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PPOWEROWERAAMPLIFIERSMPLIFIERSHesam A.Hesam A.AslanzadehAslanzadeh

Prof. EdgarProf. Edgar SSncheznchez--SinencioSinencio

AANN IINTRODUCTIONNTRODUCTION ONON

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Outline

Introduction

Power Amplifier Classes

Linear PAs

Switching PAs

Lineariziation techniques

Input

Output

Supply

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IntroductionIntroductionPerformance MetricsPerformance Metrics

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Why Power Amplifiers?

RF Power Amplifiers vast applications

Wireless and wireline communications

Output transmitted power is relatively

large portion of the total power

consumption.

Power efficiency of PAs can greatly

influence overall power efficiency.

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Power Amplifier performance metrics

Metrics definedin standards

Output Power

Spectral Mask

ACPR (Adjacent Channel Power Ratio)

Signal Modulation

Metrics not definedin standards

PAE (Power Added Efficiency)

Drain Efficiency

Power Gain

IIP3

P1-dB

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Output Power

Power delivered to the load within the band

of interest.

Load is usually an antenna with Z0 of 50

Doesnt include power contributed by theharmonics or any unwanted spurs

Sinusoidal

Modulated Signal

L

out

out R

V

P 2

2

=

== T

avgout dttvT

dppP00

/ )(1

)(

Probability profile of Modulation: Prob (Pout=p)

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Output Power

Maximum output power varies drastically

among different standards

Standard Modulation Max. Pout

AMPS FM 31 dBm

GSM GMSK 36 dBm

CDMA O-QPSK 28 dBm

DECT GFSK 27 dBm

PDC /4 DQPSK 30 dBm

Bluetooth FSK 16 dBm

802.11a OFDM 14-19 dBm

802.11b PSK-CCK 16-20 dBm

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Efficiency

Power Added EfficiencyPower Added Efficiency; Most common

efficiency metric

%100

=DC

inout

P

PPPAE

%100=DC

delivereddrain

P

P

Shows how efficiently supply DC power isconverted to RF power

Drain efficiency is often used to indicate the

efficiency of a single power amplifier stage

RFDC

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Linearity measures

Linearity Requirement can be different

based on modulation

Variable Envelope

Information is carried in the amplitude

Constant Envelope

Information is carried in the phase

AM-to-AM, AM-to-PM distortion and P1-dB

Spectral Mask

ACPR (Adjacent Channel Power Ratio)

IP3

OQPSKDQPSKand4

GMSKGFSKand

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Linearity measures

Power mask is an indication of how much

spectrum regrowth is allowed

-5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5

0

-10

-20

-30

-40

-50

ZigBee

Bluetooth

OutputPower[

dBc]

Frequency offset

[MHz]

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IntroductionIntroductionPower Amplifier Class TypesPower Amplifier Class Types

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PA Class types; Linear PAs

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Efficiency and conduction angle

QMAX

Q

pk

Q

II

I

I

I

==)2/cos(

DC part of current

nth harmonic of current

Conduction angle

To calculate power efficiency, power of main

harmony and DC current should be calculated

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Output voltage shape

If load tank filters out all harmonics,

output voltage is pure sinusoidal even

when there is current discontinuity

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Efficiency

dcdc

rmsrms

dc VI

VI

PP

.

.,1,11

==

=

=

==

.max%50

.2

22

2

2,

21

DDMAX

DDMAX

MAXdc

MAX

VI

VI

IIII

Class A:

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Efficiency

=

=

==

.max%78

.

22

2

,2

1

DDMAX

DDMAX

MAXdc

MAX

VI

VI

II

II

Class B:

Class C efficiency depends on and

ideally can reach 100% but at that

point output power also reaches zero!

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Class E

Loading network is carefully designed

so that before switch turns

on (Soft switching) :

ZVS

Non-overlapping voltage and

current minimize switch power

consumption

So low-voltage operation is neededfor reliability

0=sV

0=

t

Vs

DDD VV 6.3)max( =

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Class F

By adding odd harmonics :

Drain voltage starts to

increasingly resemble square

wave

Decreasing the voltage across

transistor during conduction

time and hence increasing

efficiency

All-harmonics-tuned=>class D

Not ZVS operation

DDD VV 2)max( =

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Linearization TechniquesLinearization TechniquesHow toHow to linearizelinearize highly efficienthighly efficient PAsPAs??

