Title: Transistor and Circuit Technologies for Tomorrow
1Transistor and Circuit Technologies for
Tomorrows Base Station Power Amplifiers
- Raymond S. Pengelly
- Cree Microwave
- Durham, NC 27703 USA
2002 IEEE Topical Workshop on Power Amplifiers
for Wireless Communications
2More and More Power!
- Assuming GSM as the reference with 0 dB Peak
to Average Ratio to cover a radius of X miles - EDGE requires 2 x power for same coverage
- CDMA requires 4 x power for same coverage
- W-CDMA requires 8 x power for same coverage
- OFDM requires 15 x power for same coverage
3There are No Free Lunches
- More data per unit time requires more bandwidth
or clever modulation schemes - Digital transmission techniques require more peak
power for the same bit error rate for greater
capacity - In order to minimize spectral re-growth and
interference transmitters have to be more linear
4Competitive Power Transistor Technologies
5New Devices
- High Power Density
- Reduced Size
- Higher Working Impedances
- Simpler Circuits
- Easier Manufacture
- Wide Bandgap transistors on 4H-SiC and AlGaN/GaN
provide superior performance to GaAs or Si
counterparts - 4 to 6 Watts/mm for SiC MESFETs
- 10 to 12 Watts/mm for AlGaN/GaN HFETs
More inherent DC to RF Efficiency and Linearity
are Key
6Envelope Distribution Functions
- Power capability is a direct function of where a
power amplifier starts to saturate - Average spectral re-growth is a function of
- Power capability
- Envelope statistics
- Clipping, even for short periods of time, is a
serious issue
7- Peak to Average Ratio is 15 dB
8W-CDMA
- For the majority of the time (gt 90) the
basestation transmitter delivers power at 1/8 its
peak power capability (but it needs to be able to
deliver any power level up to the peak) - At peak power the overall base-station is
typically 20 efficient but for most of the time
it is only 6 efficient since the PAs become
less efficient when backed-off - 2.35 Kilowatts in for 140 watts out!
9Typical Amplifier Line-up
10 30 125
Numbers are Peak Watts
10Wide-Band Power Modules
11Typical Basestation Power Amplifier
- OLD - Lots of Silicon Power (400 watts)! - But
physically LARGE - Power Density of lt 10 watts per sq. inch
- NEW LDMOS
- Power FET Modules
- increase Power
- Density to
- 25 to 100 Watts
- per sq. inch
12The Need for Smaller PAs
Macrocell Basestation Hut - Lots of Space!
Power Amplifiers with Fans
- Going to Microcell
- Higher powers in the same space
- Tower Top Arrays with no fans
13.The Difference between an LDMOS Transistor and
a Silicon Carbide MESFET for 30 Watts Output Power
LD-MOSFET
SiC MESFET
14GaN Amplifier- Comparison to GaAs pHEMT
- GaN based amplifier 6 W out to 50 W
- GaAs based amplifier 0.6 W out to 50 W
- -without impedance transformation
Device
Input
I
V
f
/f
Load
Power
max
max
t
max
Capacitance
mA/mm
(V)
GHz
impedance
(W)
Ohms
GaAs
3 pF
600
20
30/90
33
1
p-HEMT
GaN
3 pF
1200
60
30/90
50
6
HEMT
- 10x less impedance transformation - 5-10 x
Higher Bandwidth - Simpler, Smaller circuits,
High Yield, Low cost
15Thermal Conductivity is Critical for High Power
- Die size is constrained by wavelength
- - Y-dimension is limited by gate R and L
- - X-dimension is limited by phasing issues
- Key figure of merit is how much power the device
can handle in terms of W/mm2 of die area
16GaN on SiC The Thermal Advantage
- SiC has a very high thermal conductivity of 4.9
W/cm-K - - GaAs 0.4, Si 1.5, Sapphire 0.4
- SiC delivers higher power from given chip area gt
SiC has higher W/mm2 gt reduces /W
173 SiC Vs. 4 Si Wafer
- 100 W GaN HEMTs Die size on SiC 1 x 4 mm2, Die
size on Si 2 x 6 mm2 - Fabrication (not Substrate) is the more
expensive cost component
3-inch SiC 4-inch Si Total die 860
532 Non-edge die 788 484
18High Power Density PAE from SiC MESFETs
- Pulsed on-wafer power densities of 5-6 W/mm
consistently achieved on large FETs
19SiC MESFET with 7.2 W/mm
- Power density of 7.2 W/mm with 45 PAE at S-band
demonstrates the capability of the technology
20Mobile Telephone Frequency Allocations
2120-Watt Broadband SiC MESFET Amplifier
Balanced Amplifier with 10-Watt, CRF22010 FETs
- 22 W at P1dB across a 400 MHz band
- Advantage of wide bandgap transistors
power-bandwidth product greatly exceeding Si LDMOS
2275-Watt SiC MESFET Amplifier
2 GHz test fixture for 60 W MESFET development
- 75 W CW, 11 dB gain demonstrated from a single
SiC MESFET - Currently 60-Watt Class A/B MESFET transistor
being optimized, targeted for production release
by the end of 2002 - REAL POWER!
