Recent Developments of Dual-Band Doherty Power Amplifiers for Upcoming Mobile Communications Systems

Power amplifiers in modern and future communications should be able to handle different modulation standards at different frequency bands, and in addition, to be compatible with the previous generations. This paper reviews the recent design techniques that have been used to operate dual-band amplifiers and in particular the Doherty amplifiers. Special attention is focused on the design methodologies used for power splitters, phase compensation networks, impedance inverter networks and impedance transformer networks of such power amplifier. The most important materials of the dual-band Doherty amplifier are highlighted and surveyed. The main problems and challenges covering dual-band design concepts are presented and discussed. In addition, improvement techniques to enhance such operations are also exploited. The study shows that the transistor parasitic has a great impact in the design of a dual-band amplifier, and reduction of the transforming ratio of the inverter simplifies the dual-band design. The offset line can be functionally replaced by a Π-network in dual-band design rather than T-network

Doherty Power Amplifier for LTE-Advanced Systems

The design and implementation of an asymmetrical Doherty power amplifier are discussed, where two Cree GaN High Electron Mobility Transistors (HEMTs) devices are used for designing an asymmetrical Doherty power amplifier to achieve saturated power of 48 dBm and optimal back-off efficiency of 8 dB in the frequency band of 3.3–3.5 GHz. Rogers RO4350B material is used as a substrate material, a back-off of 8 dB was achieved with an average gain of 10 dB. Load-pull data are an important tool for determining the optimum load impedance that the transistor needs to see. Additionally, the measured efficiency was 50% when the designed amplifier was tested by a modulated signal of 8 dB peak-to-average-power ratio when the average output power was 40 dBm. At the same time, the linearity of the designed amplifier was measured and found 31.8 dB which can be improved using a digital pre-distorter. The gain phase measurement can be used as an indicator for compensating the phase difference between the two cells

Green and Highly Efficient MIMO Transceiver System for 5G Heterogenous Networks

The paper presents the general requirements and an exemplary design of the RF front-end system that in today’s handset is a key consumer of power. The design is required to minimize the carbon footprint in mobile handsets devices, whilst facilitating cooperation, and providing the energy-efficient operation of multi-standards for 5G communications. It provides the basis of hardware solutions for RF front-end integration challenges and offers design features covering energy efficiency for power amplifiers (PAs), Internet of Things (IoT) controlled tunable filters and compact highly isolated multiple-input and multiple-output (MIMO) antennas. An optimum design requires synergetic collaboration between academic institutions and industry in order to satisfy the key requirements of sub-6 GHz energy-efficient 5G transceivers, incorporating energy efficiency, good linearity and the potential for low-cost manufacturing. A highly integrated RF transceiver was designed and implemented to transmit and receive a picture using compact MIMO antennas integrated with efficient tunable filters and high linearity PAs. The proposed system has achieved a bit error rate (BER) of less than 10–10 at a data rate of 600 Mb/s with a wireless communication distance of more than 1 meter and power dissipation of 18–20 mW using hybrid beamforming technology and 64-QAM modulation

Load‐modulation technique without using quarter‐wavelength transmission line

A proposed method for achieving active load-modulation technique without using a quarter-wavelength transmission line is discussed and evaluated. The theoretical analysis shows that the active load-modulation can be achieved without using a quarter-wavelength line, where the main amplifier sees a low impedance when the input signal level is low, and this impedance increases in proportion to the amount of current contributed from the peaking amplifier. The peaking amplifier sees an impedance decreasing from infinity to the normalized impedance. To validate the method, a circuit was designed, simulated and fabricated using two symmetrical gallium nitride (GaN) transistors (6 W) to achieve a peak power of 12 W and 6 dB output back-off efficiency. The design operates with 400 MHz bandwidth at 3.6 GHz and showed an average efficiency of 50% at 6 dB back-off and an efficiency of 75% at peak power. The designed circuit was tested with CW and modulated signals, the amplifier showed an Adjacent Channel Power Ratio (ACPR) of 31–35.5 dB when tested with a wideband code division multiple access signal of 6 dB peak-average-power ratio (PAPR) at 35.5 dBm average power. Additional 20 dB of linearity improvement was achieved after adding a lineariser