The Ohio State University, Columbus, OH University of ... · the RF PA for shaping table design,...
Transcript of The Ohio State University, Columbus, OH University of ... · the RF PA for shaping table design,...
X‐parameter applications for characterizing and modeling power amplifiers for envelope
tracking applicationsHaedong Jang*, Andrew Zai†, Tibault Reveyrand‡,
Patrick Roblin*, Zoya Popovic†, and David E. Root§
*The Ohio State University, Columbus, OH†University of Colorado, Boulder, CO
‡XLIM-UMR CNRS, Limoges Cedex, France §Agilent Technologies, Santa Rosa, CA
more details in session TU3F-1 Tues 13:50-14:10 ref [21]
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Outline
• Introduction to ET • Introduction to X-parameters• X-parameter models for dynamic signals:
quasi-static approximation• Simulation-based X-parameter models
for ET applications• Measurement-based GaN PA X-parameter model • Future work• Conclusions
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 3
Envelope tracking
Fixed Bias PA
Wasted power
Modulated Bias
DCDC
inin
DC
in
DC
inout
IVIVG
PPG
PPP 11PAE
PDC
Pin Pout
Pdiss
PA
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 4
Envelope tracking
Shaping table depends on the properties of the RF PA, viewed as a three-terminal component.
X-parameters provides a procedural approach to characterize & model the RF PA for shaping table design, including bias and load effects.
A
EnvelopeTracker
RF PADriver
EnvelopeShaping
Delayalign
EnvelopeDetection
RFup-convert
I
Q
QI
1 23
I2 + Q2
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Envelope tracking
• Design considerations with ET• High PAR input signals• Varying supply voltage• Varying load
• XP model, which is a frequency domain black box behavioral model, is studied
• Design and characterization assumption: • SM is ideal• Interconnection impedance is
minimum• PA is quasi-static to the supply
voltage variation• Load is approximately matched
(but more on this later)PA
SM
1
2
3
Γ
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 6
Envelope tracking
Practical approach is designing the shaping using static characterization at multiple supply voltages under quasi-static assumption of the PA
9dB constant gain
5 10 15 20 25 300
2
4
6
8
10
12
2V
6V
9dB
P1dB
Gai
n (d
B)
Pout (dBm)
Maximizing efficiency using saturation point (P1dB)
Drain voltage is swept from 2 V to 6 V
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X-parameters
H a r m o n ic B a la n c eH B 2
E q u a t io n N a m e [3 ]= " Z lo a d "E q u a t io n N a m e [2 ]= " R F p o w e r "E q u a t io n N a m e [1 ]= " R F f r e q "U s e K r y lo v = n oO r d e r [1 ]= 5F r e q [1 ]= R F f r e q
H A R M O N I C B A L A N C E
Measure X-parameters-or-
Generate X-parameters from circuit-level designs
X-parameter Component :Simulate using X-
parameters
ADS, SystemVue & Genesys:Design using X-parameters
X-parameters are the scientifically correct extension of S-parameters to large-signal conditions.
