Wideband and Energy
Efficient Power Amplifiers for
Wireless Communications
Mustafa Özen
on behalf of Christian Fager
{chrisitan.fager,mustafa.ozen}@chalmers.se
Microwave Electronics Laboratory | Chalmers University of Technology
www.chalmers.se/ghz
Sweden
Göteborg
Located by the west cost of Sweden
… Founded 1829 by William Chalmers
…11000 students (1150 doctoral students)
…Long tradition in microwaves
Microwave Technologies at Chalmers
GaN HEMT technology
InP HEMT technology
Transmitters for telecom
GaN HEMT MMICs
Robust transceivers, high RF power
InP and InAs HEMT MMICs
Cryogenic low-noise amplifiers
Power amplifiers
High efficiency and linearization
THz devices & instrumentation
Mixers:
Schottky diode, varactors
Hot-electron bolometer SIS
Heterodyne receivers beyond 1 THz
III-V MMIC design
Multifunctional
THz > 300 GHz
Communication > 100 GHz
GaN HEMT VCOs
Mixed signal (>100 Gbps)
Emerging MW components
Graphene HF electronics
Ferroelectric tunable devices
Full Professors: Victor Belitsky, Spartak Gevorgian, Jan Grahn, Jan Stake, Herbert Zirath
Outline
•
•
•
4
Background
Energy efficient wideband transmitter architectures
– Varactor based dynamic load modulation
– Doherty power amplifiers (PA)
– Outphasing PAs
– Mixed Doherty-outphasing techniques
Summary
Transmitter Demands
•
A radio transmitter generates high power information carrying
electromagnetic signals.
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
0
0.1
0.2
0.3
Message
•
•
Most power hungry unit in a radio base station.
Higher transmitter efficiency for
–Lower operational costs
–Smaller environmental footprint
55
0.4
0.5
0.6
0.7
0.8
0.9
1
Transmitter Demands
•
•
Strong demand for higher data rates
Wireless providers allocate more spectrum
– 44 different bands are utilized in LTE-A
0.7 GHz 0.9 GHz 1.8 GHz 2.1 GHz 2.3 GHz 2.65 GHz
•
66
Wideband transmitters enable covering multiple bands with a
single unit
Transmitter Demands
•
Carrier aggregation in LTE-A for higher data rates
f
Intra-band contiguous
Band I
f
Intra-band non-contiguous
Band I
f
Inter-band non-contiguous
Band I
•
7
Band II
In summary: Energy efficient, large RF and signal bandwidth
transmitters
Traditional linear PA operation
•
•
8
The peak output power is determined by PA saturation
– PA efficiency is maximum close to saturation
– Operating it into compression results in severe distortion
The total PA efficiency is weighted by the signal input power
probability density function
– For this case: Peak PAE = 55%, total average PAE = 22%
Efficiency enhancement via Supply
modulation
Transistor current
Imax
High power
load line
Low power
load line
VDD2
VDD1
Transistor voltage
Dynamic reduction of VDD
•
•
Opt. supply
Fixed supply
9
Provides large RF bandwidth 
Difficult to power scale at large
instantaneous signal bandwidths 
• More suitable for handsets
Efficiency enhancement via load
modulation
Power
Amplifier
Transistor current
Imax
High power
load line
Low power
load line
Load
VDD1
Transistor voltage
•
Optimal Load
50 Ω
10
Output
High power realization at large
signal bandwidths 
• Challenging to achieve large
RF bandwidth 
Outline
•
•
•
11
Background
Energy efficient wideband transmitter architectures
– Varactor based dynamic load modulation
– Doherty power amplifiers (PA)
– Outphasing PAs
– Mixed Doherty-outphasing techniques
Summary
Varactor based DLM
•
•
•
12
Variation of output power by dynamically tuning the PA load
network
Chalmers SiC varactors
Varactors typically used as tuneable elements
– Breakdown voltage > 100V
– Low series resistance, large tuning range
Simple and efficient control electronics
– No need for high power dc converters etc.
