Adaptive RF Front-Ends for Hand-held Applications (Analog Circuits and Signal Processing)

The RF front-end – antenna combination is a vital part of a mobile phone because its performance is very relevant to the link quality between hand-set and cellular network base-stations. The RF front-end performance suffers from changes in operating environment, like hand-effects, that are often unpredictable. Adaptive RF Front-Ends for Hand-Held Applications presents an analysis on the impact of fluctuating environmental parameters. In order to overcome undesired behavior two different adaptive control methods are treated that make RF frond-ends more resilient: adaptive impedance control, and adaptive power control. Several adaptive impedance control techniques are discussed, using a priori knowledge on matching network properties, in order to simplify robust 2-dimensional control. A generic protection concept is presented, based on adaptive power control, which improves the ruggedness of a power amplifier or preserves its linearity under extremes. It comprises over-voltage, over-temperature, and under-voltage protection. Symbols. Abbreviations. 1 Introduction. 1.1 Context and trends in wireless Communications. 1.2 Resilience to unpredictably changing environments. 1.3 Improvements by adaptively controlled RF front-ends. 1.4 Aim and scope of this book. 1.5 Book outline. 2 Adaptive RF frond-ends. 2.1 Introduction. 2.2 RF front-end functionality. 2.3 Fluctuations in operating conditions. 2.4 Impact of variables. 2.5 Adaptive control theory. 2.6 Identification of variables for detection and correction. 2.7 Conclusions on adaptive RF front-ends. 3 Adaptive impedance control. 3.1 Introduction. 3.2 Mismatch detection method. 3.3 Adaptively controlled PI-networks using differentially controlled capacitors. 3.4 Adaptively controlled L-network using cascaded loops. 3.5 Adaptive series-LC matching network using RF-MEMS. 3.6 Load line adaptation. 3.7 Conclusions on adaptive impedance control. 4 Adaptive power control. 4.1 Introduction. 4.2 Safe operating conditions. 4.3 Power adaptation for ruggedness. 4.4 Power adaptation for linearity. 4.5 Conclusions on adaptive power control. 5 Conclusions. Appendix A Overview of adaptively controlled matching networks. Appendix B A dual-banding technique. Appendix C Transistor breakdown voltages. References. Summary.