Linearity Enhanced Harmonic-Modulated Impedance Inverter Doherty-Like Power Amplifier

Abstract

In a conventional Doherty Power Amplifier (DPA), harmonic isolation is typically required between the two transistors to prevent them from modulating each other at harmonic frequencies. Normally, the current is clipped at saturation, which results in poor in-band non-linearity, e.g. IMD3. Hence, mutual harmonic interaction is desirable when properly used to prevent current clipping in the active devices, thus improving linearity. In this paper, for the first time, a linearity enhancement technique for Doherty-like power amplifier (DLPA) based on harmonic interaction is presented. The proposed DLPA achieves an excellent trade-off between efficiency and in-band linearity. For demonstration purposes, a DLPA prototype is devised based on two identical 6-Watts gallium nitride HEMTs (CGH 40006P). Within the frequency band of 1.75 to 2.45 GHz, the DLPA achieves a measured power added efficiency (PAE) of greater than 45.0% and 61.9% at 6 dB output back-off and saturation, respectively. An IMD3 below −30 dBc and a PAE of greater than 53% is achieved near saturation under a two-tone signal excitation.