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One of the most representative adaptive power management techniques, namely the adaptive power management of an RF PA (Fig. 1), which requires system-level im-plications to design power supplies, is discussed in the following.
RF power amplifiers (RFPA) are the most dominant power-consuming devices in battery-operated terminals for communication systems. Systems like GSM employ modulation schemes that generate constant amplitude RF outputs in order to allow use of high-efficiency switched-mode RF power amplifiers (class-E, class-F). With the growing emphasis on channel capacity, the newer generation of communication
|Fig. 1 Envelope tracking technique for RF power amplifiers||t||t|
|Efficient switch mode PA|
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systems (such as EDGE, CDMA or WCDMA) use non-constant envelope RF sig-nals (with MHz bandwidths) associated with spectrum-efficient digital modula-tions so as to increase the channel capacity. Unfortunately, the amplification of non-constant envelope signals requires linear RF power amplifiers, which inher-ently have lower efficiency. In that scenario, Envelope Elimination and Restoration (EER) technique (Fig. 1) or, more generally, polar modulation techniques, have been proposed to improve efficiency of RFPA systems by employing an efficient switched-mode RFPA supplied from an envelope-tracking power converter. Al-though the focus is primarily on low-power battery-operated systems typical for mobile handsets, the techniques presented can also apply to high-power RFPA sys-tems commonly found in communication base stations.