A High-Performance GaN-Modified Nonuniform Distributed Power Amplifier

Abstract

This article proposes a modified nonuniform distributed power amplifier (NDPA) design to increase the output power and power-added efficiency (PAE) in wideband. In the proposed NDPA, drain-line impedances are recalculated, including the drain-source capacitances, which cannot be ignored as the transistor size becomes larger at high frequencies. In addition, instead of using a large-sized transistor in the first section of the NDPA, the design proposes a method of halving the characteristic impedance by doubling the phase of the drain line. When compared with the conventional NDPA, the modified NDPA shows the power gain and output power characteristics close to those of the ideal NDPA. To obtain high efficiency in the NDPA, a programmable gate-line termination resistance switching technique (PGT) is proposed. The power gain is increased by using the standing wave generated from the mismatched termination, enhancing the PAE. For design verification, two modified NDPA monolithic microwave integrated circuits (MMICs) were fabricated using a commercial 0.25-μm gallium nitride (GaN) high-electron-mobility transistor (HEMT) process. The two-way power-combined NDPA shows an average output power of 20 W or more and a power density of 1.9 W/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> from 6 to 18 GHz. The NDPA using the proposed PGT accomplishes an average output power of 10 W and an average PAE of 20% or more from 6 to 18 GHz.