Techniques and Challenges in Designing Wideband Power Amplifiers Using GaN and LDMOS

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JEFFREY HORF APPLICATIONS ENGINEERRF POWER GROUP, NXP SEMICONDUCTORSSEPTEMBER, 20, 2016ELECTRONIC DESIGN INNOVATION CONFERENCE (EDI CON)

TECHNIQUES AND CHALLENGES IN DESIGNING WIDEBAND POWER AMPLIFIERS USING GAN AND LDMOS

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AgendaGaN and LDMOS Parametric Comparison

• Device Technology Benefits• System Level Tradeoffs

GaN Advantages• Bandwidth, Efficiency, Power Density

Wideband PA Design and Challenges• Wideband Techniques• Thermal, Linearity, Ruggedness

GaN and LDMOS Wideband PA Applications• Nonlinear Model Simulation • CW and Pulsed Performance

NXP Power Product PortfolioConclusion

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GaN and LDMOS Technology

• GaN-on-SiC 50V technology provides higher efficiency, power density and more gain in a small package.

• GaN devices are capable of best in-class solutions for broadband applications.

• GaN’s high output impedance and low Cdscapacitance enables broadband design. Bandwidth limitation on the input match.

• For identical power level, GaN transistors have smaller parasitic capacitance, which makes the wideband matching easier than LDMOS transistors.

GaN LDMOS

• LDMOS is still demonstrating high power and efficiency in cellular and broadcast narrow-band applications.

• 50V LDMOS are primarily used for frequencies < 1.5 GHz. 28V LDMOS can provide compelling performance up to 4 GHz.

• LDMOS transistor’s large peripheries imply large Cgs/Cds capacitances which limit the bandwidth.

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GaN and LDMOS: Parametric Comparisons

Typical ParametersLDMOS (28V)

LDMOS(50V)

GaN(50V)

GaNAdvantage

Fmax (GHz) 22 15 30 High frequency operation 2.5GHz and above

Power Density (W/mm) 0.8 2 5-10 Higher Power density smaller device footprint

Efficiency @ P1dB (%) 60 < 55 70 Higher efficiency 2.5 GHz and above

Bandwidth (MHz) 100-400 100-500 500-2500 One device covers multi-bands

Cds (pf/W) Output Capacitance

0.23 ½ smaller ¼ smallerSmaller device capacitance

broadband operationCgs (pf/W) Input Capacitance

0.94 ½ smaller ½ smaller

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Leveraging the Benefits of GaN and LDMOS

• Differentiating performance exceeding LDMOS above 2.5 GHz

• Enables 5G at higher frequencies• Broadband design• High efficiency at high frequencies• Comparable thermal package as LDMOS• Compact PA design (more power in smaller

package, smaller matching circuitry)• Wideband CW and Pulse PA applications:

− 200-2600 MHz at 100 W− S-band 2.7-3.5 GHz at 700 W

GaN Benefits LDMOS Benefits

• Competitive performance to 2.7 GHz• Cost effective PA solutions• Mature process technology• High ruggedness up to 65:1 VSWR• Consistent thermal behavior• Broadband VHF/UHF below 1 GHz• Highest power up to 1.5 GHz• Narrow-band PA applications:

− Cellular bands up to 2.7 GHz− Avionics and L-band 1.2-1.4 GHz up to 1.5 kW− S-band 2.7-3.1 GHz at 300 W

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Material Characteristics Drive System Level TradeoffsMaterial Properties Device Operates Improved Device FOM System Advantage

Increased BWSmaller # of Die

Per System

Lower TotalEnergy Usage

Higher SystemFrequency

Smaller PackageCheaper Package

Relaxed SystemCooling

Power DensityPower GainEfficiency

Output Impedance

High ftHigh fmax

Smaller Die SizeMore Power/Die

HighBreakdownField

High ElectronVelocity

High ThermalConductivity

High VoltageHigh Current

High Temperature

High Frequency

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Gain Compression Comparison – P1dB, P3dB

LDMOS: Hard Gain Compression 1.2dB delta between P-1dB and P-3dB

LDMOS 32V @ 1.96 GHz

GaN: Soft Gain Compression1.8dB delta between P-1dB and P3-dB

GaN 50V @ 2.50 GHz

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52

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20 22 24 26 28 30 32 34 36 38

Pout

(dB

m)

Pin (dBm)

MMRF5014HR5 - Max Pout Load - 2.5 GHz - 50 V

Actual

Ideal

P-1dB = 50.2 dBm = 105 W

P-3dB = 52 dBm = 160.9 W

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GaN Advantage: Wider Bandwidth in S-BandMMRF5300N - 50V GaN60 W Pulsed PowerWideband over 2.7 – 3.5 GHz Flat Gain 14.6-14.9 dBEfficiency > 50%

MRF7S35120H - 32V LDMOS120 W Pulsed PowerBroadband over 3.1 – 3.5 GHzGain 12-13 dBEfficiency > 40%

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2700 2800 2900 3000 3100 3200 3300 3400 3500

IRL

(dB

)

D

rain

Eff

icie

ncy

(%)

