Browsing by Author "Khazani, Mohammad Hossein"

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    Efficiency and Bandwidth Extension of Digital Doherty Amplifiers Using Digital Signal Processing Techniques
    (2024-09-20) Khazani, Mohammad Hossein; Ghannouchi, Fadhel M.; Helaoui, Mohamed; Nielsen, John
    In this thesis, a comprehensive investigation into DDPAs was carried out. Initially, attention was directed towards phase adjustment and input power splitting, and they were explored for their impacts on efficiency and linearity. Through the utilization of complex gain splitting, which combines standalone power splitting and phase adjustment, efficiency enhancements of up to 9.7% were achieved for a 64-QAM modulated signal transmitted at the DDPA’s central frequency. However, this improvement came at the expense of the DDPA’s linearity performance. Subsequently, frequency-domain power splitting techniques were introduced. These algorithms aim to optimize splitting parameters to maximize efficiency and bandwidth but often encounter linearity issues observed in frequency-independent methods. To mitigate these issues, ACPR measurements were conducted using modulated signals, offering insight into the effects of splitting factors. An optimization algorithm was then presented, focusing on maximizing PAE and bandwidth (and gain flatness) improvement while maintaining linearity lower than that of the conventional Doherty mode by restricting ACPR growth. This algorithm shed light on the trade-off between PAE, bandwidth extension, and linearity. It was demonstrated that by adjusting the value of the desired flat gain, one or two goals of the optimization problem could be prioritized at the expense of others. Finally, RF measurements were undertaken to validate the effectiveness of the algorithm. PAE enhancements ranged from 4.16% to 6.1% at various carrier frequencies, while bandwidth extension varied between 85 and 105 MHz.