Awayday in Bath for high efficiency WiMAX power design

Bath is the centre for the UK’s latest basestation conference which is taking place this week, and among the early movers at the event are Nitronex, a GaN-on-Silicon RF power IC specialist and Nujira who are teaming up to create a WiMAX power amplifier reference design. The interesting point about this is the choice of GaN technology which should help the power efficiency which can be an issue with WiMAX transmissions. NEC first showed a gallium nitride (GaN) power transistor amplifier in 2006, which it claimed had the world’s highest output power level of 400W with low-distortion characteristics. According to the companies, using a 4 channel WCDMA waveform it has been possible to realise over 44dBm of linear power with 45% efficiency at a linearity of -55dBC.

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. “We believe that GaN devices will most clearly establish their value when combined with advanced power amplifier techniques such as offered by Nujira,” said Chris Rauh, v-p of marketing and sales at Nitronex. Nujira has perfected a RF tracking technology called High Accuracy Tracking (HAT) which has the potential to improve the efficiency of power amplifiers in basestation design. Its aim is to reach 50% efficiency. This latest collaboration goes a long way towards that goal. “Our reference design work with Nitronex very effectively demonstrates how well our technology works in a real circuit,” said Nujira v-p strategy & marketing Julian Hildersley. In a demonstration which was pretty close to real-world conditions, the amplifier achieved 43.2dBm of linear power with 43% efficiency under a WiMAX waveform with 20MHz video bandwidth and 8.2dB PAR. The same power module can equally well be applied to WiMax, WCDMA or even DVB and other transmission. The technology will be available in 3Q08.

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