Design of an S-Band Chireix Outphasing Power Amplifier Based on a Systematic Bandwidth Limitation Analysis

Abstract

This work aims at assessing the factors that limit the bandwidth of a dual input Chireix outphasing PA based on a packaged commercial GaN device. To evaluate the effects of device parasitics, compensation elements and power combiner on the bandwidth we consider several output sections of increasing complexity. Their input impedances, at the back-off level of interest, are evaluated and referred to that of the ideal, frequency independent case. The comparison of the analyzed output sections reveals that the device parasitics limit the amplifier bandwidth more than output power combiner and compensation elements. Based on such conclusion, a dual input hybrid Chireix PA for LTE operation is designed and optimized for best efficiency at 7 dB back-off in the 3.1–3.7 GHz range. Measurements report back-off drain efficiency and PAE of 50% and 41% at center frequency, and performance within 10% of the maximum is maintained over more than 200 MHz.