Cree, Inc. (Nasdaq: CREE) today announced a nonexclusive worldwide
license agreement with RFHIC Corporation, a global leader in
cutting-edge RF power amplifiers, that provides access to Cree's
pioneering Doherty amplifier-related patents. Cree's RF innovation and
novel Doherty architecture can serve as the foundation for advanced 4G
base stations that are substantially more efficient than conventional
designs. 4G mobile data networks are being deployed around the world to
address the burgeoning demand for mobile broadband services.
"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."
With Cree's advanced circuits, amplifier efficiency can be increased by
as much as five percentage points when conventional silicon LDMOS or
GaAs transistors are used. This improved performance can help 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.
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.