A Broadband Asymmetrical Doherty Power Amplifier With Optimized Continuous Mode Harmonic Impedances

Alex R Pitt, Gautam Jindal, Kevin A Morris, Tommaso Cappello

Research output: Contribution to journalArticle (Academic Journal)peer-review

1 Citation (Scopus)

Abstract

This paper presents a design methodology for an asymmetrical Doherty Power Amplifier (DPA) which achieves a high average efficiency at back off across its operating bandwidth. It is shown that by combining continuous modes with post matching techniques, it is possible to achieve excellent efficiency performance whilst maintaining broadband operation. Analysis is provided on how the knee effect can reduce the effective potential efficiency of Class J and Continuous Inverse Class F modes. An optimum combination of 2nd and 3rd harmonic impedances is then proposed for the carrier PA which can minimise this knee effect impact on efficiency performance. Also, it is shown how the drain supply can be used to improve the bandwidth over which an intrinsic optimum load can be maintained. Based on this analysis, a simple iterative design procedure is then presented which can be directly implemented with standard RF design tools. This design procedure is then verified in the design and manufacture of a prototype DPA using the Wolfspeed CG2H40010F GaN HEMT. The realised PA operates between 2.1 and 3.2 GHz with a peak power output of between 43.9 and 44.5 dBm. The PA achieves a high average drain efficiency of 64.7 % at 8-9 dB of back off. The DPA has been tested with and without digital pre-distortion (DPD) by considering a 60 MHz LTE OFDM signal with 9 dB peak-to-average power ratio (PAPR). When DPD is enabled, the presented DPA achieves a drain efficiency of between 52.1 - 64.3 with an adjacent channel power ratio (ACPR) of between -42.2 - -44.1 dB over the bandwidth of 2.1 - 3.2 GHz.
Original languageEnglish
Pages (from-to)1120-1133
Number of pages14
JournalIEEE Journal of Microwaves
Volume3
Issue number4
Early online date1 Sept 2023
DOIs
Publication statusPublished - 1 Oct 2023

Bibliographical note

Funding Information:
This work was supported by Engineering and Physical Sciences Research Council, funded by the Centre for Doctoral Training in Future Communications under Grant EP/L016656/1.

Publisher Copyright:
© 2021 IEEE.

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