Digital Predistortion¤ Digital Implementation of „Cartesian Feedback“

¤ Additional ADCs, DSP Power, Oversampling needed

¤ Loop can be opened à no Stability Problems

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Analog Predistortion

¤ Predistorter has inverse Function of Amplifier

¤ Leads to infinite Bandwidth (!)

¤ Hard to realize (accuracy)

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Analog Predistortion¤ Possible Realizations:

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LINC (Linear Amplification by Nonlinear Components)

¤ AM/AM- and AM/PM-correction

¤ Digital separation required(accuracy!)

¤ High Bandwidth,oversampling necessary

¤ Stability guaranteed

signalseparation

s(t)

s (t)1K

Ks (t)2

K(s (t)+1 s (t))=Ks(t)

2

Ks (t)1

Ks (t)2

-30 -20 -10 0 10 20 30-60

-50

-40

-30

-20

-10

0

10

rela

tive

po

we

r /

dB

relative frequency / MHz

ACPR1>60dB

ACPR2>60dB

ACPR1=18dB

ACPR2=29dB

s(t) s

1(t)

UMTS example:

44

Doherty Amplifier¤ Auxiliary amplifier supports main amplifier during saturation

¤ PAE can be kept high over a 6dB range

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Doherty Amplifier¤ Gain vs. Input Power

¤ No improvement of AM/AM- and AM/PM-distortion

¤ Behavior of auxiliary amplifier very hard (impossible) to realize

¤ Stability guaranteed

¤ Efficiency vs. Input Power

main amp. (A1)

aux. amp. (A2)

PIN

POUT

dohe

rty co

nfigu

ratio

n (A1+

A2)

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EER (Envelope Elimination and Restoration)

¤ Separating phase and magnitude information

¤ Elimination of AM/AM-distortion

¤ Application of high-efficient amplifiers(independent of amplitude distortion)

¤ Stability guaranteed

signalseparation

amplitude information

phase information

RF input

RF output

high efficiencypower amplifier

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EER (Envelope Elimination and Restoration)

¤ Analog realizationl Limiter hard to buildl Accuracy problemsl Feedback necessary

¤ Digital realizationl Oversampling + high D/A-

conversion rates requiredl High power consumption

of DSP and D/A-convertersl Possible feedback

eliminationl Compensation of AM/PM-

distortion possible

D

A

D

A

D

A

amplitude information

phase information

modulatorRF output

high efficiencypower amplifier

digitalsignal

processor

local oscillator

supply voltage amplifier

I

Q I

Qdi

gita

l ba

seb

and

inp

ut

peak detectorsupply voltage

amplifier

limiter

high efficiencypower amplifier

RF output

peak detector

RF input

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EER (Envelope Elimination and Restoration)

¤ Bandwidth of Magnitude- and phase-signal have higher than transmit signal

¤ Five times (!) oversamplingnecessary to achieve standard requirements

-30 -20 -10 0 10 20 30-60

-50

-40

-30

-20

-10

0

10

rela

tiv

e p

ow

er

/ d

B

relative frequency / MHz

MagnitudePhase

-30 -20 -10 0 10 20 30-60

-50

-40

-30

-20

-10

0

10

rela

tive

po

we

r /

dB

relative frequency / MHz

ACPR1>60dB

ACPR2>60dB

ACPR1=33dB

ACPR2=40dB

ACPR1=51dB

ACPR2=36dB

ACPR1=53dB

ACPR2=49dB

full bandwidth 3 ⋅B

0 bandwidth

5 ⋅B0 bandwidth

7 ⋅B0 bandwidth

UMTS example:UMTS example:

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Adaptive Bias¤ Varying/Switching of Bias-Voltage depending on

Input Power Level

¤ Selection of Operating Point with high PAE

¤ Applicably for nearly each type of Amplifier

RF input

peak detector

biascontrol

RF output

high efficiencypower amplifier

50

32 33 34 35 36 37 38 39 4020

30

40

50

60

70

80

90

output power / dBm

po

we

r a

dd

ed

eff

icie

ncy

/ %

VD=3.5VV

D=4.5V

VD

=6.5V

Adaptive Bias¤ Single tone PAE for switched

VDD with VG kept constant¤ Simply to implement Concept

¤ Stability guaranteed

¤ Possible problems:

l DC-DC converter with high efficiency necessary

l Possible Linearity Change (can increase and decrease)especially for HCAs

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Summary¤ Digital Realization required to achieve Accuracy

¤ Problem of Stability for high Bandwidth Application

¤ Higher Bandwidths (Oversampling) necessary,depending on Order of IMD cancellation

¤ Predistortion gives best Results while keeping Efficiency high (valid for high Output Levels > 40dBm)

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Figure References¤ F. Zavosh et al,

“Digital Predistortion Techniques for RF Power Amplifiers with CDMA Applications”,Microwave Journal, Oct. 1999

¤ Peter B. Kenington, “High-Linearity RF Amplifier Design”,Artech House, 2000

¤ Steve C. Cripps,“RF Power Amplifiers for Wireless Communications”,Artech House, 1999

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Contact Information

DI Markus Mayer

( +43-1-58801-35425

- [email protected]

DI Holger Arthaber

( +43-1-58801-35420

- [email protected]