PA Design using Measured
LP X-parameters
Design Considerations
© Copyright Agilent Technologies and bsw 2013
1
Power amplifier design and load-pull
measurements in practice
Design Considerations
• In an amplifier design, purpose of the matching network is not
only to provide a certain load line at the fundamental Fc
• Harmonic content, especially in the device output, also plays a
major role in achieving optimum output power and efficiency
• Demonstrated harmonic tuning capabilities of the measured Xparameters are thus very essential in amplifier designs
© Copyright Agilent Technologies and bsw 2013
2
Power amplifier design and load-pull
measurements in practice
Design Considerations
Amplifier Topology
We employ a single-ended Class
AB amplifier topology with a small
crossover current (about 5% of
peak Id ≈ 30mA Idq)
We target impedance matching
networks that maximize output
power and efficiency while also
Idealized drain voltage (red)
And current (blue) waveforms
minimizing output harmonics
© Copyright Agilent Technologies and bsw 2013
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Power amplifier design and load-pull
measurements in practice
Design Considerations
PCB Laminate
In a deep Class AB operation, harmonic power at the output Z0 is
generally unwanted and should either be shorted or reflected back to
the device with proper phase angle
Several matching topologies
may fulfill such requirements
Here, we employ lowpass
filter structures realized in
microstrip on a high quality
RT/Duroid 6010 laminate
© Copyright Agilent Technologies and bsw 2013
4
Power amplifier design and load-pull
measurements in practice
PA Design using Measured X-parameters
Output and Input Matching Networks
© Copyright Agilent Technologies and bsw 2013
5
Power amplifier design and load-pull
measurements in practice
Output Impedance Matching Network
Fundamental Load Reflection Coefficient (ΓL)
• Selected ΓL is a tradeoff between optimum delivered output
power (blue contours) and optimum efficiency (black contours)
dLP_Presentation..ZEff
ed_LP_Pdel..ZPoutdBm
Meas. opt. is 74.2%
(4 contours, 2% steps)
Selected ΓL at 28.5+j12Ω
Meas. opt. is +40.4dBm
(6 contours, 0.25dB steps)
© Copyright Agilent Technologies and bsw 2013
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Power amplifier design and load-pull
measurements in practice
Output Impedance Matching Network
Idealized Transformation
The chosen output match topology is based on Open Circuited Stubs
(OCS) and transmission lines (TL)
TL1
Transformation from 50Ω output
Z0 to selected ΓL is done within a
constant 0.6 Qn circle (shown as
shaded area in Smith Chart)
OCS1
OCS1
TL2
OCS2
OCS2
TL3
OCS3
OCS3
Element properties are optimized
while carefully considering
impact on harmonics
© Copyright Agilent Technologies and bsw 2013
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Power amplifier design and load-pull
measurements in practice
Output Impedance Matching Network
Circuit Simulation with MLIN Elements
• To improve 3rd harmonic output power suppression, the OCS
next to the output Z0 is designed to provide a short at 3*Fc
• Wideband attenuation is achieved using a radial stub
• Final transformation to transistor drain terminal is done using a
DC feed with an 80 degrees electrical short at 2*Fc
© Copyright Agilent Technologies and bsw 2013
8
Power amplifier design and load-pull
measurements in practice
Output Impedance Matching Network
EM Simulation in Momentum
• Estimated element properties using Kirsching MLIN models
are fine-tuned in more accurate planar Momentum simulations
© Copyright Agilent Technologies and bsw 2013
9
Power amplifier design and load-pull
measurements in practice
Output Impedance Matching Network
Simulation Results
• Blue = Circuit simulation using Kirsching MLIN models
• Red = Planar EM simulation in Momentum
m4
m5
freq=1.300GHz
freq=2.600GHz
dB(S(2,1))=-0.682 dB(S(2,1))=-14.033
m1
freq=1.300GHz
S(1,1)=0.335 / 148.662
impedance = 26.329 + j10.349 m3
m2
freq=2.600GHz
S(1,1)=0.965 / -177.093
impedance = 0.898 - j1.268
m6
freq=3.900GHz
dB(S(2,1))=-48.615
m4
0
-10
m5
dB(S(4,3))
dB(S(2,1))
S(3,3)
S(1,1)
m1
m2
-30
m6
m3
freq=3.900GHz
S(1,1)=0.984 / 128.831
impedance = 0.483 + j23.937
-50
1.0
freq (1.000GHz to 4.000GHz)
1.5
2.0
2.5
3.0
3.5
4.0
freq, GHz
© Copyright Agilent Technologies and bsw 2013
10
Power amplifier design and load-pull
measurements in practice
Input Impedance Matching Network
Fundamental Source Reflection Coefficient (ΓS)
• Purpose of the input matching network is to transform source
Z0 to impedance that yields optimum power gain and stability
• Based on (large signal) S11, selected ΓS = 15+0jΩ
• At lower frequencies, the CGH40010F has a high gain and
special attention needs to be paid to prevent instability.