– Measurement and simulation based, identifiable from a simple set of automated NVNA measurements or directly from ADS circuit-level designs
– Vector nonlinearities (Magnitude and phase of distortion)– Intrinsic DUT properties (calibrates out source impurities & multi-freq. mismatch)– Cascadable (correct behavior in mismatched environment)– Extremely accurate for high-frequency, distributed nonlinear devices– Includes bias dependence
X2PXNP1File=
21
Ref
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X-parameter use model
X
X-Parameters
Reflected Transmitted
Incident
Reflected
Incident
1 2EDA Software
Design
Agilent Nonlinear Vector Network Analyzer
Measure
Model
( )B X A
Same use model as S-parameters
but much more powerful
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 9
Complex Spectra and Nonlinear Maps
,p kB,p kA
Port IndexHarmonic Index
2 kA1kA
1kB 2 kB
, 0 , ,
, , ,0
2Z ( )
2Z
p k p k p k
p k p k p k
V A B
I A B
1V 2I
time time
0,( ) Re jk t
p p kk
i t I e 0
,( ) Re jk tp p k
k
v t V e
NVNA
, , 1,1 1,2 1,3 2,1 2,2 2,3, , , ..., , , , ...p k p kB F A A A A A A
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 10
Time-invariance and spectral linearization
,,
( ) *1
( )11
,1
( ), 1
,1( ,| |) ), ( ,( )
ef gef gh hef
S f hgh
g h
T f hg
F fe
g hf hB X DC A X DP C A DC A P AP A X
X-parameters allow us to simplify the general B(A) relations:Trade efficiency, practicality, for generality & accuracyPowerful, correct, and practical; Native Freq. Domain Model
1 1 2 2( )) (i i iB S DC A S DC A The simplest X-parameters are just linear S-parameters
new mismatch termsload & harmonic mismatchmatched response
DC dependence automatically included. NVNA controls DC supplies and synchronizes measurements with applied RF signal
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X-parameters of GSM PA
“X-parameters provide a nonlinear electronic interactive datasheet”
Mismatch versus phase at GSM_OUT
0 0.2 0.4Real
-1.7
-1.6
-1.5
-1.4
-1.3
-1.2
-1.1
-1
Imag
measured
“Hot S22”
X-params
Skyworks amp
Horn et al., EuMC 2009
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 12
Mini-Circuits LAVI-22VH+ (TB-433) Double-balanced Mixer3-ports
New measurement: IF Phase!
X datasheet__ model
X-parameters of mixers: 3 rf ports
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Simulation of dynamic signals
B2,k
A1,1
1,1( )2, 2, 1,1, j AF
k kB X DC A e
( )2,
FkX
Now assume the signal is modulated in time: 2,1 2,1( )A A t
1,1 ( )( )2, 2, 1,1( ) , ( ) j A tF
k kB t X DC A t e
Quasi-static approximation: evaluate static X-parameter function at each time instant
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 14
Simulating Dynamic signals (2)
t
tA1,1(t)
B2,1(t)B2,1
A1,1
1,1
2,1
( )( )2,1 1,1
( )
, ( ) j A tF
B t
X DC A t e
Envelope Domain:same mechanism generatesspectral regrowth from digitally modulated signals(e.g. estimates of ACPR, EVM)LIMITATIONS (Quasi-Static approximation):Symmetric intermods, independent of modulation rateNo BW dependence; No MemoryValid in the slow modulation rate limit (narrow band)
freq
freq
( )2,1
FX
1,1 ( )( )2, 2, 1,1( ) ( ), ( ) j A tF
k kB t X DC t A t e
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Envelope simulationEnvelope simulation
Simulation-based approach
• Instantaneous• AM/AM• AM/PM• PAE
• Instantaneous• AM/AM• AM/PM• PAE
Fix ETCkt
PATR
Fix ETXP
• Input signal• LTE• 16 QAM• 5 MHz
• Input signal• LTE• 16 QAM• 5 MHz
• XP models are extracted in two cases to show the sources of dynamic response contribution
– entire circuit– bare transistor
• Fixed bias performance is compared to ET operation for the reference circuit model and the two X-parameter models
six cases where there is a dynamic signal