23Broadband SiC MESFET Amplifier 200 MHz to 2200 MHz
Drain Bias
100 190 ohms
In Out
1.1 0.5
0.6 0.6 2.4
Gate Bias
All capacitor values in pF
24Ultra Broadband Amplifiers
- Broadband for Multi-Frequency and Multi-Mode
25GaN HEMTs for Power Amplifiers
Higher junction temperature, smaller pitch
higher device density, ease of packaging
26GaN HEMT with 12 W/mm
- Peak pulsed power density of 12 W/mm on a 0.5-mm
HEMT - CW power from same device of 9 W/mm
27Packaged GaN HEMTs
- P1dB of 12 W, 46 PAE at 4 GHz at 30 Volts
28Characterization of AlGaN/GaN HEMTs Using Fixed
Load at Varying Voltage Supply
29Cellular Base-Station Application
3010-Watt Broadband GaN HEMT Amplifier
- 11 W at P1dB across the 400 MHz to 2200 MHz band
- 17 dB gain with only 0.5 dB ripple
- Great for a generic driver amplifier
31GaN HEMTs for Infrastructure 2 GHz, CW Power
from a 24-mm HEMT
- Record Power exceeding 100 Watts
Peak Power 108 W CW Power Density 4.5 W/mm
- 103 W at 2.6 dB gain compression
- Peak Drain Efficiency of 54
32High Temperature Operation
- Demonstrated that at a TJ of 180OC (case
temperature of 120OC) SiC MESFET has a mission
life of gt 20 years (3 ? confidence level) - Equivalent maximum junction temperature for Si
LDMOS is 130 OC - Equivalent maximum junction temperature for GaAs
MESFET is 110 OC
33So, what does this mean for next generation
infrastructure power amplifiers?
- Easier and more tolerant designs
- Higher operating temperatures
- Removal of DC-DC converters (voltage versus
current) - Ruggedness
- Wider Band Designs
- Smaller Units
34Wide Bandgap is an Enabling Technology
- Wide Bandgap can provide a paradigm shift in the
4G infrastructure sector - Allows Tower Top Installations lowers power
requirements by at least a factor of 2 by
eliminating cable losses - Fan-less Operation will be possible enabled by
higher transistor operating temperatures - Will make cost-effective Smart Antennas viable
- Integration of SiC with other technologies in
standard Lego modules economies of scale
35Wide Bandgap enables Tower-Top Power Amplifiers
Antenna with Power amplifiers _at_ 48 volts ½ X watts
Antenna ½ X watts
Efficiency 50 x 85 x 30 12 If youre
really lucky!
3dB Loss in Cable
Efficiency 30
Power Amplifiers _at_ 28 volts (X watts)
Conventional
New Approach
36Summary of Features of Wide Bandgap Transistors
- High Power density and high operating voltage
- More convenient impedance levels than Si LDMOS or
GaAs FET - easier and more tolerant design
- broadband amplifiers
- High Temperature Operation
- High Voltage Operation
- allows drain modulation techniques (28 volts avg.
48 volts peak) for increased efficiency - Rugged
37Next Steps?
- Productization
- Customer Education
- Reliability Facts
- Acceptable Dollars/Watt
- Introduction of RFICs
- Nothing we havent been through with other
technologies - WATCH THIS SPACE!