Closed-loop adaptive impedance tuners for improving RF transmitter efficiency.

摘要

This thesis addresses the topic of controlling reflections at the output of radio frequency power amplifiers (RFPA) in cases when the amplifier load changes, such as in handset applications in which the proximity of the human operator affects antenna impedance. Specific to handset applications, the impedance mismatch between the PA and antenna is quantified for two commercial handset antennas in various positions relative to the human body and these measurements guide the design of the tuning networks. Figures of merit are established for impedance tuners, and an overview of tuner design goals and methodologies is presented. The specific parameters most relevant for tuner design and characterization include tuning range, tuner loss (a parameter specifically developed in this work), and control.;Several analog impedance tuners are designed, implemented with different tuning devices including a hybrid tuner based on varactor diodes, and a monolithic microwave integrated circuit (MMIC) tuner. In addition, experimental validation at 1.95 GHz is presented for the varactor tuner with an analysis of the figures of merit. The local optimizer tuning algorithm is used to demonstrate a closed-loop tuning system with integrated digital control. Digital impedance tuners are designed, including a pHEMT switched-capacitor MMIC tuner, as well as a tuner based on commercial MEMS switches. Experimental results for the MMIC tuner at 2.45 GHz are presented in detail. In addition, a digital implementation of a PA tuner combined with closed-loop control is discussed. The performance of the tuning algorithm for various impedance mismatches is evaluated. Finally, overall RF transmitter front end system efficiency is discussed and compared to a conventional approach with no tuning. In addition to tuning impedance, the feedback signal is used as an input to an adaptive power supply. It is shown that up to 13.2 % of total efficiency can be gained by simultaneous impedance and bias tuning for a VSWR of 4 and the specific hardware implementation discussed in this thesis.