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["Ramsey, Douglas" <>]

UCSD NEWS RELEASE

 

Media Contact: Doug Ramsey, (858) 822-5825, 

 
<mailto:>
  

 

UCSD Researchers Report World Record Efficiency for High-Power Amplifiers for 
Cellular Base Stations

 

San Diego and Palm Spring, CA, October 31, 2005 - Wireless base stations are 
only as good as the amplifiers that extend their range to provide coverage 
for cell-phone users. Yet efficiency is typically only 10 percent for 
high-power amplifiers used in the base stations of third-generation wireless 
systems, which means they require ten times more power than they generate. 
Now engineers at the University of California, San Diego and industry 
collaborators have achieved greater than 50 percent efficiency-a record which 
could foretell more powerful base stations.

 

The record was announced today at the 2005 Compound Semiconductor IC 
Symposium in Palm Springs.

 

"Using our device we achieved more power with less heat, while maintaining 
better gain," said Don Kimball, principal development engineer in the 
California Institute for Telecommunications and Information Technology 
(Calit2) at UCSD. "This technology could also boost the life span of base 
stations, which are designed to last ten years but often last less than 
three."

 

The 50.7 percent power added efficiency (PAE) is believed to be the best 
efficiency reported for a single stage base station power amplifier. At 50 
percent PAE, 60 watts of output power would require only 120 watts of DC 
power, rather than the 600 watts required by today's high power base stations 
which operate at roughly 10 percent efficiency (although previous studies 
have recorded peak efficiencies of approximately 25 percent).

 

The record was achieved during recent tests in the High-Power Amplifier 
Laboratory of the UCSD Division of Calit2. The research was partly funded by 
Nokia and the UC Discovery Grant program. 

 

Kimball's co-authors on the study include Electrical and Computer Engineering 
professors Peter Asbeck and Larry Larson; UCSD graduate students Paul 
Draxler, Chin Hsia and Jinho Jeong; Nokia's Sandro Lanfranco; as well as 
Kevin Linthicum and Walter Nagy, researchers from Nitronex, the company that 
fabricated the amplifier design.

 

High PAE is a critical factor in thermal management, reliability and cost. 
According to Kimball, the improvement was possible for two principal reasons. 
First, his team used a transistor made of gallium nitride (GaN), one of 
several advanced materials that promise better characteristics than the 
silicon on which most current amplifiers are based. GaN transistors - 
specifically, heterojunction field effect transistors, or HFETs -- can 
provide higher voltage and higher power density than other high power 
'compound' semiconductors based on materials such as gallium arsenide (GaAs), 
indium phosphide (InP), and silicon germanium (SiGe).

 

"These research results will help to cement gallium nitride as the transistor 
of the future for high-powered radio frequency amplifiers," said Kimball, 
lead author on the paper.

 

Secondly, the UCSD amplifier employed a novel architecture based on 'envelope 
tracking,' a technique involving variable power signals, instead of the 
constant feed of DC voltage that is common in high-power amplifiers. The 
technique achieves both efficiency and high linearity.

 

According to their paper*, the researchers found that "the efficiency 
attained in the envelope tracking amplifier is dramatically better than that 
obtained with constant drain voltage, because 1) the amplifier operates 
closer to saturation, 2) the transistor temperature is maintained at a lower 
value, and 3) the dynamic peak voltage reaches higher values than can be used 
for constant drain bias voltages." In short, adjusting the voltage 
dynamically provides superior results as compared to the constant voltage 
employed by most of today's high-power amplifiers.

 

"By combining gallium nitride with this advanced amplifier architecture, it 
is now clear that we can achieve dramatic improvements in base station power 
amplifiers," noted Kimball.

 

The researchers developed a WCDMA base station power amplifier using GaN 
HFETs on silicon substrates and envelope tracking, and demonstrated "very 
high efficiency and precise output performance." The average efficiency of 
50.7 percent accompanied an average output power of 37.2 watts and gain of 10 
decibels (dB). The signal envelope had a peak-to-average power ratio of 7.67 
dB.

 

Today's announcement comes just days after Kimball and his colleagues 
demonstrated the envelope tracking technique during a research exhibit to 
dedicate Calit2's new building on the UCSD campus.

 

At the Palm Springs meeting Nov. 2, Kimball will also participate in a panel 
discussion on "GaN: The Ultimate High Power, High Voltage Reliable 
Basestation PA Technology?"  

 

The IEEE Compound Semiconductor IC Symposium (CSICS) -- formerly the IEEE 
GaAs IC Symposium -- is the preeminent international forum on developments in 
integrated circuits using compound semiconductors.

 

* "50% PAE WCDMA Basestation Amplifier Implemented with GaN HFETs", Don 
Kimball, Paul Draxler, Jinho Jeong, Chin Hsia, Sandro Lanfranco, Walter Nagy, 
Kevin Linthicum, Larry Larson and Peter Asbeck. CSICS 2005. 

 

 

Related Links

 

Compound Semiconductor IC Symposium http://www.csics.org/ 
<https://exchange-jsoe.ucsd.edu/exchweb/bin/redir.asp?URL=http://www.csics.org/>
 

Don Kimball Profile 
http://www.calit2.net/people/features/1-30-03_kimball.html 
<http://www.calit2.net/people/features/1-30-03_kimball.html>