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UCSD News: Better Amplifier Technology Could Mean Stronger Signals and Wider Coverage for Cell Phone Networks

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  • From: "Ramsey, Douglas" <>
  • To: <>
  • Subject: UCSD News: Better Amplifier Technology Could Mean Stronger Signals and Wider Coverage for Cell Phone Networks
  • Date: Mon, 31 Oct 2005 12:50:01 -0800


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


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

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

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

Don Kimball Profile

  • UCSD News: Better Amplifier Technology Could Mean Stronger Signals and Wider Coverage for Cell Phone Networks, Ramsey, Douglas, 10/31/2005

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