– Potentially wideband modulation
Varactor-based DLM
High power demonstrator
[C. M. Andersson, et. al, “A Packaged 86 W GaN Transmitter with SiC Varactor-based Dynamic Load Modulation”, EuMC 2013]
Packaged (40x20mm) 100W GaN demo
Power scalable load network topology
GaN HEMT
SiC Varactor
Microchip capacitor
13
Reactive Class J DLM
Results @ 2.14 GHz
Vds = 20 V
Vds = 30 V
Vds = 40 V
•
•
•
14
Peak power = 86W
6.7 dB PAPR WCDMA signal
– ACLR < -46 dBc
– 34% average efficiency
Losses in load network limits efficiency enhancement
Dual-band Varactor-based DLM
Dual band DLM PA prototype
•
•
Dual band operation
– 700 MHz & 1900 MHz
Double stub tuner
Optimal load trajectories
15
Dual band tunable load network
Dual-band Varactor-based DLM
Dual band DLM PA prototype
•
•
Dual band operation
– 700 MHz & 1900 MHz
Double stub tuner
Lower
band
Freq 685 MHz
Upper band
80
w/o DPD
w DPD
70
-10
60
Drain efficiency [%]
-30
40
30
-40
20
-50
-20
50
40-30
30
-40
20
-50
10
16
w/o DPD
w DPD
70
-10
60
-20
50
-60
0-15
28
0
Normalized PSD [dB]
Drain efficiency
Normalized
PSD[%]
[dB]
800
10
-10
30
-5
0
5
32 Frequency
34
36
38
[MHz]
Pout [dBm]
10
40
15
42
-60
0 -15
28
30
-10
32
-5
0
5
34
36
Frequency
[MHz] 38
Pout [dBm]
10
40
15
42
Outline
•
•
Background
Energy efficient wideband transmitter architectures
– Varactor based dynamic load modulation
Main
– Doherty power amplifiers (PA)
Analog
v
– Outphasing PAs
Power
Divider
Aux
– Mixed Doherty-outphasing techniques
in
•
17
Summary
Zo
λ/4
RL
Conventional Doherty PA Concept
Transistor voltages and currents
Conventional Doherty PA
Zo
Im
Main
Class-B
vin
Analog
Power
Divider
Class-C
Aux
1
+
Vm
-
Ia
+
Va
-
0.8
Vm
λ/4
0.6
Im
0.4
RL
Ia
0.2
0
0
0.2
0.4
0.6
Input voltage
0.8
1
Ideal efficiency
Efficiency (%)
100
80
60
40
20
0
18
-15
-10
-5
back-off (dB)
0
Conventional Doherty PA Concept
Transistor voltages and currents
Conventional Doherty PA
Zo
Im
Main
Class-B
vin
Analog
Power
Divider
Class-C
Aux
1
+
Vm
-
Ia
+
Va
-
0.8
Vm
λ/4
0.6
Im
0.4
RL
Ia
0.2
0
0
0.2
0.4
0.6
Input voltage
0.8
1
Ideal efficiency
•
•
19
Higher PAPRLarger class-C
– Lower gain and PAE 
– Uneven power division 
Increased manufacturing cost 
Efficiency (%)
100
80
60
40
20
0
-15
-10
-5
back-off (dB)
0
Hypothesis
•
Large efficiency range (>6 dB) with identical devices?
Modify?
Zo
Main
vin
•
20
Analog
Power
Divider
λ/4
RL
Aux
Devices should be fully utilized
– Both devices are biased with nominal VDD
– Use all available current
Novel Symmetrical Doherty PA
Efficiency of symmetrical Doherty PA
100
Drain eff. (%)
Schematic used for the
derivations
80
60
40
20
-16 -14
•
-12 -10 -8 -6
-4
-2
Normalized output power (dB)
0
Calculate the combiner network parameters assuming identical
devices
Boundary Conditions:
– Efficiency range (arbitrary)
– Class-B and class-C impedances at peak power & back-off
21
Novel Symmetrical Doherty PA
3.5 GHz Hardware Demonstrator
load pull data
• Combiner S-parameters:
– S11 = -0.81 + j0.24
– S21 = -0.022 - j0.38
– S22 = -0.27 + j0.24
Empirical
combiner
topology
22
Load
Cut-ready simulation results
Efficiency,PAE (%)
Peak Main
100
80
60

PAE
40
20
0
30 32
34 36 38 40 42
Output power (dBm)
44
46
Novel Symmetrical Doherty PA
Experimental verification
•
A 3.5 GHz 30 watt GaN HEMT symmetical Doherty PA
prototype
Cross-verified at NXP
Fabricated prototype
Static efficiency results
(Credits Reza Abdoelgafoer)
Efficiency,PAE (%)
100
23
PAE
60
40
20
0
31
•

80
33
35
37
39
41
Output power (dBm)
43
45
A record high PAE of 55% at 8 dB back-off
– Symmetrical devices & novel load-pull based combiner
design approach
Novel Symmetrical Doherty PA
Experimental verification
•
Tested with carrier aggregated 100 MHz (5x20) OFDM signals
Output spectrum with
100 MHz OFDM signals
Pow. spec. density (dB/Hz)
Fabricated prototype
•
24
0
-10
w/o DPD
-20
w/ DPD [1]
-30
-40
-50
-60
3.3 3.35
3.4 3.45 3.5 3.55 3.6 3.65
Frequency (GHz)
3.7
-50 dBc ACLR with 100 MHz signals.
