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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.