Analysis and Design of RF-Input Doherty-Like Circulator Load Modulated Amplifier

Paper in proceeding, 2024

This paper introduces the design and analysis of an RF-input circulator load-modulated amplifier (CLMA), with Doherty-like operation and efficiency enhancement. The performance of the proposed architecture has been analyzed thoroughly for varying levels of isolation and loss. A detailed
design methodology for the RF-input CLMA prototype is provided. To demonstrate the concept’s viability, a prototype CLMA employing GaN HEMT transistors and a commercially available surface mount (SMT) circulator is constructed. Experimental results exhibit a peak and back-off output power
drain efficiency of 57% and 53%, respectively, with an output power of 42.3 dBm at 3.4 GHz. When tested with a 20-MHz orthogonal frequency division multiplexing (OFDM) signal, characterized by a peak-to-average power ratio (PAPR) of 7 dB, the prototype circuit exhibits an average efficiency of 51%, with an adjacent channel leakage ratio (ACLR) better than -51.6 dBc after applying digital pre-distortion (DPD). To the best of our knowledge, this is the first RF-input Doherty-like CLMA with a SMT circulator.