A novel formulation for the voltage waveforms in high efficiency linear power amplifiers is described. This formulation demonstrates that a constant optimum efficiency and output power can be obtained over a continuum of solutions by utilizing appropriate harmonic reactive impedance terminations. A specific example is confirmed experimentally. This new formulation has some important implications for the possibility of realizing broadband >10% high efficiency linear RF power amplifiers.

The design and implementation of a class-J mode RF power amplifier is described. The experimental results indicate the class-J mode's potential in achieving high efficiency across extensive bandwidth, while maintaining predistortable levels of linearity. A commercially available 10 W GaN (gallium nitride) high electron mobility transistor device was used in this investigation, together with a combination of high power waveform measurements, active harmonic load-pull and theoretical analysis of the class-J mode. Targeting a working bandwidth of 1.5-2.5 GHz an initial power amplifier (PA) design was based on basic class-J theory and computer-aided design simulation. This realized a 50% bandwidth with measured drain efficiency of 60%-70%. A second PA design iteration has realized near-rated output power of 39 dBm and improved efficiency beyond the original 2.5 GHz target, hence extending efficient PA operation across a bandwidth of 1.4-2.6 GHz, centered at 2 GHz. This second iteration made extensive use of active harmonic load-pull and waveform measurements, and incorporated a novel design methodology for achieving predistortable linearity. The class-J amplifier has been found to be more realizable than conventional class-AB modes, with a better compromise between power and efficiency tradeoffs over a substantial RF bandwidth.

The paper presents the power amplifier design. The introduction of a practical harmonic balance capability at the device measurement stage brings a number of advantages and challenges. Breaking down this traditional barrier means that the test-bench engineer needs to become more aware of the design process and requirements. The inverse is also true, as the measurement specifications for a harmonically tuned amplifier are a bit more complex than just the measurement of load-pull contours. We hope that the new level of integration between both will also result in better exchanges between both sides and go beyond showing either very accurate, highly tuned device models, or using the device model as the traditional scapegoat for unsuccessful PA designs. A nonlinear model and its quality can now be diagnosed through direct comparison of simulated and measured wave forms. The quality of a PA design can be verified by placing the device within the measurement system, practical harmonic balance emulator into the same impedance state in which it will operate in the actual realized design.

The extended continuous class-F mode RF power amplifier (PA) is presented for the first time. The introduction and experimental validation of this novel PA mode demonstrates a new design space over a wide band of frequencies. This paper will show that high output power and drain efficiency, equivalent to the class-F mode, can be maintained by varying the reactive components of fundamental and second harmonic impedances in accordance with the new formulation of the voltage waveform. Additionally it will be shown that, by varying both phase and magnitude of the fundamental and second harmonic impedances, a yet wider design space can be achieved, where the efficiency is maintained at a level greater than a certain target value. For the validation of this new theory, an experimental investigation was carried out on GaAs pseudomorphic HEMT devices and demonstrates that high output power and drain efficiency between 75%-83% can be achieved over a wide range of fundamental and second harmonic loads.

In this paper, an extended version of the continuous class-F^-1 mode power amplifier (PA) design approach is presented. A new formulation describing the current waveform in terms of just two additional parameters, while maintaining a constant half-wave rectified sinusoidal voltage waveform, allows multiple solutions of fundamental and second-harmonic impedances that provide optimum performance to be computed. By varying only the imaginary parts of fundamental and second-harmonic impedances, it is shown that output performance in terms of power and efficiency is maintained constant and equal to that achievable from the standard class-F^-1 . Indeed, when presenting resistive second-harmonic impedances, it will be demonstrated that the fundamental load can be adjusted to maintain satisfactory output performances greater than a certain predetermined target value. The measurements, conducted on a GaAs pHEMT device at 1 GHz, show a good agreement with the theoretical analysis, revealing drain efficiencies greater than 70% for a very large range of load solutions, which can translate to an ability to accommodate reactive impedance variations with frequency when designing broadband PAs.

This paper presents a comprehensive study on the effective utilization of large-signal measurement data in the nonlinear computer-aided design (CAD) process. To achieve this goal two distinctive, yet mutually complementary, approaches have been integrated. Measured nonlinear data was, in the first instance, directly integrated into a nonlinear CAD simulator, and in the second instance, utilized for a direct extraction of behavioral model parameters. The formulation of the developed model is based on the polyharmonic distortion approach. The combination of both the direct utilization of nonlinear data and the subsequent model generation into an integrated nonlinear design procedure offers rapid, yet reliable, deployment of the CAD-based design environment for complex large-signal simulations.