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Case 1(whole PA)
Case 2(bare transistor)
Simulation-based extraction
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 17
DC
Generating the X-parameters (1)
Fixed gate Vdd sweep3-6 V
Fixed load
Input power sweep-10~37 dBm
Entire PA
W2305 X-parameter generator
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Generating the X-parameters (2)
Fixed Vgs = 1.75 VInput power sweep-20~27 dBm
Vdd sweep1.5-6 V
Load sweepMag:0.69 – 0.89Phase:154.6°-160.6°
Transistor
Suggested: Sweep load over a large region in the Smith Chart.Sometimes active LP needed to go beyond it
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LTE UL16 QAM
Envelope Tracking Implementation
MeasEqn
1
Ref3
2
ENVELOPE
VarEqn
DAC
VarEqn
VarEqn
Drain_Bias
Vload
Vs_high
Vinput Vload
X3P
VCVS
VAR
VAR
SDD2P
DataAccessComponent
R
SDD3P
VAR
VtDataset
V_DC
MeasEqn
C
C
Envelope
Term
I_Probe
I_Probe
I_Probe
IQ_DemodTuned
R
XNP1
SRC4
VAR2
VAR3
SDD2P1
DAC1
R2
SDD3P1
DEMOD1
VAR1
SRC3
SRC1
C2
C1
Env1
Term2
Iload
Is_high
I_input
Precompute_data_to_dataset
R1
File="xparam_sample_PA.xnp"
R2=0 OhmR1=50 OhmG=1
Detected_Pin_dBm=10*log(mag(_v1)/100+1e-10)+30
Delta_Vdrain=Vdrain-3.25Vdrain=file{DAC1, "voltage"}
Cport[1]=C[1]=I[2,0]=-(Delta_Vdrain)/50.0I[1,0]=0
iVal1=Detected_Pin_dBmiVar1="Pin_dBm"ExtrapMode=Constant ExtrapolationFile="Vdrain_vs_Pin_dBm_iso_gain_Andy.mdf"
R=50 Ohm
Cport[1]=C[1]=I[3,0]=0I[2,0]=-(_v1**2+_v3**2)/50I[1,0]=0
Rout=50 OhmFnom=RFfreq
RFfreq=850 MHzGain=4.2
Step=32.5520833 nsecStop=50 usecOrder[1]=9Freq[1]=RFfreq
Expression="Waveform"Dataset="LTE_UL_TxSpectrum.ds"
Vdc=3.25
C=1.0 uF
C=1.0 uF
Freq=RFfreq
R=50 Ohm
Z=50Num=2
XnP Componentfor the sample PA
ADS ET examples can be downloaded from [1]: http://edocs.soco.agilent.com/display/eesofkcads/Applying+envelope+tracking+to+Improve+Efficiency
Ideal envelope tracking
ShapingTable from X-parmodel
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 20
Fixed ET
0 10 20 30-5
0
5
AM
-AM
(dB
)
0 10 20 30-40
-20
0
20
40
Pout (dBm)
AM
-PM
( )
0 10 20 30-5
0
5
0 10 20 30-50
0
50
Pout (dBm)
Simulation-based validation
Circuit
XP (Transistor)
XP (PA)
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 21
• Instantaneous PAE was calculated using LTE signals and drawn over the histogram of the signals.
• Both XP and circuit model predict PAE improvement over fixed bias as expected.• It is interesting to notice that, under ET, the instantaneous PAE predicted by the
circuit model shows wider spreading than fixed bias.
Simulation-based validation
PAEavg (%)
XP(ET) 43.3
Ckt(ET) 42.4
Ckt(Fix) 31.7
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 22
Measurement-based X-parameters
• GaN HEMT 8 W Class-F-1 (Triquint TGF2023-02)• Drain voltage sweep : 12 ~ 30 V • Load-pull performed with VTD SWAP-X402 (now Agilent)
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 23
X-par extraction for 8 W GaN PA
PNA-XN5242A
DUT
F = 2.14 GHzGain = 15~21 dBPpeak = 38 dBmA
C
-10 dBm -20 dBm
-20 dBm-10 dBm
+38 dBm
+22 dBm (ET)
4142
0 ~ +25 dBm (DT)9 dBm (ET)
Couplers CF = -16dB
83020AGain >= 30dB Pmax = +30 dBm (1 W)P@1dB = 28 dBmF = 2 – 26.5 GHz
30 dB
20 dB(1W)
0 dB
13 dB(1W)
30 dB
Source 1-20 ~ 5 dBm (DT)
J11
Source 2-11 dBm (ET)-2 dBm (ET)
0 dB
20 dB(1W)
6 dB (5W)DC-18 GHz28 dBm (ET)
25 dBm (DT)
J8
Source Out
6 dB (0.5W)DC-26.5 GHz
10 dB (1W)
R1
R3
VGS = -3.8 VVDS = 12~30V
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 24
Validation of measurement-based X-parameter model
Tuner Load Set 1
X-parameters at 50 ohmLoad-pull with tunerNVNA 50 ohm
Vdd increasing
Load-sensitivity of X-par model
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 25
Validation of measurement-based X-parameter model
Tuner Load Set 2
