Techniques and Challenges in Designing Wideband Power Amplifiers Using GaN and LDMOS
- 1. PUBLIC JEFFREY HO RF APPLICATIONS ENGINEER RF POWER GROUP, NXP SEMICONDUCTORS SEPTEMBER, 20, 2016 ELECTRONIC DESIGN INNOVATION CONFERENCE (EDI CON) TECHNIQUES AND CHALLENGES IN DESIGNING WIDEBAND POWER AMPLIFIERS USING GAN AND LDMOS
- 2. PUBLIC11 Agenda GaN 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 Portfolio Conclusion
- 3. PUBLIC2 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 Cds capacitance 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.
- 4. PUBLIC3 GaN and LDMOS: Parametric Comparisons Typical Parameters LDMOS (28V) LDMOS (50V) GaN (50V) GaN Advantage 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 smaller Smaller device capacitance broadband operationCgs (pf/W) Input Capacitance 0.94 ½ smaller ½ smaller
- 5. PUBLIC4 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
- 6. PUBLIC5 Material Characteristics Drive System Level Tradeoffs Material Properties Device Operates Improved Device FOM System Advantage Increased BW Smaller # of Die Per System Lower Total Energy Usage Higher System Frequency Smaller Package Cheaper Package Relaxed System Cooling Power Density Power Gain Efficiency Output Impedance High ft High fmax Smaller Die Size More Power/Die High Breakdown Field High Electron Velocity High Thermal Conductivity High Voltage High Current High Temperature High Frequency
- 7. PUBLIC6 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 Compression 1.8dB delta between P-1dB and P3-dB GaN 50V @ 2.50 GHz 36 38 40 42 44 46 48 50 52 54 56 58 20 22 24 26 28 30 32 34 36 38 Pout(dBm) 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
- 8. PUBLIC7 GaN Advantage: Wider Bandwidth in S-Band MMRF5300N - 50V GaN 60 W Pulsed Power Wideband over 2.7 – 3.5 GHz Flat Gain 14.6-14.9 dB Efficiency > 50% MRF7S35120H - 32V LDMOS 120 W Pulsed Power Broadband over 3.1 – 3.5 GHz Gain 12-13 dB Efficiency > 40% -20 -10 0 10 20 30 40 50 60 13 13.5 14 14.5 15 15.5 16 16.5 17 2700 2800 2900 3000 3100 3200 3300 3400 3500 IRL(dB)DrainEfficiency(%) PowerGain(dB) Frequency (MHz) PMRF5300N Performance at 60W Pulsed Vdd=50V, Idq=60mA, Vgs=-3V, 300us Pulse Width, 20% Duty Cycle Power Gain Drain Efficency IRL
- 9. PUBLIC8 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
- 10. PUBLIC9 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
- 11. PUBLIC10 Wideband PA Design Techniques 1. Multi-sections LC matching networks 2. Multi-sections quarter-wave line transformers Consider Factors: 1. Power level 2. Package 3. PCB size 4. Phase shift 5. Broadband matching Lower Q Matching
- 12. PUBLIC11 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
- 13. PUBLIC12 Wideband PA Design Techniques • Multi-sections transmission lines – broadband matching over 400-3000 MHz
- 14. PUBLIC13 Wideband PA Design Techniques 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:
- 15. PUBLIC14 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
- 16. PUBLIC15 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
- 17. PUBLIC16 GAN AND LDMOS WIDEBAND PA APPLICATIONS SINGLE-ENDED VS. PUSH-PULL AMPLIFIERS
- 18. PUBLIC17 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
- 19. PUBLIC18 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
- 20. PUBLIC19 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
- 21. PUBLIC20 MMRF5014H GaN Wideband Circuit Simulation Results 800 MHz 800 MHz 800 MHz
