Envelope-tracking power supplies for RF power amplifiers in portable applications

This thesis is a top-down study of the realization of highly-efficient multi-mode RF PA (Radio-Frequency Power Amplifier) polar transmitter with the emphasis on the envelope tracking power supply design and implementation.; Higher data rates and more spectrally efficient transmission within wireless communication evolution generally translate to higher power consumption or shorter battery life in a recharging cycle for mobile electronics. The main reason is the trade-off between power efficiency and amplification linearity. Approaches to increasing RF PA system efficiency are of high interest because RF PA is a major power consumer in a mobile set.; Polar modulation technique with separation and re-combination of AM (Amplitude Modulation) and PM (Phase Modulation) theoretically can improve RF PA linearity and efficiency. By this architecture, a nonlinear high-efficiency RF PA can be used to deal with the RF PM signal, while the AM is provided by an envelope tracker that generates a time-varying supply voltage to the RF PA.; Starting with the modeling of the entire polar transmitter and development of an experimental test bed, the objective is to provide a platform for envelope tracker design and transmitter performance evaluation under specifications of the GSM (Global System for Mobile Communications)/EDGE (Enhanced Data Rate for GSM Evolution) communication standard.; The main part of the thesis discusses the high efficiency envelope tracking switcher design. Buck power stage design is first introduced, based on small-signal and large-signal average models, followed by investigation of two feedback control schemes: constant-frequency pulse-width modulation (PWM) control and sliding-mode control. Finally, efficiency optimization of the power stage in a standard 0.5 mum CMOS (Complementary Metal Oxide Semiconductor) process and an adaptive digital dead-time control technique for the high frequency envelope tracking switcher are presented.; System-level experimental verifications of the proposed polar transmitter are included at the end. Experimental results include baseband evaluation of envelope trackers and RF verifications of the complete system with the class-E RF PA. The RF PA output spectrum meets the EDGE spectral mask, and the efficiency of the experimental polar EDGE transmitter power stage is 50%, given the output power level of 23 dBm.