X-parameters at 50 ohmLoad-pull with tunerNVNA 50 ohm
Vdd increasing
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 26
Validation of measurement-based X-parameter model
Tuner Load Set 3
X-parameters at 50 ohmLoad-pull with tunerNVNA 50 ohm
Vdd increasing
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 27
Validation of measurement-based X-parameter model
Tuner Load Set 4
X-parameters at 50 ohmLoad-pull with tunerNVNA 50 ohm
Vdd increasing
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 28
Validation of measurement-based X-parameter model
Tuner Load Set 5
X-parameters at 50 ohmLoad-pull with tunerNVNA 50 ohm
Vdd increasing
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 29
Load-dependence of shaping table
Loads variation Shaping table
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 30
ET measurement setup
• The WCDMA test signal was fed to the RF signal generator through arbitrary signal generator
• The shaped signal based on the XP model was fed the supply modulator through another synchronized arbitrary signal generator
• The supply modulator from [4], which has 70 MHz bandwidth and 32 Vmax, was used for the test
• WCDMA test model 1• 3.84 MHz• 10.3 dB PAR• 30.72 MHz sample rate• 1 ms repetition• 28.8 dBm Pout.avg
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 31
Results for GaN PA
ET Fixed (26 V) Fixed (28 V) Fixed (30 V)
10 15 20 255
15
25
Gai
n (d
B)
10 15 20 25-30
0
30
Pin (dBm)
AM
-PM
( )
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 32
Discussion
• Static XP model based shaping table design shows significant PAE improvement under ET operation
• ET operation showed more gain compression and wider AM-PM spreading than under constant bias operation– lack of linearity improvement might be attributed to increased
memory effects under dynamic biasing different from the ideal assumption in the simulation
– Quasi-static assumption is likely valid when the supply modulator is ideal
– Supply modulator output impedance and inter-connection impedance between the modulator and the PA may not be ideal
– Slew-rate and bandwidth of the tracking amplifier are high and are not likely the problem
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 33
Suggestions for future work
• Treat RFPA as three-terminal “incommensurate mixer” X-parameter model
1,[1,0 ] 3,[0 ,1]
1,[1,0 ] 3,[ 0 ,1]
( )2,[ , ] 2,[ , ] 1,[1,0] 3,[0,1]
( ) ' '2,[ , ]; ,[ ', '] 1,[1,0] 3,[0,1] ,[ ', ']
', ',
( )2,[ , ]; ,[ ', '] 1,[1,0] 3,[0,
( ) , ( ) ( ) ( )
( ) , ( ) ( ) ( )
( ) ,
F n mn m n m
S n n m mn m p n m p n m
n m p
Tn m p n m
B X A t A t P t P t
X A t A t A P t P t
X A t A
,[ ', '] 1,[1,0 ] 3,[ 0 ,1]
* ' '1]
', ',( ) ( ) ( )
p n m
n n m m
n m pt A P t P t
See talk WE3D-4 14:50-15:10 ref. [22]
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 34
Suggestions for future work (2)
• Application of Dynamic X-parameters to ET applications: beyond quasi-static approximation
• Characterize the modulator and take it into better account in the design
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 35
Conclusions
• The envelope simulation and measurement results show good quantitative agreement for the static nonlinearity of the PA versus power and drain voltage, and also as a function of load
• The load-sensitivity of the lookup table predicted by the XP model was independently validated by time-domain loadpull measurement
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 36
Acknowledgment
• This work was supported by a Grassroots grant from Agilent Technologies and in part by ONR under the DARPA MPC Program N00014-11-1-0931.
• The authors thank A. Howard, J. Horn, R. Biernacki, M. Marcu, P. Cain, A. Cognata, J. Xu, and A. Cidronali for support and valuable discussions.
