Engineering - RF Power Amplifier Design - eBook

8/8/2019 Engineering - RF Power Amplifier Design - eBook

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RF Pow er Am pl i f ier Design

Markus Mayer & Ho lger A r thaber

Department 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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3

Ef f ic ienc y Def in i t ions

Drain Efficiency:

Power Added Efficiency:

DC

OUT

DP

P=

=

=

GP

PPD

DC

INOUTPA

11

4

Idea l FET Input and Output Charact er is t i c s

DD

KDD

V

VV =

0VGS

IDS

Im

2VP VP VDSmaxVDDVKVDS

0

V =VGS P

V =0GS

Ohmic Saturation Breakdown

gm


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5

Max imum Outpu t Pow er Matc h

m

KDS

OPT I

VV

R

=max

0VGS

IDS

Im


0

V =VGS P

V =0GS

Ohmic Saturation Breakdown

gm

6

Class A

0VGS

IDS

Im


0

VGS VDS

2p

p

Q

IDS

Im

0 2ppQ


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7

Class A Ci rcu i t

VDD

RLDG

S

48%

dB)14(e.g.

50%

PA =

=

=

A

D

GG

8

Class B

0VGS

IDS

Im


0

VGS VDS

2p

p

Q

IDS

Im

0 2ppQ


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9

Class C

0VGS

IDS

Im


0

VGS VDS

2p

p

Q

IDS

Im

0 2ppQ

10

Class B and C Ci rc u i t

%65

dB)(86dB-

%78

PA =

=

=

A

D

GG

%0

1

%100

PA

G

D

VDD

RL

DG

S

f0

Class B Class C


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11

In f luence of Conduc t ion Angle

12

Class F (HCA . .. harmonic con tro l led am pl i f ier )

0VGS

IDS

Im


0

VGS VDS

2p

p

Q

IDS

Im

0 2ppQ


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13

hHCA (ha lf s inuso ida ll y d r i ven HCA)

0VGS

IDS

Im


0

VGS VDS

2p

p

Q

IDS

Im

0 2ppQ

14

Cl ass F and hHCA Ci rcu i t

VDD

RLVDS

ID Ze(n)

0, n=eveninf, n=even

Zo(n)

0, n=1inf, n=odd

%87

dB)(95dB-

0%10

PA =

=

=

A

D

GG

Class F hHCA

%96

dB)(151dB

0%10

PA =

+=

=

A

D

GG


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15

hHCA Thi rd Harmoni c Peak ing

0VGS

IDS

Im


0

VGS VDS

2p

p

Q

IDS

Im

0 2ppQ

16

Thi rd Harmonic Peak ing Ci rcu i t

VDD

RLD

GS

f03f0

%87

dB)(14.60.6dB

91%

PA =

+=

=

A

D

GG


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17

L inear i t y Aspec t s

18


Class A

Class B

Class AB

Class C


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Ideal strongly nonlinear model Strong-weak nonlinear model

20

Ampl i f ier Des ign An Ex ample

Balanced Amplifier Configuration

Port 1Z=50 Ohm Port 2

Z=50 Ohm


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Ampl i f ier Des ign Simula t ion

Gate & Drain Waveforms

0 500 1000 1300

Time (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 1300

Time (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

22

Ampl i f ier Des ign Simula t ion

Dynamic Load Line & Power Sweep

0 3 6 9 12 15

Voltage (V)

Dynamic load line

-2000

0

2000

4000

6000

8000IVCurve (mA)

IV_Curve

Dynamic Load Line (mA)

Amp

0 5 10 15 20 24

Power (dBm)

Power Sweep 1 Tone

0

10

20

30

40

0

10

20

30

40

50

60

70

80

Output Power (L, dBm)

Amp

PAE (R)

Amp


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23

Ampl i f ier Des ign Measurements

Single Tone & Two Tone

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35Pin[dBm]

Pout[dBm],Gain[dB]

0

10

20

30

40

50

60

70

80PAE[%]

Pout

Gain

GammaIn

PAE

1dBCP

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35Pin [dBm]

Pout[dBm],IMDD[dBc],Gain[dB]

0

10

20

30

40

50

60PAE[%]

Pout

IMDD

Gain

PAE

24

Am pl i f ier Nonl inear it y

Gain and Phase depends on Input Signal

3rd Order Gain-Nonlinearities:


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25

Am pl i f ier Nonl inear it y

Higher Output Level (close to Saturation) resultsin more Distortion/Nonlinearity

26

Nonl inear it y leads t o?

Generation of Harmonics

Intermodulation Distortion / Spectral Regrowth

SNR (NPR) Degradation

Constellation Deformation


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I nt e rmodu la t i on and Harmon ics

28

Spec t ral Regrow t h

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

relativepower/dB

relative frequency / MHz

ACPR1>60dB

ACPR2>60dB

ACPR1=16dB

ACPR2=43dB


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Reduc ed NPR (Noise Pow er Rat io)

Input Signal

Degradation of Inband SNR

Noisy Constellation

Output Signal ofNonlinear Amplifier

30

Conste l la t ion Deformat ion

Input Signal Output Signal ofNonlinear Amplifier(with Gain- and Phase-Distortion)


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Mode l ing o f Nonl ineari t i es

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)(

r

rrg

r

rrf

a

a

+=

+=

better

performance

32

AM/AM- and AM/PM-Conve rsion

GaAs-PA


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AM/AM- and AM/PM-Conve rsion

LDMOS-PA

34

How t o preserve Linear i t y?

