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  • Publication
    Broadband High Efficiency Power Amplifiersfor RF Front-Ends of Wireless Transmitters
    (University College Dublin. School of Electrical and Electronic Engineering, 2022) ;
    0000-0002-2562-9599
    This thesis explores Power Amplifier (PA) architectures for Radio Frequency (RF) front-ends of transmitters in Fifth Generation (5G) wireless communication systems. New PA operation classes and new efficiency enhanced architectures are presented with comprehensive analyses, well-designed state-of-art prototypes, and excellent experimental results. Firstly, a new class of PA, designated as Class-iF-1, is proposed, which utilizes input harmonics to achieve high efficiency with enhanced linearity performance beyond the conventional Class-F-1 PA. The Amplitude-to-Amplitude (AM/AM) profile of the conventional Class-F-1 PA is mathematically modeled as a function of input drive level. Theoretical derivation shows that the appropriate utilization of input nonlinearity poses a solution to rectify the double inflection characteristics of conventional Class-F-1 PA, which consequently, can be realized by proper manipulation of second harmonic source impedance. A broadened second harmonic design space over the open-circuit region is proposed. Secondly, a new solution for phase compensation in the Sequential Load Modulated Balanced Amplifier (SLMBA) architecture is presented. By using proper harmonic tuning in the control amplifier carrier branch, the load trajectory of the balanced amplifier can be made close to the real axis, which is beneficial to recovering peak output power and efficiency at both Output Power Back-Off (OPBO) and saturation of the SLMBA in wideband operation. Thirdly, a novel Waveform Engineered Sequential Load Modulated Balanced Amplifier (W-SLMBA) is proposed, which uses a continuous Class-F-1 Control Amplifier (CA) to manipulate the impedance trajectory of the Balanced Amplifier (BA). It is demonstrated that the use of the continuous Class-F-1 CA can trigger a unique impedance load modulation mechanism by which the fundamental impedance of the BA is shaped by the varying second harmonic load reactance of the CA. Theoretical derivations reveal that this special load modulation yields extended design space for the SLMBA, wherein high efficiency can be achieved over a wide bandwidth and OPBO. Fourthly, the design methodology of a broadband RF-input SLMBA is introduced, with extended high efficiency design space, by introducing the second harmonic load manipulation over an enlarged range for the CA. The extension of CA load design space not only can provide the time-domain varying drain current waveform inside the entire design continuum, but also allows maintaining high efficiency OPBO over an extended operation bandwidth. Last but not least, the impact of input nonlinearity in SLMBA architecture is investigated. The Class-F-1 operation is selected as the solution for CA branch due to its advantage of high OPBO performance, efficiency flatness and immunity versus second harmonic source phase ¿G2S, which leads to the adoption of Class-B/J operation for BA. While Class-F-1 CA is immune to the second harmonic source variation, the safe design space for BA lands in the region where ¿G2S is over (-90¿, 90¿).
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