UBC Theses and Dissertations

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UBC Theses and Dissertations

Radio frequency switch mode power amplifiers and synchronous rectifiers for wireless applications Abbasian, Sadegh


This thesis focuses on identifying and evaluating device, circuit, and system level issues that affect the power efficiency of class-D and class-F switch-mode amplifiers, and class-F synchronous rectifiers. The amplifier and rectifier circuits are used to implement pulse encoded switch-mode power amplifier systems. A detailed power efficiency analysis of current mode class-D amplifiers is presented for variable duty cycle pulse trains. A device model with current saturation in the switch is introduced and gives insight into how to select an appropriate load line for variable duty cycle switching conditions. Other new results include the effect of capacitive switching losses which are usually neglected in current mode amplifiers. The analytical results are compared with simulation results and confirm that the model can provide good predictions of power efficiency for a more general class of pulse encoded signals. Class-F amplifiers are also investigated in this work. The work investigates how input harmonic matching impedances at the gate affect amplifier power efficiency. Second harmonic matching is very important and desensitizes the circuit to nonlinear capacitances in the device. Third harmonic input terminations are much less significant. A comparison of voltage and current mode circuits is also made and the current mode is better in terms of maximizing power efficiency. The work is supported by experimental results. Class-F amplifier circuits are reconfigured into synchronous rectifiers using the theory of time-reversal duality. Time-reversal duality is usually applied in the context of lossless circuits and a discussion of how loss impacts the circuit duals is presented. The rectifier dual always has slightly higher power efficiency and insights into why this occurs are described. Experimental results are shown for voltage and current mode class-F rectifiers as well as a wideband current mode class-F rectifier. The thesis concludes with the analysis and experimental results for an energy recycling switch-mode power amplifier. A signal splitting network is implemented at the output of the amplifier and out-of-band power is rectified to enhance the power efficiency of the amplifier. Experimental results confirm that energy recycling can increase power efficiency. Concluding remarks based on this research are summarized in the context of how best to use these circuits for implementing high efficiency amplifiers and rectifiers for wireless applications.

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Attribution-NonCommercial-NoDerivs 2.5 Canada