A high-efficiency linear RF power amplifier with a power-tracking dynamically adaptive buck-boost supply

Energy efficiency of RF transceivers is critical and paramount for longer battery life in portable devices, which is improved by operating the power amplifiers (PAs) with higher efficiency. In this paper, the applicability of dynamic-converter-supplied RF PAs' efficiency-enhancement schemes is compared and evaluated for code-division multiple-access (CDMA) applications. The tradeoffs involved in designing switching converters with wide bandwidth (BW) and high efficiency over Wide loading conditions are considered. Given the highly variable nature of the batteries (e.g., 2.7-4.2 V for Li ion), to operate the systems at their peak performance levels, even when the battery is close to fully discharged, and to achieve higher average efficiency, a power-trucking dynamically adaptive noninverting buck-boost converter-supplied PA topology is proposed. To demonstrate the validity of the scheme, a prototype system was designed and tested using a 915-MHz carrier frequency with a 1.25-MHz baseband BW CDMA signal. The supply voltage for the PA (operating in a class-A/class-AB configuration) is adjusted dynamically from 0.5 to 3.6 V, depending on the input RF power from a 3.0-V input supply, which can vary from 2.4 to 3.4 V. The dynamic-supply PA meets the adjacent-channel power-ratio requirements of CDMA, IS-95 specifications, and the overall error vector magnitude remains less than 6% throughout its output power range from -50 to 27 dBm. The weighted average efficiency of the dynamically adaptive system (6.78%) is 4.43 times compared to the fixed supply PA efficiency (1.53%), which translates to a 88% increase in battery life, assuming that the PA consumes 20% of the total transceiver power.

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