NEC develops Gallium Nitride transistor amplifier for 3G base stations

August 21, 2006

NEC announced the successful development of a compact gallium nitride (GaN) power transistor amplifier, which boasts the world's highest output power level of 400W while featuring low-distortion characteristics, for 3G base stations. This amplifier is composed of a single transistor package, which achieves the world's greatest power output amplification under a W-CDMA scheme, without using any power-combining circuits. This research has been carried out under the "High-Power, High-Frequency Gallium Nitride Device Project" (Project leader: Professor Yasushi Nanishi of Ritsumeikan University) of the Research and Development Association for Future Electron Devices (FED) that is supported by the New Energy and Industrial Technology Development Organization (NEDO).

The features of the newly developed GaN amplifier are as follows:

-- The GaN power transistor achieves high output power density under high-current (1A/mm) and high voltage (45V) operation owing to NEC's proprietary field-modulating plate technology.

-- The single-ended GaN power amplifier boasting a compact configuration decreases the number of assembled RF components.

-- Newly developed output bias networks inside the amplifier suppress the memory effect of the amplifier, thereby achieving excellent linearity with a digital predistorter placed within.

The need to achieve a large-capacity and high-speed system is becoming more crucial with the rapid increase in traffic accompanying the swelling number of 3G mobile subscribers and increasingly sophisticated and diversified 3G services worldwide. To achieve 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 gallium arsenide (GaAs) transistors require power-combining circuits due to the small output power of each transistor. As a result, the amplifier is larger in size and there is an increased loss in power. These factors make it difficult to achieve a high output power amplifier with compact size and high efficiency.

The features of the newly developed power amplifier for 3G base stations include:

-- Single-ended GaN amplifier with a digital predistorter for W-CDMA base stations

-- Operation voltage: 45 Volts

-- Peak output power of W-CDMA signal: 400W (2.14 GHz)

-- Third order intermodulation distortion -50 dBc (At average output power of over 60W).

-- Drain efficiency: 25% (At average output power of 60W)

Undoubtedly, this new research result will play an important role in increasing output power, as well as downsizing and energy savings of base station amplifiers for the third generation and beyond. To this end, NEC will continue to carry out aggressive research and development of the technology toward its early commercialization aimed at toward the end of 2008.

The transistors used for this amplifier are made on a GaN epitaxial wafer, which was developed under the NEDO "High-Power, High-Frequency Gallium Nitride Device Project," and manufactured by Toyoda Gosei.