World's First Ultra-Fast GaN Envelope-Tracking PA for Next-Gen Wireless Base Stations

Mitsubishi, Nokia Bell Labs and the Center for Wireless Communications at UC San Diego have together developed the world’s first ultra-fast gallium nitride (GaN) envelope-tracking power amplifier. The amplifier supports a modulation bandwidth up to 80 MHz and is expected to reduce energy consumption in next-generation wireless base stations. 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 ratios (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 (more than 6 dB 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 because of 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 80 MHz modulated LTE signals. This is four times wider than the signals reportedly used in other envelope-tracking power amplifiers. The technology achieves a world-class drain efficiency of 41.6% 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 80 MHz signals, which satisfies the wireless communication standards. This new envelope-tracking power amplifier is believed to be a highly promising candidate for next-generation wireless base stations.