Zhen Zhang, Yifei Li, and Nathan M. Neihart
Iowa State University
MWSCAS 2015 – Fort Collins, CO
Architecture Comparison for
Concurrent Multi-Band Linear
Power Amplifiers
Outline
Motivation
Theoretical Comparisons
Efficiency
Linearity
Area
Conclusions
208/05/15
Motivation
Multiband radio is a basic requirement for today’s wireless devices
Current 4G standards propose carrier aggregation Intra-band and inter-band
Contiguous and non-contiguous
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GSM 850 MHzGSM 1900 MHz
Then
EDGE 800/900 MHzEDGE 1800/1900 MHz
UMTS 2100 MHzUMTS 1900 MHz
AWS 1700 MHzUMTS 850 MHzUMTS 900 MHz
LTE Band 13LTE Band 17LTE Band 20LTE Band 25
Diversity Band 1Diversity Band 2Diversity Band 3Diversity Band 4
GPS Band 1GPS Band 2
WLAN 2 GHzWLAN 5 GHz
Now
400 MHz
1300 MHz
2200 MHz
3100 MHz
4000 MHz
LTE
UMTS
GSM
CDMA-2000
WiFi
iPhone 5 mother board
Motivation
Current approach consists of packing ever more separate PAs into a device Large area
Complex signal routing
Complex control
Such architectures do not inherently support simultaneous multi-band signals
In light of this, researchers are now beginning to develop simultaneous multi-band PA architectures
08/05/15 4
PA Modules
Each IC contains
several separate
power amplifiers
Motivation
There are two primary approaches for realizing concurrent multi-band PAs
Multiple parallel single-band PAs Larger area
Must have some way of combiningthe output signals
Single multi-band PA Fewer components
Theoretical drop in efficiency
Which approach is “better”?
08/05/15 5
IMN
OMN
M1PIN1 @ f1
IMN
OMN
M2PIN2 @ f2
IMN
OMN
MMPINM @ fM
+P01 + P02 + … + P0M
Parallel Single-Band
IMN
OMN
M1+
P01 + P02 + … + P0M
Multiband
PINM @ fM
PIN1 @ f1
PIN2 @ f2
Concurrent Multi-Band
Efficiency Comparison
Drain efficiency is defined as:
𝜼 =𝑷𝑳
𝑷𝑫𝑪
Multi-band output power is defined to be the total power in ALL DESIRED bands
𝑷𝑳 = 𝑷𝒇𝟏 + 𝑷𝒇𝟐 Assuming a linear device and 2 bands, the drain current is:
𝑰𝑫,𝑷𝑺 = 𝑰𝑫𝑪,𝑴 + 𝒊𝒓𝒇,𝑴𝒄𝒐𝒔 𝟐𝝅𝒇𝑴𝒕 + 𝜽𝑴
𝑰𝑫,𝑴𝑩 = 𝑰𝑫𝑪 + 𝒊𝒓𝒇𝒄𝒐𝒔 𝟐𝝅𝒇𝟏𝒕 + 𝒊𝒓𝒇𝒄𝒐𝒔 𝟐𝝅𝒇𝟐𝒕 + 𝜽
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Single Stage in Parallel Single-Band
Concurrent Multiband
Load Current
Load Current of single stage
𝑃𝐿 – Power delivered to the load
𝑃𝐷𝐶 – Power consumed from the DC supply
Efficiency Comparison
The drain current swing is fixed such that 𝟎 ≤ 𝑰𝑫 ≤ 𝟏
Parallel, single-band architecture Class A: 𝑖𝑟𝑓,𝑀 = 0.5 and 𝐼𝐷𝐶 = 0.5
Class B: 𝑖𝑟𝑓,𝑀 = 1 and 𝐼𝐷𝐶 = 0
Class C: 𝑖𝑟𝑓,𝑀 = 1.25 and 𝐼𝐷𝐶 = -0.25
Single, multi-band architecture Numerical methods are used to set 𝑖𝑟𝑓
and 𝐼𝐷𝐶 for each class of operation
Sweep 𝒇𝟐/𝒇𝟏 from 1 to 10
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0 1 2 3 4 50
0.5
1
Dra
in C
urr
en
t (A
)
0 1 2 3 4 50
0.5
1
Dra
in C
urr
en
t (A
)
Time (sec)
Parallel Single-band
SingleMulti-band
Class-A 50 % 25 %
Class-B 78.5 % 62 %
Class-C 82 % 71 %
2-Band Parallel Architecture
2-Band Concurrent Architecture
Efficiency Comparison
