Ultra-Fast GaN Envelope Tracking PA for Next-Gen Wireless Base Stations

Mitsubishi Electric Corporation, Nokia Bell Labs and the Center for Wireless Communications at UC San Diego announced their joint development of the world’s first ultra-fast GaN envelope tracking (ET) power amplifier, which supports modulation bandwidth up to 80 MHz and will reduce energy consumption in next-generation wireless base stations.

To help meet the demand for increasing wireless capacity, mobile technologies are shifting to complex modulated signals with large peak-to-average power ratio (PAPR) and wide modulation bandwidth. This requires that power amplifiers operate most of the time at backed-off power levels, well below saturation. Generally, power amplifiers achieve high efficiency near saturation, with significantly degraded efficiency when backed off. ET power amplifiers have been studied extensively, as a means to enhance power amplifier efficiency, but the supply modulator circuit has been the bottleneck limiting modulation bandwidth for advanced wireless communications (e.g., LTE-Advanced).

The newly developed ultra-fast GaN ET power amplifier achieves state-of-art performance by using Mitsubishi Electric’s GaN transistor technology and design innovation for the GaN supply modulator circuit. Using Nokia Bell Labs’ real-time digital predistortion (DPD) system, the bias-controlled power amplifier has demonstrated efficient operation even with 80 MHz modulated LTE signals.

Key Features

The new GaN ET power amplifier uses Mitsubishi Electric high frequency GaN in the supply modulation circuits, which enables high speed operation. The result is highly efficient amplification of complex signals with modulation bandwidth up to 80 MHz, 4x wider than the signals reported in other ET power amplifiers. The technology achieves a drain efficiency of 41.6 percent in wide bandwidth operation, which reduces base station energy consumption.

The real-time DPD system enables predistortion for wideband signals, correcting the output signal from the power amplifier and resulting in an adjacent channel leakage ratio (ACLR) of −45 dBc for 80 MHz LTE signals; this satisfies wireless communication standards.

Specifications

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