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2004 IEEE Topical Workshop on Power Amplifiers
Load-Pull Based Design of Ultra-Linear
W-CDMA Base-Station Power AmplifiersSrdjan Pajić and Zoya Popović
Department of Electrical and Computer EngineeringUniversity of Colorado, Boulder
William McCalpindBm Engineering, Boulder, CO, USA
Funded by:
dBm Eng.WPAFBDARPA IRFFE
2004 IEEE Topical Workshop on Power Amplifiers
Overview
• Motivation for load-pull based PA design
• Description of method for linearity design (~2GHz, 60W LDMOS, -45dBc ACPR)
• Resulting PA characterization
• Discussion: other PAs designed using load-pull (high-efficiency with dynamic biasing etc.)
2004 IEEE Topical Workshop on Power Amplifiers
Usual Approach to PA Design
PA Specs
Device Selection
Nonlinear modelavailable?
YES NO
Performance/ tradeoffanalysis using nonlinear sim.
Small-signal analysisLoad-line analysis
Load-pull
Target impedancesZL, ZS
Matching / biasing networksynthesis
Layout, fabrication, assembly
Performance measurement
Meet the specs?
YES
NOTuning
END
80-90% of time
10-20% of time
2004 IEEE Topical Workshop on Power Amplifiers
Load-pull Based PA Design, Systemathic ApproachGiven Uncharacterized
Power Transistor(Internally prematched)
Static DC Characterization
Target impedances selectionZL, ZS
Initial matching / biasingnetwork design
Break apart PA fixture design
Performance measurement
Meet the specs?
YES
YES
Fine tuning
END
POUT, ZL and ZS estimation(load-line theory)
Test-fixture prematchingnetwork design
Lo
ad-p
ull
char
acte
riza
tio
n
Automated load-source pullcharacterization using
prematching tuners
Parameter sensitive?(low impedance levels, high-Q transistor
impedances, wide bandwidth
NO
EM Modeling of microstripdiscontinuities
Lumped component modeling or measurement
Matching network redesign
Tuning analysis
YES
NO
Pretuning10% of the design time
2004 IEEE Topical Workshop on Power Amplifiers
Design Example: WCDMA Base-Station PA
Commercial load-pull system (Focus Microwaves)
Experimental (uncharacterized) device:
• LDMOS, 42-finger, internally matched to ~3• VDDMAX= 66V, IDDMAX= 11 A (DC pulsed testing) • Frequency range: 2.11GHz – 2.17GHz• Expected CW output power: 70W• Expected power gain: 12 dB• Recommended drain voltage: 28V
2004 IEEE Topical Workshop on Power Amplifiers
ACPR = - 45 dBc
3GPP Test Model 1, 16 DPCH, 10dB peak/av., 0.01% CCDF
ZS = (8.5 + j0) f = 2.11 GHz ZL = (1.5 – j3.25)
Source-Pull Load-Pull
Design Example: WCDMA Base-Station PA
2004 IEEE Topical Workshop on Power Amplifiers
Design Example: WCDMA Base-Station PAACPR = - 45 dBc
3GPP Test Model 1, 16 DPCH, 10dB peak/av., 0.01% CCDF
ZS = (7 + j0) f = 2.17 GHz ZL = (1.5 – j3.0)
Source-Pull Load-Pull
2004 IEEE Topical Workshop on Power Amplifiers
Final PA
Input Bias
Input Matching
Output Bias
Output MatchingPA matching and biasing network
microstrip substrate: h = 0.787 mm, R = 2.5
Design Example: WCDMA Base-Station PA
2004 IEEE Topical Workshop on Power Amplifiers
Parameter variations:
• microstrip line dimension width: ±100 m
• capacitor tolerance: 5% ZL variation:
Re {ZL}: (1.3 1.6) Im {ZL}: -(2.6 3.3)
Expected performance variation:
Output power @ ACPR < -45 dBc: 0.5 dB
Power gain @ ACPR < -45 dBc: 0.75 dB
Yield analysis of the output matching network
Constant Power Gain (dashed)
Constant Output Power (solid)
Design Example: WCDMA Base-Station PA
2004 IEEE Topical Workshop on Power Amplifiers
Tuning response
C1,2 C3
Output PA circuit half
C1 C2
C3
C4
Comparison for output matching network
Initially measured
ZL
ADS ZL Target ZL
Momentum ZL
Design Example: WCDMA Base-Station PA
2004 IEEE Topical Workshop on Power Amplifiers
Source impedance Load impedance
2.11GHz
2.17GHz
2.11GHz
2.17GHz
Measured ZS 2.11GHz Measured ZL
Target ZS Target ZL
Pre-tuning / verification circuit and tuning results
C1
C2
C3
C4
12.7 mm
Design Example: WCDMA Base-Station PA
2004 IEEE Topical Workshop on Power Amplifiers
f = 2.11 GHz f = 2.17 GHz
Measured power-sweep parameters of the PA designed using this method
Load-pull, ACPR = -45 dBc Final PA , ACPR = -45 dBc
f [GHz] Pout [dBm] Gain [dB] Pout [dBm] Gain [dB]
2.11 38.5 12.3 38.6 11.8
2.17 39 12.2 38.9 11.8
Design Example: WCDMA Base-Station PA
2004 IEEE Topical Workshop on Power Amplifiers
DiscussionSystematic design procedure leads to one-pass PA design:
• DC characterized device output power estimates
• load-line theory approximate range of load impedances
• multiple prematching load-pull characterization accurate and reliable target impedances ZS and ZL
• matching network synthesis using EM modeling of microstrip lines and lumped element modeling (or measurement) initial load/source impedances close to targets
• pretuning of amplifier halves using calibrated break-apart test fixture avoids extensive postproduction tuning.
Example design – 60W WCDMA base station PA (and many others…)
Approach can be applied for wide frequency and power range and practically any kind of linearity/efficiency requirements. For example…
2004 IEEE Topical Workshop on Power Amplifiers
A High-Efficiency High-Frequency Example
First principles assisted by load-pull measurements for first-pass success- 10-GHz class-E hybrid PA
2004 IEEE Topical Workshop on Power Amplifiers
Two-stage class-E PA designed for increased gain, using “bias-pull” and same impedances for the 2 stages
2004 IEEE Topical Workshop on Power Amplifiers
AM-PM characterization:Switched-mode PAs enable amplitude modulation through bias
PA alone with varying Vds
PA with constant Vds
PA with closed-loop dynamic bias control
Maintaining high efficiency while output power varies
Adaptive amplifier
2004 IEEE Topical Workshop on Power Amplifiers
High-efficiency signal-adaptive X-band PA, slow and fast dynamic biasing
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