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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, ...
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 2
3
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 −
=κ
0VGS
IDS
Im
2VP VP VDSmaxVDDVKVDS
0V =VGS P
V =0GS
Ohmic Saturation Breakdown
gm
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 3
5
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 4
7
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 5
9
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 6
11
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 7
13
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 8
15
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 9
17
Linearity Aspects
18
Linearity Aspects
¤ Class A
¤ Class B
¤ Class AB
¤ Class C
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 10
19
Linearity Aspects
¤ Ideal strongly nonlinear model ¤ Strong-weak nonlinear model
20
Amplifier Design – An Example ¤ Balanced Amplifier Configuration
Port 1Z=50 Ohm Port 2
Z=50 Ohm
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 11
21
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
22
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 12
23
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
24
Amplifier Nonlinearity¤Gain and Phase depends on Input Signal
¤ 3rd Order Gain-Nonlinearities:
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 13
25
Amplifier Nonlinearity¤ Higher Output Level (close to Saturation) results
in more Distortion/Nonlinearity
26
Nonlinearity leads to?¤Generation of Harmonics
¤ Intermodulation Distortion / Spectral Regrowth
¤ SNR (NPR) Degradation
¤ Constellation Deformation
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 14
27
Intermodulation and Harmonics
28
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 15
29
Reduced NPR (Noise Power Ratio)
¤ Input Signal
¤ Degradation of Inband SNR
¤ „Noisy“ Constellation
¤ Output Signal of Nonlinear Amplifier
30
Constellation Deformation¤ Input Signal ¤ Output Signal of
Nonlinear Amplifier(with Gain- and Phase-Distortion)
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 16
31
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
32
AM/AM- and AM/PM-Conversion¤GaAs-PA
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 17
33
AM/AM- and AM/PM-Conversion¤ LDMOS-PA
34
How to preserve Linearity?¤ Backed-Off Operation of PA
lSimplest Way to achieve Linearity
¤ Linearity improving Concepts
lPredistortion
l Feedforward
l ...
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 18
35
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
36
Direct (RF) Feedback
¤ Classical Method
¤ Decrease of Gain à Low Efficiency
¤ Feedback needs more Bandwidth than Signal
¤ Stability Problems at high Bandwidths
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 19
37
Distortion Feedback
¤ 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 à -31dB Cancellation2.5° Phase Error à -27dB Cancellation
¤ Well suited for narrowband application
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 20
39
-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:
40
Digital Predistortion¤ Digital Implementation of „Cartesian Feedback“
¤ Additional ADCs, DSP Power, Oversampling needed
¤ Loop can be opened à no Stability Problems
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 21
41
Analog Predistortion
¤ Predistorter has inverse Function of Amplifier
¤ Leads to infinite Bandwidth (!)
¤ Hard to realize (accuracy)
42
Analog Predistortion¤ Possible Realizations:
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 22
43
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 23
45
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)
46
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 24
47
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
48
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:
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 25
49
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 26
51
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)
52
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
RF Power Amplifier Design June 11, 2001
Markus Mayer & Holger Arthaber, EMST 27
53
Contact Information
DI Markus Mayer
( +43-1-58801-35425
DI Holger Arthaber
( +43-1-58801-35420