Mitsubishi Electric, Nokia Bell Labs and the Center for Wireless Communications at UC San Diego have announced the joint development of what is claimed as the first ultra-fast gallium nitride (GaN) envelope-tracking power amplifier, offering support for modulation bandwidth up to 80 MHz and designed to reduce power consumption in next-generation wireless base stations.
To companies explained that to address demand for greater wireless capacity, mobile technologies are adopting systems that use complex modulated signals with high peak-to-average power ratio (PAPR) and extra-wide modulation bandwidth. This requires power amplifiers to often operate at backed-off power levels below their saturation levels, while power amplifiers are typically efficient near to their saturation power level and not at backed off levels, as with 4G LTE signals (>6 dB PAPR).
As a result, envelope-tracking power amplifiers have been evaluated as a means to enhance power-amplifier efficiency, although to date the supply-modulator circuit has proved a bottleneck limiting modulation bandwidth for advanced wireless communications, such as LTE-Advanced.
The newly-developed ultra-fast GaN envelope-tracking power amplifier delivers high performance leveraging Mitsubishi Electric’s high-frequency GaN transistor technology and its design for the GaN supply-modulator circuit. Utilising Nokia Bell Labs’ real-time digital pre-distortion (DPD) system, the power amplifier has demonstrated efficient operation, including with 80 MHz modulated LTE signals.
The partners claim that this represents the widest modulation bandwidth achieved for this application to date, and is around four times higher than signals used in other envelope-tracking power amplifiers. In addition, the technology delivers a drain efficiency of 41.6% in this wide-bandwidth operation, helping to reduce base-station energy consumption as well as increase wireless communication speed and capacity.
Additionally, the Nokia Bell Labs’ 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 -45 dBc for LTE 80 MHz signals, which is compatible with wireless communication standards.
Specifications of the GaN envelope-tracking power amplifier include: support for carrier frequency of 0.9 to 2.15 GHz; output power of 30.0-30.7 dBm; drain efficiency of 36.5-41.6%; ACLR of -45 dBc; and modulation signal of 80 MHz LTE Advanced with 6.5 dB PAPR.
The University of California, San Diego, is a leading university for mixed-signal, microwave and mmWave RFICs, digital communications, applied electromagnetics, RF MEMS and nano-electronics research and hosts the Center for Wireless Communications (CWC), is a university-industry partnership that includes Mitsubishi Electric and Nokia.