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 37
References
• [1] A. Howard, “Simulating envelope tracking with Agilent ADS – a “Proof of Concept” example, “ Agilent EesofKnowledge Center, http://edocs.soco.agilent.com/display/eesofkcads/Applying+envelope+tracking+to+Improve+Efficiency
• [2] G. Wimpenny, “Understand and characterize envelope-tracking power amplifiers,” EETimes Design line, http://eetimes.com/design/microwave-rf-design/4233749/Understand-and-characterize-envelope-tracking-power-amplifiers?pageNumber=0
• [3] S. Baker, “Envelope tracking for efficient RF transmitters,” IEEE International Microwave Symposium, Montreal, June 2012
• [4] J. Hoversten, S. Schafer, M. Roberg, M. Norris, D. Maksimovic, Z. Popovic, “Codesign of PA, supply, and signal processing for linear supply-modulated RF transmitters,“ IEEE Trans. MTTS, vol. 60, no. 6, Jun. 2012
• [5] L. Sankey, Z. Popovic, “Adaptive tuning for handheld transmitters,” IEEE International Microwave Symposium Digest, pp. 225-228, June 2009
• [6] M. Roberg, J. Hoversten, and Z. Popovic, “GaN HEMP PA with over 84% power added efficiency,” Electronics letters, 11th, Vol. 46, No. 23, Nov. 2010
• [7] M. Hassan, L. E. Larson, V. W. Leung, D. E. Kimball, and P. M. Asbeck, “A wideband CMOS/GaAs HBT envelope tracking power amplifier for 4G LTE mobile terminal applications,” IEEE trans. MTTS, Vol. 60 No. 5. May 2012
• [8] D. Kim, D. Kang, J. Choi, J. Kim, Y. Cho, and B. Kim, “Optimization for envelope shaped operation of envelope tracking power amplifier,” IEEE trans. MTTS. Vol. 59, No. 7, Jul. 2011
• [9] J. Horn, D. E. Root, and G. Simpson, “GaN device modeling with X-parameters,” IEEE CSICS Oct. 2010• [10] P.M. Asbeck, H. Kobayashi, M. Iwamoto, G. Hanington, S. Nam, L.E. Larson, “Augmented behavioral
characterization for modeling the nonlinear response of power amplifiers,” IEEE MTT-S Intl. Microw. Symp. Dig. 2002
WSO: Transceiver and Technologies for Femto/Pico Cell Comm. Systems IMS2013, Seattle, June 2-7, 2013 38
References
• [11] J. Xu, J. Horn, M. Iwamoto, and D. E. Root, “Large-signal FET model with multiple time scale dynamics from nonlinear vector network analyzer data,” IEEE MTTS International Microwave Symposium Digest, May 2010.
• [12] J. Verspecht and D. E. Root, “Poly-harmonic distortion modeling,” IEEE MTTS Microwave Magazine, June 2006• [13] J. Verspecht, J. Horn, L. Betts, D. Gunyan, R. Pollard, C. Gillease, and D. E. Root, “Extension of X-parameters to
include long-term dynamic memory effects,” IEEE MTTS International Microwave Symposium Digest, pp741-744, June 2009
• [14] J. Verspecht, J. Horn and D. E. Root, “A simplified extension of X-parameters to describe memory effects for wideband modulated signals,” IEEE ARFTG 75th, May 2010
• [15] A. Soury and E. Ngoya, “Implementation of X-parameter models in harmonic-balance simulators,” IEEE MTTS International Microwave Symposium, June 2012
• [16] A. Soury and E. Ngoya, “Handling long-term memory effects in X-parameter model,” IEEE MTTS International Microwave Symposium, June 2012
• [17] E. Ngoya, C. Quindroit and J. M. Nebus, “On the continuous-time model for nonlinear-memory modeling of RF power amplifiers,” IEEE trans. MTTS Vol. 57. No. 12, Dec. 2009
• [18] D. K. Su, and W. J. McFarland, “An IC for linearizing RF power amplifiers using envelope elimination and restoration,” IEEE JSSC, Vol. 33, No. 12, Dec. 1998
• [19] http://www.agilent.com/find/x-parameters• [20] http://www.agilent.com/find/NVNA• [21] H. Jang, A. Zai, T. Reveyrand, P. Roblin, Z. Popovic, D. E. Root, “Simulation and Measurement-based X-parameter
Models for Power Amplifiers with Envelope Tracking,” IEEE International Microwave Symposium, June, 2013• [22] G. Casini, A. Cidronali, G. Manes, “Investigation of X-parameters Modeling for Accurate Envelope Tracking Power
Amplifier System Simulations,” IEEE International Microwave Symposium, June, 2013