Inverted-load network for high-power Doherty amplifier

In this article, a high-power, high-efficiency inverted Doherty power amplifier (PA), having a more compact load network than that of the conventional Doherty amplifier, was designed and implemented for wide-band code-division multiple access (WCDMA) base-station applications. Its configuration and working principle are compared with the conventional Doherty amplifier. For experimental verification, we implemented an inverted Doherty amplifier, using a 190 W peak-envelope-power (PEP) laterally diffused metal-oxide-semiconductor (LDMOS) field-effect transistors (FETs). Using a four-carrier down-link WCDMA signal, we achieved a high power-added efficiency (PAE) of 32% and an average output power level as high as 46.3 dBm at a given adjacent channel leakage ratio (ACLR) level of --30 dBc. This is a 9.5% improvement in efficiency and 1 dB improvement in output power under the same ACLR conditions from those of the balanced class-AB operation using the same devices.

Introduction

High efficiency, high linearity, and compact size are demanded for most wireless communication systems. PAs in the base-transceiver or repeater systems must have ultra-high linearity for communication quality. Some additional circuits or complex control apparatuses are further required to improve the linearity of PAs. In addition, they have to be operated at the backed-off output power levels due to the high peak-to-average ratio (PAR) of the signals used for systems such as WCDMA, WiMAX, and WLAN [1]–[4]. Thus, efficiency is degraded. Numerous efficiency enhancement techniques and methods for PAs have been tried. Among these, the Doherty amplifier has successfully penetrated the market thanks to its higher efficiency and linearity without complex additional circuitry [2]–[6].