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To improve the efficiency of cell phone base station transmitters, it is desirable to run the RF Power Amplifier (RFPA) with an envelope modulating power supply that provides the RFPA with the voltage and current needed for maximum efficiency. However, cell phone transmission varies the RF output power considerably over short periods, with the average power significantly less than the peak transmission power, which is difficult for traditional power supplies to support efficiently. This paper describes a switched-mode 8-phase buck envelope modulating power supply with a lookup table that varies the duty cycle and operating frequency to maintain soft switching under all operating conditions, and with dynamic timing correction to keep the phases uniformly distributed in time except when tracking signal dynamics that require simultaneous switching of multiple phases. The power supply does not require active compensation to keep the phase currents balanced. The experimentally demonstrated power supply provides 10 MHz large signal bandwidth, >;40 A/μsec current slew rate, with switching frequency of up to 15 MHz at 95% efficiency. The supply is suitable for 2-carrier WCDMA and LTE cell phone base stations.
Date of Conference: 5-9 Feb. 2012