Look-up table method for optimising coupling ratio in broadband sequential power amplifiers

• Published in: IET microwaves, antennas & propagation antennas & propagation, 2020-10, Vol.14 (13), p.1626-1634
• Main Authors: Chen, Peng, Quaglia, Roberto, Lees, Jonathan, Merrick, Brian M, Alt, Alexander, Tasker, Paul J
• Format: Article
• Language: English
• Subjects: adjacent channel leakage ratio levels; broadband sequential power amplifiers; digital predistortion; directional couplers; drain efficiency; error vector magnitude; frequency 1.5 GHz to 2.4 GHz; frequency 20.0 MHz; high‐efficiency SPA design; key design parameters; look‐up table method; LTE signal; main peaking amplifiers; modified efficiency formulation; optimising coupling ratio; optimum design parameters; phase relationship; relative phase difference; required coupling ratio; Research Article; sequential power amplifier; SPA efficiency; table lookup; UHF power amplifiers; wideband amplifiers; wideband directional coupler
• ISSN: 1751-8725; 1751-8733
• DOI: 10.1049/iet-map.2019.1102

This study reappraises the optimum design parameters for the sequential power amplifier (SPA) when taking relative phase difference into account. By including the phase relationship between the main and peaking amplifiers, a modified efficiency formulation is derived that reveals the impacts of the key design parameters on the SPA efficiency at output power back-off. To optimise a wideband high-efficiency SPA design, a look-up table method is used to predict the required coupling ratio for a wideband directional coupler. To validate the design approach, a 1.5–2.4 GHz SPA is designed and measured, showing drain efficiency higher than 40% at 6 dB back-off across the band. When characterised using a 20 MHz long term evolution (LTE) signal and digital predistortion, the SPA shows good linearity with error vector magnitude