Efficiency can be increased by slightly overdriving the amplifier Non-linear model presented in RF Power Amplifiers for Wireless
Communication by S. Cripps is used for this investigation
Parallel, single-band architecture
Single, multi-band architecture
𝒗𝒓𝒇 and 𝑽𝑫𝑪 are set such that
𝟎 ≤ 𝑽𝑮 𝒕 ≤ 𝟏
08/05/15 8-0.5 0 0.5 1 1.5
0
0.2
0.4
0.6
0.8
1
Normalized Input Voltage (V)
No
rma
lize
d D
rain
Cu
rre
nt
(A)
Weakly
Nonlinear
Strongly
Nonlinear
Strongly
Nonlinear
Class A
Class B/C
𝑽𝑮 𝒕 = 𝑽𝑫𝑪 + 𝒗𝒓𝒇𝒄𝒐𝒔 𝟐𝝅𝒇𝑴𝒕 + 𝜽𝑴
𝑽𝑮 𝒕 = 𝑽𝑫𝑪 + 𝒗𝒓𝒇𝒄𝒐𝒔 𝟐𝝅𝒇𝟏𝒕 + 𝒗𝒓𝒇𝒄𝒐𝒔 𝟐𝝅𝒇𝟐𝒕 + 𝜽
𝑰𝑫 𝒕 = 𝟑𝑽𝑮𝟐 𝒕 − 𝟐𝑽𝑮
𝟑 𝒕
2 4 6 8 1030
40
50
60
Cla
ss A
DE
(%
)
2 4 6 8 1060
70
80
90
Cla
ss B
DE
(%
)
2 4 6 8 1070
75
80
85
90
Frequency Radio f2/f
1
Cla
ss C
DE
(%
)
Parallel, single-band
Single, multi-band
Parallel, single-band
Parallel, single-band
Single, multi-band
Single, multi-band
Efficiency Comparison
Compressed drain efficiency for parallel single-band power amplifier Class-A: 𝜂𝑎𝑣𝑒 = 56%
Class-B: 𝜂𝑎𝑣𝑒 = 80%
Class-C: 𝜂𝑎𝑣𝑒 = 84%
Compressed drain efficiency for single multi-band power amplifier Class-A: 𝜂𝑎𝑣𝑒 = 31%
Class-B: 𝜂𝑎𝑣𝑒 = 67%
Class-C: 𝜂𝑎𝑣𝑒 = 75%
Outputs are ideally filtered to remove all non-linear distortion at the LOAD
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Efficiency Comparison
There is a significant drop in efficiency in the single, multi-band architecture Class-A: Reduction of 25%
Class-B: Reduction of 13%
Class-C: Reduction of 9 %
This is due to the reduced power in each band This is improved by overdriving the
amplifier
Variation in efficiency as a function of frequency ratio can be predicted by the peak-to-average-ratio of the input Lower PAR leads to higher drain
efficiency
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0 1 2 3 4 50
0.5
1
Dra
in C
urr
en
t (A
)
0 1 2 3 4 50
0.5
1
Dra
in C
urr
en
t (A
)
Time (sec)
Freq.DC fL fH
0.25 0.25
0.5
Freq.DC fL fH
0.5 0.50.5
Single, multi-band Parallel, single-band
Linearity Comparison
Linearity is especially critical in concurrent multi-band systems
Parallel, single-band architecture Nonlinear distortion causes harmonic generation only
Linearity of diplexer may be an issue
No limitations on frequency separation
Single, multi-band architecture Nonlinear distortion causes harmonic AND intermodulation components
Restrictions on frequency choices Becomes much more complicated for larger number of bands
Both cases will require good filtering at the output Filtering in the parallel, single-band case will depend on the diplexer
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Area Comparison
Component count can be a good indication of board area
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Component Count
Input L-Match 2M
Output L-Match 2M
RF Chock 2M
RF Bypass 2M
Power Transistor M
Power Combiner 1
Total 9M+1*M is the number of supported bands
IMN
OMN
M1
IMN
OMN
M2
IMN
OMN
MM
+P01 + P02 + … + P0M
VDD
VB
Component Count for Parallel
Single-band Architecture
Area Comparison
