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18 August 2006


NEC develops 400W GaN amplifier for 3G base-stations

Japan's NEC Corp has developed a compact, single-ended GaN power transistor amplifier with peak output power of 400W (at 2.14GHz), together with low-distortion characteristics, for 3G W-CDMA base-stations. The amplifier
is composed of a single transistor package, which achieves what NEC claims is record power output amplification under a W-CDMA scheme, without using any power-combining circuits.

High output power density under high-current (1A/mm) and high-voltage (45V) operation is due to NEC's proprietary field-plate-modulation technology, which reduces the electric field strength at the gate edge, leading to
improved breakdown voltage. Also, newly developed output bias networks inside the amplifier suppress its memory effect, achieving excellent linearity with a digital pre-distorter inside. At average output power of 60W, third-order intermodulation distortion is -50dBc and drain efficiency is 25%.

The need to achieve a large-capacity and high-speed system is becoming more crucial with the rapid increase in traffic accompanying the growing number of 3G mobile subscribers and increasingly sophisticated and diversified 3G services worldwide, says NEC. For such a system, a power amplifier with higher output power and high linearity for 3G base-stations is vital. For the above purposes, the amplifier also needs to realize energy savings and compact size. Conventional amplifiers composed of silicon LDMOS transistors or GaAs transistors require power-combining circuits due to the small output power of each transistor, so the amplifier is larger and there is increased power loss. These factors make it difficult to achieve a high output power amplifier with compact size and high efficiency, says NEC.

The research has been carried out as part of the 'High-Power, High-Frequency Gallium Nitride Device Project' (led by Ritsumeikan University's professor Yasushi Nanishi) of the Research and Development Association for Future
Electron Devices (FED), supported by the New Energy and Industrial Technology Development Organization (NEDO). The project comprises researchers from nine organizations, including NEC, Toyoda Gosei Co Ltd (which supplied the GaN epiwafers), Ritsumeikan University and the National
Institute of Advanced Industrial Science and Technology (AIST). Begun in 2002, the project is scheduled to end in 2007.

NEC says that the research result will play an important role in increasing output power, as well as downsizing and energy savings of base-station amplifiers for 3G and beyond. To this end, NEC will continue to carry out
aggressive R&D of the technology toward its early commercialization toward the end of 2008.

Visit: http://www.nec.co.jp