Mitsubishi Electric, Nokia Bell Labs, UCSD develop first ultra-fast GaN envelope-tracking power amplifier for next-gen wireless base stations

Tokyo-based Mitsubishi Electric Corp, Nokia Bell Labs and the Center for Wireless Communications at University California San Diego (UCSD) have announced their joint development of what is claimed to be the first ultra-fast gallium nitride (GaN) envelope-tracking power amplifier, which supports modulation bandwidth up to 80MHz 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 in Honolulu, Hawaii, USA (4-9 June).

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 (PAE), 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 what is said to be state-of-art performance due in part to Mitsubishi Electric’s high-frequency GaN transistor technology and design innovation for the GaN supply-modulator circuits (which enable high-speed operation). 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, it is claimed – four times wider than the signals used in other envelope-tracking power amplifiers).

The technology achieves a drain efficiency of 41.6% in such wide-bandwidth operation, 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.