To now we have assumed ideal summation of the
output signals
Practical implementations will use diplexer
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Ref.Insertion
LossArea
TDK 202690DT ~0.4 dB 2 × 1.3 mm2
TDK 105950DT ~0.5 dB 1 × 0.5 mm2
Zou et al., MWCL 2012 ~0.5 dB 14 × 8.2 mm2
Dai et al., ICMMT 2012
~0.5 dB 3 × 4 mm2
Chongcheawchamnanet al., MWCL 2006
~3.4 dB 55 × 31 mm2
Hayati et al., TMTT 2013
~3.5 dB 90 × 90 mm2
IMN
OMN
M1
IMN
OMN
M2
IMN
OMN
MM
+
VDD
VB
Practical
summation block
cannot be ignored
3-ba
nds
2-ba
nds
Area Comparison
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Component Count
Input L-Match 2M
Output L-Match 2M
RF Chock 2
RF Bypass 2
Power Transistor 1
Power Combiner N/A
Total 4M+5*M is the number of supported bands
Component Count for Single, Multi-
band Architecture
IMN
OMN
M1
VB
Area Comparison
Area is further compared using an example implementation Assume a lumped-element implementation of both architectures
Assume dual-band support
20% added to account for routing
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ComponentArea/
(Technology)
Parallel Single-Band Single Multi-Band
Num. of
ComponentsArea
Num. of
ComponentsArea
Inductor/Capacitor (Matching Network)
0.125 mm2/(0201)
8 1 mm2 8 1 mm2
RF Choke Inductor 0.5 mm2/(0402) 4 2 mm2 2 1 mm2
RF Bypass Capacitor
31 mm2/(2917) 4 124 mm2 2 62 mm2
Power Transistor36 mm2/
Cree GaN FET2 72 mm2 1 36 mm2
Diplexer40 mm2/Ave. 2-band diplexers
1 40 mm2 0
Total 19 286 mm2 13 120 mm2
Conclusions
Two popular power amplifier architectures for supporting concurrent multi-band signaling have been compared
Efficiency Parallel, single-band architecture
Much higher efficiency for class-A
Gap is reduced for class-B and –C
Additional reduction in efficiency due to diplexer
Single, multi-band architecture Reduced output power, per band, for the same DC bias
Efficiency depends upon frequency ratio as well as initial phase offset
Linearity Parallel, single-band architecture
Essentially the same linearity requirements as traditional single-band amplifiers
Single, multi-band architecture Significant harmonic and inter-modulation distortion
Limits the choice of frequency bands
Becomes more severe as the number of supported bands increases
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Conclusions
Area Parallel, single-band architecture
Requires significantly more components
Diplexer
Single, multi-band architecture
Requires only a single set of RF choke and RF bypass devices
The need for a diplexer will be the limiting factor for the parallel, single-band architecture Large – Ranging from 0.5 to 115 mm2 for dual band and
12 to 8100 mm2 for triple band
Lossy – Triple-band diplexers have insertion losses of several dB
Expensive – Commercial examples cost in the dollar range
Unclear how more than three bands can be supported
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Acknowledgements
18
Zhen Zhang
and
Yifei Li
08/05/15
Thank You
1908/05/15