Investigation of Input-Output Waveform Engineered High-Efficiency Broadband Class B/J Power Amplifier

Abstract

This work introduces a new broadband Class B/J power amplifier (PA) design methodology by considering the input-output waveform shaping due to nonlinear CGS-VGS profile in gallium nitride (GaN) radio frequency (RF) devices. A comprehensive time domain modeling of drain voltage and drain current as a function of input nonlinearity is presented to predict continuous Class B/J PA performance. The proposed theory shows that continuous-mode operation can no longer maintain constant PA performance with varying fundamental and second harmonic impedances as predicted by the ideal class-J theory. This paper demonstrates that continuous-mode class B/J operation with input-output waveform shaping yields a new design space with two distinct regions: one advantageous region with capacitive second harmonic load terminations in which PA performance can be enhanced significantly; and another within an inductive second harmonic load area where the performance is degraded compared to that of a classical class B/J PA. For practical validation, source pull measurements and load pull analyses are presented and a broadband Class B/J PA is designed with the proposed second harmonic load and source termination. Source/Load-pull measurements/simulations confirm the theoretical predictions in terms of performance variation across the design space. A high efficiency design space is then identified for broadband PA design. The PA protype demonstrates drain efficiency of (60-73) % with output power above 40 dBm and corrected adjacent channel power ratio (ACPR) better than -55 dBc with digital predistortion (DPD) using 10 MHz LTE signal across (2.2-3.4) GHz.