© Copyright Agilent Technologies and bsw 2013
11
Power amplifier design and load-pull
measurements in practice
Input Impedance Matching Network
Circuit Simulation with MLIN Elements
For frequency octaves lower than Fc, a series resonator is
added to limit the effective source reflection coefficient
m2
DC gate bias feed
S(3,3)
is established using
a high impedance
m1
freq=1.300GHz
S(3,3)=0.561 / 175.385
impedance = Z0 * (0.281 + j0.037)
m2
freq=2.600GHz
S(3,3)=0.932 / 133.234
impedance = Z0 * (0.042 + j0.432)
m1
m3
m3
freq=3.900GHz
S(3,3)=0.462 / -54.439
impedance = Z0 * (1.163 - j1.113)
λ/4 transformer
freq (1.000GHz to 4.000GHz)
© Copyright Agilent Technologies and bsw 2013
12
Power amplifier design and load-pull
measurements in practice
Input Impedance Matching Network
EM Simulation in Momentum
• Estimated element properties using Kirsching MLIN models
are fine-tuned in more accurate planar Momentum simulations
© Copyright Agilent Technologies and bsw 2013
13
Power amplifier design and load-pull
measurements in practice
Input Impedance Matching Network
Simulation Results
• Blue = Circuit simulation using Kirsching MLIN models
• Red = Planar EM simulation in Momentum
m4
m5
freq=1.300GHz
freq=2.600GHz
dB(S(2,1))=-2.392 dB(S(2,1))=-9.448
m1
freq=1.299GHz
S(1,1)=0.546 / 174.898
impedance = 14.696 + j2.036
m4
0
m2
m5
-10
m1
m3
m3
freq= 3.900GHz
S(1,1)=0.810 / -18.776
impedance = 140.549 - j213.249
dB(S(4,3))
dB(S(2,1))
S(3,3)
S(1,1)
m2
freq=2.600GHz
S(1,1)=0.851 / 138.104
impedance = 4.611 + j18.999
m6
freq=3.900GHz
dB(S(2,1))=-35.554
-30
m6
-50
1.0
freq (1.000GHz to 4.000GHz)
1.5
2.0
2.5
3.0
3.5
4.0
freq, GHz
© Copyright Agilent Technologies and bsw 2013
14
Power amplifier design and load-pull
measurements in practice
Final Power Amplifier Schematic
• Simulation results are based on the X-parameter model and
EM simulations of final input and output matching networks
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15
Power amplifier design and load-pull
measurements in practice
PA Design using Measured X-parameters
Measurement Results
© Copyright Agilent Technologies and bsw 2013
16
Power amplifier design and load-pull
measurements in practice
The Fabricated Power Amplifier
© Copyright Agilent Technologies and bsw 2013
17
Power amplifier design and load-pull
measurements in practice
PA Measurement Results
Delivered Output Power & Drain Efficiency
• Simulation at PA board coaxial reference planes compared to
measurements with 5 different CGH40010F samples
45
80
70
Simulated
Measured
40
Drain efficiency [%]
Pdel [dBm]
60
35
30
50
40
30
20
25
10
Simulated
Measured
20
5
10
15
20
25
30
0
15
20
25
30
35
40
Pavs [dBm]
Pdel [dBm]
Simulated sat. Pdel = +41.4dBm
Simulated max. eff. = +65.9%
Measured sat. Pdel = +41.2dBm
Measured max. eff. = +64.3%
45
© Copyright Agilent Technologies and bsw 2013
18
Power amplifier design and load-pull
measurements in practice
Summary
• A measurement setup for accurate nonlinear characterization and
X-parameter modeling of a high-power RF device was presented
• Measured X-parameters were shown to accurately model important
device properties such as RF power spectra and drain efficiencies
• Using the measured X-parameters, a high-power, high efficiency
power amplifier was designed entirely inside the circuit simulator
• Fabricated PA confirms a first-pass design success with less than
0.2dB Psat and 1.6 percent point drain efficiency deviation from the
measured mean on 5 different transistor samples
© Copyright Agilent Technologies and bsw 2013
19
Power amplifier design and load-pull
measurements in practice