GaN: Applications in RF Systems Beyond The PA - RF Micro Devices

GaN: Applications in RF
Systems Beyond The PA
Rama Vetury, RFMD

Outline
• Properties of GaN
• System Challenges
• System Advantages Afforded by GaN
• GaN Components
• Summary

• GaN Is Natural Fit For High Power Applications
Properties of GaN
High
Voltage
High
Current
Density
High
Frequency
High
Power
Amp

• GaN Also Enables Applications Beyond The HPA
Properties of GaN
Ruggedness
Power
Handling
Low Loss,
Low Noise
UNREALIZED
Potential
Other
RF
Functions

Challenges in RF systems
Civilian &
Military Radar
Electronic Warfare
• Efficiency
• Weight
• Size
COST
-OR -
• Thermal Management
CATV
Cellular and
Broadcast
Communications
Military and Mobile
Communications

Communication Systems
• Key System Requirements
• Range
• Weight & Form Factor
• Efficiency
• Inter-operability / Waveform Versatility / SDR
• Key RF Component Requirements (apart from PA)
• Broadband, High Power & High Efficiency Switching Function
• Low Noise & High Power VCO
• Robust & Wideband LNA

Radar Systems
Passive Phased Array
BeamFormer
• Active Phased Array Radar Systems Advantages
Active Phased Array
• Low Loss, Higher Sensitivity
• More Reliable, Graceful Degradation
• Increased capability (multiple digital beamforming, improved clutter attenuation)
• Solid State T/R module Key Enabler of Advanced Active PAR systems
• Fully GaN MMIC T/R module improves system design tradeoffs
• Range, Resolution, Efficiency
• Size, Weight
• Environmental Ruggedness
LNA
HPA
T/R
T/R
T/R
BeamFormer
Receiver
Exciter

Radar Systems
GaAs
LNA
GaAs
HPA
• All GaN MMIC T/R Enables
• Limiter Reduction/Elimination
• Circulator Elimination
• Improved NF & Resolution
• dc power distribution efficiency (48V)
• System Benefits
Limiter &
Protection
Circulator
• Lower Cost
• Improved Range & Search Volume
GaN
Attenuator
GaN
Phase Shifter
GaN
Switch
GaN
HPA
GaN
LNA
GaN
Switch
• Key GaN component Requirements
– LNA
– Robustness
– Low NF, High DR
– Switch
– High Power, High Efficiency
– HPA
– Power density, Efficiency, BW, Gain

Commercial CATV Transmission
• Key Next Gen System Requirements
• ‘Fiber Deep’ architectures
• Greater Throughput
• Increased Bandwidth
• GaN Enables
• Better Linearity Amplifier
• Fewer Repeaters
• 20% Lower Energy Costs
• System Insertion
• Trunk Amplifiers
• Optical Nodes
• Line Extenders
Optical Node

GaN RF Components
Ruggedness
Power
Handling
Low Loss,
Low Noise
UNREALIZED
Potential
� GaN CATV Hi Linearity Amp
� GaN LNA
� GaN Switch
� GaN VCO
� GaN Mixer
� GaN Gain Block
� GaN Phase shifters
� GaN Var. Attenuators

CATV Linear Amplifier Block Diagram
Forward Path
Input
Return Path
Output
Push Pull Hybrid
Duplex Filter
Pre-Amplifier Output Amplifier
Power Doubler Hybrid
Return Path Amplifier Duplex Filter
Reverse Hybrid
Forward Path
Output
Return Path
Input

CATV Hybrid Linear Amplifier
Block Diagram
Simplified Schematic
Port
RFin
TF
TF1
R
R1
R
R2
GaAsFET
FET1
R
R3
GaAsFET
FET2
� Maintain Linearity
� Increase Power
� Eliminate ESD protection
� Lower Overall System Costs
R
R4
GaAsFET
FET3
GaAsFET
FET4
Port
24V
XFERTAP
XFer1
Replace GaAs
with GaN
Port
RFout

Linearity Requirements
• Key System Requirements
• Linearity
• Cost
• Linearity Metrics
• CIN
• CTB
• Xmod
• Temperature Dependence
• GaN Technology Advantages
• Intrinsic Linearity
• ESD Ruggedness
• Temperature Capability
550MHz 870MHz1GHz

Increase in Linear Power
3.5 dB
For CIN = 67 dB
Output level increases 3.5 dB
RFMD GaAs GaAs -1 GaAs -2
equivalent to 13.5dB tilt and 56.5dBmV
extrapolated to 1GHz
� GaN - improved CIN - enables higher power capability

