An Ultrawideband Back-Off Efficiency-Enhanced Power Amplifier Utilizing In-Band Mode Transition Between Switchless Class-G and Doherty

This article proposes a novel theory that overcomes the fundamental bandwidth limitations caused by matching network phase shifts in traditional load-modulated power amplifiers (PAs). It begins with a rigorous analysis demonstrating that seamless PA operation transition can be achieved between the switchless Class-G and Doherty modes when the PA main-path phase shift varies with frequency. This consequently allows the proposed PA to deliver optimal back-off efficiency under any phase shift condition while maintaining constant saturation power ( $P_{\mathbf {sat}}$ ) and output back-off (OBO) performances, effectively eliminating bandwidth constraints due to network phase shifts. The proposed theory then guides the development of an ultrawideband PA operating from 0.6 to 3.6 GHz. Continuous-wave measurement reveals that the proposed PA delivers $P_{\mathbf {sat}}$ of 38.7–40.2 dBm and drain efficiency (DE) of 40%–57% and 44%–57% at 7.5- and 6-dB OBO power, respectively, across the entire 0.6–3.6-GHz range. Furthermore, under a 40-MHz 256-QAM signal with a peak-to-average power ratio of 7.5 dB, the PA demonstrates a strong average DE of 38%–50% and good linearizability with an error vector magnitude (EVM) below 1.1% and adjacent channel power ratio (ACPR) better than −45 dBc after digital predistortion.