Pow

er G

ain

(dB

)

Frequency (MHz)

PMRF5300N Performance at 60W PulsedVdd=50V, Idq=60mA, Vgs=-3V, 300us Pulse Width, 20% Duty Cycle

Power Gain

Drain Efficency

IRL

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GaN Advantage: Higher Efficiency

GaN provides high efficiency at peak power, and 6dB power back-off efficiency across wide bandwidth

Power drive-up gain response is less sensitive to bias current variation. Flat gain response can achieve over a wide power dynamic range

GaN is well suited for high efficiency amplifiers, such as classes D/E modes and switch-mode PA’s, where transistor operates like a switch

GaN on SiC technology is continuously improving linearized efficiency for Doherty PA operation at 7-8 dB peak power back-off

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GaN Advantage: High Efficiency and Output Power

PAE and Output Power vs. Frequency for NXP GaN and LDMOS devices

High Efficiency Beyond 2.5 GHz High Power Beyond 3.5 GHz

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Wideband PA Design Techniques1. Multi-sections LC matching networks2. Multi-sections quarter-wave line transformers

Consider Factors: 1. Power level2. Package3. PCB size4. Phase shift5. Broadband matching

Lower Q Matching

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Wideband PA Design Techniques

• Broadband impedance transformer < 1 GHz− Coaxial 4:1 transformer with ferrite beads can extend frequency range from 50 to 1000 MHz

Zcoax= Z1 * Z2 = 12.5 * 50 = 25 ohm

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• Multi-sections transmission lines – broadband matching over 400-3000 MHz

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1 2 3

Reactive Matching makes gain adjustment

across wideband by mismatching at the input, but results in higher input

VSWR.

L-R Lossy Matching absorbs gain to achieve

flat gain across wide band. Reduce low frequency

gain.

R-C Feedback improves the input and output match to achieve

broadband matching. Improve circuit stability by

reducing gain at low frequency.

Bandwidth Enhancement Techniques:

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Wideband PA Design Challenges

• At high power density, GaN is in the high end of its operating junction temperature

• GaN on SiC can reduce thermal resistance in air cavity ceramic and plastic-molded packages

• GaN die design to spread heat sources evenly and use highly conductive copper flange packages

GaN Thermal Challenges GaN Linearity Challenges

• GaN drain lags result in poor linearity, which results in a slow drain current response to fast change in drain amplitude swing

• GaN is being optimized for better DPD correction for switching signals in TDD based systems

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Wideband PA Design Challenges

• 50V LDMOS is designed for high breakdown voltage and can survive 65:1 VSWR and >3 dB input overdrive

• 50V GaN is designed for high ruggedness 20:1 VSWR

Device Ruggedness Device Reliability

• Use Mean-Time-To-Failure (MTTF) product calculators to determine device electromigration failure rate for a given set of operating conditions, junction-case temperature (Tj-c) and thermal resistance

• MTTF vs. Tj-c is calculated for CW conditions and pulse applications

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GAN AND LDMOSWIDEBAND PA APPLICATIONS

SINGLE-ENDED VS. PUSH-PULL AMPLIFIERS

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MMRF5014H GaN Wideband PA Application

• 50 V GaN on SiC Wideband Transistor• 100 W CW, 12 dB min Gain, 40% min

Efficiency covers 450-2500 MHz• Single-ended Compact

Wideband Amplifier• Full CW & Pulse Operation• Housed in NI-360 air-cavity

ceramic package • Thermal Resistance = 0.86 °C/W *

* Refer to App Note AN1955

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MMRF5014H GaN 450-2500 MHz Wideband Design• Broadband design using multi-section

transmission lines methodology with MMRF5014H non-linear device model

• Load and source impedances generated from load pull techniques to develop broadband matching networks

• ADS harmonic balance simulation to optimize power gain and efficiency

• Design Goals:−100 W across 450-2500 MHz−CW Gain >12 dB −Efficiency >40 %

MMRF5014H Source and Load Impedance

Freq (MHz) Zsource(ohm) Zload (ohm)

500 1.3+j3.9 5.9+j3.5

1000 1.0+j0.3 5.5+j2.9

1500 0.8-j0.5 3.4+j2.0

2000 1.2-j2.0 4.7+j0.3

2500 2.7-j3.8 3.7+j1.4

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MMRF5014H GaN Wideband Circuit Simulation – 450-2500 MHz

Input Matching Circuit

Output Matching Circuit

NXP can provide ADS device model to enable nonlinear circuit simulation

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MMRF5014H GaN Wideband Circuit Simulation Results

800 MHz 800 MHz 800 MHz

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MMRF5014H GaN 450 – 2500 MHz CW Measurement

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Effic

ienc

y (%

)

Gai

n (d

B)

Output Power (W)

MMRF5014H CW Power Drive-up

500 MHz Gain 1000 MHz Gain 1500 MHz Gain 2000 MHz Gain 2500 MHz Gain500 MHz Eff 1000 MHz Eff 1500 MHz Eff 2000 MHz Eff 2500 MHz Eff

