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Efficiency limits of envelope amplifiers based on hybrid topologies for highly efficient and linear RF PA. M. Vasić.
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Efficiency limits of envelope amplifiers based on hybrid topologies for highly efficient and linear RF PA M. Vasić In the last years, RF power amplifiers are taking advantage of the switched dc-dc converters to use them in several architectures that may improve the efficiency of the RF amplifier, keeping a good linearity. The use of linearization techniques such as Envelope Elimination and Restoration (EER) and Envelope Tracking (ET) requires a very fast dc-dc power converter to provide variable voltage supply to the RF PA. Several power topologies have been explored and efficiency limit of each has been discussed. Project sponsored by Efficient and Linear Power Amplifier is mandatory DC-DC converter Envelope Amplifier • Variable voltage • Wide Bandwidth Linear Regulator Hybrid Switching Converter • High Efficiency Series Configuration Parallel Configuration Analysis has been performed for: • Maximum output voltage: 20 V • Maximum output power: 100 W Base station Kahn’sTechnique • Bandwidth of RF signal: 2 MHz Switching converter in series with a linear regulator DC current source in parallel with a linear regulator Optimization parameters • Number of cells • Distribution of cells fswavg<< BWenvelope Optimization parameters • Value of the buck’s current • Simple control • Width of the hysteresis • Value of the inductor • High Efficiency Limited by losses in the Multilevel conv. Limited by the architecture DC bias is of crucial importance! Switching converter in parallel with a linear regulator GaN devices bring higher efficiency Optimization parameters • Bandwidth of dc-dc converter Normally ON GaN HEMT Collaboration with ISOM UPM in order to obtain custom made, application optimized device! • Switching device Further optimization is necessary! • Number of transistors in parallel inside the device • Geometry of each device CONCLUSIONS Depending on the end application and system’s specifications the optimal architecture for Envelope Amplifier may vary. Each hybrid architecture that has been analyzed has different optimization variables that has to been taken into account in order to obtain optimal design from the point of view of system’s efficiency and size.