- 22. PUBLIC21 MMRF5014H GaN 450 – 2500 MHz CW Measurement 20 30 40 50 60 70 80 4 6 8 10 12 14 16 20 30 40 50 60 70 80 90 100 110 Efficiency(%) Gain(dB) Output Power (W) MMRF5014H CW Power Drive-up 500 MHz Gain 1000 MHz Gain 1500 MHz Gain 2000 MHz Gain 2500 MHz Gain 500 MHz Eff 1000 MHz Eff 1500 MHz Eff 2000 MHz Eff 2500 MHz Eff VDD = 50 V IDQ = 300 mA Device shows no gain expansion at selected bias current
- 23. PUBLIC22 MMRF5014H GaN 450 – 2500 MHz CW Measurement 0 10 20 30 40 50 60 70 80 8 10 12 14 16 18 20 22 24 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 Efficiency(%) Gain(dB) Frequency (MHz) MMRF5014H 450-2500 MHz CW at 100 W 100 W Gain 10 W Gain 100 W Eff VDD = 50 V IDQ = 300 mA
- 24. PUBLIC23 MMRF5014H GaN 450 – 2500 MHz Pulse Measurement 0 10 20 30 40 50 60 70 80 8 10 12 14 16 18 20 22 24 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 PulseEfficiency(%) Gain(dB) Frequency (MHz) MMRF5014H 500-2500MHz Pulse at 100 W 200usec pulse width, 20% duty cycle 100 W Gain 100 W Pulse Eff VDD = 50 V IDQ = 300 mA Higher gain due to non-thermal heating effects in pulse operation
- 25. PUBLIC24 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
- 26. PUBLIC25 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
- 27. PUBLIC26 MMRF1305H LDMOS Broadband Circuit Simulation 400-1000 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
- 28. PUBLIC27 MMRF1305H LDMOS Broadband Circuit Simulation Results
- 29. PUBLIC28 MMRF1305H LDMOS 400 – 1000 MHz CW Measurement 10 20 30 40 50 60 70 80 4 6 8 10 12 14 16 18 10 20 30 40 50 60 70 80 90 100 110 120 130 Efficiency(%) Gain(dB) Output Power (W) MMRF1305H 400-1000 MHz CW Power Drive-up 400 MHz Gain 700 MHz Gain 1000 MHz Gain 400 MHz Eff 700 MHz Eff 1000 MHz Eff VDD = 50 V IDQ = 400 mA Device exhibits gain expansion at low drive power and specified bias current
- 30. PUBLIC29 10 15 20 25 30 35 40 45 50 55 60 10 12 14 16 18 20 22 24 26 28 30 400 450 500 550 600 650 700 750 800 850 900 950 1000 DrainEff(%) Gain(dB) Frequency (MHz) MMRF1305H 400-1000MHz CW at 100 W 100 W Gain 10 W Gain 100 W Eff VDD = 50 V IDQ = 400 mA MMRF1305H LDMOS 400 – 1000 MHz CW Measurement
- 31. PUBLIC30 MMRF1305H LDMOS 400 – 1000 MHz Pulse Measurement 10 15 20 25 30 35 40 45 50 55 60 10 12 14 16 18 20 22 24 26 28 30 400 450 500 550 600 650 700 750 800 850 900 950 1000 DrainEff(%) Gain(dB) Frequency (MHz) MMRF1305H 400-1000MHz Pulse at 100 W 200usec pulse width, 20% duty cycle 100 W Gain 100 W Eff VDD = 50 V IDQ = 400 mA Higher gain due to non-thermal heating effects in pulse operation
- 32. PUBLIC31 GaN and LDMOS Wideband Application Comparison Parameters GaN MMRF5014H LDMOS 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
- 33. PUBLIC32 LDMOS Power Product Portfolio • 1 1.8 MHz 500 MHz 915 MHz 1400 MHz 2900 MHz 3500 MHz 10W 100W 1kW 1200 MHz S-BandRadar2700-3100 Industrial FM/VHF Broadcast Aerospace UHF Broadcast Industrial Aerospace 2450 MHz 1.5kW MRF1K50N To 500MHz, 1500W CW Cellular ICs 28V class AB Cellular3400-3600 Cellular1800-2050 Cellular2100-2200 L-BandRadar IFF 50V LDMOS 28/32V LDMOS Cellular2300-2700 ISM2500 Aerospace Industrial500W Frequency (MHz) PeakPower(W)
- 34. PUBLIC33 GaN Power Product Portfolio – Compliments LDMOS to Address High Frequency, High Power Applications Frequency (MHz) 1000 400 100 10 2 PeakPower(W)
- 35. PUBLIC3434 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 for GaN and LDMOS product solutions