– 5 dB margin to spectral mask.
– High efficiency with excellent linearity
[1] S. Afsardoost, T. Eriksson, and C. Fager, "Digital Predistortion Using a Vector-Switched Model," IEEE TMTT, 2012
A Novel Wideband Doherty
[D. Gustafsson et al., "A Modified Doherty Power Amplifier With Extended Bandwidth and Reconfigurable Efficiency," IEEE T-MTT, Jan. 2013]
ZL
Frequency
Frequency
response
response
at the
at back-off
peak power
 f
Z Z
1 T
Z Z
1 T
Doherty PA topology
Z Z
1 T
Z  jZ tan(
L
T
2
R  jZ tan(
L
T

Z  jZ tan( 2
T
L
2
Z  jR tan(
T
L
2
)
ffo
)
ffo )
ffo
)
fo
Doherty PA
Back-off efficiency is
strongly
frequency dependent!
25
A Novel Wideband Doherty
[D. Gustafsson et al., "A Modified Doherty Power Amplifier With Extended Bandwidth and Reconfigurable Efficiency," IEEE T-MTT, Jan. 2013]
Doherty PA topology
•
•
26
Doherty PA
– Backoff efficiency bandwidth limited by
l/4 impedance inverter
– ZT ≠RL
Proposed PA
– ZT ≡ R L
– New drive scheme and biasing
A Novel Wideband Doherty
Bandwidth performance
Doherty PA
•
•
27
Frequency independent backoff efficiency
Extended average efficiency bandwidth
Proposed PA
A Novel Wideband Doherty
GaN MMIC Demonstrator
2.9 mm
•
•
•
•
TriQuint 0.25µm GaN process
5.7-8.8 GHz (42% bandwidth)
PAE: 30-39% @ 9 dB BO
Reconfigurable PAE shape by
Vdd/Vgg adjustments only
Large PAE bandwidth
28
2.9 mm
Reconfigurable PAE @ 6.4 GHz
Outline
•
•
Background
Energy efficient wideband transmitter architectures
– Varactor based dynamic load modulation
Main
– Doherty power amplifiers (PA)
Analog CMOS
v
– Outphasing PAs
Power
Divider
Aux
– Mixed Doherty-outphasing techniques
Zo
Δt
λ/4
SMPA
in
•
29
Summary
Sout(Δt)
RL
SMPA
Outphasing Transmitter Architecture
•
•
Two constant envelope signals are summed to achieve
amplitude modulation
Possibility for high efficiency switch mode operation
S1
2.5
2
1.5
1
0.5
0
-0.5
S1
1
-1
0.8
-1.5
0.6
0.4
-2
0.2
-2.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
-0.2
-0.4
-0.6
-0.8
-1
Signal
splitter
0
1
2
3
4
5
6
7
8
1
0.8
0.6
Combiner
0.4
0.2
0
-0.2
-0.6
-0.8
0
1
2
3
4
5
6
7
8
Power
Amplifier
30
𝜃
-0.4
-1
•
Sout
Sin
Sin
S2
Combiner determines the interaction between the PAs
Chireix Outphasing Combiner
•
Chireix outphasing combiner enables proper load modulation
and thus high efficiency.
Chireix combiner
Branch 2
input
0.8
2
0.6
1.5
0.4
1
0.2
0
Probability
Branch 1
input
Drain efficiency
Efficiency of Chireix System
0.5
0
0.2
0.4
0.6
0.8
0
1
Output amplitude
•
31
Combiner is inherently narrowband (~5% efficiency bandwidth).
– Mainly due to quarter wave transformers.
