GaN Power Amplifiers for Next- Generation Wireless ... · GaN Power Amplifiers for Next-Generation...

GaN Power Amplifiers for Next-Generation Wireless Communications

Jennifer Kitchen Arizona State University

Students: Ruhul Hasin, Mahdi Javid, Soroush Moallemi, Shishir Shukla, Rick Welker

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Wireless Communications Circuits Lab - ASU

- 19 students focused on PA, RF supply modulators, and RF transceiver circuits.- Over 1000 sq ft. laboratory space.

- RF measurement capability up to 40GHz.- PA characterization capability up to ~ 8GHz.

RF Probe Station PA Load-Pull Station

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• Motivations & Objective for this Work• GaN-on-Si – Initial Explorations

- Class AB PA- Switched-Mode Power Amplifiers:

Transformer-Coupled Class D PA with SiGe DriverOther Switched-mode PA Topologies

• GaN-on-SiC – Initial Explorations- High Power MMIC- Cubesat Applications- Doherty w/Dynamic Load Modulation

• Conclusion

Outline

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Motivation for Our Work

Our Motivation:• Higher Efficiency• Lower Cost• Higher Levels of Integration (Smaller Form Factor)• Performance to meet future wireless standards → 5G?

PA + PM ~ 70-80% of Power

RFDigital Base-Band

&Memory

OthersAnalog

Base-Band

Wireless Handset Transceiver’s Power Consumption:

[2005] [2014]

PA > 60% of Power

Power Management DSP

RF/AFE

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Applications to Industry & Technology

Future-generation wireless devices: smartphones, pico/femto cell basestations, Cubesats, transceivers for IoT, beamforming MIMO systems with multiple transceivers, wearable electronics

→  smaller sizes, →  lower power consumption, →  higher data rates, →  lower hardware cost

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Main Objective

To build modulation-agnostic (and multi-band) ‘Linear’ Transmitters for handset and femtocell/picocell basestationapplications.

Requirements:

Maintain PA Efficiency over the entire output power range.

Low Spurious Emissions & Good Signal Quality [ACLR, EVM].

Multi-Band Legacy RF Transmitters

A single PA?

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How?

[2011]

We work with these architectures

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Research Objectives

- To explore GaN-on-SiC/GaN-on-Si as a potential process technology for implementing commercial PAs.

- To innovate and implement wideband, high-efficiency GaNPAs with low cost and hardware overhead.

- To improve the interface between signal processing in silicon and GaN power stages.

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Our 2-Path Approach

Modulation-Agnostic, High-Efficiency Amplifiers in GaN

Efficiency-Enhancement & Linearization of Load-Modulated PAs

‘Digital’ Transmitters EmployingSwitched-mode PAs

RF PowerDACs

Digital RF & SM PAs

AdvancedDoherty

DynamicLoad

Modulation

• Low-loss switches• High-efficiency drivers• Low-jitter, high-speed switching

• Programmable/tunable load• High-efficiency supply modulators• Hardware overhead

Envelope/PowerTracking PAs

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GaN as an Enabler for Revolutionary PA Performance

- Historically, low levels of integration.- Low yield.- Minimal reduction in “knee voltage”.- Requires high supply voltages for highest efficiencies.

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GaN Processes

We design amplifiers in both GaN-on-Silicon and GaN-on-Silicon Carbide (GaN-on-SiC)

Each process has its own advantages/disadvantages:

GaN-on-Si: Lower cost, lower frequencies. Commercial applications.

GaN-on-SiC: Higher cost, higher frequencies, higher power. Basestation, space, and government applications.

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• Motivations & Objective for this Work• GaN-on-Si – Initial Explorations

- Class AB PA- Switched-Mode Power Amplifiers:

Transformer-Coupled Class D PA with SiGe DriverOther Switched-mode PA Topologies

• GaN-on-SiC – Initial Explorations- High Power MMIC- Cubesat Applications- Doherty w/Dynamic Load Modulation

• Conclusion

Outline

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GaN-on-Si Initial Explorations

- Is the process capable of handling power/heat with low-cost assembly solutions?