CIN over Temperature
RFMD
GaN
equivalent to 13.5dB tilt and 56.5dBmV extrapolated to
1GHz
Other
GaAs
Other
GaAs
� GaN - Improved Intrinsic Linearity vs GaAs
� GaN - Maintains Linearity Over Temperature Better than GaAs

CATV Technology Revolution
GaAs to GaN
Revolution
Si to GaAs Revolution
� GaN offers improved Linearity AND improved Bandwidth

Why GaN for LNA ?
• LNA Design Goals
• OIP3 and NF
• Bandwidth & Input and Output Match
• Robustness & Manufacturability
• Technology Choice
• GaAs E-mode pHEMT
• Design Choices
• Active bias circuitry
• Fully Monolithic Integration
• GaN Advantages
• Sub 1dB NF
• OIP3 higher -> higher DR
• Wide Band Performance
• Survivability & Robustness
OIP3 (dBm)
55
50
45
40
35
30
25
GaN ?
OIP3 vs. Noise Figure
for Commercial LNAs, Discretes & GBs
pHEMT
FET
Low Noise
HFET
0 2 4 6 8
Noise Figure (dB)
HFET
HBT

Fabricated GaN MMIC LNA-PA
GaN LNA PA
• RC feedback
• Ls noise match
• Wg = 1.2 mm
• Vdd = 5-15V
• Idd = 200-400mA
Chip size - 1.7x1.7 mm 2

Noise Figure - High Bias
Gain (dB)
20
18
16
14
12
10
8
6
4
2
0
Gain & Noise Figure
15V/400mA
Gain
NF
T = 25C
Gain @ -30C
Gain @ 25C
NF @ -30C
NF @ 25C
NF ~ 0.25-0.45 dB
T = -30C
1 2 3 4 5 6 7 8
Frequency (GHz)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Noise Figure (dB)

Noise Figure - Medium Bias
Gain (dB)
20
18
16
14
12
10
8
6
4
2
0
Gain & NF over Temperature
12V/200mA
Gain
NF
T = -30C
T = 25C
1 2 3 4 5 6 7
Frequency (GHz)
Gain @ -30C
Gain @ 25C
NF @ -30C
NF @ 25C
NF ~ 0.1-0.2 dB
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Noise Figure (dB)

Wide-band S-par, High Bias
Gain, Return-Loss (dB)
20
10
0
-10
-20
-30
S 21
Vdd= 15V, Idd= 200mA
Temperature = -30C, 0C, 25C
S 11
S 22
0 1 2 3 4 5 6 7 8
Frequency (GHz)

Output Compression at 2 GHz
Pout (dBm), Gain(dB),
PAE(%)
40
35
30
25
20
15
10
5
0
Pout = -30C
Gain T=-30C
PAE T=-30C
Pout = 25C
Gain T= 25C
PAE T= 25C
Pout @ 2 GHz
15V/400mA
Gain
Pout
P1dB = 32.8 dBm
PAE@P1= 25%
1.59 W/mm @ P1dB
PAE
-20 -15 -10 -5 0 5 10 15 20 25
Pin (dBm)

Wide Band IP3 Performance
Output IP3 (dBm)
48
46
44
42
40
38
36
34
32
30
GaN MMIC Low Noise PA
15V, 400 mA
12V, 400 mA
5V, 400 mA
5V, 200 mA
1 2 3 4 5 6 7
Frequency (GHz)
IMS – Honolulu June 3-5, 2007,
Kobayashi, et.al.

GaN LNA
OIP3 (dBm)
55
50
45
40
35
30
25
OIP3 vs. Noise Figure
for Commercial LNAs, Discretes & GBs
This GaN LNA
0 2 4 6 8
Noise Figure (dB)
�LNA Result Validates GaN promise

Why GaN for RF Switches ?
• GaN:
• Engineer C OFF, low R on
• high BKDN
• high ID,max • Low R TH
• High Max T CH
• Si PIN:
• Drive Current Dependence
• GaAs pHEMT:
• Lower BKDN
Si PIN GaAs FET GaN FET
Small Signal
Insertion Loss
Isolation
Large Signal
0.1dB Compression V & I Margin
Switching Speed
Linearity
IIP3, 2nd & 3rd Harmonic
Robustness
High Power RF Switch Technology
Comparision 1
Need High
Drive Current
Degrade at
Higher Power
V & I Margin
VSWR ruggedness
Lower Max
Temp
BKDN, Max T
Max RF Power
System Factors
Size
Efficiency
Complexity
BKDN, Max T
1 compared at f= 2GHz