VDD = 50 VIDQ = 300 mA

Device shows no gain expansion at selected bias current

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MMRF5014H GaN 450 – 2500 MHz CW Measurement

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Effic

ienc

y (%

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Gai

n (d

B)

Frequency (MHz)

MMRF5014H 450-2500 MHz CW at 100 W

100 W Gain 10 W Gain 100 W Eff


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MMRF5014H GaN 450 – 2500 MHz Pulse Measurement

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e Ef

ficie

ncy

(%)

Gai

n (d

B)

Frequency (MHz)

MMRF5014H 500-2500MHz Pulse at 100 W200usec pulse width, 20% duty cycle

100 W Gain 100 W Pulse Eff


Higher gain due to non-thermal heating effects in pulse operation

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MMRF1305HR5 LDMOS Broadband PA

• 50 V Wideband LDMOS Transistor• 100 W PEP, 14 dB min Gain, 30%

min Efficiency• Push-pull Amplifier covers 400-1000

MHz• Broadband Coaxial transformer

design• Housed in a NI-780H air-cavity

ceramic package • Low Thermal Resistance = 0.38

°C/W *

* Refer to App Note AN1955

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MMRF1305HR5 LDMOS 400-1000 MHz Broadband Design• Broadband design using two-section

impedance transformer with MMRF1305HR5 nonlinear device model

• ADS load pull and source pull techniques to obtain maximum power impedances between 400 MHz to 1 GHz

• ADS harmonic balance simulation to optimize power gain and efficiency

• Design Goals:−100 W across 400-1000 MHz−CW Gain >14 dB −Efficiency >30 %

MMRF1305H Source and Load Impedance (Simulated in balanced configuration)

Freq (MHz) Zsource (ohm) Zload (ohm)

400 4.21-j0.85 6.63+j0.27

500 3.82-j1.05 6.82+j0.18

600 3.44-j0.97 6.98+j0.01

700 3.23-j0.75 7.09-j0.25

800 3.21-j0.55 7.11-j0.55

900 3.31-j0.49 7.00-j0.88

1000 3.50-j0.60 6.80-j1.16

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MMRF1305H LDMOS Broadband Circuit Simulation400-1000 MHz

Output Matching Circuit

NXP can provide ADS or AWR MWO device models to enable nonlinear circuit simulation

Balun

Balun

Input Matching Circuit

4:1 Impedance Transformer

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MMRF1305H LDMOS Broadband Circuit Simulation Results

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MMRF1305H LDMOS 400 – 1000 MHz CW Measurement

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ienc

y (%

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Gai

n (d

B)

Output Power (W)

MMRF1305H 400-1000 MHz CW Power Drive-up

400 MHz Gain 700 MHz Gain 1000 MHz Gain400 MHz Eff 700 MHz Eff 1000 MHz Eff


Device exhibits gain expansion at low drive power and specified bias current

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in E

ff (%

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Gai

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MMRF1305H 400-1000MHz CW at 100 W

100 W Gain 10 W Gain 100 W Eff


MMRF1305H LDMOS 400 – 1000 MHz CW Measurement

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MMRF1305H LDMOS 400 – 1000 MHz Pulse Measurement

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MMRF1305H 400-1000MHz Pulse at 100 W200usec pulse width, 20% duty cycle

100 W Gain 100 W Eff


Higher gain due to non-thermal heating effects in pulse operation

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GaN and LDMOS Wideband Application Comparison

ParametersGaN

MMRF5014HLDMOS

MMRF1305H

Circuit Topology Single-ended Push-pull

Bandwidth @ 100 W 450-2500 MHz 400-1000 MHz

Gain @ 100 W 12-14 dB 13-17.5 dB

Efficiency @ 100 W > 39 % > 32 %

P3dB 160 W 140 W

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LDMOS Power Product Portfolio

• 1

1.8 MHz 500 MHz 915 MHz 1400 MHz 2900 MHz 3500 MHz

10W

100W

1kW

1200 MHz

S-Ba

nd R

adar

270

0-31

00

Industrial

FM/VHF Broadcast

Aerospace

UHF Broadcast

Industrial

Aerospace

2450 MHz

1.5kW MRF1K50NTo 500MHz, 1500W CW

Cellular ICs28V class AB

Cel

lula

r 34

00-3

600

Cel

lula

r 180

0-20

50C

ellu

lar 2

100-

2200

L-B

and

Rad

ar

IFF

50V LDMOS

28/32V LDMOS

Cel

lula

r 230

0-27

00IS

M 2

500

AerospaceIndustrial500W

Frequency (MHz)

Pea

k P

ower

(W)

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GaN Power Product Portfolio – Compliments LDMOS to Address High Frequency, High Power Applications

Frequency (MHz)

1000

400

100

10

2

Pea

k P

ower

(W)

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Conclusion• Benefits have been presented for GaN and

LDMOS technologies. Including device parameters with performance trade-offs, design challenges, and wideband PA applications.

• GaN devices have great potential for high-power cellular and defense aerospace markets in wideband, multi-band PA applications

• NXP provides full product support forGaN and LDMOS product solutions