Backed-Off Operation of PA

lSimplest Way to achieve Linearity

Linearity improving Concepts

lPredistortionl Feedforward

l ...


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How t o preserve Ef f ic iency?

Efficiency improving Concepts

lDohertylEnvelope Elimination and Restoration

l ...

Linearity improving Concepts

lHigher Linearity at constant Efficiency Higher Efficiency at constant Linearity

36

Direc t (RF) Feedbac k

Classical Method

Decrease of Gain Low Efficiency

Feedback needs more Bandwidth than Signal

Stability Problems at high Bandwidths


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37

Dist or t ion Feedbac k

Feedback of outband Products only

Higher Gain than RF feedback

Stability Problems due to Reverse Loop

38

Feedforward

Overcomes Stability Problem by forward-only Loops

Critical to Gain/Phase-Imbalances0.5dB Gain Error -31dB Cancellation2.5Phase Error -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

relativepower/dB


original signalpredistorted signal

Cart esian Feedbac k

AM/AM- andAM/PM-correction

High Feedback-Bandwidth

Stability Problems

I

Q

I

Q

I

Q

modulator

demodulator

OPAs

main amp.

localoscillator

RF-output

baseb

and

input

UMTS example:

40

Digi ta l Predis tor t ion

Digital Implementation of Cartesian Feedback

Additional ADCs, DSP Power, Oversampling needed

Loop can be opened no Stability Problems


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Analog Predis tor t ion

Predistorter has inverse Function of Amplifier

Leads to infinite Bandwidth (!)

Hard to realize (accuracy)

42

Analog Predis tor t ion

Possible Realizations:


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LINC (Linear Ampl i f ica t ion by Nonl inear Components)

AM/AM- andAM/PM-correction

Digital separation required(accuracy!)

High Bandwidth,oversampling necessary

Stability guaranteed

signal

separations(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

relativepower/dB


ACPR1>60dB

ACPR2>60dB

ACPR1=18dB

ACPR2=29dB

s(t)s

1(t)

UMTS example:

44

Doherty Am pl i f ier

Auxiliary amplifier supports main amplifier during saturation

PAE can be kept high over a 6dB range


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Doherty Am pl i f ier

Gain vs. Input Power

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

Behavior of auxiliary amplifier very hard (impossible) to realize


Efficiency vs. Input Power

main amp. (A1)

aux. amp. (A2)

PIN

POUT

dohe

rtyconfig

uratio

n(A

1+A2)

46

EER (Envelope El im inat i on and Restorat ion)

Separating phase and magnitude information

Elimination of AM/AM-distortion

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


signalseparation

amplitude information

phase information

RF input

RF output

high efficiencypower amplifier


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Analog realization

l Limiter hard to build

l Accuracy problemsl Feedback necessary

Digital realization

l Oversampling + high D/A-conversion rates required

l High power consumptionof DSP and D/A-converters

l Possible feedbackelimination

lCompensation of AM/PM-distortion possible

D

A

D

A

D

A

amplitude information

phase information

modulator

RF output


digitalsignal

processor

local oscillator

supply voltage amplifier

I

Q I

Q

digitalbasebandinput

peak detectorsupply voltage

amplifier

limiter


RF output

peak detector

RF input

48


Bandwidth of Magnitude- andphase-signal have higher thantransmit signal

Five times (!) oversamplingnecessary to achieve standardrequirements

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

-50

-40

-30

-20

-10

0

10

relativepower/dB


MagnitudePhase

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

-50

-40

-30

-20

-10

0

10

relativepower/dB


ACPR1>60dB

ACPR2>60dB

ACPR1=33dB

ACPR2=40dB

ACPR1=51dB

ACPR2=36dB

ACPR1=53dB

ACPR2=49dB

full bandwidth3 B

0

bandwidth

5 B0 bandwidth7 B

0bandwidth

UMTS example:UMTS example:


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Adapt ive Bias

Varying/Switching of Bias-Voltage depending onInput Power Level

Selection of Operating Point with high PAE

Applicably for nearly each type of Amplifier

RF input

peak detector

biascontrol

RF output


50

32 33 34 35 36 37 38 39 4020

30

40

50

60

70

80

90

output power / dBm

poweraddedefficiency/%

VD

=3.5V

VD

=4.5V

VD

=6.5V

Adapt ive Bias

Single tone PAE for switchedVDD with VG kept constant

Simply to implement Concept


Possible problems:

l DC-DC converter with highefficiency 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 keepingEfficiency high (valid for high Output Levels > 40dBm)

52

Figure Referenc es

F. Zavosh et al,Digital Predistortion Techniques for RF PowerAmplifiers 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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Contac t In format ion

DI Markus Mayer

( +43-1-58801-35425

- [email protected]

DI Holger Arthaber

( +43-1-58801-35420

- [email protected]

Engineering - RF Power Amplifier Design - eBook

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