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Mitsubishi, Nokia Bell Labs and UC San Diego Develop ultra-fast GaN Envelope-tracking amplifier


Modulation bandwidth of 80MHz is four times that of other envelope tracking devices

Mitsubishi Electric, Nokia Bell Labs and the Center for Wireless Communications at UC San Diego have developed an ultra-fast GaN envelope-tracking power amplifier (PA)  for next next-generation wireless base stations. 

Believed to be a world first, the PA supports a modulation bandwidth up to 80MHz, which is four times wider than the signals reportedly used in other envelope-tracking power amplifiers. 

Technical details will be presented during the IEEE MTT International Microwave Symposium (IMS) 2017, which will be held in Honolulu, Hawaii, USA from June 4 to 9.

To help meet the demand for increasing wireless capacity, mobile technologies are shifting to next-generation systems that use complex modulated signals with large peak-to-average power ratio (PAPR) and extra-wide modulation bandwidth. This will require power amplifiers to operate most of the time at backed-off power levels that are well below their saturation levels. Generally, power amplifiers achieve high efficiency near their saturation power levels, but significantly degraded efficiency at backed off levels, as in the case of 4G LTE* signals (>6dB PAPR).

Envelope-tracking power amplifiers have been studied extensively as a means to enhance power-amplifier efficiency, but so far the supply-modulator circuit has been the bottleneck limiting modulation bandwidth for advanced wireless communications, such as LTE-Advanced.

The newly developed ultra-fast GaN envelope-tracking power amplifier achieves state-of-art performance thanks in part to Mitsubishi Electric's high-frequency GaN transistor technology and design innovation for the GaN supply-modulator circuit. 

Using Nokia Bell Labs' real-time digital pre-distortion (DPD) system, the power amplifier has demonstrated efficient operation even with 80MHz modulated LTE signals, the world's widest modulation bandwidth for this purpose as of May 19, 2017.

The new GaN envelope-tracking power amplifier uses Mitsubishi Electric high frequency GaN in supply-modulation circuits, which enable high-speed operation. The result is highly efficient amplification of complex signals with modulation bandwidth up to 80MHz. 

The technology achieves a world-class drain efficiency of 41.6 percent in such wide-bandwidth operation, thereby reducing base-station energy consumption while increasing wireless communication speed and capacity.

 Further, the real-time DPD system enables pre-distortion for wideband signals to correct the output signal from the power amplifier, resulting in an adjacent channel leakage ratio (ACLR) of -45dBc for LTE 80MHz signals, which satisfies the wireless communication standards. In view of its leading system-level performance, the new envelope-tracking power amplifier is believed to be a highly promising candidate for next-generation wireless base stations. 

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