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GaN Power Amplifiers for Next-Generation Wireless Communications
Jennifer Kitchen Arizona State University
Students: Ruhul Hasin, Mahdi Javid, Soroush Moallemi, Shishir Shukla, Rick Welker
2
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
3
• 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
4
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
5
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
6
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?
7
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.
9
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
10
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.
11
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.
12
• 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
13
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)?
14
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
15
Measured Class AB PA Performance
Measured output power, gain and power added efficiency (PAE)
16
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.
17
• 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
18
Legacy vs. ‘Digital’ Tx Architecture
Presented Work
Ongoing Work
19
‘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.
20
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).
21
GaN-on-Si Switching Power Stage
22
Coding Efficiency x PA Efficiency
Digital Transmitter Efficiency
transmitter =coding * PA
Coding efficiency directly affects transmitter efficiency.
Vrms2
23
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%
24
GaN Class-D PA w/SiGe Driver
25
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
26
Power Amplifier Die-to-Die Assembly
27
Power Amplifier Board Assembly
DieBalun
Differential Input
Differential Output
28
Power Amplifier MeasurementsSingle-Carrier WCDMA: 6dB PAR
29
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
30
• 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
31
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?
32
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.
33
+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
34
High Power Density PA MMIC & Module
Single PA MMIC
Integrated Module• High Power Density• Small Size• Advanced GaN
35
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
36
Simulated Performance Summary
11 dB back-off
Gain (dB) vs Output Power (dBm) and Drain Efficiency vs Output Power (dBm) at 1.9 GHz
37
Simulated Performance Summary
State of the art performance, highest reported efficiency at 10dB power backoff, and wide bandwidth of operation
38
• 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
39
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?