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The RF front-end – antenna combination of a mobile phone is a vital part of the transmitter and receiver chain because its performance is very relevant to the quality of the wireless link between hand-set and cellular network base-stations.
This chapter is devoted to adaptive impedance matching techniques that have been investigated as a means to improve the link quality of mobile phones under fluctuating operating conditions. Adaptive techniques are attractive because they provide resilience to changes in body-effects and phone form factor. In principle, they can preserve maximum radiated power, power amplifier linearity, receiver sensitivity,...
During the last century, technological innovations have been changing our ways of communication tremendously. The inventors and pioneering engineers of both the telephone [1] and radio [2, 3] were fascinated by the idea of exchanging real-time information over large distances, and their audience of first successful demonstrations were astonished and excited.
Cellular phone power amplifiers usually operate in strongly fluctuating environments. The output power varies over a wide range to compensate for fluctuations in propagation path loss. The collector load impedance varies due to fluctuations in antenna body-effects [14, 15] and it varies as a function of the transmitting frequency due to the narrow bandwidth of miniaturized antennas. In addition, the...
Cellular phone power amplifier transistors have to withstand extreme voltages, temperatures and currents. Requirements on IC and packaging technology are relaxed by using over-voltage and over-temperature protection. To avoid breakdown, protection circuits are used that detect the collector peak voltage and die temperature to limit the output power once a threshold level is crossed. For a supply voltage...
Power amplifier transistors suffer from overheating when they operate under extreme conditions. To prevent destructive breakdown an adaptive output power control concept is proposed that makes use of the detected die temperature to limit the output power once a threshold level is crossed. Output power is limited by reducing the effective power control voltage and thereby avoids opposite actuation...
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