This text gives an overview of critical technology challenges for high efficiency power amplifiers used in future mobile broadband systems. Implementation aspects of efficient wideband multi-band transmitters are discussed. Simulations of and design implications for a multi-band 1.8-2.7 GHz high efficiency power amplifier using GaN transistors are presented. Finally possible transmitter architectures with potential of meeting ambitious efficiency, flexibility and frequency range goals are briefly analyzed.

In this paper, we discuss a load-pull analysis technique to charaterize the efficiency performance of class-E amplifier in an outphasing power combining scheme. Class-E amplifier has the potential to deliver high efficiency. Class-E amplifier is not an ideal current or voltage source as is required for the traditional analysis of outphasing structures. It requires a phase modulated input signal and has a non-linear transfer characteristic which is a function of load impedance. Here we define an operating load locus based on the load-pull analysis which can be used to predict the non-linear transfer function, efficiency, output power, input drive phase and many other factors associated with the outphasing class-E amplifier. This scheme could also be used to characterize any amplifier class in an outphasing structure.

In this article, two class D -1 amplifiers is presented, both implemented with GaN MESFETs and working around 900 MHz, delivering 20.7/51.1 W output power with 75/78% peak drain-efficiency. A simple nonlinear model optimized for switched mode operation is developed from basic device data, and is used to predict intrinsic current and voltage waveforms during the design process. In general, very good agreement between modeled and simulated data is obtained considering the limited amount of parasitic parameters covered by the device model.

The efficiency performance of a Class E amplifier and its anti-parallel diode derivative are compared for two different operational modes, pulse width modulation (PWM) and load modulation. The effect of modulated signals is investigated. The anti-parallel diode proved effective in doubling the efficiency of the load modulation method, but this still did not surpass the efficiency of the traditional PWM mode of operation where an efficiency of 45% was indicated for a 8 dB peak to average Rayleigh enveloped signal