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Linearization Techniques

Non-linear power amplifier can reach great efficiencies

But they lack linearity

Linearization techniques can be applied to non-linear PAs to get

a goodlinearity and a modestefficiency

Control is applied at

InputInput

Back-off

Pre-distortion

Cartesian feedback

Polar feedback

OutputOutput

Feed-forward

LINC (Linearization using Nonlinear Components)

SupplySupply

EER (Envelope Elimination and Restoration)

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Input: Back-off

Outp

utPower(dB

m)

5

10

15

20

25

30

35

-20 -15 -10 -5 0 5 10

Back - off

1-dB compression point

Target Output Power

Simplest and most common linearization

PAE is greatly reduced

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Input: Pre-distortion

Predistortion Modulator PA

Gain

Phase

Tracking gain and change variations of amplifier is

very challenging using analog techniques

Digital Look-up tables often used PA gain and phase response varies with bias,

temperature and supply changes

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Input: Cartesian Feedback

LPF

Quadrature

ModulatorPA

PhaseAdjustment

Quadrature

Demodulator

LPF

LO

I

Q

Feedback is used to increase linearity

Large loop gain is needed to improve linearity;

very difficult to achieve at RF frequencies Down-converting alleviates this problem

Stability is a big challenge

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Input: Polar feedback

PD Filter PA

EnvelopeDetector

Filter

VCO

VGA

r

Two loop controls gain and phase

Gain loop

PLL

Doesnt require up/down conversion

If AM/PM distortion of PA is not severe, phase feedback is not

needed Stability challenging

Polar feedback loops should operate at wider bandwidth

compared to Cartesian feedback

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Output: Feed-forward

PA Delay

Auxil iary

amp

attenuator

Delay

Vo Vout

A

A

1/A

1

2

3

Distortion is calculated and subtracted from output:

Precise matching of A1, A2, A3 needed

Tracking over process, time and temp is tough

Constant analog Delay is challenging

Stability is not a problem

Operates at the bandwidth of carrier frequency rather than base

band hence applicable in multi-carrier systems

vx

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Output: Feed-forward Analysis

ind

oout

din

oxdino

AVAVAVV

A

VV

A

VVVAVV

==

==+=

)(

,

PA Delay

Aux il iary

amp

attenuator

Delay

Vo Vout

A

A

1/A

1

2

3

vx

2

1cos1213

++

+=

AA

AAIP

Gain and phase mismatch

can degrade linearity of

power amplifier [*]:

[*] B. Razavi, RF Microelectronics

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Output: LINC(Linear Amplification using Nonlinear Components)

PA

PA

SignalSeparatorVin

Theoretically any non-constant envelope signal on a

carrier can be split into two constant-envelopesignals

A complex conversion at RF is very challenging task

Signal combination at output is practicallyproblematic

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Output: LINC Analysis

PA

PA

Signal

Separator

Vin

[ ]

[ ]

[ ]

=

+=

++=

+=+=

0

1

02

01

21

)(sin)(

)()(sin2

1)(

)()(sin2

1)(

)()()(cos)(

V

tat

tttVtv

tttVtv

tvtvtttav

c

c

cin

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Supply: EER

(Envelope Elimination and Restoration)

PALimiter

Envelope

Detector

Supply

Modulator

Vin

Vo

Amplitude and phase are amplified separately

Amplitude information is fed at the output by supply

Substantial power could be dissipated in the supply

modulation circuitry providing the whole current of PA

Dc-to-dc can be used but still delivered current is quite large

Delay mismatch between two paths introduces distortion

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For more information:

Power Amplifier notes of MIT OpenCourseWare

Steve C. Cripps,Advanced Techniques in RF

Power Amplifier Design, Artech House Publishers

Mohammed Ismail and Mona Hella, RF Cmos

Power Amplifiers: Theory, Design and

Implementation

Several Thesis on PAs

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Some Research Ideas

Design a non-linear Power Amplifier for output

power of 10 dBm delivered to the load of 50

antenna at the operating frequency of 2.4 GHz.

Optimize the efficiency. Measure linearity (IIP3).

Then use one linearization technique to increase

IIP3 to 30 dBm. Efficiency will be decreased as aresult of overhead circuits. Can we come up with a

different kind of linearization technique to reduce

complexity and power consumption of overhead?

Design a signal separator at 2.4 GHz to be used in

LINC technique.