- What output power/efficiency are the devices capable of providing at low supply voltage?

- Can we accurately predict performance for switched-mode PA applications?

- Can we design high-efficiency switched-mode PAs for advanced communications standards (i.e. LTE, other)?

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What Output Power/Efficiency are the Devices Capable of Providing?

• Build a distributed amplifier: BW = 0.4-4 GHzPsat = 3.5W 23% efficiency

• Build a class AB PA: low [10V] supply, low-thermally conductive die attach, small-form factor

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Measured Class AB PA Performance

Measured output power, gain and power added efficiency (PAE)

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Comparison with Other Class AB PAs

Reference Process Frequency (GHz)

Saturated Output

Power (dBm)

PeakPAE (%)

Linearity

[2] SOI CMOS 0.13 µm

1.9 32.4 47 ACPR of -33 dBc(WCDMA) @ avg. Pout of 28.7 dBm

[3] 65 nm CMOS

0.9 28.9 69.9 --

[4] GaN-on-Si 2.45 34.6 42.5 --[5] GaAs HBT 0.824-0.849 28 36.76 ACPR of -54.61 dBc

(CDMA) @ Pout of 28 dBm

This Work GaN-on-Si200 nm

0.82 – 0.90 30 55.44 Two tone IM3 > -40 dBc @ 6 dB back off

from P1-dB

GaN-on-Si process promises substantial improvements in PAperformance when used in “advanced” architectures.

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• Motivations & Objective for this Work• GaN-on-Si – Initial Explorations

- Class AB PA- Switched-Mode Power Amplifiers:

Transformer-Coupled Class D PA with SiGe DriverOther Switched-mode PA Topologies

• GaN-on-SiC – Initial Explorations- High Power MMIC- Cubesat Applications- Doherty w/Dynamic Load Modulation

• Conclusion

Outline

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Legacy vs. ‘Digital’ Tx Architecture

Presented Work

Ongoing Work

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‘Digital’ Tx Design Challenges

- How do we efficiently amplify digital waveforms?- Process technologies: GaN-on-Si .- High-efficiency switched-mode PA architectures.- Novel coding schemes: RF PWM/PPM, RF M.

- How do we predict transmitter and PA performance?- Transient device models.- Performance verification in a system-level context.

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GaN-on-Si Switching Power Stage

• ParBERT generates 2.25Gb/s switching signals with adequate power for driving 1200m devices.

• High impedance probes for measuring output power at 1.125GHz.

• Power level is adjusted via the RF input signal pulse-width (PWM).

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GaN-on-Si Switching Power Stage

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Coding Efficiency x PA Efficiency

Digital Transmitter Efficiency

transmitter =coding * PA

Coding efficiency directly affects transmitter efficiency.

Vrms2

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Coding Efficiency for Various Digital Processing Schemes

M on FPGA (Systolic Array) Coding Efficiency1.0 Bit 4:1 RZ 18.6%1.5 Bit 4:1 RZ 37.6%

Continuous Time M1 Bit 4:1 NRZ 35.9%

Asynchronous M1.5 Bit 43.8%

Pulse-Width Modulation1 Bit 4:1 RZ 46.8%

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GaN Class-D PA w/SiGe Driver

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SiGe ‘Driver Chip’ Specifications

Specification ValueCapacitive Load Range 1.25pF - 8pFRise/Fall Time at Output <40psOn-Chip Input Termination 50 Output Swing 4.0 V single-endedSupply Voltage 5.0 VPower Consumption 0.5 - 1.6W Temperature Range -40C to 125C

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Power Amplifier Die-to-Die Assembly

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Power Amplifier Board Assembly

DieBalun

Differential Input

Differential Output

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Power Amplifier MeasurementsSingle-Carrier WCDMA: 6dB PAR

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Comparison of This Work to Other Switched-Mode PAs

Reference Freq(GHz)

Class Pout(W)

Gp(dB)

PAE(%)

