Date:13th Dec 2011
RFHIC licenses doherty amplifier patents
Cree, Inc. has licensed its Doherty amplifier-related patents
to RF amplifier maker RFHIC. Cree says its RF innovation
and novel Doherty architecture can serve as the foundation
for advanced 4G base stations that are substantially more
efficient than conventional designs.
"Cree is a leader in the development of GaN HEMT technology
for RF and microwave applications," said Jim Milligan,
Cree, director of RF. "From our early work in maximizing
the efficiency of silicon LDMOS amplifiers to our current
initiatives using GaN-based devices, Cree has successfully
developed innovative circuits that enhance the performance
of the classic Doherty architecture."
Cree claims With its advanced circuits, amplifier efficiency
can be increased by as much as five percentage points when
conventional silicon LDMOS or GaAs transistors are used
to meet the stringent efficiency and linearity requirements
of upcoming 4G LTE base stations, and related wireless systems,
that use high peak-to-average ratio signal modulation. When
these circuit innovations are implemented using Cree's high-frequency,
high-power GaN HEMTs and the latest generation digital pre-distortion
systems, the resulting efficiency improvements can be up
to a staggering 15 percentage points greater than that achieved
by a conventional Doherty amplifier implemented with silicon
LDMOS, as per Cree.
The Doherty amplifier is a fundamental RF amplifier architecture
invented by William Doherty in 1936 using vacuum tubes.
Modern implementations of the Doherty amplifier use power
transistors. The fundamental Doherty architecture uses two
parallel, equal power split transistors, a carrier amplifier
transistor for low level signals and a peaking amplifier
transistor for high level signals. The fundamental, equal
power split Doherty architecture offers up to a 40 percent
improvement in efficiency over traditional non-Doherty Class
A/B approaches. Interest in Doherty amplifiers has grown
with increased demand for higher-efficiency systems employing
digital modulation formats, such as those used for 3G W-CDMA
networks. Online applications including video chat and streaming
video are driving a need for still higher-efficiency amplifiers
to support 4G LTE systems.
"Cree innovations in Doherty amplifier technology
can set the standard for the newest generation of 4G network
deployments requiring high-efficiency macro and pico cell
base stations. Cree's advancements on the fundamental two-transistor,
parallel Doherty architecture can yield significant efficiency
improvements," Milligan added.