Three-level buck converter for envelope tracking in RF power amplifiers

This paper proposes a three-level buck converter for efficient wide-bandwidth envelope tracking in RF power amplifiers (RFPA). The focus is on low-power battery-operated systems, and the goal is to enable practical implementation of the envelope elimination and restoration (EER) technique, which theoretically allows realization of a highly linear, highly efficient RFPA for non-constant envelope modulations. In terms of ripple, switching frequency and bandwidth tradeoffs, it is shown that the three-level buck converter is similar to the two-phase configuration, while employing a single inductor in the power stage. Additionally, a digital control technique for regulation of the flying capacitor voltage is proposed to ensure signal tracking fidelity. Experimental results show the improved performance of a three-level buck converter prototype as regards efficiency and ripple rejection for the illustrative case of tracking the envelope of a two-tone test signal.