Novel Outphasing Combiner Design
Approach
•
Combiner network parameters are derived from the boundary
conditions
– The transistors experience optimal class-E impedances at
peak and average power levels
Class-E PA Waveforms
Branch 1
switch
32
+ P1
V1
-
I2
2 Port P2 +
V2
-
Combiner network,
including load
Z nB
Vie -jθ
Branch 2
switch
3
2
2
1
0
0.5
1
t/T
0
1.5
Current
Vi
I1
Voltage
Z nA
Wideband Outphasing Transmitter
Realization
•
A 25 W 750-1050 MHz CMOS-GaN HEMT transmitter prototype
– Combiner S-parameter continuum is mapped to the
frequency response of practical network
VDD=6 V
Combiner
Combiner S-parameters
+j1.0
+j0.5 Synthesized
Calculated
S11 +j5.0
f
2.0
1.0
S12
0.5
0.0
VDD
0.2
+j0.2
50 Ω
+j2.0
5.0
VDD1 = 28 V
VDD1 = 28 V
-j0.2
-j5.0
S22
-j0.5
-j2.0
-j1.0
CMOS
33
GaN

Theory
Circuit
Wideband Outphasing Transmitter
Experimental Results
Measured Drain efficiency
Fabricated prototype
Branch 1
input
CMOS
•
34
Branch 2
input
GaN
Antenna
Drain efficiency (%)
100
80
60
0.75 GHz
0.80 GHz
0.90 GHz
1.00 GHz
1.05 GHz
40
20
Class-B
0
21 23 25 27 29 31 33 35 37 39 41 43 45
Output power (dBm)
Efficiency improvement is 20 to 40 percentage units
– Efficiency enhancement, large RF bandwidth (33%) and
possibility for high level of integration
Outline
•
•
•
35
Background
Energy efficient wideband transmitter architectures
– Varactor based dynamic load modulation
– Doherty power amplifiers (PA)
CMOS
– Outphasing PAs
– Mixed Doherty-outphasing techniques
Summary
Δt
SMPA
SMPA
Sout(Δt)
Outphasing/Doherty continuum
[C. Andersson et al., "A 1–3-GHz Digitally Controlled Dual-RF Input Power-Amplifier Design Based on a Doherty-Outphasing Continuum Analysis," IEEE T-MTT, 2013]
Average efficiency
General dual-input PA
Doherty
180
70
160
65
140
60
120
Outphasing
55
2
100
Doherty
Doherty
80
50
Outphasing
60
45
40
40
20
0
0
20
40
60
Doherty
80
100
120
140
160
180
1
Doherty (θ1 = 90°, θ2 = 0°)
36
Outphasing (θ1 = 114°, θ2 = 57°)
Outphasing/Doherty continuum
[C. Andersson et al., "A 1–3-GHz Digitally Controlled Dual-RF Input Power-Amplifier Design Based on a Doherty-Outphasing Continuum Analysis," IEEE T-MTT, 2013]
Average efficiency
General dual-input PA
Doherty
180
70
160
65
140
60
120
Outphasing
55
2
100
Doherty
Doherty
80
50
Outphasing
60
45
40
40
20
0
0
20
40
60
Doherty
80
100
120
1
•
•
37
Continuum between Doherty and outphasing operation
Potential for >octave bandwidth and efficient operation
– Class B (short circuited harmonics) assumed
140
160
180
Outphasing/Doherty continuum
Demonstrator results
ADS simulations
38
Measurements
Outphasing/Doherty continuum
Excellent 1-3 GHz performance
•
•
39
CW measurements
– Pmax = 44 ± 0.9 dBm
– >45 % PAE at 6 dB OPBO
from 1.0 – 3.0 GHz
DPD linearized measurements
– 5 MHz WCDMA
– ACPR < -57 dBc
– PAE > 40/50%
Class-B @ 6dB
Summary
•
•
40
Dynamic load modulation architectures
– Varactor-based dynamic load modulation
– Doherty PA
– Outphasing PA
– Mixed Doherty and outphasing techniques
New circuits and design techniques
– Enabling large RF bandwidhts (1-3 GHz)
– Excellent linearity with 100 MHz carrier agg. OFDM signals
– Reduced cost solutions (Symmetrical Doherty)
Acknowledgments
•
…past and present power amplifier research collaborators
C. Fager
(Assoc. Prof.)
S. Gustafsson
(PhD stud)
•
41
T. Eriksson
(Prof.)
Adj. Prof. R. Jos
(NXP)
Dr. P. Landin
(post-doc)
Dr. U. Gustavsson Dr. A. Soltani (Qamcom)
(Ericsson)
& Dr. H. Cao (Ericsson)
Dr. M. Özen
(post-doc)
Dr. P. Saad
(Ericsson)
Dr. C. Sanchez K. Hausmair
(post-doc)
(PhD stud)
Dr. H. Nemati
(Ericsson)
S. Afsardoost
(Ericsson)
J. Chani
(PhD stud)
Dr. C. Andersson
(Mitsubishi)
Companies and research funding agencies
D. Gustafsson
(PhD stud)
X. Bland
(SATIMO)
W. Hallberg
(PhD stud)
F. Johansson
(MSc stud)