Chireix power combining with saturated class-B power amplifiers

This paper describes the realization of a Chireix power combining part of an outphasing system for 2.14 GHz consisting of two saturated class-B power amplifiers and a Chirelx power combiner circuit. The Chireix power combining scheme can be used in Chireix outphasing architecture, wbich is currently together with EER and the Doherty amplifier one of the most prominent research topics in power amplifier linearization I efficiency enhancement area. In an outphasing system, also known as LlNC (Linear Amplification of Nonlinear Components), an amplitude and phase modulated signal is separated into two constant envelope signals containing only phase modulation. The original signal waveform can subsequently be reconstructed by varying the phases of the two constant envelope signal branches, thus enabling, ideally, linear amplification of the original signal with system eff'ciency comparable to the efficiency of the used PAS. In this paper, the design and implementation as well as the measurement results of a microstrip-liue Chireixcombiner together with saturated class-B pHEMT power amplifiers for WCDMA downlink band 2.11-2.17 GHz are reported. The measurement results verify that the concept is indeed functional, and significant efficiency improvement over traditional power combining can be attained. At peak envelope power 37.4 dBm system efficiency of 77 % was measured, and at 4 dB back-off, representing the computational average point for WCDMA signal, system efiiciency of 43 % was measured.