“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. 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.
The nonexclusive license agreement between RFHIC, headquartered in Suwon, South Korea, and Cree underscores each company’s commitment to developing products that enhance the telecommunications infrastructure, while respecting the value and importance of intellectual property.