(%) Device Modulation

1 2.14 E 20 13 70 73 GaN Non‐ConstEnvelope

2 2 F 16.5 13 85.5 91 GaN Const Envelope

3 0.9 CMCD20.7/51.1 ‐ ‐ 75 GaN ConstEnvelope

4 2 E 11.4 12.6 74 ‐ GaN Const Envelope

5 2 E 4 ‐ 57 62 GaN Const Envelope

6 2.14 F 10.5 12.2 70.9 75 GaN Const Envelope

7 2.14 CMCD 50 14.3 60.3 63 GaN Const Envelope

8 0.9 CMCD 870m ‐ 71 ‐ GaAs Const Envelope

9 0.337/1.125 VMCD 1.82 29.5 GaN Non‐Const

Envelope

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• Motivations & Objective for this Work• GaN-on-Si – Initial Explorations

- Class AB PA- Switched-Mode Power Amplifiers:

Transformer-Coupled Class D PA with SiGe DriverOther Switched-mode PA Topologies

• GaN-on-SiC – Initial Explorations- High Power MMIC- Cubesat Applications- Doherty w/Dynamic Load Modulation

• Conclusion

Outline

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GaN-on-SiC Initial Explorations

- What are the frequency and power limitations for GaN as a MMIC?

- How do we integrate multiple MMICs at a module-level and manage thermal requirements?

- How do we design for high-reliability and long-term field deployment?

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High-Power MMIC

- 40 Watt single-MMIC Output Stage: 4-6GHz (currently in fab).

- Thermal analysis shows good heat dissipation. Junctions remain within ‘safe’ operating temperatures.

- The ability to simulate, analyze, and measure PA temperature ‘hot spots’ is instrumental to increasing efficiency and power.

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+30GHz PA for Cubesat Application

Build revolutionary power amplifiers for +30GHz aerospaceand satellite applications.

Requirements:

Robust, Radiation Tolerant,Wide Temperature Range

+30GHz operation with >30W output power (Psat)

>50% PA Efficiency

Small form factor –integrated package solutions

Specification Value

Frequency Range 35.5-36.5GHz

Saturated Output Power (0.5dB Compression)

32 W

PA MMIC PAE ~25 %

Gain ~25 dB

Linearity

IM3@35dBm/tone:-31dBc

IM5@35dBm/tone:-37dBc

TID Hardness [krad] 3,000

Temperature Range -55C to +125C

Fabrication PA MMIC/ Integrated Module

PA MMIC Process Qorvo GaN0.15um

Power Supply 22 V

Ka-Band CubeSat PA

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High Power Density PA MMIC & Module

Single PA MMIC

Integrated Module• High Power Density• Small Size• Advanced GaN

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Dynamic Load Modulation (DLM) Doherty Design

No additional λ/4 transformer required

- CREE GaN-on-SiC devices.- Doherty Architecture w/DLM in the Main PA.- High efficiency at high power backoff.- Smaller form factor by removing the /4 at output.

DLM

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Simulated Performance Summary

11 dB back-off

Gain (dB) vs Output Power (dBm) and Drain Efficiency vs Output Power (dBm) at 1.9 GHz

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Simulated Performance Summary

State of the art performance, highest reported efficiency at 10dB power backoff, and wide bandwidth of operation

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• Motivations & Objective for this Work• GaN-on-Si – Initial Explorations

- Class AB PA- Switched-Mode Power Amplifiers:

Transformer-Coupled Class D PA with SiGe DriverOther Switched-mode PA Topologies

• GaN-on-SiC – Initial Explorations- High Power MMIC- Cubesat Applications- Doherty w/Dynamic Load Modulation

• Conclusion

Outline

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Summary

• We have explored GaN-on-Si and GaN-on-SiC for various applications:– Commercial cellular– Next generation ‘digital’ architectures– Cubesat applications

• GaN-based amplifiers show promise for:– Medium power commercial applications.– High frequency Cubesat, Satcom, or government applications.

• Is the cost worth the performance?