S
RFMD Switch Model
TL3 R21
R20
TL4
SRC4 PRC2
SRC3
• Simple small signal model
chosen
• Power Performance
Estimated By
• Device breakdown
• Maximum Current
• Good agreement between
model & measurement
G
D
(dB)
(dB)
0
‐1
‐2
‐3
‐4
‐5
‐6
0
‐10
‐20
‐30
‐40
‐50
Insertion Loss
Model
Meas
0 5 10 15 20
Isolation
Frequency (GHz)
0 5 10 15 20
Frequency (GHz)
Model
Meas
40
30
20
10
0
‐10
‐20
120
100
80
60
40
20
degree
degree

RFMD SPDT Switch
Model Validation
Bias Ron(Ohm‐mm)
(V) Coff(pF/mm)
Switch FOM
(GHz)
0 2.24 NA
10 0.27 268
20 0.20 359
30 0.17 431
40 0.14 508
• SS FOM comparable to GaAs pHEMT
•C OFF Bias Dependence
• SPDT switch design
- ss model based
- Power based on Technology Metrics
X9
Simplified Topology
Recieve1
R2
X6 X7
R1 R4
Port
Vcontrol1
Antenna1
R
R3
Port
Vcontrol2
X8
Transmit1

(dB)
0
‐0.2
‐0.4
‐0.6
‐0.8
‐1
RFMD GaN Switch – Insertion Loss
Insertion Loss
Model
Meas
0.5 1 1.5 2 2.5 3
Frequency (GHz)
• Good agreement to Model
• Excellent Performance to 3GHz
(dB)
0
‐5
‐10
‐15
‐20
‐25
‐30
‐35
Input Return Loss
Model
Meas
0.5 1 1.5 2 2.5 3
Frequency (GHz)

RFMD GaN Switch – Isolation
(dB)
0
‐10
‐20
‐30
‐40
‐50
Isolation (RFC-RF)
Model
Meas
0.5 1 1.5 2 2.5 3
Frequency (GHz)
• Measured Isolation less than simulated
• Excellent Performance to 3GHz

RFMD GaN Switch - Linearity
• Basic Limitations
• On State: Resistance Increase
• Off State:
• Diode Turn On
• Breakdown
• GaN advantages
• Higher Idss, Idmax
• Decreased Ron non linearity
• BKDN > 100V
• Allows for Voltage Margin
• Engineer C OFF for Low Distortion

Power Handling (W)
Power Performance
250
200
150
100
50
0
Switch Off‐State Power Handling
0 50 100 150
Vbr‐Vpo (V)
Off State Power
Handling
50% DeRated
Power Handling (W)
100
80
60
40
20
0
Switch Power Handling vs Control
‐100 ‐80 ‐60 ‐40 ‐20 0
Control Voltage (V)
Key GaN advantages
- Higher Breakdown Voltage -> High Off State Power Handling
- Larger Vcontrol possible
- More Voltage Margin for VSWR mismatch & process variation
50% DeRated
Power Handeling

Insertion Loss (dB)
Power Performance
0
‐0.1
‐0.2
‐0.3
‐0.4
‐0.5
‐0.6
‐0.7
‐0.8
‐0.9
‐1
Insertion Loss vs Power
0 10 20 30 40
Input Power (W)
ON State Compression
• Measured Insertion Loss
- bias -40V
• IL change < 0.1dB
-Input Power ~ 38 W
• Measurement System Limited

Summary
�GaN CATV Linear Amp
�GaN LNA
�GaN Switch
� GaN VCO
� GaN Mixer
� GaN Gain Block
� GaN Phase shifters
� GaN Var. Attenuators
� Successful Demonstration of key GaN based components
� Expect Successful Launch of other GaN based RF components in
Future
Contributions by Kevin Kobayashi (GaN LNA) and Rainer Hillermeier
(GaN CATV amp) and David Hodge (GaN Switch) are acknowledged
RFMD acknowledges support of AFRL (Monitor: Dr. John Blevins)
and ONR (Monitor: Dr. Paul Maki) in developing its core GaN
technology used in some of this work

References
• www.microwaves101.com
• International Microwave Symposium, June 3-5, 2007, Kobayashi et.
al.