A 900MHz Doherty Amplifier Implemented with Lumped Elements Y. Zhao, M. Iwamoto, D. Kimball, L....
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Transcript of A 900MHz Doherty Amplifier Implemented with Lumped Elements Y. Zhao, M. Iwamoto, D. Kimball, L....
A 900MHz Doherty Amplifier Implemented with Lumped Elements
Y. Zhao, M. Iwamoto, D. Kimball, L. Larson, P. Asbeck
University of California, San Diego
04/18/23
To increase overall efficiency of RF PA Use Doherty structure
To shrink circuit size for integration Use lumped elements to replace transmission lines
To achieve good linearity Use DSP to control Doherty Amplifier
Introduction
04/18/23
Agenda
Doherty amplifier architecture
Doherty with lumped elements Design issues
Simulations
Measurements
DSP application in Doherty amplifier DSP control mechanism
Measurement Results
Conclusions
04/18/23
Low power range only Main-PA operates
High power range Main-PA goes into
saturation Aux-PA turns on
Iout
Vout
High power operation
Low power operation
Load-line of main amplifier
Doherty Architecture
04/18/23
Size of 90° transmission line
900M --- 48mm
2.4G --- 19mm
5.2G --- 8.7mm
Size of a general PA package 4mm x 4mm
Lumped Doherty --- Design issues
Design requirements
Impedance inversion
Phase compensation lin ZKZ /2
inZ lZ
CLK /1
Er = 3.48
04/18/23
Lumped Doherty --- Design issues
C-L-C (9.1pF, 2.7nH) Impedance inverter 90 degrees delay Provide VDD to Aux-PA Harmonic trap
L-C-L (1.8nH, 15pF, 3.3nH) 90-degree phase shifter part of the matching DC block
L-match (13pF, 2.2nH) Output impedance match DC block
04/18/23
Lumped Doherty --- Measurement
Drain efficiency, PAE and Gain
1dB Bandwidth ~ 110MHz
Frequency
S211dB/div
A GaAs MESFET-based hybrid Doherty amplifier was built with lumped elements
Bandwidth
CDMA needs 25MHz/836MHz
802.11b,g need 83MHz/2.44GHz
50MHz/Div
04/18/23
PAE vs. Pout
Lumped Doherty vs. a simulated Class AB
IS-95 CDMA PDF
Lumped Doherty – 14.1% > 3X Class AB – 4.4%
Lumped Doherty --- Measurement
Pdiss
PinPoutPAE average
04/18/23
Similar PAE performance
Comparison --- Lumped and distributed
ADS simulation
Same devices and design
Check 1dB bandwidth/900MHz
the lumped Doherty 130MHz
the distributed Doherty 150MHz
Slightly narrower bandwidthfor lumped Doherty
04/18/23
schematic
Comparison --- Lumped and distributed
Size reduction by using lumped elements is dramatic
Connection lines and components in hybrid circuit can be further shrunk in a IC module
Circuit area
Quarter-wave lines
04/18/23
Potential problem --- Linearity
0
10
20
30
40
50
60
5 10 15 20 25 30
Average Power (dBm)
PA
E (
%)
-60
-50
-40
-30
-20
-10
0
AC
PR
(d
Bc
)
Non-ideal gain and phase in high power region can cause a linearity problem
For CDMA signal, ACPR may not be good enough
04/18/23
DSP Linearization Strategy
System block diagram Gain control Change Vgg2 according to the instantaneous envelope of the input CDMA signal
Phase control Baseband phase predistortion
Open loop control with lookup table
“Doherty Amplifier with DSP Control to Improve Performance in CDMA Operation,”
2003 IEEE MTT-S Digest, p687-690
04/18/23
Measurement --- linearized IS-95 signal
-80
-70
-60
-50
-40
-30
-20
5 10 15 20 25 30
Average Power (dBm)
AC
PR
(d
Bc)
uncorrected
DSP corrected
0
10
20
30
40
50
60
5 10 15 20 25 30
Average Power (dBm)
PA
E (
%)
6
8
10
12
14
16
18
20
Gai
n (
dB
)
High efficiency is maintained
ACPR improvement of up to 9dB is achieved; CDMA ACPR specifications are met
Peak power is limited by the device size 0.5MHz/Div
10dB/Div
-42dBc
DSP corrected
uncorrected
04/18/23
Conclusions Doherty amplifier helps achieve high efficiency over wide
output power range
Doherty amplifier with lumped elements shrinks circuit size while maintaining good performance
Linearity of the Doherty amplifier can be substantially improved by DSP to meet the CDMA ACPR specification
A promising approach for CDMA handset and other wireless applications such as 802.11
Conclusions